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Geology of the Fraser River Valley between Lillooet and Big Bar Creek Trettin, Hans Peter 1960

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GEOLOGY OF THE FRASER RIVER VALLEY BETWEEN LILLOOET AND BIG BAR CREEK by HANS PETER TRETTIN Ph.D., U n i v e r s i t y o f Hamburg,  1952  M . S c , U n i v e r s i t y o f B r i t i s h Columbia,  1957  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Doctor o f P h i l o s o p h y i n t h e Department of GEOLOGY  We accept t h i s t h e s i s as conforming t o t h e required standard  THE UNIVERSITY OF BRITISH COLUMBIA I960  In p r e s e n t i n g  this thesis i npartial fulfilment of  the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t t h e L i b r a r y s h a l l make it  freely  a v a i l a b l e f o r r e f e r e n c e and s t u d y .  agree t h a t p e r m i s s i o n f o r e x t e n s i v e  I further  copying of t h i s  thesis  f o r s c h o l a r l y purposes may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s .  I t i s understood  that copying or p u b l i c a t i o n o f t h i s t h e s i s f o r g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n  Department o f  GEOLOGY  The U n i v e r s i t y o f B r i t i s h Columbia, Vancouver 8, Canada. Date  January,  26, I 9 6 0  financial  permission.  ii  ABSTRACT An a r e a o f 550 square m i l e s between L i l l o o e t and Big  B a r , B.C. was mapped by t h e author u s i n g t h e s c a l e o f one  mile to the inch. I n t h e s o u t h e r n p a r t o f t h e Bowman Range f o u r members are recognized i n the Middle  ( ? ) and Upper Permian M a r b l e  Canyon f o r m a t i o n w h i c h i s p a r t l y composed o f r e e f a l  limestone.  T h i s f o r m a t i o n forms a n o r t h w e s t e r l y t r e n d i n g a n t i c l i n o r i u m overturned  to the northeast.  The c h e r t s , a r g i l l i t e s ,  limestones,  and v o l c a n i c r o c k s west o f t h e Bowman Range, o r i g i n a l l y r e f e r r e d t o t h e Permo-Pennsylvanian Cache Creek group a r e shown to be P e r m o - T r i a s s i c and a r e here a s s i g n e d t o t h e P a v i l i o n group, a new group w h i c h i s made up o f two D i v i s i o n s .  Micro-  s c o p i c and s t r a t i g r a p h i c e v i d e n c e i s g i v e n t h a t t h e c h e r t s o f t h i s group a r e o f r a d i o l a r i a n o r i g i n . The Lower C r e t a c e o u s L i l l o o e t group here i s s u b d i v i d e d into three u n i t s .  D i v i s i o n s A and B a r e shown t o form a  northwesterly trending a n t i c l i n e . Three members a r e now r e c o g n i z e d i n D i v i s i o n A o f the Lower C r e t a c e o u s J a c k a s s Mountain group. The Lower C r e t a c e o u s Spences B r i d g e group i s subd i v i d e d i n t o s e v e r a l l o c a l and s t r a t i g r a p h i c u n i t s .  Two  u n i t s p r e v i o u s l y a s s i g n e d t o t h e Spences B r i d g e group a r e c o r r e l a t e d w i t h t h e K i n g s v a l e group on t h e b a s i s o f new fossil  collections.  iii  Some v o l c a n i c and sedimentary  rocks o r i g i n a l l y r e -  f e r r e d t o the Miocene Kamloops group a r e here c o r r e l a t e d w i t h Miocene to P l e i s t o c e n e r o c k s o f the Quesnel map-area. West o f L i l l o o e t a b e l t o f s e r p e n t i n i t e was mapped t h a t has s t r u c t u r a l and l i t h o l o g i c a l s i m i l a r i t i e s t o the Upper T r i a s s i c u l t r a b a s i c i n t r u s i o n s o f the Shulaps  Range.  G r a n i t i c r o c k s o f t h r e e ages are r e c o g n i z e d and range from e a r l y Lower Cretaceous  o r o l d e r to mid-Lower  Cretaceous.  I t had e a r l i e r been shown t h a t the F r a s e r R i v e r f a u l t zone c o n s i s t s o f s e v e r a l normal f a u l t s w i t h r e l a t i v e downward movement to the e a s t .  East o f t h e s e f a u l t s the  author  r e c o g n i z e s another f a u l t w i t h r e l a t i v e downward movement to the west.  Lower C r e t a c e o u s  and e a r l y T e r t i a r y r o c k s  thus  occupy a graben between P e r m o - T r i a s s i c u n i t s t o the n o r t h e a s t and to the southwest.  T h i s graben p r o b a b l y c o n t r o l l e d  the  d e p o s i t i o n o f D i v i s i o n s B and C o f the J a c k a s s M o u n t a i n group. The  f a u l t i n g may  g r a n i t i c masses.  be r e l a t e d t o the i s o s t a t i c r i s e o f a d j a c e n t Evidence  i s g i v e n t h a t the l a t e s t movement  on one o f the f a u l t s t o o k p l a c e i n m i d - T e r t i a r y t i m e .  iv TABLE OF CONTENTS  Page  INTRODUCTION  1  1. 2. 3. 4. 5. 6.  1 1 2 3 6 7  L o c a t i o n and Access Previous G e o l o g i c a l Work F i e l d Work Physiography and P l e i s t o c e n e and Recent Geology C l i m a t e , Vegetation, Wild L i f e Industries CHAPTER I  GENERAL GEOLOGY Introductory  9 Statement  9  Table o f Formations 1.  10  SEDIMENTARY AND VOLCANIC ROCKS  17  CACHE CREEK GROUP  17  Introduction  17  MOUNT SOUES DIVISION MARBLE CANYON FORMATION 1. 2. 3. 4. 5.  Distribution L i t h o l o g y and Thickness Structure Mode o f O r i g i n Age o f C o r r e l a t i o n  PAVILION GROUP  20 .  21 21 21 25 27 30 34  Introduction  34  DIVISION I  34  1. 2. 3. 4. 5.  34 34 38 40 42 44  6.  D i s t r i b u t i o n and Thickness Lithology Metamorphism Structure Mode o f O r i g i n Age  V  DIVISION I I 1. 2.  3.  4. 5.  D i s t r i b u t i o n and T h i c k n e s s B i g B a r Assemblage A. Lithology B. Structure P a v i l i o n Assemblage A. Lithology B. Met amor p h i snr and A l t e r a t i o n C. Structure . Mode o f O r i g i n Age and C o r r e l a t i o n  LILLOOET GROUP 1. 2.  3. 4. 5. 6.  D i s t r i b u t i o n and T h i c k n e s s Lithology Division A Division B Division C The P r o b l e m o f A l b i t i z a t i o n Structure . . . . . Mode o f O r i g i n Age and C o r r e l a t i o n  JACKASS MOUNTAIN GROUP 1. 2.  3. 4. 5. 6.  D i s t r i b u t i o n and T h i c k n e s s Lithology Division A Member A I Member A l l Member A I I I Division B Division C The P r o b l e m o f A l b i t i z a t i o n Structure Mode o f O r i g i n Age and C o r r e l a t i o n  SPENCES BRIDGE GROUP Introduction LOWER DIVISION 1. 2.  B a s a l Member Gibbs Creek Assemblage A. D i s t r i b u t i o n and T h i c k n e s s B. Lithology Member A Member B Member C C. Structure ,  44  . . . .  44 45 45 46 47 47 53 57 59 59 60 60 61 61 62 70 74 77 77 79 80 80 81 81 81 85 86 87 88 95 95 96 100 102 102  . . . 103 103 104 104 105 105 105 107 108  vi  UPPER DIVISION 1. 2. 3.  Distribution Lithology S t r u c t u r e , Age, C o r r e l a t i o n  KINGSVALE GROUP 1. 2. 3. 4.  D i s t r i b u t i o n and T h i c k n e s s Lithology Division A Division B Structure Mode o f O r i g i n , Age, C o r r e l a t i o n  109 109 109 I l l I l l I l l I l l I l l 112 113 114  SPENCES BRIDGE GROUP OR KINGSVALE GROUP  115  FOUNTAIN VALLEY ASSEMBLAGE  118  WARD CREEK ASSEMBLAGE  122  FRENCH BAR FORMATION  125  VOLCANIC ROCKS OVERLYING THE FRENCH BAR FORMATION  .  129  MIDDLE OR LATE TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 1.  2. 3.  S e d i m e n t a r y Rocks near P a v i l i o n A. D i s t r i b u t i o n and T h i c k n e s s B. L i t h o l o g y C. S t r u c t u r e D. Mode o f O r i g i n E. Age Sedimentary Rocks a s s o c i a t e d w i t h t h e O l i v i n e B a s a l t s near Leon Creek and on B i g B a r Creek Olivine Basalt A. D i s t r i b u t i o n and T h i c k n e s s B. L i t h o l o g y C. S t r u c t u r e D. Mode o f O r i g i n E. Age  130 130 130 131 132 132  133  134 136 136 137 140 141 142  vii 2.  INTRUSIVE ROCKS  143  ULTRABASIC INTRUSIONS  143  ULTRABASIC ROCKS NEAR LILLOOET  143  1. 2. 3. 4. 5.  Distribution Lithology Serpentinization Carbonate-silica Age and Origin  Alteration  143 144 145 146 147  PERIDOTITE INTRUDING THE PAVILION GROUP  148  60AST INTRUSIONS  149  I. EARLY LOWER CRETACEOUS OR OLDER 1. 2. 3. 4. 5.  Distribution Lithology Associated Mineralization Structure, Mode of Origin Age  I I . EARLY LOWER CRETACEOUS 1. 2. 3.  Distribution Lithology Age  I I I . LATE BARREMIAN (?) 1. 2. 3. 4.  Distribution Lithology Associated Mineralization Age  GABBRO AND DIABASE NEAR LILLOOET 1. 2. 3. 4.  D i s t r i b u t i o n , Structure Lithology Metamorphism and A l t e r a t i o n Age  ANDESITIC AND BASIC DYKES  149 149 150 153 154 154  155 155 155 156  157 157 157 158 158  159 159 159 163 163 164  viii  CHAPTER I I THE FRASER RIVER FAULT ZONE 1. 2. 3. 4. 5.  165  Introduction 165 D e s c r i p t i o n o f t h e F r a s e r R i v e r F a u l t Zone . . 167 Associated A l t e r a t i o n 173 History 174 Causes o f F a u l t i n g 176 CHAPTER I I I  GEOLOGICAL HISTORY OF THE AREA  177  BIBLIOGRAPHY  182  APPENDIX I . - DETERMINATION OF MINERAL COMPOSITIONS . . 186 APPENDIX I I .  PHOTOGRAPHS  ix  LIST OF FIGURES Figure 1.  2.  Page Geology o f t h e F r a s e r R i v e r v a l l e y between L i l l o o e t and B i g Bar Creek. (In pocket)  ]n  ^  o h t  Composition o f fragments, sandstones, L i l l o o e t group  75  Composition of fragments, sandstones, J a c k a s s Mountain group  92  S i z e d i s t r i b u t i o n i n sand and c o a r s e silt-grade, thin-section analysis.of 2 specimens from D i v i s i o n C, one specimen from member A l l , J a c k a s s M o u n t a i n group  93  5.  Geology o f G l e n F r a s e r a r e a  117  6.  The F r a s e r R i v e r f a u l t zone  168  3. 4.  X  LIST OF PHOTOGRAPHS (Appendix I I ) Plate I II Ill  TV  V VI  VII VIII IX  X  XI  XII  XIII  The F r a s e r R i v e r v a l l e y near F o u n t a i n . View t o t h e southwest. The F r a s e r R i v e r v a l l e y near Moran. View t o t h e n o r t h e a s t . The F r a s e r R i v e r v a l l e y between S i w a s h Creek and Leon Creek. View t o t h e Northwest. U n c o n s o l i d a t e d P l e i s t o c e n e sediments r e s t i n g on c h e r t and a r g i l l i t e o f t h e P a v i l i o n group, D i v i s i o n I , Upper Permian o r T r i a s s i c . Lower p a r t o f K e l l y Creek. View t o t h e n o r t h . Mount Bowman.  View t o t h e s o u t h .  C a l c a r e n i t e , thin-bedded to laminated. M a r b l e Canyon f o r m a t i o n , member I I I , Upper Permian. About two m i l e s n o r t h w e s t o f Mount Bowman. Mount Soues.  View t o t h e n o r t h .  S y n c l i n e o n Mount K e r r .  View t o t h e n o r t h w e s t .  I n t e r b e d d e d l i m e s t o n e and c h e r t , showing boxt y p e o f f o l d s . M a r b l e Canyon f o r m a t i o n , member I l i a , Upper Permian. About one m i l e west o f Mount K e r r . View t o t h e n o r t h w e s t . R a d i o l a r i a n c h e r t nodules i n a r g i l l a c e o u s m a t r i x . A r g i l l a c e o u s c h e r t from P a v i l i o n group, D i v i s i o n I , Upper Permian o r T r i a s s i c . P h o t o - m i c r o g r a p h . C r o s s e d n i c o l s x25. R a d i o l a r i a n c h e r t n o d u l e , showing r a d i a t i n g s p i n e s . P a v i l i o n group, D i v i s i o n I , Upper Permian o r T r i a s s i c . Photo-micrograph. O r d i n a r y l i g h t and c r o s s e d n i c o l s x 1 9 0 . O o l i t i c l i m e s t o n e . P a v i l i o n group, D i v i s i o n I , Upper Permian o r T r i a s s i c . Photo-micrograph. C r o s s e d n i c o l s x35. M i g m a t i t e c o n s i s t i n g o f hornblende h o r n f e l s and d i o r i t i c i n t r u s i o n s . West shore o f F r a s e r R i v e r , o p p o s i t e t h e mouth o f K e l l y Creek. View t o t h e northwest.  Plate XIV  XV  XVI XVII XVIII XIX XX XXI  XXII  XXIII  XXIV  V o l c a n i c a r e n i t e , f i n e - g r a i n e d . Specimen 2 o f f i g u r e 4. J a c k a s s Mountain group. D i v i s i o n C. Barremian. Photo-micrograph. Ordinary l i g h t x32. P l a g i o c l a s e c r y s t a l , showing t w i n n i n g and o s c i l l a t o r y normal z o n i n g , from t u f f , Spences B r i d g e group, Gibbs Creek assemblage, member B, A p t i a n . Photo-micrograph. Crossed n i c o l s x30. The F r e n c h B a r f o r m a t i o n , Upper Eocene o r O l i g o cene, near F r e n c h B a r Canyon. A i r - p h o t o g r a p h . Conglomerate o f t h e F r e n c h B a r f o r m a t i o n , Upper Eocene o r O l i g o c e n e , near B i g B a r Creek. O l i v i n e b a s a l t , Middle or Late T e r t i a r y . About 2 m i l e s n o r t h o f McKay Creek. View t o t h e n o r t h . Olivine basalt. x32.  Photo-micrograph.  Crossed n i c o l s  S l i d e of Middle or Late T e r t i a r y o l i v i n e b a s a l t near Leon Creek. A i r - p h o t o g r a p h . A l t e r e d u l t r a b a s i c r o c k . U l t r a b a s i c b e l t west o f L i l l o o e t , Upper T r i a s s i c ( ? ) . P h o t o - m i c r o g r a p h . Crossed n i c o l s x 3 2 . S t e e p l y d i p p i n g s t r a t a o f t h e J a c k a s s M o u n t a i n group, D i v i s i o n C, B a r r e m i a n , near f a u l t "d" on t h e east s i d e o f t h e F r a s e r R i v e r , between S a l l u s Creek and Gibbs Creek; v i e w t o t h e southwest. A n d e s i t e and b a s a l t o f t h e Spences B r i d g e group, Upper D i v i s i o n , A p t i a n , d i p p i n g s t e e p l y t o t h e n o r t h e a s t near f a u l t c o n t a c t w i t h t h e P a v i l i o n group, D i v i s i o n I I , T r i a s s i c , ( f a u l t " e " ) . Lower p a r t o f McKay Creek. View t o t h e n o r t h w e s t . F a u l t "e  11  i n B i g B a r Canyon.  View t o t h e s o u t h ;  '-.  xii  ACKNOWLEDGMENTS  The work was c a r r i e d o u t f o r t h e F r a s e r R i v e r Board o f t h e P r o v i n c e o f B r i t i s h Columbia under t h e s u p e r v i s i o n o f t h e Department o f M i n e s .  The author  H. S a r g e n t and S . S . H o l l a n d f o r support During  i s indebted to Drs. and encouragement.  t h e seasons o f 1957 and 1958 t h e author was v e r y  ably  a s s i s t e d by Mr. L . V . H i l l s , and d u r i n g one month o f 1958 by Mr. D. Leeming.  P r o f e s s o r K.C.McTaggart v i s i t e d t h e author  on s e v e r a l o c c a s i o n s  i n t h e f i e l d , a d v i s e d him i n t h e course  o f t h i n - s e c t i o n s t u d i e s , and read the m a n u s c r i p t .  Help w i t h  f i e l d - w o r k , l a b o r a t o r y - w o r k , and m a n u s c r i p t was a l s o r e c e i v e d from P r o f e s s o r W.H.Mathews.  The author  i s f u r t h e r indebted  t o P r o f e s s o r s W.R.Danner, V . J . O k u l i t c h , J.V.Ross, J . S . S t e v e n s o n , R.M. Thomson, and W.H. W h i t e f o r a d v i c e .  The  i d e n t i f i c a t i o n o f f o s s i l s by P r o f e s s o r W.H. Danner, D r . J . J e l e t z k y , and P r o f e s s o r G.E. Rouse i s g r a t e f u l l y acknowledged. I n t h e F r a s e r R i v e r a r e a f r i e n d l y h e l p was g i v e n by Mr. and Mrs. Ostensoe o f L i l l o o e t , Mr, and Mrs.  Hay and Mr. and M r s .  H i g h o f P a v i l i o n , and Mr. and Mrs. M a r r i o t o f B i g B a r .  1  INTRODUCTION 1. The  L o c a t i o n and Access  a r e a mapped, e l o n g a t e and  irregular, lies  along  the F r a s e r R i v e r between L i l l o o e t and F r e n c h Bar Canyon and i n c l u d e s the a d j a c e n t Bowman Range and p a r t s o f the M o u n t a i n s , the Camelsfoot Range, and F o u n t a i n The  Pavilion  Ridge.  e a s t e r n s i d e o f the F r a s e r R i v e r , and the west  s i d e i n the v i c i n i t y o f L i l l o o e t , are s e r v e d by highway, the P a c i f i c Great E a s t e r n R a i l w a y , and secondary roads and I n the c e n t r a l and n o r t h e r n p a r t s o f the map  a r e a the west  s i d e i s a c c e s s i b l e by a c a b l e c a r near P a v i l i o n and a t the mouth o f B i g Bar Creek.  trails.  From t h e s e two  a ferry  crossings only  pack t r a i l s and a few wagon roads p r o v i d e f u r t h e r access the w e s t e r n p a r t s o f the map 2. The 1871  area.  P r e v i o u s G e o l o g i c a l Work  e a r l i e s t g e o l o g i c a l work i n the a r e a was  by J . R i c h a r d s o n  group and  to  and A.R.C. Selwyn.  done i n  The Cache Creek  the J a c k a s s M o u n t a i n group are named and  described  f o r the f i r s t time i n Selwyn's r e p o r t (1872). I n 1877  G.M.  Dawson (1877-78) mapped the Kamloops  a r e a on a s c a l e o f e i g h t m i l e s to the i n c h . were c a r r i e d out i n the seasons o f 1888, i n 1895  a r e p o r t and a map  were p u b l i s h e d .  1889  Further }  studies  and 1890,  and  on a s c a l e o f 4 m i l e s to the i n c h  Dawson e s t a b l i s h e d a l l o f the major r o c k u n i t s  2  o f t h e p r e s e n t map a r e a , and h i s map and r e p o r t a r e s t i l l the o n l y source o f i n f o r m a t i o n f o r some o f t h e n o r t h e r n p a r t s o f t h e Kamloops A r e a . I n 1918 and 1919 Leopold the m i n e r a l d e p o s i t s a d j a c e n t  R e i n e c k e (1920) who examined  t o t h e P a c i f i c Great  Eastern  r a i l w a y between L i l l o o e t and P r i n c e George d e s c r i b e d a few d e p o s i t s i n t h e p r e s e n t map a r e a . A reconnaissance  survey from t h e F r a s e r R i v e r t o  Taseko Lake was c a r r i e d o u t i n 1920 by J.D.McKenzie whose map and r e p o r t cover t h e west s i d e o f t h e F r a s e r R i v e r between Watson B a r Creek and F r e n c h B a r Creek. From 1945 t o 1947 S. D u f f e l l and K.C.McTaggart r e mapped t h e A s h c r o f t a r e a on a s c a l e o f 4 m i l e s t o t h e i n c h . T h e i r most important  c o n t r i b u t i o n s t o t h e geology o f t h e  p r e s e n t map a r e a c o n c e r n t h e Lower C r e t a c e o u s s e d i m e n t a r y r o c k s , and t h e F r a s e r R i v e r f a u l t zone. I n 1955 J . McCammon and H. Wasmith (1956) s t u d i e d p o s s i b l e dam s i t e s i n t h e n o r t h e r n p a r t o f t h e map a r e a . They d i s c o v e r e d s e v e r a l f a u l t s w h i c h proved t o be n o r t h e r n e x t e n s i o n s o f t h e F r a s e r R i v e r f a u l t zone. Some o f t h e n o r t h w e s t e r n a r e here d e s c r i b e d f o r t h e f i r s t 3.  p a r t s o f t h e a r e a mapped time.  F i e l d Work  F i e l d work was c a r r i e d out f o r a t o t a l o f 9 months d u r i n g t h e summers o f 1957 and 1958 and f o r one week i n 1959.  3 The  d r y c l i m a t e and good a c c e s s i b i l i t y o f t h e a r e a  u n i n t e r r u p t e d work.  allowed  I n most o f t h e a r e a t h e geology was  p l o t t e d on base maps on a s c a l e o f 1/2 m i l e t o t h e i n c h .  Near  the F r a s e r R i v e r base maps on s c a l e s o f 1000 f e e t and 500 f e e t t o t h e i n c h were a v a i l a b l e .  L o c a t i o n s were e s t a b l i s h e d by  c r o s s b e a r i n g s , a l t i m e t e r r e a d i n g s , and pace and compass traverses.  The geology o f t h e Bowman Range was p l o t t e d on a i r  photographs and,  by means o f r a d i a l p l o t t i n g , t r a n s f e r r e d t o  base maps showing photo c e n t e r s . 4.  P h y s i o g r a p h y and P l e i s t o c e n e Geology  Three major elements o f t h e topography can be distinguished: Middle  M i d - T e r t i a r y and o l d e r mountain r a n g e s ,  o r Late T e r t i a r y upland s u r f a c e s and P l e i s t o c e n e and  Recent v a l l e y s . The main mountain ranges o f t h e map a r e a a r e t h e P a v i l i o n Mountains and t h e Bowman Range i n t h e east by t h e Upper and (?) M i d d l e Permian M a r b l e Canyon  underlain formation,  and t h e C a m e l s f o o t Range and F o u n t a i n R i d g e i n t h e w e s t , u n d e r l a i n by Lower C r e t a c e o u s s e d i m e n t a r y r o c k s . The Bowman Range and t h e P a v i l i o n Mountains c o n s i s t m o s t l y o f p a r a l l e l r i d g e s formed by s t e e p l y d i p p i n g stones.  I n t h e n o r t h e r n p a r t o f t h e Bowman Range a p l a t e a u -  l i k e topography has been produced by g e n t l y d i p p i n g beds.  lime-  As i n t h i s a r i d c l i m a t e l i m e s t o n e  limestone  i s very r e s i s t a n t  to w e a t h e r i n g t h e h i g h e s t mountains o f t h e map-area a r e found i n t h i s b e l t (Mount Bowman 7350 f e e t )  4 The Camelsfoot Range i s u n d e r l a i n by m o d e r a t e l y d i p p i n g l i t h i c sandstones and conglomerates t h a t a r e h i g h l y r e s i s t a n t to weathering.  I t has s t e e p s l o p e s , and i s t r a n s e c t e d by  numerous v a l l e y s , some o f w h i c h a r e d e e p l y i n c i s e d and narrow. F o u n t a i n Ridge i s a narrow remnant o f t h e same mountain mass. I n t h e p r e s e n t map a r e a t h e e l e v a t i o n s o f t h e Camelsfoot Range are m o s t l y between 4500 and 5500 f e e t but r i s e up t o 6900 f e e t . The a l t i t u d e s o f F o u n t a i n Ridge range from 4200 t o 5500 f e e t . Mount M a r t l e y , whose rounded t o p reaches an a l t i t u d e o f 6700 f e e t a t t h e s o u t h e a s t e r n edge o f t h e p r e s e n t map a r e a , i s formed b y - h i g h l y r e s i s t a n t g r a n i t i c  rocks.  The s t e e p l y d i p p i n g but weakly r e s i s t a n t s e d i m e n t a r y and v o l c a n i c r o c k s o f t h e P a v i l i o n group form h i l l y  tracts  o r mountains o f l e s s e r h e i g h t w h i c h r a r e l y r i s e above 5000 feet. G e n t l y d i p p i n g C r e t a c e o u s and e a r l y T e r t i a r y v o l c a n i c r o c k s , not v e r y r e s i s t a n t t o w e a t h e r i n g form a b e l t o f l o w mountains t h a t o n l y i n t h e n o r t h e r n p a r t o f t h e a r e a r i s e t o e l e v a t i o n s o f more t h a n 6000 f e e t . F l a t l y i n g s e d i m e n t a r y and v o l c a n i c r o c k s o f M i d d l e o r L a t e T e r t i a r y age form s m a l l p l a t e a u s a t a l t i t u d e s r a n g i n g a p p r o x i m a t e l y from 3000 t o 4000 f e e t near P a v i l i o n , between McKay Creek and Watson B a r Creek, and on B i g B a r Creek.  North  o f P a v i l i o n , s o u t h o f Watson B a r C r e e k , and i n t h e v i c i n i t y o f B i g B a r Creek some o f t h e s e d e p o s i t i o n a l s u r f a c e s a r e cont i n u o u s w i t h younger g e n t l y s l o p i n g e r o s i o n a l s u r f a c e s , w h i c h a r e c o v e r e d o n l y w i t h a t h i n veneer o f u n c o n s o l i d a t e d P l e i s t -  5  ocene and Recent d e p o s i t s .  These M i d d l e or L a t e T e r t i a r y  s u r f a c e s a r e p a r t s o f the f l o o r o f a v a l l e y t h a t p o s s i b l y extended from G l e n F r a s e r to B i g Bar M o u n t a i n and was  connected  a l o n g B i g Bar Creek w i t h the e x t e n s i v e p l a t e a u east o f the Bowman  Range.  The v a l l e y p a r t l y c o i n c i d e s w i t h the p r e s e n t  R i v e r v a l l e y but has not been r e c o g n i z e d The  Fraser  south o f G l e n F r a s e r .  p r e s e n t v a l l e y o f the F r a s e r R i v e r i s younger t h a n  t h e s e M i d d l e or L a t e T e r t i a r y s u r f a c e s and was i n P l e i s t o c e n e time.  I n most o f the a r e a i t i s  probably  developed  approximately  p a r a l l e l to the s t r i k e o f the r o c k s and t o the F r a s e r R i v e r f a u l t zone, except f o r a p e c u l i a r S-shaped t u r n near  Fountain.  I t might be suggested t h a t the R i v e r o r i g i n a l l y f l o w e d F o u n t a i n v a l l e y but was  d i v e r t e d i n t o the B r i d g e R i v e r .  The P l e i s t o c e n e v a l l e y bottom p r o b a b l y approximately between 900  w i t h the p r e s e n t  and 650  f i l l e d , probably 1000  coincided  s u r f a c e o f the r i v e r w h i c h l i e s  f e e t above sea l e v e l .  This v a l l e y  was  i n the l a t e s t P l e i s t o c e n e , w i t h more t h a n  f e e t o f u n c o n s o l i d a t e d m a t e r i a l s r a n g i n g from  g r a v e l to mud  along  (See P l a t e I V ) .  The  boulder  s t r a t i g r a p h y of these  de-  p o s i t s changes over s h o r t d i s t a n c e s and t h e i r h i s t o r y i s complicated.  Much o f the m a t e r i a l showing d e l t a i c  cross-bedding  appears to have been d e p o s i t e d by b r a i d e d streams.  Some o f  e x t e n s i v e s i l t d e p o s i t s between P a v i l i o n and B i g Bar Creek have been l a i d down i n g l a c i a l l a k e s . been d e p o s i t e d on a l l u v i a l fans o f  the may  Mudflows appear to have  tributaries.  I n Recent time t h e r i v e r has been r e j u v e n a t e d and has cut t h r o u g h t h e u n c o n s o l i d a t e d sediments  i n t o bedrock.  This  r e j u v e n a t i o n p r o b a b l y was caused by a decrease o f t h e d e t r i t a l load i n p o s t - g l a c i a l time.  (Thornbury, 1954, p. 1 4 4 ) .  A l t h o u g h t h e a r e a was covered by g l a c i e r s ( D u f f e l l and McTaggart, 1953) p. 69) g l a c i a l e r o s i o n i s s l i g h t and t i l l -very rare.  P r o b a b l y no- r a p i d movements took p l a c e i n t h i s  r e g i o n w h i c h l i e s o n l y some 50 m i l e s t o t h e s o u t h o f a major g l a c i a l d i v i d e ( G e o l . A s s n . o f Canada, 1958; W.H.Mathews, 1941, p. 6 4 ) . A t h i n l a y e r o f Recent v o l c a n i c a s h has been found i n the v i c i n i t y o f B i g B a r and Jesmond.  W.H.Mathews ( o r a l communi  c a t i o n ) suggests t h a t t h e a s h was e j e c t e d by a c i n d e r cone on t h e upper B r i d g e R i v e r .  H. Nasmith  ( o r a l communication) re->/  p o r t s Recent v o l c a n i c a s h i n t h e v i c i n i t y o f P a v i l i o n . 5.  - «• <.•>  y  v  Climate, Vegetation, Wild L i f e  The a r e a l i e s i n t h e "dry b e l t " o f t h e I n t e r i o r o f B r i t i s h Columbia w h i c h i s s h e l t e r e d from r a i n and snow by t h e Coast M o u n t a i n s .  The average annual p r e c i p i t a t i o n a t L i l l o o e t  over 41 y e a r s was 12.35 i n c h e s . winters cool.  The summers a r e warm and t h e  The extremes a t L y t t o n , some t h i r t y m i l e s s o u t h  o f t h e map a r e a i n 1956 were -9° i n January and 106° i n J u l y ; the extremes r e c o r d e d w i t h i n 30 y e a r s a r e -25° and 1120. ( P r o v i n c e o f B. C. Dept. o f A g r i c u l t u r e , 1957). The v e g e t a t i o n i s r e l a t i v e l y s p a r s e .  Some p a r t s o f  t h e a r e a a r e covered by f o r e s t s , some a r e p a r k - l i k e , and o t h e r s  open g r a s s - l a n d .  The  s l o p e s o f the w e s t e r n p a r t a r e more  d e n s e l y f o r e s t e d than those o f the e a s t e r n p a r t . trees are pines  Most o f the  ( l o d g e - p o l e p i n e , ponderosa p i n e ) ; w h i t e  spruce  balsam f i r and Douglas f i r , are common o n l y i n the h i g h e r c o o l e r a r e a s t h a t r e c e i v e more p r e c i p i t a t i o n .  Only a few moun-  t a i n s r i s e above timber l i n e w h i c h l i e s near 6500 f e e t . f l a t s a r e c h a r a c t e r i z e d by sage b r u s h , bunch grass and The a r e a i s noted  f o r b i g game.  and  Valley cactus.  Deer, moose, and  black  bears a r e common i n the Bowman Range and on the west s i d e o f the F r a s e r R i v e r ; goats were observed  on the west s i d e o f the  r i v e r , southwest o f P a v i l i o n . 6.  Industries  The main i n d u s t r y o f the a r e a i s c a t t l e r a n c h i n g . The  s o i l s o f the F r a s e r R i v e r v a l l e y , p a r t i c u l a r l y wind blown  s i l t s , w h i c h were seen i n many l o c a l i t i e s , are v e r y  fertile,  but the r a i s i n g o f c a t t l e f e e d depends on i r r i g a t i o n , and  only  a few c r e e k s c a r r y water a l l summer. Logging  i s second i n importance.  I n 1956  and  1957  o n l y f o r e s t s on the east s i d e o f the F r a s e r R i v e r near P a v i l i o n K e l l y L a k e , and Jesmond were logged but p r e p a r a t i o n s f o r the e x p l o i t a t i o n o f the west s i d e were b e i n g made. Mining i s r e l a t i v e l y unimportant.  I n 1958  only  two  p l a c e r mines were o p e r a t i n g , one on the F r a s e r R i v e r , o p p o s i t e Fountain  (M3) and the o t h e r one on Watson Bar Creek.  e x p l o r a t i o n work was  Some  done on the c l a i m s o f the Monty group  (M2), southwest o f Ward Creek.  8 T o u r i s m and b i g game h u n t i n g p r o v i d e another o f income f o r l o c a l A power dam  source  people. on the F r a s e r R i v e r would h e l p the  local  i n d u s t r i e s g r e a t l y by p r o v i d i n g cheap e l e c t r i c i t y , a l l o w i n g e x t e n s i v e i r r i g a t i o n , and by a t t r a c t i n g t o u r i s t s 1959).  (Warren,  9 CHAPTER I  GENERAL GEOLOGY  I n t r o d u c t o r y Statement The g e n e r a l geology o f t h e a r e a i s summarized on t h e following table o f formations.  The term D i v i s i o n was used  f o r c e r t a i n u n i t s by D u f f e l and McTaggart (1952).  The usage  i s f o l l o w e d here and t h e term i s a p p l i e d t o o t h e r u n i t s t h a t a r e r o u g h l y e q u i v a l e n t t o f o r m a t i o n s but n o t w e l l enough known t o j u s t i f y f o r m a t i o n a l names.  L o c a l u n i t s o f somewhat un-  c e r t a i n s t r a t i g r a p h i c p o s i t i o n a r e termed "assemblage" and d e s i g n a t e d by t h e name o f t h e a r e a i n w h i c h they o c c u r .  TABLE OF FORMATIONS Succession  System  Series  Quaternary  Recent and Pleisto -cene  Stage  Group  Format i o n or Division  Assemblage  Member  . L i t h o l o g y and  Contacts  Alluvium, v o l c a n i c ash, r i v e r g r a v e l , sand, and s i l t , mudflows, t u f f , conglomerate, g l a c i a l outwash and t i l l . - unconformity -  Cenozoic  Tertiary  o l i v i n e b a s a l t , minor andesite.  Middle or l a t e Tertiary  - conformable  contact -  l i t h i c a r e n i t e , conglome r a t e , minor s h a l e - angular unconformity -  Eocene Oligocene or younger  t u f f , f e l s i t e , andesite, b a s a l t , minor c o a l . - conformable  EoceneOligocene  French Bar Formatior  contact -  conglomerate, v o l c a n i c a r e n i t e , minor s i l t s t o n e , p l a n t seams. - unconformity -  Cenoz o i c or Mesozoic  Pre-Oligocene post e a r l y Lower Cretaceous  Ward Creek assemblage  andesite, dacite, f e l s i t e , t u f f , minor b a s a l t , volcanic arenite, coal. - not i n c o n t a c t -  Succession  Cenoz o i c or Mesozoic  System  Series  Stage  Group  Format i o n or Division  •Assemblage  Member  Lower C r e t a c eous or younger /  L i t h o l o g y and C o n t a c t s  gabbro and d i a b a s e dykes - not i n c o n t a c t Albian? or  Spences Bridge Group ? or K i n g svale Grp. ?  Fountain Valley assemblage  C B A  a n d e s i t e , minor v o l c a n i c a r e n i t e , volcanic brec c i a , p l a n t seams felsite a n d e s i t e , f e l s i t e , minor conglomerate. - not i n c o n t a c t -  Aptian?  Spences B r i d g e Grp. lower D i v . or K i n g s v a l e Grp. D i v . B.  Glen Fraser ass em.  andesite, dacite.  - c o n t a c t not exposed a n d e s i t e , d a c i t e , minor t u f f , volcanic arenite.  Div.B  Mesozoic  Cretaceous  Lower Cretaceous  Albian?  Kingsv a l e Grp  - conformable Div.  A  contact -  v o l c a n i c a r e n i t e , cong l o m e r a t e , minor s i l t s t o n e , p l a n t seams. - unconformity -  Succession  System  Series  Stage  Group  'Forma t i o n or Division  Assemblage  'Member  a n d e s i t e , minor d a c i t e , volcanic arenite, s i l t stone.  Upper Division  Mesozoic  C r e t a - Lower Cretaeous eous  Aptian?  Spences Bridge Group  L i t h o l o g y and C o n t a c t s  - not i n c o n t a c t Lower Division  Gibbs Creek assemblage  C B  A  a n d e s i t e , minor d a c i t e , volcanic arenite, s i l t stone. andesite, f e l s i t e , v o l canic a r e n i t e , s i l t s t o n e , conglomerate, a r g i l l i t e , t u f f , agglomerate, andesite - not i n c o n t a c t -  Lower Division  Basal mem.  andesite, dacite, t u f f , andesitic breccia. - angular unconformity w i t h P a v i l i o n Group -  ro  S u c c e s s i o n System  Series  Stage  Group  FormAssema t i o n or blage Division  Member  L i t h o l o g y and C o n t a c t s  porphyritic quartz-diorite dykes and s i l l s . - i n t r u s i v e contact Div. C Barremiari(? ) Jackass Mtn. Grp,  volcanic arenite, a r g i l l i t e , conglomerate; minor p l a n t seams. - conformable  Div. B  contact -  conglomerate, v o l c a n i c a r e n i t e , minor a r g i l l ite. - l o c a l unconformities -  Mesozoic  Crelower baceous C r e taceous  Div. A  A I I I s i l t s t o n e , v o l c a n i c areni t e a r g i l l i t e , minor limestone. A l l v o l c a n i c a r e n i t e , minor siltstone, argillite, conglomerate, conglomerate, t u f f a c e o u s AI sandstone, v o l c a n i c a r e n i t e , minor p l a n t seams. - unconformity -  Succession  System  Series  Stage  Group  Lillooet Grp.?  AssemForma t i o n or blage Division Div. C  Member  L i t h o l o g y and C o n t a c t s  volcanic arenite (tuffaceous ) , c o n g l o m e r a t e , siltstone, argillite. - f a u l t contact with D i v i s i o n B, a n g u l a r unconformity? -  Mesozoic  Cretaceous  Lower Cretaceous  porphyritic quartz-diori t e dykes and s i l l s and a small q u a r t z - d i o r i t e pluton.  Neocomian?  - i n t r u s i v e contact Lillooet Grp.  Div. B  volcanic arenite, s i l t s t o n e , a r g i l l i t e , conglomerate. - gradational contact -  Div. A  argillite, siltstone, v o l c a n i c a r e n i t e , minor coal. - not i n c o n t a c t -  Succession  System  Series  Stage  Group  Forma t i o n or Division  Assemblage  Lower Cretaceous or older  Member  L i t h o l o g y and C o n t a c t s  quartz-diorite, diorite, g r a n o d i o r i t e s t o c k s and p o r p h y r i t i c dykes and s i l l s - i n t r u s i v e contact P a v i l i o n group -  Upper Triass i c (?)  serpentinized peridotite and c a r b o n a t e - s i l i c a alteration.  Mesozoic  - i n t r u s i v e contact P a v i l i o n group Triassi c (?) Div.II  Pavilion assera.  Big Bar assem.  -  t u f f , l i t h i c sandstone, a r g i l l i t e , chert, v o l canic flows. - gradational contact  Pavilion Grp.  Div.I  with  t u f f , v o l c a n i c a r e n i t e and greywacke, v o l c a n i c f l o w s , a r g i l l i t e , chert, limes t o n e ; minor b r e c c i a , s i l t stone, amphibolite, hornf e l s , meta-quartzite. - not i n c o n t a c t  Pavilion Grp.  M e s o z o i c and/ T r i a s s i c : and/ o r P a l e o z o i c or Upper P e r mian  with  -  c h e r t , a r g i l l i t e , minor t u f f , limestone, volcanic flows. - gradational contact  -  vn  Succession  System  Series  Stage  Group  FormAssema t i o n or blage Division  Upper Permian  Paleozoic  Permian  Upper Permian and/or Middle Permian  Member  IV Cache Creek Group  Marble Canyon Formation  Southern Bowman Range  III II I  L i t h o l o g y and C o n t a c t s  chert, a r g i l l i t e , limestone, t u f f , v o l c a n i c flows. limestone chert, a r g i l l i t e , limestone, t u f f , v o l c a n i c flows. limestone w i t h i n t e r bedded r i b b o n c h e r t . - conformable c o n t a c t  Middle Permian and/or Older  ii  Mt. Soues Div.  -  chert, a r g i l l i t e , t u f f , volcanic flows, limestone.  ON  17 1  K  SEDIMENTARY AND VOLCANIC ROCKS  CACHE CREEK GROUP  Introduction The Cache Creek group was f i r s t d e s c r i b e d by S e l w y n , i n 1872, who d i v i d e d i t i n t o a lower and an upper p a r t . lower p a r t , s t u d i e d i n o u t c r o p s  The  a l o n g t h e C a r i b o o Highway be-  tween M a r t e l and C l i n t o n , was s a i d t o c o n t a i n l i m e s t o n e ,  black  s h a l e , r o c k s r i c h i n e p i d o t e and c h l o r i t e a s s o c i a t e d w i t h t a l c and  s e r p e n t i n e , d i o r i t e , and f e l s i t i c  porphyries.  Brachiopods  from t h i s u n i t i n d i c a t e d an age somewhere between t h e o l d e s t Devonian and t h e youngest Permian.  The upper p a r t , i n v e s t i -  gated between C l i n t o n and P a v i l i o n , was found t o c o n t a i n l i m e s t o n e , m a r b l e , d o l o m i t e , c h l o r i t i c and e p i d o t i c r o c k s , and black shales.  F o r a m i n i f e r a from t h e M a r b l e Canyon  limestone  were m i s i d e n t i f i e d by W.J. Dawson as L o f t u s i a and c o n s i d e r e d t o be Eocene o r C r e t a c e o u s i n age. G.M. Dawson's r e p o r t on t h e Kamloops a r e a (1895) contains the f i r s t  comprehensive d e s c r i p t i o n o f t h e Cache Creek .  " f o r m a t i o n " o f t h e type a r e a .  Dawson d e s c r i b e d t h e d i s t r i b u t i o n  o f major l i t h o l o g i c a l u n i t s as f o l l o w s :  t h e M a r b l e Canyon l i m e -  s t o n e s , shown as a s e p a r a t e map u n i t , form a n o r t h w e s t e r l y t r e n d i n g b e l t , t h a t extends from t h e C o r n w a l l H i l l s t o t h e northwestern  e x t r e m i t y o f t h e map a r e a but i s c o n c e a l e d by  T e r t i a r y r o c k s i n t h e v i c i n i t y o f Hat Creek.  Immediately t o  18 the east o f t h e l i m e s t o n e , i n t h e a r e a o f C a t t l e V a l l e y , McLean Lake, and M e d i c i n e stone a r e dominant.  Creek, v o l c a n i c rocks a s s o c i a t e d w i t h l i m e F a r t h e r e a s t , on B o n a p a r t e R i v e r and  Thompson R i v e r , c h e r t y q u a r t z i t e s and a r g i l l i t e s abundant.  To t h e west o f t h e l i m e s t o n e  a r e most  b e l t , i n t h e Edge H i l l s ,  i n t h e w e s t e r n p a r t o f t h e P a v i l i o n M o u n t a i n s , and on Mount M a r t l e y , c h e r t and a r g i l l i t e a r e dominant; f a r t h e r w e s t , on P a v i l i o n Creek and Leon C r e e k , most o f t h e r o c k s a r e v o l c a n i c . Dawson, as d i d S e l w y n , c o n s i d e r e d  t h e M a r b l e Canyon  limestones  to be t h e upper p a r t o f t h e f o r m a t i o n but s t r e s s e d t h e i r graphic c o n t i n u i t y w i t h the underlying As t h e l i m e s t o n e  strati-  rocks.  b e l t i s f l a n k e d t o t h e east and west by  " o l d e r " r o c k s he thought t h a t t h e r e g i o n a l s t r u c t u r e was a major s y n c l i n e m o d i f i e d by numerous minor f o l d s .  H i s summary o f t h e  s t r a t i g r a p h y o f t h e Cache Creek group i s based on a composite s e c t i o n t h r o u g h t h e e a s t e r n l i m b o f t h a t " s y n c l i n e " (l895»p.46B): Feet 1.  M a s s i v e l i m e s t o n e s (Marble Canyon l i m e s t o n e ) w i t h some minor i n t e r c a l a t i o n s o f v o l c a n i c r o c k s , a r g i l l i t e s and e h e r t y q u a r t z i t e s . A t l e a s t 1000 f e e t seen i n some s i n g l e exposures. T o t a l t h i c k n e s s probably at l e a s t  3000  2.  V o l c a n i c m a t e r i a l s and l i m e s t o n e s , w i t h some a r g i l l i t e s , c h e r t y q u a r t z i t e s , e t c . , Minimum t h i c k n e s s about 2000  3.  Cherty q u a r t z i t e s , a r g i l l i t e s , v o l c a n i c m a t e r i a l s and s e r p e n t i n e s w i t h some l i m e stone. The t h i c k n e s s o f t h e s e beds, o r o f a p a r t o f them, was r o u g h l y e s t i m a t e d i n two p l a c e s as between 4000 and 5000 f e e t . Minimum t o t a l t h i c k n e s s say 4500 9500  19 Dawson r e t a i n e d the o r i g i n a l i d e n t i f i c a t i o n o f L o f t u s i a but because o f accompanying f u s u l i n i d s r e f e r r e d i t to the C a r boniferous iferous  and d e f i n e d the Cache Creek as an e s s e n t i a l l y Carbon-  formation. As more i n f o r m a t i o n about the f u s u l i n i d s a c c u m u l a t e d ,  Dawson's age  d e t e r m i n a t i o n was  revised.  Dunbar (1932), Thompson  and Wheeler (1942), and Wickenden ( D u f f e l l and McTaggart, p. 23)  a l l agreed on a Permian age but d i s a g r e e d on the  1952,  specific  p o s i t i o n i n that period. D u f f e l l and McTaggart c a l l e d the Cache Creek a group and the M a r b l e Canyon l i m e s t o n e s  a formation.  Their report i s i n  c l o s e agreement w i t h Dawson's but o f f e r s two a l t e r n a t i v e hypotheses about the major s t r u c t u r e and i n the group.  The  s t r a t i g r a p h i c order  with-  f i r s t i s Dawson's concept t h a t two major u n i t s  a r e a r r a n g e d i n a s y n c l i n e ; the second t h a t the "group c o n s i s t s o f two  successions  l i m e s t o n e s , and  o f a r g i l l i t e s , c h e r t s , g r e e n s t o n e s , minor  q u a r t z i t e s , separated  the M a r b l e Canyon l i m e s t o n e s . " f i r s t hypothesis  (p. 1 7 ) .  According  to  the Cache Creek group i s a p p r o x i m a t e l y  feet t h i c k , according The  by the t h i c k s e r i e s o f  to the second h y p o t h e s i s  the 10,000  20,000 f e e t .  l a t t e r t h i c k n e s s i s comparable, as D u f f e l l and McTaggart have  p o i n t e d o u t , to a s e c t i o n o f 24,000 f e e t measured by Armstrong i n the F o r t S t . James a r e a (1949) t h a t i n c l u d e s t h r e e stone u n i t s and  four separate  chert  lime-  successions.  I n an attempt t o s o l v e the problems r e s u l t i n g from the e a r l i e r work the M a r b l e Canyon F o r m a t i o n was detail.  s t u d i e d i n some  F o s s i l s from the upper p a r t o f t h a t f o r m a t i o n  are  20  a s s i g n e d by W.R. Danner t o t h e Upper and (?) M i d d l e Permian. In t h e s o u t h e r n p a r t o f t h e Bowman Range t h e Marble  Canyon  f o r m a t i o n i s a p p r o x i m a t e l y 6000 f e e t t h i c k and c o n t a i n s c h e r t , a r g i l l i t e , t u f f , v o l c a n i c f l o w s , and about 2500 f e e t o f l i m e stone.  I t here forms a n o r t h w e s t e r l y t r e n d i n g a n t i c l i n o r i u m  that i s overturned to the northeast.  I n the core o f the a n t i -  c l i n o r i u m , on t h e s o u t h s l o p e o f Mount Soues an o l d e r u n i t , about 1500  f e e t t h i c k c o n t a i n i n g l i t t l e l i m e s t o n e i s exposed w h i c h i s  here c a l l e d Mount Soues D i v i s i o n .  The r o c k s t o t h e west o f Bowman  Range and P a v i l i o n Mountains appear t o o v e r l i e t h e M a r b l e Canyon f o r m a t i o n conformably.  A f o s s i l found i n these r o c k s i s  p r o b a b l y o f T r i a s s i c age. As t h e Cache Creek group has been d e f i n e d as a Permo-Pennsylvanian u n i t (Armstrong, 1949> p. 50) the P e r m o - T r i a s s i c r o c k s o v e r l y i n g t h e Marble Canyon f o r m a t i o n a r e a s s i g n e d t o a new u n i t , t h e P a v i l i o n group. MOUNT SOUES DIVISION On t h e s o u t h e a s t s l o p e o f Mount Soues r i b b o n c h e r t , a r g i l l i t e , v o l c a n i c flow-rocks mostly o f basic composition, t u f f , and l i m e s t o n e a r e exposed.  The assemblage d i f f e r s from  r o c k s o f t h e P a v i l i o n group i n two r e s p e c t s :  t h e presence o f  l i m e s t o n e s t h a t a r e i n t e r l a m i n a t e d w i t h r i b b o n c h e r t , and t h e r e l a t i v e abundance o f b a s i c v o l c a n i c f l o w s .  The o u t c r o p zone  i s about two m i l e s wide and pinches o u t t o t h e n o r t h w e s t . t h i c k n e s s o f t h e u n i t w h i c h i s o v e r l a i n conformably  The  by t h e  Marble Canyon f o r m a t i o n i s e s t i m a t e d as a p p r o x i m a t e l y 1500 f e e t . The r o c k s a r e f o l d e d and f a u l t e d and seem t o occupy t h e c o r e o f an  21  anticlinorium formed by the basal member of the Marble Canyon formation.  As the Marble Canyon Formation i s Middle (?) and  Upper Permian the Mount Soues D i v i s i o n probably i s Middle Permian and/or older. MARBLE CANYON FORMATION 1. D i s t r i b u t i o n In the present map area the Marble Canyon formation underlies the Bowman Range and the central part of the P a v i l i o n Mountains.  In the Bowman Range where the formation has been  mapped i n i t s f u l l width i t occupies a belt approximately 8 miles wide. 2.  Lithology and Thickness  Because of facies changes, complications by f a u l t i n g and f o l d i n g , and the scarcity of marker beds, bedding  attitudes,  and stratigraphic top determinations i t has been almost impossible to work out the structure and stratigraphy of the Marble Canyon formation.  An attempt to establish a s t r a t i -  graphic sequence could be made only i n the southern part of the Bowman Range.  Four members I, I I , I I I , IV are distinguished  here, and a f i f t h I l i a i s recognized i n the central and northern parts of the area.  The stratigraphy described on the following  pages i s v a l i d only for the southern part of the Bowman Range; i t i s impossible, for example, to recognize the same members i n the Marble Canyon.  22  Member I , a p p r o x i m a t e l y 200 t o 300 f e e t t h i c k i s composed o f l i m e s t o n e and r i b b o n c h e r t . massive,  The l i m e s t o n e i s p a r t l y  and p a r t l y i n t e r l a m i n a t e d w i t h r i b b o n c h e r t .  o f c h e r t a r e one t o t h r e e i n c h e s t h i c k .  Laminae  Most o f t h e laminae  are e x t e n s i v e but a t some l o c a l i t i e s they form s h o r t u n i t s one to s e v e r a l f e e t l o n g .  The l i m e s t o n e seems t o be c o n t i n u o u s  over most o f t h e a r e a , but i n t h e v i c i n i t y o f F i f t y - S e v e n Creek i t a p p a r e n t l y forms d i s c o n t i n u o u s l e n s e s t h a t i n t e r f i n g e r w i t h chert.  No f o s s i l s were found i n t h e u n i t . Member I I , w h i c h o v e r l i e s I i s p o o r l y exposed.  I t com-  p r i s e s c h e r t , a r g i l l i t e , t u f f , s m a l l l e n s e s and beds o f l i m e s t o n e , and v o l c a n i c f l o w r o c k s .  A l t h o u g h t h e member appears t o  be 3200 f e e t t h i c k i t p r o b a b l y has been r e p e a t e d by f o l d i n g , and t h e t r u e t h i c k n e s s perhaps l i e s between 500 and 1000 f e e t . Member I I I , i s composed m a i n l y o f l i m e s t o n e but l o c a l l y c o n t a i n s s m a l l amounts o f i n t e r b e d d e d c h e r t and a r g i l l i t e . The member forms a h i g h r i d g e , about 13 m i l e s l o n g , t h a t c u l m i n a t e s i n Mount Bowman ( P l a t e V ) .  S o u t h o f P o r c u p i n e Creek t h e  l i m e s t o n e i s a p p r o x i m a t e l y 1000 f e e t t h i c k ; s o u t h o f Two-Mile Creek i t t a p e r s and f i n a l l y d i s a p p e a r s .  N o r t h o f P o r c u p i n e Creek t h e  s t r u c t u r e p r o b a b l y i s c o m p l i c a t e d by f a u l t i n g and f o l d i n g and n e i t h e r t h e f u l l s t r i k e - l e n g t h nor t h e s t r a t i g r a p h i c t h i c k n e s s o f t h e l i m e s t o n e mass a r e c e r t a i n .  The l i m e s t o n e masses on  Mount K e r r (about 2500 t o 3000 f e e t t h i c k ) a r e perhaps i n t h e same s t r a t i g r a p h i c p o s i t i o n as t h e ones on Mount Bowman but t h e two a r e n o t connected  by o u t c r o p ; p o s s i b l y these bodies a r e  23  lenticular.  Most o f t h e l i m e s t o n e i s pure and massive and  shows no bedding.  I n some l o c a l i t i e s , however, a l t e r n a t i n g  l i g h t g r e y and.; dark grey l a y e r s a r e v i s i b l e t h a t a r e from a few m i l l i m e t e r s t o one c e n t i m e t e r t h i c k .  Under t h e m i c r o s c o p e  the l a y e r s a r e seen t o d i f f e r i n g r a i n s i z e and i n t h e p r o p o r t i o n o f minute i n c l u s i o n s i n t h e c a r b o n a t e .  Some o f t h e r o c k s a r e  c a l c a r e n i t e s and show graded b e d d i n g , r i p p l e marks, and i n t r a formational  breccias.  (Plate VI).  B r e c c i a s made up o f fragments  t h a t range from a few m i l l i m e t e r s t o one i n c h i n s i z e l o c a l l y o c c u r w i t h i n t h e massive l i m e s t o n e .  I n the northern part o f the  map a r e a some r o c k s t h a t may be c o r r e l a t i v e w i t h member I I I contain oolites.  F o s s i l s a r e r e l a t i v e l y r a r e ; remains o f c o l o n i a l  c o r a l s , o f c r i n o i d s , e c h i n o i d s , a l g a e , and f u s u l i n i d s have been found a t a few l o c a l i t i e s . I n t h e s y n c l i n e on Mount K e r r t h e t h i c k massive l i m e stone o f member I I I i s o v e r l a i n by a bed o f l i m e s t o n e , imately  500 f e e t t h i c k , t h a t c o n t a i n s  of i n t e r l a m i n a t e d  laminae o f c h e r t .  approxA sheet  l i m e s t o n e and c h e r t forms t h e c r e s t o f t h e  Bowman Range between Mann Creek and Jesmond Creek.  Scattered  o u t c r o p s o f a s i m i l a r t y p e o c c u r between Jesmond Creek and t h e northern extremity  o f t h e Bowman Range.  These r o c k s a r e t e n t a -  t i v e l y r e f e r r e d t o member I l i a , but I t i s not c e r t a i n whether a l l o f them a r e i n t h e same s t r a t i g r a p h i c p o s i t i o n . A t h i n - s e c t i o n o f c h e r t from t h i s u n i t cons i s t s o f a n h e d r a l q u a r t z g r a i n s showing undulose e x t i n c t i o n t h a t range from a few m i c r o n s t o .2 mm i n d i a m e t e r . Some s p h e r i c a l aggregates w i t h a d i a m e t e r o f .08 mm and a few s p i n e - l i k e s t r u c t u r e s about .4 mm l o n g and ,05 mm wide composed o f v e r y f i n e - g r a i n e d s i l i c a a r e v i s i b l e ; they a r e p r o b a b l y of r a d i o l a r i a n o r i g i n .  24 A hand specimen o f l i m y c h e r t c o n s i s t s o f f i n e b l u e grey s t r i n g e r s , t h a t a r e one t o two c e n t i m e t e r s l o n g and a few m i l l i m e t e r s t h i c k , embedded i n a l i g h t grey groundmass. The s t r i n g e r s a r e c r e n u l a t e d and f r a c t u r e d . Under t h e m i c r o scope they a r e seen t o c o n s i s t o f f i n e - g r a i n e d s i l i c a , d o m i n a n t l y q u a r t z w i t h undulose e x t i n c t i o n , and s m a l l amounts o f c h a l c e d o n y . The l i g h t grey m a t r i x comprises about 50% carbonate g r a i n s p a r t o f w h i c h , showing rhombohedral h a b i t , a r e p r o b a b l y d o l o m i t e , and $0% q u a r t z and chalcedony. S i l i c a and carbonate a r e u n i f o r m l y d i s t r i b u t e d . A s p h e r i c a l s t r u c t u r e , about 12 mm i n diameter i s made up o f f i n e - g r a i n e d s i l i c a i n t h e c e n t e r and r e l a t i v e l y c o a r s e - g r a i n e d q u a r t z w i t h undulose e x t i n c t i o n at the periphery. Member IV ,. c o n s i s t s o f a r g i l l i t e , c h e r t , l i m e s t o n e , t u f f , t u f f a c e o u s sandstone,  and v o l c a n i c f l o w r o c k s , but o n l y  the l i m e s t o n e s a r e w e l l exposed.  The l a t t e r o c c u r i n l e n s e s and  beds r a n g i n g from a few hundred f e e t t o 8 m i l e s i n s t r i k e l e n g t h . Some a r e o f f a i r l y c o n s t a n t t h i c k n e s s , o t h e r s v a r y c o n s i d e r a b l y i n t h i c k n e s s along s t r i k e .  A mass on P a v i l i o n M o u n t a i n , f o r  example, t h a t i s about 2 m i l e s l o n g , ranges from 2 0 0 f e e t t o about 2000 f e e t i n t h i c k n e s s . show b e d d i n g .  Most o f t h e l i m e s t o n e s do n o t  I n a few l o c a l i t i e s o o l i t e s were n o t i c e d , and i n  o t h e r s f u s u l i n i d s , a l g a e , c o r a l s , p e l e c y p o d s , and.echinoderms ( ? ) . In t h e v i c i n i t y o f i n t r u s i o n s t h e l i m e s t o n e has r e c r y s t a l l i z e d to a f i n e - g r a i n e d marble w h i c h l o c a l l y shows a f o l i a t i o n i n the form o f f i n e dark l a y e r s r i c h i n carbonaceous m a t t e r .  The  t h i c k n e s s o f t h i s member i s u n c e r t a i n because i t s s t r u c t u r e c o u l d n o t be worked o u t .  On t h e west s i d e o f t h e Bowman Range  i t o c c u p i e s a b e l t one m i l e t o 1-1/2 m i l e s wide. o f t h e u n i t i s perhaps between 3000 and 6000  feet.  The t h i c k n e s s  The  s u c c e s s i o n i n t h e Marble Canyon f o r m a t i o n i n t h e  south-western  p a r t o f t h e Bowman Range may be summarized as  follows: Member  IV  " "  III II  1000 500-1000  I  200- 300  11  3000-6000 f e e t . " 11  11  Chert, a r g i l l i t e , limestone, t u f f , volcanic flows. Limestone Chert, a r g i l l i t e , limestone, t u f f , volcanic flows. Limestone w i t h i n t e r b e d d e d ribbon chert.  4700-8300 f e e t . The Marble Canyon f o r m a t i o n i n t h i s a r e a then i s a p p r o x i m a t e l y 6000 f e e t t h i c k and c o n t a i n s perhaps 2500 f e e t of limestone.  As t h e l i m e s t o n e forms conspicuous  the o t h e r r o c k s a r e m o s t l y c o n c e a l e d by overburden  c l i f f s and the pro-  p o r t i o n o f l i m e s t o n e i n t h e f o r m a t i o n has been o v e r e s t i m a t e d by p r e v i o u s  workers. 3.  Structure  Because o f f a c i e s changes, l a c k o f marker beds, and the s c a r c i t y o f bedding a t t i t u d e s and s t r a t i g r a p h i c t o p d e t e r minations  ( r e l a t e d to the r e e f a l character o f the limestones)  t h e whole s t r u c t u r a l p i c t u r e has n o t been worked o u t .  Some  s u c c e s s , however, was a c h i e v e d i n t h e s o u t h e r n p a r t o f t h e Bowman Range, and t h e i n f o r m a t i o n o b t a i n e d i n t h i s a r e a may b s u f f i c i e n t t o e s t a b l i s h t h e age r e l a t i o n o f t h e M a r b l e Canyon f o r m a t i o n t o t h e P a v i l i o n group. The  f o l l o w i n g t h r e e c r i t e r i a have been used f o r t h e  recognition of folds:  26 The most i m p o r t a n t c r i t e r i o n a r e bedding  attitudes.  However, s y s t e m a t i c changes i n s t r i k e and d i p c o u l d not observed  be  i n a l l o f the p o s t u l a t e d f o l d s . A V-shaped o r U-shaped l i m e s t o n e o u t c r o p v i s i b l e  on  a i r photographs i s s u g g e s t i v e o f the nose o f a p l u n g i n g f o l d because t h e l i m e s t o n e s i n most l o c a l i t i e s form conspicuous  out-  crops whereas the o t h e r r o c k t y p e s , w h i c h are l e s s r e s i s t a n t to w e a t h e r i n g , a r e m o s t l y covered by overburden.  However, t h i s  c r i t e r i o n a l o n e , i s not used to e s t a b l i s h a f o l d because the same o u t c r o p s i t u a t i o n c o u l d be produced  by the d i f f e r e n t i a l  w e a t h e r i n g o f a s o l i d mass o f l i m e s t o n e o r by f a c i e s changes. The t h i r d c r i t e r i o n i s f a u l t i n g i n the c r e s t a l o f a n t i c l i n e s o r i n the troughs o f s y n c l i n e s . f o l d i n g was  accomplished  of the s t r a t a .  areas  A p p a r e n t l y the  by v e r y l i t t l e flowage and much f r a c t u r i n g  I n the extreme case a box-type o f f o l d i s produced  w i t h s t e e p l y d i p p i n g l i m b s , a f l a t l y i n g c r e s t , and f a u l t s tween the c r e s t and the l i m b s . ( P l a t e IX)  be-  However, i n most  l o c a l i t i e s the c r e s t s or troughs a r e c h a r a c t e r i z e d by  irregular  contortions. I n t h e s o u t h e r n p a r t o f the Bowman Range Member I appears t o form a n o r t h w e s t e r l y p l u n g i n g a n t i c l i n o r i u m  which  i s o v e r t u r n e d to the n o r t h e a s t and i s composed o f a t l e a s t a n t i c l i n e s and the c o r r e s p o n d i n g s y n c l i n e s . F-F ). 1  (Plate VII)  shown on the map;  five  (Cross-section  A few f a u l t s , m o d i f y i n g t h e a n t i c l i n o r i u m are  o t h e r s a r e p r o b a b l y c o n c e a l e d by  The o n l y f o l d r e c o g n i z e d w i t h assurance  overburden.  i n the c e n t r a l  p a r t o f the Bowman Range i s an u p r i g h t , b r o a d , open s y n c l i n e on  i  Mount K e r r , w h i c h plunges t o t h e s o u t h e a s t  and f i t s between two  n o r t h w e s t e r l y p l u n g i n g a n t i c l i n e s o u t l i n e d by Member I . VIII)  A change i n t h e d i r e c t i o n o f d i p s and s t r o n g  (Plate  distortions  are w e l l d i s p l a y e d i n t h e c e n t r a l p a r t o f t h e s y n c l i n e w h i c h i s formed by t h e i n t e r l a m i n a t e d l i m e s t o n e and c h e r t o f Member I l i a . I n t h e n o r t h e r n p a r t o f t h e Bowman Range t h e d i p s o f the s t r a t a a r e m o s t l y moderate t o l o w ; t h e i r d i r e c t i o n s a r e u n i f o r m w i t h i n s m a l l areas but change a b r u p t l y from one a r e a t o another.  No f o l d s c o u l d be o u t l i n e d .  A few f a u l t s a r e shown  on t h e map.  I t i s b e l i e v e d t h a t many o t h e r s a r e h i d d e n by  overburden.  I t seems t h a t t h e s t r a t a here a r e broken i n t o  numerous f a u l t b l o c k s t i l t e d i n t o v a r i o u s d i r e c t i o n s .  The  dominance o f f a u l t i n g over f o l d i n g i n t h e n o r t h e r n p a r t o f t h e map a r e a p r o b a b l y to  i s due t o t h e g r e a t t h i c k n e s s o f t h e s t r a t a ,  their lenticular  ( ? ) shape and t o l o w heat and p r e s s u r e  d u r i n g t h e time o f d e f o r m a t i o n . 4.  Mode o f O r i g i n  The absence o f c o a r s e - g r a i n e d  c l a s t i c r o c k s and t h e  dominance o f b i o l o g i c a l , c h e m i c a l , o r f i n e - g r a i n e d c l a s t i c m a t e r i a l suggests t h a t t h e source a r e a was o f low r e l i e f o r a t a g r e a t d i s t a n c e from t h e b a s i n o f d e p o s i t i o n . Three types o f l i m e s t o n e can be d i s t i n g u i s h e d . first Ilia). to  The  t y p e i s i n t e r l a m i n a t e d w i t h r i b b o n c h e r t (member I and These d e p o s i t s a r e m o d e r a t e l y t h i c k , r a n g i n g from 200  500 f e e t i n t h i c k n e s s and may cover as much as 100 square  miles.  As they a r e a s s o c i a t e d w i t h c h e r t t h a t i s p o s s i b l y o f  28 r a d i o l a r i a n o r i g i n , an analogous o r i g i n i s suggested f o r t h e limestone:  i t may have formed by t h e a c c u m u l a t i o n o f f r e e  f l o a t i n g calcareous  organisms, p o s s i b l y f o r a m i n i f e r a .  no f o s s i l s have been found i n t h e s e r o c k s .  Perhaps t h e s e d i -  ments were d e p o s i t e d v e r y s l o w l y and s u b j e c t e d r e c r y s t a l l i z a t i o n on t h e s e a f l o o r .  However,  t o s o l u t i o n and  The a l t e r n a t i v e i s i n o r g a n i c  p r e c i p i t a t i o n , but i t i s u n c e r t a i n whether t h e c o n d i t i o n s f o r such a process e x i s t e d . The second type o f l i m e s t o n e (up t o 2500 f e e t ) but p r o b a b l y and  echinoids  these rocks.  deposit i s extremely t h i c k  narrow.  C o r a l s , algae, bryozoa  ( t o g e t h e r w i t h f u s u l i n i d s ) have been found i n The f o s s i l s and t h e shapes o f t h e d e p o s i t s  that they are r e e f s .  suggest  However, Lowenstam (1950) argues t h a t not  any mass o f f o s s i l i f e r o u s l i m e s t o n e  showing r e e f l i k e dimensions  s h o u l d be c a l l e d a r e e f and r e q u i r e s e v i d e n c e t h a t sediment b i n d i n g organisms were p r e s e n t w h i c h were a b l e t o e r e c t wave resistant structures.  C e r t a i n c o l o n i a l c o r a l s s u c h as  Waagenophyllum ( ? ) w h i c h a r e l o c a l l y f a i r l y abundant may have been r e e f b u i l d e r s o f t h e type r e q u i r e d .  The t h i c k  limestone  masses i n t h e v i c i n i t y o f Mount K e r r a r e b e l i e v e d t o be r e e f s . A t h i r d t y p e , o c c u r r i n g i n t h e members I I and IV i s l e n t i c u l a r o r p o d - l i k e and ranges from one hundred f e e t t o several miles i n s t r i k e length.  Many o f t h e s e b o d i e s have  d i m e n s i o n s s i m i l a r t o t h o s e o f r e e f s but most o f them a r e l a c k i n g in fossils.  Perhaps some were r e e f s composed o f a l g a l s t r u c t u r e s  t h a t a r e no l o n g e r r e c o g n i z a b l e . is  uncertain.  The o r i g i n o f t h e s e d e p o s i t s  29  C a l c a r e n i t e s and b r e c c i a s i n t h e members I I I and i n d i c a t e l o c a l current a c t i v i t y . o o l i t e s may have been d e p o s i t e d wave a c t i o n ( I l l i n g ,  1954,  Ilia  Some o f the beds c o n t a i n i n g a t s h a l l o w d e p t h i n the zone o f  pp. 35-44).  The o r i g i n o f t h e r i b b o n c h e r t i s a c o n t r o v e r s i a l subject.  According  both fresh-water respect  t o modern e x p e r i m e n t a l  work ( K r a u s k o p f ,  and sea-water a r e h i g h l y u n d e r s a t u r a t e d  1956)  with  t o s i l i c a and n e i t h e r changes i n p.H. (below a p.H. o f  9) nor i n s a l i n i t y a p p r e c i a b l y substance.  a f f e c t the s o l u b i l i t y o f that  O n l y t h r e e o f t h e v a r i o u s hypotheses f o r t h e o r i g i n  o f c h e r t seem r e a s o n a b l e i n v i e w o f t h e r e q u i r e d c o n d i t i o n s e s t a b l i s h e d by K r a u s k o p f :  chemical  the d e p o s i t i o n of c o l l o i d -  a l s i l i c a from s i l i c e o u s s o l u t i o n s t h a t may be r e l a t e d t o volcanlsm and  ( D a v i s , 1918;  C a i r n e s , 1924b, p. 4 1 ) ; t h e l e a c h i n g  r e d e p o s i t i o n o f s i l i c a from v i t r i c  tuff, a material  that  d i s s o l v e s much f a s t e r t h a n m i n e r a l i c m a t t e r ( G o l d s t e i n and Hendricks,  1953)  and t h e a c c u m u l a t i o n o f d e b r i s from s i l i c e o u s  organisms ( B r a m l e t t e ,  1946).  B o t h v o l c a n i c f l o w s , and t u f f s  a r e p r e s e n t i n t h e M a r b l e Canyon f o r m a t i o n .  There i s however,  no s t r i k i n g a s s o c i a t i o n o f c h e r t and v o l c a n i c f l o w s and t h e r e l a t i v e l y s m a l l p r o p o r t i o n o f t u f f appears i n s u f f i c i e n t as s o u r c e o f the much l a r g e r volume o f c h e r t .  However,  thin-  s e c t i o n s o f c h e r t show s p i n e - l i k e and n o d u l a r s t r u c t u r e s c o u l d be o f o r g a n i c o r i g i n .  that  B e t t e r p r e s e r v e d specimens o f t h e  same t y p e have been found i n g r e a t e r D i v i s i o n I o f the P a v i l i o n group.  quantity i n the cherts o f  Therefore i t i s believed  that  t h e c h e r t o f t h e M a r b l e Canyon F o r m a t i o n i s l a r g e l y o f o r g a n i c origin.  30  5.  Age and C o r r e l a t i o n  F o s s i l s c o l l e c t e d a t 11 l o c a l i t i e s i n t h e Bowman Range (see G e o l o g i c a l Map) were i d e n t i f i e d by W.R.Danner: Fl  Locality:  On r i d g e , about 1 m i l e east o f Jesmond r o a d , 1.25 m i l e s n o r t h w e s t o f P o r c u p i n e C r e e k , upper p a r t .  Member IV Yabeina sp. Schwagerina sp. Verbeekina sp. Glomospira sp. G y r o p o r e l l a sp. associated: Age: F2  algae, c o r a l , small  fusulinids  Upper Permian.  Locality:  On r i d g e , about 1 m i l e east o f Jesmond road, 2 miles southeast  o f Mt. Bowman.  Member I I I Yabeina sp. one s m a l l V e r b e e k i n a type f u s u l i n i d f o r a m i n i f e r a , one s i m i l a r t o P a c h y p l o i a T e t r a t a x i s sp. Gyroporella sp. associated: Age:  echinoid d e b r i s , mollusc a coral.  Upper Permian.  s h e l l s , and  The assemblage c o u l d be s l i g h t l y o l d e r t h a n those from t h e other l o c a l i t i e s .  Locality:  On r i d g e about 2 m i l e s east o f Jesmond r o a d , 2 m i l e s n o r t h e a s t o f head o f P o r c u p i n e Creek  Member: I I I Yabeina minuta Schwagerina a c r i s Condonofusinella sp. T e x t u l a r i a sp. Age:  Upper Permian.  Locality:  Two m i l e s s o u t h e a s t o f Mt. K e r r , .7 m i l e s northwest o f F i f t y - s e v e n Creek.  Member I I I Yabeina columbiana ?Neoschwagerina s p . ?Verbeekina sp. Associated:  Age:  other f o r a m i n i f e r a ( ? ) , c o r a l s , algae, c o a r s e p l a t e s o f echninoderms, c r i n o i d stems, a b r y o z o a n fragment, and o o l i t e s .  Upper Permian.  Locality:  1.5 m i l e s west o f Mt. K e r r  Member I I I Yabeina minuta Schwa^erina a c r i s Condonofusinella sp. Age:  Upper Permian.  32  F6  3.2 m i l e s east o f Mt. Bowman, .2 m i l e s  Locality:  n o r t h o f Mann Creek Member  III?  Yabeina sp. Condonofusinella sp. Glomospira sp. Age: F7  Upper Permian 3.5 m i l e s e a s t - n o r t h e a s t o f Mt. Bowman,  Locality:  .5 m i l e s n o r t h o f Mann Creek. Member  III?  ?Waageno phy Hum s p . Associated: Age: F8  a t l e a s t two Permian type  Permian. 2 m i l e s east o f Mt. Bowman, .5 m i l e s west o f head o f Mann Creek  Locality: Member  fusulinids.  south-  III?  Yabeina sp. Age: F9  Upper Permian about 5 m i l e s east o f Jesmond, 1 m i l e n o r t h e a s t o f head o f Jesmond Creek  Locality: Member  III?  Two bryozoan fragments, c o r a l s ( ? ) , p r i m i t i v e f u s u l i n i d s ( ? ) a l g a l remains ( ? ) , o o l i t e s . Age: F10  unknown but p r o b a b l y Upper P a l e o z o i c .  Locality: Member  About 1/2 m i l e n o r t h northwest o f F 9  III?  C o r a l s , f o r a m i n i f e r a , e c h i n o i d stems. Age:  unknown.  33 Fll  Locality:  E a s t e r n bank o f B i g B a r Creek, about 2.5 m i l e s northwest o f Jesmond.  Member IV Fusulinids, Age:  pelecypods, c o r a l , algae or  echinoderms.  Permian.  W.R.Danner s t a t e s t h a t most o f t h e c o l l e c t i o n s c o n t a i n f u s u l i n i d s common t o t h e American "The  and A s i a t i c Tethys s e a .  a s s o c i a t i o n o f Yabeina-Schwa^erina-Condonofusinella i s  t y p i c a l as f a r as i s known f o r t h e uppermost f u s u l i n i d zone i n N o r t h A m e r i c a and i s c o n s i d e r e d t o be Upper Permian".  According  to Danner c o l l e c t i o n #2 might be s l i g h t l y o l d e r t h a n t h e o t h e r s but t h e f u s u l i n i d s a r e t o o r e c r y s t a l l i z e d t o e s t a b l i s h whether they a r e Neoschwagerina and hence a zone lower i n t h e Upper Middle  Permian. A l l f o s s i l s were c o l l e c t e d  i n t h e members I I I and IV  or i n r o c k s t h a t a r e b e l i e v e d t o be c o r r e l a t i v e w i t h these members.  B o t h members t h e r e f o r e appear t o be m o s t l y Upper  Permian; but t h e lower p a r t o f I I I may be Upper M i d d l e The members I and I I a r e perhaps M i d d l e  Permian.  Permian.  34 PAVILION GROUP Introduction The P e r m o - T r i a s s i c P a v i l i o n group i s composed o f c h e r t , a r g i l l i t e , v o l c a n i c f l o w - r o c k s and t u f f , v o l c a n i c sands t o n e s , l i m e s t o n e , s i l t s t o n e , conglomerate,  sedimentary  and t h e metamorphic e q u i v a l e n t s o f these r o c k s .  breccia  Two D i v i s i o n s  a r e d i s t i n g u i s h e d . Chert and a r g i l l i t e a r e dominant i n t h e lower p a r t ( D i v i s i o n I ) and v o l c a n i c r o c k s and sandstones i n the upper p a r t ( D i v i s i o n I I ) .  The t o p o f t h e Upper Permian  M a r b l e Canyon l i m e s t o n e marks t h e boundary o f t h e P a v i l i o n group w i t h t h e Permo-Pennsylvanian Cache Creek group.  The  r o c k s now a s s i g n e d t o t h e P a v i l i o n group were f o r m e r l y i n c l u d e d w i t h t h e Cache Creek group. DIVISION I 1.  D i s t r i b u t i o n and T h i c k n e s s  D i v i s i o n I extends e x t r e m i t y o f t h e map-area.  from t h e s o u t h e a s t e r n t o t h e n o r t h e r n On B i g B a r Creek, where t h e D i v i s i o n  i s c o n t i n u o u s l y exposed and i t s b o u n d a r i e s w i t h t h e u n d e r l y i n g and o v e r l y i n g f o r m a t i o n s a r e w e l l exposed, i t forms a zone about 5-1/2 m i l e s w i d e . and  I t s t h i c k n e s s may be anywhere between 1000  5000 f e e t and i s p o s s i b l y i n t h e v i c i n i t y o f 3000 f e e t . 2.  Lithology  D i v i s i o n I c o n s i s t s dominantly  o f c h e r t and a r g i l l i t e  35  and t h e i r metamorphie e q u i v a l e n t s and some l i m e s t o n e , t u f f , and l i t h i c sandstone.  V o l c a n i c flows are r a r e or absent.  Large b o d i e s o f t u f f and l i m e s t o n e , l o c a l l y accompanied by l i t h i c s a n d s t o n e , a r e found o n l y i n the v i c i n i t y o f the F r a s e r R i v e r between K e l l y and B u t c h e r C r e e k s . belong i n the upper p a r t o f D i v i s i o n I .  They p r o b a b l y  S m a l l masses o f t u f f ,  l i m e s t o n e , and r a r e l y l i t h i c sandstone o c c u r a t v a r i o u s l o c a l i t i e s and p r o b a b l y occupy d i f f e r e n t s t r a t i g r a p h i c  positions.  The c h e r t v a r i e s from l i g h t g r e y t o b l u i s h b l a c k i n color.  I t m o s t l y o c c u r s as " r i b b o n c h e r t " , t h a t i s i n l a y e r s  w h i c h a r e i n the o r d e r o f one t o t h r e e i n c h e s t h i c k and a r e s e p a r a t e d by t h i n s h e e t s o f a r g i l l i t e o r p h y l l i t e .  The c h e r t  l a y e r s have a c h a r a c t e r i s t i c s w e l l i n g and p i n c h i n g c r o s s section.  Cherty a r g i l l i t e s or cherts that c o n t a i n a h i g h  p r o p o r t i o n of a r g i l l a c e o u s m a t e r i a l are mostly massive. L i g h t grey c h e r t i s composed dominantly o f q u a r t z , and t o a s m a l l p r o p o r t i o n o f chalcedony and " c l a y " , t h a t i s c l a y s i z e d m i n e r a l s o f the c h l o r i t e - e p i d o t e - a n d  mica-groups.  Dark c h e r t c o n t a i n s s m a l l amounts o f carbonaceous  matter.  The q u a r t z i s p r e s e n t i n a n h e d r a l g r a i n s w h i c h range from a few t o a p p r o x i m a t e l y 30 m i c r o n s i n d i a m e t e r and show undulose extinction.  The q u a r t z e i t h e r forms a s t r u c t u r e l e s s  mosaic  or nodules.  These nodules a r e c o a r s e r g r a i n e d t h a n t h e  "mosaic" and have a h i g h e r c o n t e n t o f chalcedony and a lower content of "clay".  The nodules a r e s p h e r i c a l o r e l l i p t i c a l i n  s e c t i o n and range from . 0 3  t o . 3 mm  i n d i a m e t e r ; the  d i a m e t e r p r o b a b l y l i e s between .15 and  .2 mm.  average  A few nodules  36  show a r a d i a t i n g p a t t e r n around t h e m a r g i n ; one has a s p i n e like  p r o j e c t i o n ( P l a t e X, X I ) .  They bear a c l o s e resemblance t o  r a d i o l a r i a n c h e r t s i n w e l l p r e s e r v e d specimens o f C a l i f o r n i a ( J e n k i n s , 194-3, pp. 315, 319). C h e r t o f t h i s type was seen i n 13 o u t o f 18 t h i n - s e c t i o n s o f specimens  from v a r i o u s  localities.  Most s e c t i o n s c o n t a i n numerous minute v e i n l e t s o f q u a r t z and carbonate. the  Carbonate a l s o o c c u r s i n i s o l a t e d g r a i n s w i t h i n  chert. The a r g i l l i t e i s b l u i s h b l a c k and l a m i n a t e d t o m a s s i v e .  Under t h e m i c r o s c o p e minute c r y s t a l s o f m i c a , c h l o r i t e ,  car-  b o n a t e , and p a r t i c l e s o f carbonaceous m a t t e r a r e seen t o be embedded i n a groundmass o f low b i r e f r i n g e n c e t h a t i s t o o fine-grained f o r identification.  The o r g a n i c m a t t e r i s d i s -  p e r s e d t h r o u g h o u t t h e a r g i l l i t e but i n p h y l l i t i c concentrated i n p a r a l l e l l a y e r s .  specimens i t i s  Some o f t h e a r g i l l i t e  contains  m a s s i v e o r n o d u l a r a g g r e g a t e s o f f i n e - g r a i n e d s i l i c a and grades into chert.  Most o f t h e a r g i l l i t e has a s i l t - f r a c t i o n ,  com-  posed l a r g e l y o f f e l d s p a r f r a g m e n t s . The t u f f s do n o t form beds but l e n t i c u l a r masses w h i c h i n most l o c a l i t i e s  are associated with limestone.  A hand specimen o f a l i t t l e a l t e r e d t u f f a c e o u s r o c k i s b r o w n i s h g r e e n and composed o f a n g u l a r or l e n t i c u l a r fragments r a n g i n g from a f r a c t i o n o f a m i l l i m e t e r t o about 3 mm i n d i a m e t e r . The s e c t i o n c o n s i s t s dominantly o f f i n e - g r a i n e d h i g h l y a l t e r e d g r a i n s o f v o l c a n i c r o c k s some o f w h i c h are v e s i c u l a r o r a m y g d a l o i d a l , a s m a l l e r p r o p o r t i o n o f c h l o r i t e , w h i c h may r e p r e s e n t a l t e r e d v o l c a n i c g l a s s , and a few p e r c e n t o f q u a r t z , f e l d s p a r , h o r n b l e n d e , c l i n o - p y r o x e n e , and " i r o n ore". The t u f f a c e o u s o r i g i n o f t h e r o c k i s apparent from two f e a t u r e s : t h e c l i n o - p y r o x e n e , a  37 mineral which has not been observed by the writer as a d e t r i t a l mineral i n any sedimentary rock of the map-area, shows subhedral to euhedral forms; and the quartz has inclusions and rims of extremely fine-grained volcanic rock, probably r h y o l i t e or dacite. As the t u f f was deposited i n water i t may have incorporated some d e t r i t a l material. A specimen from the slope north of the upper part of Siwash Greek probably represents a sheared and altered limy t u f f . The hand specimen i s b l u i s h green and contains l i g h t to dark colored, rather angular fragments i n a l i g h t green groundmass. The fragments range from one centimeter to about one m i l l i meter i n s i z e . The t h i n section shows fragments of volcanic rocks embedded i n an abundant matrix of c h l o r i t e and carbonate. The fragments are porphyritic and vitrophyric and mostly amygdaloidal. They show l a t h - l i k e microlites and broad prisms of plagioclase i n a groundmass that i s altered to c h l o r i t e and very fine-grained deep brown carbonate. The carbonate of the cement i s strongly twinned, i n some places i n a feathery fashion. The c h l o r i t e of the groundmass occurs i n narrow stringers and large patches made up of radiating sheaves or f e l t e d masses. The limestones of D i v i s i o n I form pods and lenses. Short beds were observed i n only a few l o c a l i t i e s .  The largest  of the l e n t i c u l a r masses i s located on the slope north of the upper part of Siwash Creek and has been mapped as a separate unit. Except for gastropods, no f o s s i l s have been found i n these limestones.  Some of the limestones contain o o l i t e s and p i s o l i t e s  that range from a f r a c t i o n of a millimeter to several millimeters i n diameter.  Most of them are e l l i p s o i d a l ;  are spherical or spindle-shaped.  less commonly they  The o o l i t e s are made up of  concentric layers of very fine-grained carbonate. ures are rarely developed.  Radial s t r u c t -  The centre of the o o l i t e s i s occupied  by coarse-grained c a l c i t e , i n some specimens by a single c r y s t a l or, less commonly, by c h l o r i t e and chert nodules (Plate X I I ) .  Most o f the l i m e s t o n e s a r e a s s o c i a t e d w i t h t u f f s , near the c o n t a c t s the two r o c k s are mixed.  and  Some o f the l i m e -  stone near the c o n t a c t s c o n t a i n s g r e e n i s h o r b r o w n i s h w e a t h e r i n g s t r i n g e r s o f c h l o r i t e w h i c h i n some specimens a r e a s s o c i a t e d w i t h chalcedony.  A n g u l a r fragments o f l i m e s t o n e o r  irregular  b l e b s w i t h rounded o u t l i n e s a r e i n c o r p o r a t e d i n the t u f f .  The  s i z e o f t h e s e i n c l u s i o n s ranges from t e n s o f f e e t t o a f r a c t i o n of a centimeter. The chert.  l i t h i e sandstones  occur w i t h t u f f , a r g i l l i t e ,  At some l o c a l i t i e s they show graded bedding  and  and  are  s i m i l a r i n appearance t o those o f D i v i s i o n I I . 3.  Metamorphism  Where r o c k s o f D i v i s i o n I a r e i n c o n t a c t w i t h Coast I n t r u s i o n s they are h i g h l y metamorphosed.  Most o f the meta-  morphism i s r e l a t e d t o t h e p l u t o n between K e l l y Creek and  Leon  Creek and the best exposures a r e on b o t h banks o f the F r a s e r R i v e r near the mouth o f K e l l y Creek where a m i g m a t i t e  complex  c o n s i s t i n g o f d i o r i t i c dykes, a m p h i b o l i t e s and banded h o r n f e l s e s has been mapped as a s e p a r a t e u n i t .  I t i s not  certain,  however, i f a l l o f the r o c k s belong t o D i v i s i o n I ; some o f the r o c k s on the west shore may  be p a r t o f D i v i s i o n I I .  Near the mouth o f K e l l y C r e e k , a f a c i e s o f D i v i s i o n I r i c h i n t u f f a c e o u s r o c k s has been i n t r u d e d by d i o r i t i c dykes. The c o n t a c t between the dykes and the host r o c k i s g e n e r a l l y g r a d a t i o n a l and the host r o c k i s cut by numerous l e n s e s and v e i n l i k e s t r i n g e r s r i c h i n q u a r t z and f e l d s p a r . ( P l a t e X I I I )  39 A t y p i c a l specimen o f t h e t r a n s i t i o n r o c k , a blue-grey, f i n e - g r a i n e d , massive amphibolite i s cut by f i n e g r e y i s h w h i t e q u a r t z = f e l d s p a r v e i n l e t s t h a t a r e from one t o a few m i l l i m e t e r s wide. A t h i n - s e c t i o n from t h i s r o c k c o n t a i n s a p p r o x i m a t e l y 75%> o f hornblende ( g r a i n s i z e a p p r o x i m a t e l y .05-.5 mm) a s s o c i a t e d w i t h " i r o n o r e " and a t r a c e o f b i o t i t e , and 25% o f f i n e r g r a i n e d (.005-.25 mm) q u a r t z and f e l d s p a r . The p l a g i o c l a s e , c a l c i c andes i n e , i s p a r t l y a n h e d r a l , p a r t l y s u b h e d r a l , and m o s t l y twinned. A large proportion of the feldspar is water-clear. A p a r t o f t h e r o c k s on t h e w e s t e r n bank o f t h e F r a s e r R i v e r i n t h e same a r e a a r e f i n e l y l a y e r e d a m p h i b o l i t e s and hornfelses.  The r o c k s belong i n t h e h o r n b l e n d e - h o r n f e l s  f a c i e s ( F y f e , Turner and Verhoogen, 1958, p. 209), and may o r i g i n a l l y have been p h y l l i t e s o r s t r o n g l y j o i n t e d  argillites.  A specimen o f t h e s e f o l i a t e d r o c k s i s composed o f l i g h t grey and b l a c k l a y e r s r a n g i n g from one m i l l i m e t e r t o 1.5 c e n t i m e t e r i n t h i c k n e s s t h a t show f i n e c r e n u l a t i o n s . The dark l a y e r s c o n s i s t m a i n l y o f s u b h e d r a l hornblende c r y s t a l s , about .1 mm l o n g t h a t a r e s t r o n g l y p l e o c h r o i c ( z : b l u i s h green; y: g r e e n , x: p a l e b r o w n i s h g r e e n ) . The l i g h t c o l o r e d l a y e r s a r e made up o f c l o u d y , p a r t l y twinned c a l c i c o l i g o c l a s e w i t h a g r a i n s i z e o f a p p r o x i m a t e l y .05 mm, and a l i t t l e q u a r t z . Hornblende and p l a g i o c l a s e a r e p r e s e n t i n a p p r o x i m a t e l y equal proportions. A g r e y , m a s s i v e , v e r y f i n e - g r a i n e d specimen showing some medium-sized g r a i n s o f f e l d s p a r i s c h a r a c t e r i s t i c o f another  l a r g e group o f r o c k s on t h e west s i d e o f t h e F r a s e r  R i v e r , o p p o s i t e t h e mouth o f K e l l y Creek. o f t h e r o c k , w h i c h now belongs  The o r i g i n a l  nature  i n the epidote-albite hornfels  f a c i e s , i s u n c e r t a i n ; perhaps i t was an a c i d i c v o l c a n i c f l o w .  40  I t c o n s i s t s o f a p p r o x i m a t e l y $0% o f f e l d s p a r , 42% o f q u a r t z , 5% o f e p i d o t e , 2% o f c h l o r i t e , 1% o f c a r b o n a t e and t r a c e s o f sphene and " i r o n o r e " . The groundmass i s a t i g h t l y i n t e r l o c k e d aggregate o f a n h e d r a l q u a r t z , and s u b h e d r a l t o a n h e d r a l f e l d s p a r , b o t h r a n g i n g a p p r o x i m a t e l y from .05 t o .5 mm i n s i z e , t h a t i s c u t by s t r i n g e r s o f e p i d o t e , c h l o r i t e , and c a r b o n a t e . The f e l d s p a r c o n s i s t s m o s t l y o f twinned s o d i c a l b i t e ; p o t a s s i c f e l d s p a r i s r a r e o r a b s e n t . The a l b i t e o f t h e groundmass i s cloudy w i t h i n c l u s i o n s o f epidote; the l a r g e r c r y s t a l s , forming a n h e d r a l , twinned g r a i n s up t o 1.5 mm l o n g c o n t a i n i n c l u s i o n s o f q u a r t z , but n o t o f e p i d o t e . The f i n e - g r a i n e d c l o u d y f e l d s p a r o f t h e groundmass and some o f t h e q u a r t z a r e thought to be o r i g i n a l c o n s t i t u e n t s o f t h e r o c k s ; t h e i n c l u s i o n - f r e e p l a g i o c l a s e , and some o f t h e q u a r t z may have been i n t r o d u c e d . 4. The  Structure  c o n t a c t between D i v i s i o n I and t h e M a r b l e Canyon  f o r m a t i o n i s exposed o n l y i n t h e v i c i n i t y o f S a l l u s Creek and K e a t l e y C r e e k , n o r t h o f P a v i l i o n L a k e , and on B i g B a r Creek. I n these l o c a l i t i e s n e i t h e r an u n c o n f o r m i t y  n o r a major f a u l t  was o b s e r v e d a l t h o u g h t h e c o n t a c t s between l i m e s t o n e beds and a r g i l l i t e a r e l o c a l l y sheared. the p r o p o r t i o n o f i n t e r b e d d e d ward d i r e c t i o n .  The c o n t a c t i s g r a d a t i o n a l and limestone  i n c r e a s e s i n an e a s t -  As D i v i s i o n I i s i n c o n t a c t w i t h t h e upper-  most p a r t o f t h e M a r b l e Canyon f o r m a t i o n one might c o n c l u d e t h a t i t o v e r l i e s the limestones.  However t h e westward t r a n s i t i o n  from l i m e s t o n e t o c h e r t and a r g i l l i t e c o u l d r e p r e s e n t a f a c i e s change i n i s o c l i n a l l y f o l d e d s t r a t a , and i n t h i s case D i v i s i o n I would be p a r t l y contemporaneous w i t h t h e upper M a r b l e Canyon Formation.  41 I n most l o c a l i t i e s the s t r a t a o f D i v i s i o n I s t r i k e n o r t h w e s t e r l y and d i p s t e e p l y .  Marker beds are s c a r c e and  s t r a t i g r a p h i c tops c o u l d be determined  o n l y at a few  localities.  J u d g i n g from the w e l l s t r a t i f i e d and p l a s t i c n a t u r e o f the r o c k s they a r e t i g h t l y f o l d e d ; the p a t t e r n o f f o l d i n g may  be  similar  t o t h a t o f the younger L i l l o o e t group, w h i c h has a comparable lithology.  D r a g f o l d s a r e developed  o n l y i n the v i c i n i t y  f a u l t s and a r e here o f v e r y v a r i e d p l u n g e .  of  I n some l o c a l i t i e s  the l i m e s t o n e s show a l i n e a t i o n i n t h e form o f g r o o v e s ,  but  the plunges o f these l i n e a t i o n s are a l s o i r r e g u l a r .  Division  I i s p a r t l y bounded by f a u l t s (see page 57 ) but no  extensive  i n t e r n a l f a u l t s were r e c o g n i z e d .  However, t h e r e a r e  broad  areas u n d e r l a i n by sheared r o c k s t h a t a r e c r o s s e d by numerous minor i r r e g u l a r f a u l t s .  The most e x t e n s i v e o f t h e s e  zones i s exposed between Moran and K e l l y Creek.  shear  Other  shear  zones o f t h i s type were seen on the s l o p e n o r t h o f Gibbs C r e e k , i n H i g h Bar Canyon, and on the s l o p e s above B i g Bar C r e e k , near the mouth o f S t a b l e Creek.  I n a d d i t i o n t o these l a r g e zones  shown on the map  t h e r e are numerous s m a l l ones t h a t have not  been i n d i c a t e d .  Almost a l l c o n t a c t s between massive r o c k s ,  such as l i m e s t o n e , t u f f o r l i t h i c sandstone on the one and l a m i n a t e d a r g i l l i t e and c h e r t on the o t h e r hand are Some o f t h e d i s t o r t i o n s may movements o f sedimentary  have been caused by  hand, sheared.  differential  s t r a t a d u r i n g f o l d i n g , o t h e r s seem t o  be r e l a t e d to movements o f Coast I n t r u s i o n s .  42 5.  Mode o f O r i g i n  Remnants o f r a d i o l a r i a n s k e l e t o n s  i n the chert  suggest  t h a t D i v i s i o n I was l a i d down i n a marine environment.  The  presence o f carbonaceous m a t t e r i n d i c a t e s a " r e s t r i c t e d " env i r o n m e n t (Krumbein and G a r r e l s , 1952). coarse-grained grained  The s c a r c i t y o f  c l a s t i c sediments and t h e dominance o f f i n e -  c l a s t i c and b i o c l a s t i c sediments i n d i c a t e s t h a t t h e  s o u r c e a r e a was o f low r e l i e f o r a t a g r e a t d i s t a n c e from t h e site of deposition. area.  There was l i t t l e v o l c a n i c a c t i v i t y i n t h e  The environment o f D i v i s i o n I appears s i m i l a r t o t h a t  o f t h e M a r b l e Canyon f o r m a t i o n ,  except t h a t c o n d i t i o n s f o r t h e  growth o f r e e f s were r a r e o r l a c k i n g .  I f Division I i s partly  contemporaneous w i t h t h e M a r b l e Canyon f o r m a t i o n was d e p o s i t e d  i t probably  seaward from t h e r e e f zone.  The o r i g i n o f t h e c h e r t , t u f f , and l i m e s t o n e ,  pose  s p e c i a l problems. Microscopic  e x a m i n a t i o n shows t h a t t h e c h e r t s a r e com-  posed o f a c o n s i d e r a b l e  p r o p o r t i o n o f n o d u l e s t h a t resemble  the r a d i o l a r i a n remains o f r e l a t i v e l y w e l l p r e s e r v e d (Compare J e n k i n s , 194-3) pp. 315  }  319) r o c k s .  A few o f t h e s e n o d u l e s  show r a d i a t i n g s p i n e - l i k e s t r u c t u r e s around t h e margins are s t r o n g l y suggestive microscopic  o f an o r g a n i c  origin.  that  Because o f t h e  e v i d e n c e and t h e s c a r c i t y o f v o l c a n i c c e n t e r s i n  the a r e a i t i s b e l i e v e d t h a t t h e c h e r t i s o f o r g a n i c  origin.  The a l t e r n a t i o n s o f c h e r t and a r g i l l i t e may be due t o s e a s o n a l changes t h a t governed t h e l i f e o f t h e s i l i c e o u s organisms o r  43 t h e d e p o s i t i o n o f the a s s o c i a t e d i n o r g a n i c m a t t e r . The  l e n t i c u l a r shape o f the t u f f b o d i e s and  features of  b r e c c i a t i o n near t h e i r margins i n d i c a t e t h a t the t u f f s were  de-  p o s i t e d by c u r r e n t s , perhaps d e n s i t y c u r r e n t s t h a t o r i g i n a t e d when t h e t u f f a c e o u s m a t e r i a l entered The o r i g i n o f the l i m e s t o n e  the water. in Division I is a  diffi-  c u l t problem. The  b i g , p o d - l i k e mass n o r t h o f S i w a s h Creek i s r e e f -  l i k e i n shape, but no f o s s i l s have been found i n i t . t h e s m a l l e r b o d i e s two  c o n s i s t e n t f e a t u r e s may  Regarding  be o f  genetic  s i g n i f i c a n c e : the a s s o c i a t i o n o f the l i m e s t o n e w i t h t u f f s ,  and  t h e s i g n s o f c u r r e n t a c t i v i t y such as o o l i t e s and c e r t a i n features of b r e c c i a t i o n . d i f f e r e n t ways.  The  These r e l a t i o n s c o u l d be e x p l a i n e d  l i m e s t o n e s may  be i n o r g a n i c and  their  p r e c i p i t a t i o n c o u l d have been caused by the c u r r e n t s c a r r i e d the t u f f a c e o u s m a t t e r .  that  The  s o l u b i l i t y of calcium  bonate i n sea water ( R e v e l l e , 1934)  depends on the c a r b o n  d i o x i d e content and pH.  The  o f the w a t e r , on i t s t e m p e r a t u r e ,  o f some c a l c i u m c a r b o n a t e .  thus caused the  car-  pressure  c u r r e n t s d e s c e n d i n g from the s u r f a c e may  warmed up the bottom w a t e r s and  have  precipitation  However, the amount o f  limestone  produced by such a p r o c e s s would be r e l a t i v e l y s m a l l .  It is  a l s o p o s s i b l e t h a t the c u r r e n t s c o l l e c t e d u n c o n s o l i d a t e d  limy  m a t e r i a l from the sea bottom and  with  the t u f f a c e o u s m a t e r i a l .  swept i t a l o n g t o g e t h e r  A t h i r d p o s s i b i l i t y i s that  d e p o s i t i o n o f b o t h t u f f and l i m e s t o n e was p r e s s i o n s on the sea f l o o r .  The  the  c o n t r o l l e d by  l i m e s t o n e may  in  de-  have been de-  p o s i t e d i n such d e p r e s s i o n s  owing t o b i o l o g i c a l o r p h y s i c o -  c h e m i c a l c o n d i t i o n s and t h e d e n s i t y c u r r e n t s may have dropped t h e i r l o a d here because o f dynamic f a c t o r s . 6.  Age  The s t r u c t u r a l r e l a t i o n s show t h a t D i v i s i o n I i s e i t h e r contemporaneous w i t h t h e upper p a r t o f t h e M a r b l e Canyon f o r m a t i o n o r younger. bably T r i a s s i c .  I t i s o v e r l a i n by D i v i s i o n I I w h i c h i s p r o -  Therefore  i t i s Upper Permian and/or T r i a s s i c  i n age. DIVISION I I 1.  D i s t r i b u t i o n and T h i c k n e s s  Rocks a s s i g n e d areas.  t o D i v i s i o n I I u n d e r l i e two s e p a r a t e  They have been c o r r e l a t e d because o f t h e i r  similar  l i t h o l o g y but they may n o t be e x a c t l y o f t h e same age. The o u t c r o p s  o f t h e B i g B a r assemblage form a zone about  3 m i l e s l o n g and up t o 1-1/2 m i l e s wide i n t h e v i c i n i t y o f t h e lower p a r t o f B i g B a r Creek.  Their thickness i s o f the order  o f 2500 f e e t . The P a v i l i o n assemblage u n d e r l i e s an a r e a about 10 m i l e s l o n g and up t o t h r e e m i l e s wide s i t u a t e d m o s t l y on t h e west s i d e o f t h e F r a s e r R i v e r between S a l l u s Creek and Moran.  The u n i t i s  bounded by f a u l t s , and so l i t t l e i s known about i t s i n t e r n a l s t r u c t u r e t h a t an a c c u r a t e statement o f t h e t h i c k n e s s cannot be given.  S e v e r a l thousand f e e t o f s t r a t a a r e p r o b a b l y  present.  2. A.  B i g Bar  Assemblage  Lithology Because o f f a c i e s changes and l a c k o f o u t c r o p the  s t r a t i g r a p h y o f t h e B i g B a r assemblage has not been worked o u t . A broad b e l t o f l i t h i c sandstone w i t h i n t e r l a m i n a t e d argillite Big  extends from t h e west s l o p e o f Mount K o s t e r i n g a c r o s s  B a r Creek t o t h e s o u t h s l o p e o f B i g Bar M o u n t a i n .  contacts of t h i s b e l t are g r a d a t i o n a l . bedding and abundant  The  The r o c k s show graded  c o n t o r t i o n s t h a t a p p a r e n t l y were produced  before the l i t h i f i c a t i o n  o f the s e d i m e n t s .  To the east o f  t h i s b e l t i n the v i c i n i t y o f B i g Bar C r e e k , f l o w s o f a n d e s i t e and d a c i t e a r e exposed.  The o t h e r p a r t s o f t h e a r e a a r e under-  l a i n by t u f f , r i b b o n c h e r t , a r g i l l i t e , and l i m e s t o n e .  The  l i m e s t o n e o c c u r s i n beds, not e x c e e d i n g h a l f a m i l e i n s t r i k e l e n g t h , i n l e n s e s and pods a s s o c i a t e d w i t h t u f f , o r i n t h i n layers interlaminated with a r g i l l i t e . A t y p i c a l specimen o f i n t e r l a m i n a t e d a r g i l l i t e ,  silt-  s t o n e , and sandstone from the w e s t - s l o p e o f Mount K o s t e r i n g weathers b r o w n i s h green.  I t s laminae o f a r g i l l i t e a r e from one  c e n t i m e t e r t o a f r a c t i o n o f a m i l l i m e t e r t h i c k ; a l a y e r cons i s t i n g m o s t l y o f sandstone and s i l t s t o n e i s about 3 c e n t i meters t h i c k .  A p p r o x i m a t e l y two t h i r d s o f t h e a r g i l l i t e  con-  s i s t o f c l a y - s i z e d m i n e r a l s , one t h i r d o f s i l t - s i z e d c a r b o n a t e , f e l d s p a r , and q u a r t z , and a s m a l l f r a c t i o n o f carbonaceous matter. of  The sandstone and t h e s i l t s t o n e a r e made up d o m i n a n t l y  c a r b o n a t e , f e l d s p a r , and q u a r t z , and a s m a l l e r p r o p o r t i o n o f  clay.  The specimen shows graded bedding and some c r o s s - b e d d i n g .  46 A graded u n i t ranges from v e r y f i n e - g r a i n e d sandstone at the bottom t h r o u g h s i l t s t o n e t o a r g i l l i t e .  The c o n t a c t between two  graded u n i t s i s marked by a c o n c e n t r a t i o n o f carbonaceous m a t t e r and f l u t i n g s i n the a r g i l l i t e , and by an abrupt change i n grain-size. The v o l c a n i c f l o w r o c k s weather g r e e n i s h grey and mostly p o r p h y r i t i c .  Two  are  specimens o f a l t e r e d a n d e s i t e con-  s i s t d o m i n a n t l y o f a l b i t e w h i c h forms m i c r o l i t e s and phenoc r y s t s , and a s m a l l e r p r o p o r t i o n o f e p i d o t e , ( l a r g e l y i t e ) , c h l o r i t e , and c a r b o n a t e ; one specimen shows by p r e h n i t e .  The l a c k o f z o n i n g , the a l b i t i c  pistac-  replacement  composition,  and  the abundance o f e p i d o t e , i n d i c a t e s t h a t the p l a g i o c l a s e has been a l t e r e d . In a L t h i n - s e c t i o n o f m e t a - d a c i t e , phenoc r y s t s o f c a l c i c a l b i t e are embedded i n a f i n e g r a i n e d groundmass c o n s i s t i n g l a r g e l y o f a l b i t e and q u a r t z . The p l a g i o c l a s e has r e l a t i v e l y few i n c l u s i o n s . The p a r t l y jagged o u t l i n e s o f t h e c r y s t a l s and undulose e x t i n c t i o n i n d i c a t e r e c r y s t a l l i z a t i o n . The r o c k i s v e i n e d by q u a r t z and e p i d o t e . B.  Structure The  southwestern  c o n t a c t o f t h e B i g Bar assemblage, ex-  posed near the road t o the H i g h Bar f e r r y p r o b a b l y i s f a u l t e d . The r o c k s a r e s t r o n g l y s h e a r e d , and the t r a n s i t i o n from t u f f to c h e r t and a r g i l l i t e gradational.  i s abrupt.  The n o r t h e a s t e r n c o n t a c t i s  No major f a u l t i s v i s i b l e h e r e , but t h e c o n t a c t s  between masses o f t u f f and c h e r t and a r g i l l i t e a r e sheared and a l t e r e d . forms a nose.  locally  I n the s o u t h e a s t t h e u n i t t a p e r s  The n o r t h w e s t e r n  c o n t a c t i s not exposed.  and The  s t r a t a s t r i k e approximately steeply northeast.  N 40° ¥ and d i p m o d e r a t e l y t o  A t many d i f f e r e n t l o c a l i t i e s i n t h e s o u t h -  w e s t e r n h a l f o f t h e u n i t t h e s t r a t i g r a p h i c tops were found t o face the northeast.  At three l o c a l i t i e s i n the northeastern  h a l f t h e y were seen t o f a c e t h e southwest.  I t appears t h a t  the s t r a t a form a s y n c l i n e w h i c h i s o v e r t u r n e d west and p r o b a b l y  plunges t o t h e n o r t h w e s t .  to the south-  I n the c e n t r a l  p a r t o f t h e u n i t on t h e s l o p e n o r t h o f B i g B a r Creek g e n t l y d i p p i n g s t r a t a were seen t h a t appeared t o l i e u p s i d e down. I t i s u n c e r t a i n whether t h e s e anomalous a t t i t u d e s were p r o duced by d i s t u r b a n c e s rocks.  before or a f t e r the l i t h i f i c a t i o n o f the  The f o l d i n g o f t h e u n i t p r o b a b l y  was accompanied by  much d i f f e r e n t i a l s l i p p a g e on bedding p l a n e s w h i c h may e x p l a i n the sheared and f a u l t e d c o n t a c t s . northwesterly  A s c h i s t o s i t y which s t r i k e s  and d i p s s t e e p l y t o t h e n o r t h e a s t was o n l y  o b s e r v e d i n t h e c e n t r a l p a r t s o f t h e B i g B a r assemblage, t h a t i s near t h e a x i a l p l a n e o f t h e i n f e r r e d s y n c l i n e . 3. A.  P a v i l i o n Assemblage  Lithology A p p r o x i m a t e l y two t h i r d s o f t h e P a v i l i o n assemblage a r e  made up o f v o l c a n i c r o c k s , m o s t l y t u f f s and l e s s f l o w s , and about one t h i r d c o n s i s t s o f l i t h i c s a n d s t o n e , a r g i l l i t e ,  lime-  s t o n e , s i l t s t o n e , b r e c c i a , and conglomerate. The  t u f f s a r e g r e e n i s h l e a t h e r i n g massive r o c k s w h i c h  show f i n e , a n g u l a r  fragments o n l y on f r e s h s u r f a c e s .  Tuffs  r i c h i n l i t h i c m a t e r i a l can h a r d l y be d i s t i n g u i s h e d from  48 v o l c a n i c greywacke.  The v i t r i c  fragments a r e a l t e r e d t o  c h l o r i t e or f i n e l y r e c r y s t a l l i z e d ; shard-like outlines are r a r e l y preserved.  The c r y s t a l f r a c t i o n c o n s i s t s m o s t l y o f  twinned p l a g i o c l a s e and a s m a l l p r o p o r t i o n o f q u a r t z ; h o r n blende i s r a r e .  Some p y r o c l a s t i c c r y s t a l s a r e e u h e d r a l , o t h e r s  a r e b r o k e n ; they a r e f r e s h e r l o o k i n g and l e s s rounded t h a n d e t r i t a l g r a i n s i n t h e s e d imentary r o c k s . The v o l c a n i c r o c k s o f t h e P a v i l i o n a r e a range basalt to f e l s i t e .  from  Many o f them c o n t a i n p h e n o c r y s t s o f q u a r t z .  A g r e y i s h green w e a t h e r i n g a p h a n i t i c ( t h o l e i t i c ) b a s a l t c o n t a i n s a p p r o x i m a t e l y 8% o f q u a r t z , 3% o f e n d i o p s i d e (+2v moderate; ny 1.673) w h i c h forms m i c r o - p h e n o c r y s t s , and 10% o f c h l o r i t e and f i n e - g r a i n e d a l t e r a t i o n m i n e r a l s ; t h e b a l a n c e i s made up o f twinned and zoned p l a g i o c l a s e m i c r o l i t e s w h i c h range from c a l c i c l a b r a d o r i t e t o s o d i c b y t o w n i t e i n c o m p o s i t i o n . The r o c k i s c r o s s e d by narrow zones o f m y l o n i t e and by v e i n s o f c a r b o n ate and c h l o r i t e . A b l u e grey p o r p h y r i t i c a p h a n i t i c f l o w r o c k of f e l s i t i c c o m p o s i t i o n comprises about 4-0% o f f r a c t u r e d and c o r r o d e d p h e n o c r y s t s ( g r a i n s i z e 2 mm - .5 mm) i n an e x t r e m e l y f i n e - g r a i n e d p a r t l y g l a s s y groundmass ( g r a i n s i z e a p p r o x i m a t e l y 1 - 5 m i c r o n s ) . Most o f t h e p h e n o c r y s t s a r e o f q u a r t z ; a s m a l l e r number c o n s i s t s o f zoned and twinned a n d e s i n e , and a few g r a i n s a r e o f " i r o n o r e " , w h i c h p r o b a b l y has r e p l a c e d a m a f i c m i n e r a l . The groundmass i s t o o f i n e - g r a i n e d f o r i d e n t i f i c a t i o n . B e s i d e s q u a r t z and f e l d s p a r m i n e r a l s o f t h e c h l o r i t e and m i c a groups a r e abundant. The s p e c i men i n c l u d e s a few fragments o f r e l a t i v e l y c o a r s e g r a i n e d a c i d i c f l o w r o c k s . I t i s v e i n e d and r e p l a c e d by q u a r t z , c a r b o n a t e , and r a d i a t i n g c h l o r i t e . A g r e y i s h p o r p h y r i t i c v o l c a n i c rock which a p p a r e n t l y has been metamorphosed has about 30% o f p l a g i o c l a s e p h e n o c r y s t s ( g r a i n s i z e .5 mm - 3 mm) and a m o s a i c - l i k e groundmass composed o f a n h e d r a l q u a r t z , p l a g i o c l a s e , and p o t a s s i c f e l d s p a r . The p h e n o c r y s t s , unzoned but twinned a l b i t e a r e r e -  p l a c e d around t h e margins by t h e groundmass and c o n t a i n numerous i n c l u s i o n s o f q u a r t z , e p i d o t e , and minor f e l d s p a r . Some v e r y f i n e - g r a i n e d a l i g n e d i n c l u s i o n s o f q u a r t z resemble m y r m e k i t i c i n t e r growths. Quartz p r o b a b l y has been i n t r o d u c e d i n t o the r o c k . The specimen i s v e i n e d by m i n e r a l s o f the e p i d o t e group, m o s t l y p i s t a c i t e . A b e l t o f l a m i n a t e d l i t h i c sandstone w i t h some argillite,  c o n g l o m e r a t e , b r e c c i a , and s i l t s t o n e i s exposed i n  the  v i c i n i t y o f t h e r a i l r o a d between P a v i l i o n and Moran.  the  c o n t a c t s o f t h i s b e l t a r e g r a d a t i o n a l and p o o r l y  i t c o u l d not be mapped as a s e p a r a t e u n i t .  As  exposed  The r o c k s show  graded bedding and c o n t o r t i o n s formed b e f o r e t h e l i t h i f i c a t i o n of  the sediments. The l i t h i c sandstone weathers b r o w n i s h green and i s  grey on f r e s h s u r f a c e s .  Three specimens a n a l y z e d c o n t a i n  a p p r o x i m a t e l y 10-40$ o f f e l d s p a r , 1% o f q u a r t z , 45-85$ o f l i t h i c fragments and c h l o r i t e , and l e s s t h a n 1% o f " i r o n o r e " and e p i d o t e .  The f e l d s p a r i s m o s t l y twinned and zoned  c l a s e t h a t has n o t been a l b i t i z e d .  plagio-  The l i t h i c fragments a r e  m o s t l y d e r i v e d from v o l c a n i c r o c k s ( d o m i n a n t l y o f i n t e r m e d i a t e c o m p o s i t i o n ) and some from c h e r t and a r g i l l i t e .  Some spec-  imens show graded bedding and a r e w e l l s o r t e d but i n o t h e r s the  s o r t i n g i s poor.  A c o m p a r a t i v e l y u n a l t e r e d r o c k has o n l y  a s m a l l c o n t e n t o f c l a y m a t r i x ( l e s s t h a n 10%), and i t s p a r t i c l e s a r e rounded o r subrounded.  Others a r e too h i g h l y  a l t e r e d t o determine t h e o r i g i n a l roundness and c l a y c o n t e n t . These r o c k s a r e c l a s s i f i e d as v o l c a n i c a r e n i t e s .  A sedimentary r o c k t r a n s i t i o n a l from c o a r s e - g r a i n e d greywacke t o g r a n u l e conglomerate has t h e f o l l o w i n g c o m p o s i t i o n : plagioclase quartz c h l o r i t e and e p i d o t e hornblende and " i r o n ore" v o l c a n i c fragments limestone chert  10% 1% 1% -1%  67% 20% 1%  The fragments a r e embedded i n a c l a y m a t r i x w h i c h p r o b a b l y makes up more t h a n 10% o f the r o c k . s o r t i n g a r e poor.  B o t h r o u n d i n g and  The g r a i n s i z e ranges from 4 mm  A s s o c i a t e d w i t h t h e l i t h i c sandstone and are  size  t o .1  mm.  conglomerate  b r e c c i a s t h a t a r e made up o f the same components but  l o c a l l y c o n t a i n a l a r g e r f r a c t i o n o f l i m e s t o n e , c h e r t , and argillite.  These b r e c c i a s a r e between 2 and 20 f e e t t h i c k and  can be t r a c e d a l o n g s t r i k e f o r a few hundred f e e t .  I n most  b r e c c i a s the fragments do not exceed a few c e n t i m e t e r s i n diameter.  However, on the r i d g e n o r t h o f K e a t l e y C r e e k , about  2 m i l e s n o r t h e a s t o f G l e n F r a s e r , a s e c t i o n was measured t h a t contains s e v e r a l very coarse b r e c c i a s or conglomerates. Thickness i n Feet  Lithology Top o f measured s e c t i o n  4  L i t h i c sandstone w i t h g r a n u l e s and sandsized grains of limestone.  3  Laminated sandstone and s i l t s t o n e showing some c r o s s - b e d d i n g .  12 3  L i t h i c sandstone w i t h fragments o f l i m e s t o n e up t o one i n c h l o n g . L i t h i c sandstone w i t h abundant a r g i l l a c e o u s m a t r i x and a s m a l l e r p r o p o r t i o n o f sand t h a n n o r m a l .  51  Thickness i n Feet 24  Lithology Limy c o n g l o m e r a t e , c o n s i s t i n g m o s t l y o f l i m e s t o n e c o b b l e s , about 4 i n c h e s i n d i a m e t e r , some f r a g ments o f l i t h i c sandstone and c h e r t , and one l e n s of a r g i l l i t e , about 6 i n c h e s l o n g . Laminated sandstone and s i l t s t o n e l o c a l l y show graded bedding. The conglomerate i s c l o s e l y packed and t h e fragments a r e w e l l rounded and s i z e - s o r t e d .  2  Covered  2  C a l c a r e n i t e and g r a n u l e conglomerate w i t h l i m y fragments i n a m a t r i x o f l i t h i c sandstone.  2  C a l c a r e n i t e and g r a n u l e conglomerate c o n s i s t i n g o f l i m e s t o n e fragments i n a m a t r i x o f l i t h i c sandstone.  1  Covered  2  Lithic  2  Fine-grained  8  L i t h i c sandstone w i t h g r a n u l e s o f l i m e s t o n e g r a d i n g downward i n t o c o b b l e conglomerate cont a i n i n g d o m i n a n t l y fragments o f l i m e s t o n e and minor a r g i l l i t e . Towards t h e t o p o f t h e l a y e r the sand g r a i n s become s c a r c e r and t h e m a t r i x more a r g i l l a c e o u s .  12  interval.  interval. sandstone. calcarenite.  Dominantly a r g i l l i t e mixed w i t h m a r l and l i t h i c sandstone. The upper 6 f e e t c o n t a i n w e l l rounded c o b b l e s o f l i m e s t o n e and a r g i l l i t e about 6 i n c h e s i n diameter.  4  Lithic  6  G r a n u l e conglomerate. One t h i r d o f t h e fragments are o f l i m e s t o n e and two t h i r d s o f c h e r t . The matrix c o n s i s t s dominantly o f limestone.  6  Lithic  5  Covered  16  sandstone.  sandstone. interval.  B r e c c i a c o n s i s t i n g dominantly o f limestone pebbles, a p p r o x i m a t e l y 1 i n c h i n d i a m e t e r , and a few f r a g ments o f a r g i l l i t e about 6 i n c h e s l o n g i n a m a t r i x of l i t h i c sandstone.  52 Thickness i n Feet  Lithology  6  Coarse l i m e s t o n e b r e c c i a . Most o f t h e l i m e s t o n e i s b l u e g r e y , some b r o w n i s h fragments may be d o l o m i t i c . Some b o u l d e r s a r e a n g u l a r o t h e r s rounded. A s m a l l f r a c t i o n o f t h e fragments r a n g i n g up t o 6 i n c h e s i n l e n g t h a r e composed o f c h e r t . The m a t r i x c o n s i s t s o f l i t h i c sandstone.  6  L i t h i c sandstone w i t h s c a t t e r e d g r a n u l e s o f limestone.  6  Lithic  6 1 32  sandstone.  Argillite. Covered i n t e r v a l :  fault?  Coarse b r e c c i a composed m o s t l y o f l i m e s t o n e and some c h e r t . The s i z e o f t h e l i m e s t o n e fragments ranges from pebbles 1/2 i n c h i n diameter t o a b o u l d e r 8 f e e t l o n g , 4 f e e t wide. Most fragments a r e w e l l rounded, t h e l a r g e r ones m o s t l y e l l i p s o i d a l . The m a t r i x i s l i t h i c sandstone; t h e g r a n u l e grade i s p o o r l y r e p r e s e n t e d .  4  Lithic  sandstone.  1  F i n e b r e c c i a . Fragments d o m i n a n t l y o f l i m e s t o n e and minor c h e r t , a r g i l l i t e , and v o l c a n i c r o c k s a r e embedded i n a m a t r i x o f l i t h i c sandstone. The fragments a r e up t o one i n c h i n diameter and m o s t l y w e l l rounded. Fault.  18 1  L i t h i c sandstone w i t h g r a n u l e t o pebble fragments o f l i m e s t o n e .  sized  Argillite.  48  L i t h i c sandstone t h a t i s m o s t l y m a s s i v e but shows bedding i n t h e form o f b l u i s h , s i l t y o r a r g i l l a c eous laminae near t h e c o n t a c t w i t h t h e o v e r l y i n g argillite. C o n t a i n s a few e l l i p s o i d a l fragments o f a r g i l l i t e and some l i m e s t o n e p e b b l e s .  68  Covered  5  interval.  Fine-grained d i o r i t e  sill.  Thickness i n Feet  Lithology  3  F o s s i l i f e r o u s limestone containing c o r a l s , g a s t r o p o d s , b r a c h i o p o d s , g a s t r o p o d s , and e c h i n o i d s and some o o l i t e s . The l i m e s t o n e i s i n t e r m i t t e n t l y exposed f o r about 200 f e e t . In some p l a c e s l i t h i c sandstone and t u f f a c e o u s material i s interlaminated.  4  Ribbon c h e r t . Bottom o f measured s e c t i o n  323 f e e t L i m e s t o n e , a minor component o f t h i s D i v i s i o n , o c c u r s i n pods o r l e n s e s t h a t do not exceed two hundred f e e t i n l e n g t h . The  g r e a t e s t c o n c e n t r a t i o n o f such b o d i e s o c c u r s near P a v i l i o n  Creek about 1/2 m i l e east o f the F r a s e r R i v e r . i t i e s f o s s i l s were found.  At o n l y two  C r i n o i d stems were c o l l e c t e d on  localthe  east s i d e o f the F r a s e r R i v e r about one m i l e s o u t h o f t h e mouth o f McKay C r e e k , and fragments o f c o r a l s , p e l e c y p o d s ,  gastropods  and  e c h i n o i d s about two m i l e s n o r t h e a s t o f G l e n F r a s e r  B.  Metamorphism and  (F12).  Alteration  As the P a v i l i o n assemblage i s i n t r u d e d by numerous d i o r i t i c bodies a c o n s i d e r a b l e p r o p o r t i o n o f the r o c k s show c o n t a c t metamorphism.  B o t h the h o r n b l e n d e - h o r n f e l s  a l b i t e - e p i d o t e h o r n f e l s f a c i e s are r e p r e s e n t e d . a r e t r a n s i t i o n a l between t h e s e two groups.  and  Some specimens  (See T a b l e 1 ) .  Most o f the metamorphic r o c k s a r e dark g r e e n , g r a i n e d ( g r a i n - s i z e .01 - .15 mm) a m p h i b o l i t e s w h i c h may  the  fine-  m a s s i v e or weakly f o l i a t e d  have been d e r i v e d from t u f f s ,  lithic  sandstones,  and b a s a l t s .  I n some o f t h e specimens an o r i g i n a l  f r a g m e n t a l c h a r a c t e r can s t i l l be d e t e c t e d under t h e m i c r o s c o p e , but p y r o c l a s t i c r o c k s cannot be d i s t i n g u i s h e d from rocks.  sedimentary  A l l o f t h e s e r o c k s c o n t a i n more than 40% o f amphibole  and most o f them have 20-4-5% o f p l a g i o c l a s e . I n r o c k s o f a moderate grade o f metamorphism t h e amphibole i s r e p r e s e n t e d by hornblende.  The m i n e r a l v a r i e s i n h a b i t from broad t o s l e n d e r  p r i s m a t i c and i s s t r o n g l y p l e o c h r o i c ( z : b l u e - g r e e n ; y: green o r g r e e n i s h w i t h a brown t i n t ; x: p a l e b r o w n i s h green o r p a l e brown.)  I n a specimen showing r e t r o g r e s s i v e metamorphism t h e  hornblende  i s p a r t l y r e p l a c e d by c h l o r i t e .  A low-grade meta-  morphic r o c k c o n s i s t s d o m i n a n t l y o f a c i c u l a r , p l e o c h r o i c ( z : blue-green)  actinolite.  from c a l c i c andesine  The p l a g i o c l a s e , r a n g i n g i n c o m p o s i t i o n  to a l b i t e , i sanhedral, f u l l of inclusions  o f e p i d o t e and amphibole, and p a r t l y twinned.  E p i d o t e appears i n  a p p r e c i a b l e q u a n t i t y o n l y i n r o c k s o f i n t e r m e d i a t e t o low grade o f metamorphism.  Quartz forms up t o 30% o f some specimens.  As  a c c e s s o r i e s " I r o n o r e " , sphene, and a p a t i t e a r e p r e s e n t . Some metamorphosed l i t h i c sandstones  have t h e same  m i n e r a l a s s o c i a t i o n s as these a m p h i b o l i t e s but a r e r e l a t i v e l y poor i n amphibole.  Where l i t h i c sandstone was i n t e r l a m i n a t e d  w i t h a r g i l l i t e , a l t e r n a t i o n s o f h o r n b l e n d e - r i c h and f e l s i c l a y e r s a r e v i s i b l e w h i c h i n some l o c a l i t i e s show boudinage s t r u c t u r e s . Two g r e y i s h , f i n e - g r a i n e d , m a s s i v e r o c k s c o n s i s t i n g dominantly  o f f e l d s p a r ( a l b i t e i n one specimen; a l b i t e and  55  o r t h o c l a s e i n the o t h e r ) , q u a r t z , and s m a l l amounts o f c h l o r i t e , e p i d o t e , " i r o n o r e " , and carbonate a p p a r e n t l y  have been meta-  morphosed under c o n d i t i o n s o f the a l b i t e - e p i d o t e h o r n f e l s facies.  The p o r p h y r i t i c t e x t u r e o f one specimen and the f i n e -  grained l a t h - l i k e h a b i t o f the p l a g i o c l a s e i n the other i n d i c a t e that they were  ( a c i d i c ) v o l c a n i c flow  one  rocks.  Near i n t r u s i o n s the r i b b o n c h e r t s have been metamorphosed to q u a r t z i t e and the limestones  to marble.  As the u n i t i s bounded by major f a u l t s and broken i n t e r n a l l y by numerous minor ones, b r e c c i a t i o n and myIoni z a t i o n are common i n these r o c k s . metamorphism quartz.  A s s o c i a t e d with the dynamic  i s a l t e r a t i o n by carbonate,  e p i d o t e , c h l o r i t e , and  TABLE 2 M i n e r a l - c o m p o s i t i o n o f some metamorphic  a>  C O C O  C D •H <M rHW «H E i o riO C O) o C O  o  58MB  r 58 M5  (+)2v,_010, x' 010 (maximum = 24 ) A  nx' on (001) 1.5485 (-)2v nx' on 001 = 1.538  +3  <M m  Determination o f Plagioclase  o  cu  a>  -a  rH  Spec, -No.  r o c k s , P a v i l i o n Group, D i v i s i o n II.  rH  X>  O rl  •H rH  c! <kn -H  O  C D o  o  o  +3  o  O  «H P.  C D u  o  o o m  An 44  46  .5  49  minor  mino  An  22  28  41  minor  10  2 0  M3  (+)2v 010, x' 010 =14 A  max. An3  57 Au104  58 M5-3  47  minor  (+)2v _i_010 X * A 010=14° (Maximum?)  Albite  32  minor  minor  minor  50  minor  75$ but partly replaced by c h l o r ite  25  50  10  JHC O § C D 3 iH C DC O p<  O  +J O  hornfels Hornblendehornfels  4  58  •H Xi  minor  8  Hornblendehornfels transi t i o n a l to a l bite-epidote hornfels Retrogressive from hornblendeh o r n f e l s to a l bite-epidote hornfels Albite-epidote hornfels  ON  57 C.  Structure To the west the P a v i l i o n assemblage i s i n f e r r e d to be  i n f a u l t c o n t a c t w i t h Lower Cretaceous  volcanic rocks.  The  con-  t a c t i s nowhere exposed but i s b e l i e v e d to be a f a u l t because the Lower Cretaceous  s t r a t a seem to d i p under those o f the  Cache Creek group. ( P l a t e X X I I I )  The  r o c k s o f the P a v i l i o n  assemblage i n the v i c i n i t y o f t h i s c o n t a c t a r e s h e a r e d , i a t e d , and l o c a l l y  brecc-  altered.  To the east the assemblage i s i n c o n t a c t w i t h D i v i s i o n I.  The n a t u r e and exact l o c a t i o n o f t h i s boundary a r e o n l y  p a r t l y known.  The  c o n t a c t i s W e l l exposed o n l y on the s l o p e  n o r t h o f P a v i l i o n Creek.  Here an abrupt break from amphi-  b o l i t e s i n the southwest t o r i b b o n c h e r t i n the n o r t h e a s t be seen.  The  can  c h e r t a d j a c e n t to the c o n t a c t i s s t r o n g l y sheared  and p a r t l y c a r b o n a t i z e d ; the a m p h i b o l i t e i s sheared  and  altered  i n some p l a c e s and a p p a r e n t l y l i t t l e d i s t u r b e d i n o t h e r s .  Be-  tween t h i s l o c a l i t y and the s l o p e above Moran the boundary o f the two  u n i t s i s covered by o v e r b u r d e n .  I t seems to cut  a c r o s s the r e g i o n a l s t r i k e o f the s t r a t a i n a n o r t h w e s t e r l y direction.  Southeast  o f Moran the c o n t a c t i s not exposed but  can be l o c a t e d w i t h i n a few hundred f e e t .  The appearance o f  the r o c k s on e i t h e r s i d e o f the c o n t a c t i s the same as  on  P a v i l i o n Creek.  be-  I t seems to be c e r t a i n t h e r e f o r e t h a t  tween P a v i l i o n Creek and Moran the boundary between the Divisions i s a fault.  There a r e almost no o u t c r o p s  the r a i l r o a d and the F r a s e r R i v e r i n t h i s v i c i n i t y . west s i d e o f the F r a s e r R i v e r , a p p r o x i m a t e l y  two  between On  the  two m i l e s down-  s t r e a m from the mouth o f K e l l y C r e e k , a sharp break was  noticed  from h o r n f e l s i c r o c k s i n the n o r t h e a s t t o l i t t l e metamorphosed sedimentary  and t u f f a c e o u s r o c k s i n the southwest.  between the two r o c k s i s not exposed.  The  contact  The h o r n f e l s e s near the  c o n t a c t appear l i t t l e d i s t u r b e d but the sedimentary  and  tuff-  aceous r o c k s a r e i n some p l a c e s s c h i s t o s e and c a r b o n a t i z e d . contact approximately Moran and may  l i n e s up w i t h the f a u l t s o u t h e a s t  be i t s c o n t i n u a t i o n .  However, i t i s not  This  of entirely  c e r t a i n whether the metamorphic r o c k s belong t o D i v i s i o n I . S o u t h o f P a v i l i o n Creek the c o n t a c t i s p o o r l y exposed. O n l y on the r i d g e n o r t h o f K e a t l e y Creek can i t be l o c a t e d w i t h a c c u r a c y , but i t s n a t u r e i s u n c e r t a i n .  The  l a c k of a  t r a n s i t i o n zone between l i t h i c s a n d s t o n e , t u f f , and in  the west and c h e r t and a r g i l l i t e i n the e a s t , t h e  amphibolite unusual  narrowness o f D i v i s i o n I w h i c h i s here o n l y about one m i l e wide and the o r i e n t a t i o n o f the s t r a t i g r a p h i c tops w h i c h f a c e the n o r t h e a s t suggest a f a u l t  contact.  Because o f the s c a r c i t y o f marker beds, i n s u f f i c i e n t e x p o s u r e , and t h e d i f f i c u l t y to determine the r e l a t i v e o f the s t r a t i g r a p h i c tops i n sheared  position  and a l t e r e d a r e a s ,  i n t e r n a l s t r u c t u r e of D i v i s i o n I I i s l i t t l e  the  understood.  Between P a v i l i o n and Moran the g e n e r a l s t r i k e o f the s t r a t a i s 5° - 10° west o f n o r t h , and the d i p s are s t e e p . marker bed o f c h e r t shows extreme l o c a l d i s t o r t i o n s but u n i f o r m t r e n d over l a r g e d i s t a n c e s . in  A few s t r a t i g r a p h i c  the e a s t e r n p a r t o f the a r e a f a c e the east and at  one  A  a tops  59 l o c a l i t y i n the w e s t e r n p a r t t h e west. A g r e a t number o f zones composed o f r u s t y o r s c h i s t o s e r o c k s a r e exposed between P a v i l i o n and Moran.  Most o f these  z o n e s , p r o b a b l y f a u l t s , a r e p a r a l l e l t o the r e g i o n a l A few o f t h e l a r g e r ones a r e shown on the 4.  strike.  map.  Mode o f O r i g i n  F o s s i l s i n d i c a t e a marine environment, and t h e presence o f carbonaceous m a t t e r i n the a r g i l l i t e shows t h a t i t was o f the " r e s t r i c t e d " t y p e i n w h i c h the carbonaceous m a t t e r has not been o x i d i z e d .  Graded bedding and the d e p o s i t i o n o f b r e c c i a s  are a t t r i b u t e d to t u r b i d i t y c u r r e n t s .  Contortions that probably  formed b e f o r e t h e l i t h i f i c a t i o n o f t h e sediments a r e p r o b a b l y due t o submarine s l u m p i n g . may  B o t h t u r b i d i t y c u r r e n t s and slumping  be r e l a t e d t o t e c t o n i c movements t h a t were p r o b a b l y accom-  p a n i e d by v o l c a n i c a c t i v i t y .  The p r e s e n c e o f a c i d i c v o l c a n i c  f l o w s s u g g e s t s t h a t some o f the v o l c a n i c c e n t e r s l a y i n the v i c i n i t y o f P a v i l i o n and B i g B a r . 5.  Age and C o r r e l a t i o n  The B i g Bar assemblage appears t o o v e r l i e D i v i s i o n I conformably.  As D i v i s i o n I o v e r l y i n g t h e uppermost  Permian  f u s u l i n i d zone i s Upper Permian and/or T r i a s s i c , D i v i s i o n I I may be T r i a s s i c .  The P a v i l i o n assemblage w h i c h i s i n f a u l t  c o n t a c t w i t h D i v i s i o n I has been c o r r e l a t e d w i t h t h e B i g Bar assemblage l i t h o l o g i c a l l y . o r younger.  I t i s b e l i e v e d t o be  contemporaneous  60 Helen Duncan of the United States Geological Surveyreports on a few corals found i n the P a v i l i o n Assemblage on the ridge north of Keatley Creek, near the contact with D i v i s i o n I, as follows: (F12) The corals i n l o t s A8 F l a and A8 F1H are very much r e c r y s t a l l i z e d and corroded, but I am v i r t u a l l y p o s i t i v e they are hexacorals. So far as I can t e l l , they look l i k e things that have been i d e n t i f i e d as M o n t l i v a u l t i a by Squires and i n the l i t e r a t u r e . The specimens c e r t a i n l y are not the type of thing I should expect to find i n the Permian, so I think a T r i a s s i c assignment i s the best p o s s i b i l i t y on the evidence available. The P a v i l i o n group cannot be correlated with the Upper T r i a s s i c Nicola group of the Ashcroft map-area because no ribbon chert has been reported i n that unit.  As the P a v i l i o n  group i s intruded by Upper T r i a s s i c (?) ultrabasic dykes i t may  be older than Upper T r i a s s i c . (See p. 145).  LILLOOET GROUP 1.  D i s t r i b u t i o n and  Thickness  The L i l l o o e t group i s exposed i n the v i c i n i t y of the Fraser River betx^een the mouth of the Bridge River and the town of L i l l o o e t . A, B, and C.  It has been subdivided into three d i v i s i o n s ,  Because of folding and f a u l t i n g the true thickness-  es of these units are not known.  The base of d i v i s i o n A, which  appears i n the centre of an anticlinorium, i s not exposed. In the present map-area i t i s probably less than 3000 feet. D i v i s i o n B has a minimum thickness of 2 ^ 0 0 feet.  C does not  d i r e c t l y o v e r l i e B but i s i n fault contact with that D i v i s i o n .  The  exposed t h i c k n e s s o f C i s a p p r o x i m a t e l y 900 f e e t .  The  c o n c e a l e d p a r t o f D i v i s i o n C may be o f c o n s i d e r a b l e t h i c k n e s s . 2.  Lithology  Division A D i v i s i o n A c o n s i s t s m o s t l y o f a r g i l l i t e t h a t i s massive or  i n t e r b e d d e d w i t h s i l t y a r g i l l i t e , s i l t s t o n e , and f i n e -  g r a i n e d l i t h i c sandstone.  I n d i v i d u a l laminae range from a few  m i l l i m e t e r s t o a few c e n t i m e t e r s i n t h i c k n e s s .  Graded  bedding  and c r e n u l a t i o n s a t t r i b u t e d t o d e f o r m a t i o n s o f t h e sediments before t h e i r l i t h i f i c a t i o n is rare.  a r e common f e a t u r e s ; c r o s s - b e d d i n g  L o c a l l y the a r g i l l i t e contains limy concretions. The a r g i l l i t e  i s dark b l u e g r e y .  I t c o n t a i n s about  10$ o f carbonaceous m a t t e r and a few p e r c e n t o f s i l t matrix.  i n a clay  The carbonaceous m a t t e r i n many specimens i s concen-  t r a t e d i n layers a f r a c t i o n o f a m i l l i m e t e r t h i c k along j o i n t s a r e developed.  which  The s i l t f r a c t i o n c o n s i s t s o f f e l d s p a r ,  c h l o r i t e , q u a r t z , and c a r b o n a t e . L i t h i c sandstone D i v i s i o n A.  and g r a n u l e conglomerate  are rare i n  About 2 m i l e s s o u t h o f S e t o n Creek on t h e west  s i d e o f t h e F r a s e r R i v e r a few f e e t o f v o l c a n i c a r e n i t e and a seam o f c o a l a r e i n t e r b e d d e d w i t h t h e a r g i l l i t e . has a p p r o x i m a t e l y t h e f o l l o w i n g c o m p o s i t i o n : feldspar l i t h i c fragments c h l o r i t e and m i c a carbonate and " i r o n ore" quartz  30$ 43$ 2$ % 20$  The a r e n i t e  62 The f e l d s p a r i s m o s t l y a l b i t e . are  The l i t h i c  fragments  l a r g e l y from v o l c a n i c r o c k s and h i g h l y a l t e r e d ; some a r e  probably chert.  The fragments a r e o f medium t o f i n e sand g r a d e ,  s u b a n g u l a r t o subrounded, and f a i r l y  w e l l sorted.  T h e i r cement  c o n s i s t s o f r u s t y w e a t h e r i n g c a r b o n a t e and i r o n o x i d e . Division B D i v i s i o n B c o n s i s t s o f l i t h i c sandstone, s i l t s t o n e , argillite, or  and conglomerate.  The l o w e s t beds o f sandstone  conglomerate i n t h e L i l l o o e t group t h a t a r e a t l e a s t a few  f e e t t h i c k , mark t h e base o f t h a t D i v i s i o n .  Argillite  i s the  most common r o c k i n t h e lower p a r t , but h i g h e r i n t h e s e c t i o n l i t h i c sandstone becomes dominant, and t h e p r o p o r t i o n o f pebble conglomerate  increases.  A s t r a t i g r a p h i c s e c t i o n measured i n t h e upper  part  of  D i v i s i o n B near t h e mouth o f B r i d g e R i v e r on t h e west  of  t h e F r a s e r R i v e r shows t h e i n c r e a s e o f c o a r s e r sediments  upwards.  ( P e r c e n t a g e s o f r o c k - t y p e s a r e based on r a p i d  estimates).  shore  63 Feet Top o f m e a s u r e d  section.  26  L i t h i c sandstone, b l u e - g r e y , blue grey to green weathering, mostly f i n e - g r a i n e d , p y r i t e , t h i c k bedded t o l a m i n a t e d , graded b e d d i n g , r e s i s t a n t ; g r a d e s downward i n t o s i l t s t o n e , l i g h t g r e y t o b l u e g r e y , l i g h t - g r e y to blue grey weathering; s i l t stone grades i n t o a r g i l l i t e , dark b l u i s h g r e y , dark b l u i s h g r e y w e a t h e r i n g , r e c e s s i v e ; s i l t s t o n e and a r g i l l i t e laminated to t h i n - b e d d e d ; pene-contemporaneous d e f o r m a t i o n s , s s . 90$ s t : 5$ a r g : 5$  7  L i t h i c s a n d s t o n e , medium t o v e r y c o a r s e - g r a i n e d , g r a d e s downward i n t o g r a n u l e c o n g l o m e r a t e , includes f r a g m e n t s o f a r g i l l i t e , up t o 2 f e e t l o n g .  9  L i t h i c sandstone, mostly f i n e - g r a i n e d , thick-bedded to laminated, s i l t s t o n e w i t h p y r i t e , a r g i l l i t e . s s : 50$ s t : 45$ a r g : 5$  8  Covered  1.5  L i t h i c sandstone,  1  Argillite, Fault,  10  interval medium-grained,  g r a d i n g downwards i n t o  laminated. siltstone,  pyrite.  contortions.  L i t h i c s a n d s t o n e , medium t o a r g i l l i t e ; thin-bedded, s s , s t : 90$ a r g : 10$  fine-grained,  siltstone,  Fault. 10  C o n g l o m e r a t e , v o l c a n i c p e b b l e s and g r a n u l e s , rounded to sub-angular, matrix of l i t h i c sandstone, poorly sorted, massive, c l i f f - f o r m i n g . .  8  L i t h i c sandstone, mostly f i n e - g r a i n e d , a r g i l l i t e ; thin-bedded to laminated, s s : 50$ s t : 30$ a r g : 20$  7  L i t h i c sandstone, f i n e to medium-grained, p y r i t e , f r a g m e n t s o f a r g i l l i t e 2 mm l o n g , m a s s i v e .  2  Siltstone,  thin-bedded to  5  Argillite,  massive,  laminated.  strongly  contorted.  siltstone,  64 Feet 45 1 16  L i t h i c sandstone, f i n e t o medium-grained, m a s s i v e . A r g i l l i t e , medium-bedded. S i l t s t o n e , m o s t l y m a s s i v e , p a r t l y thin-bedded t o laminated, a r g i l l i t e massive, s t : 60$ a r g : 40$  7  S i l t s t o n e , a r g i l l i t e ; thin-bedded t o l a m i n a t e d , s t : 80$ a r g : 20$  2  S i l t s t o n e and a r g i l l i t e as above, sheared and carbonated. Fault.  1  L i t h i c sandstone, t h i c k - b e d d e d , s t r o n g l y  1  S i l t s t o n e , a r g i l l i t e , thin-bedded to laminated, carbonated, s t : 50$ a r g : 50$  1.5  L i t h i c sandstone, medium-grained, c a r b o n a t e d .  4.5  Siltstone,  1  S i l t s t o n e , a r g i l l i t e ; thin-bedded to laminated, carbonated, s t : 60$ a r g : 40$  4  S i l t s t o n e , a r g i l l i t e ; thin-bedded to laminated, s t : 90$ a r g : 10$  15  L i t h i c sandstone, f i n e - g r a i n e d , m o s t l y m a s s i v e .  20  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone; mediumbedded t o l a m i n a t e d , pene-contemporaneous d e f o r mations. s t : 40$ a r g : 40$ s s : 20$  12 10 4  carbonated.  massive.  L i t h i c s a n d s t o n e , f i n e t o medium-grained, m a s s i v e . S i l t s t o n e , a r g i l l i t e ; thin-bedded to laminated, s t : 90$ a r g : 10$ L i t h i c sandstone, f i n e - t o medium-grained, t h i n bedded t o l a m i n a t e d .  65  Feet 4 17  4  Siltstone, argillite; s t : 90$ a r g : 10$  thin-bedded to laminated  Conglomerate, m o s t l y g r a n u l e s , p a r t l y pebbles o f v o l c a n i c r o c k s , p o o r l y t o m o d e r a t e l y s o r t e d and rounded, l a r g e fragments o f s i l t s t o n e and a r g i l l i t e forming i n t r a f o r m a t i o n a l b r e c c i a ; massive. S i l t s t o n e , a r g i l l i t e , l i t h i c s a n d s t o n e , mediumgrained; thin-bedded to laminated, s t : 85$ a r g : 10$ s s : 5$ Fault.  6  S i l t s t o n e , l i t h i c sandstone, c o a r s e - t o f i n e - g r a i n e d , a r g i l l i t e ; thin-bedded to laminated, s t : 50$ s s : 40$ a r g : 10$  11  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, f i n e - g r a i n e d ; thin-bedded to laminated. s t : 60$ a r g : 30$ s s : 10$  5.5 25  1  14  Diabase  sill.  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, c o a r s e - t o f i n e - g r a i n e d ; t h i n - b e d d e d t o l a m i n a t e d , graded b e d d i n g , s t : 65$ a r g : 30$ s s : 5$ S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, coarse- to f i n e - g r a i n e d ; medium-bedded, graded b e d d i n g , s t : 65$ a r g : 30$ s s : 5$ S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, f i n e - g r a i n e d ; thin-bedded to laminated, s t : 50$ a r g : 40$ s s : 10$  3  Argillite,  massive, platey  jointing.  4  L i t h i c sandstone, medium- t o f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; medium-bedded t o l a m i n a t e d , graded b e d d i n g , s s : 50$ s t : 30$ a r g : 20$  12  S i l t s t o n e , massive.  26  L i t h i c s a n d s t o n e , medium t o c o a r s e - g r a i n e d , m a s s i v e .  5.5  2.5  L i t h i c sandstone, f i n e - g r a i n e d , a r g i l l i t e , s i l t s t o n e ; t h i n - b e d d e d t o l a m i n a t e d , pene-contemporaneous deformations. s s : 40$  a r g : 40$  Diabase  sill.  s t : 20$  S i l t s t o n e , a r g i l l i t e ; thin-bedded to laminated, strongly indurated by s i l l s . Diabase  sill.  L i t h i c sandstone, f i n e - to medium-grained, s i l t s t o n e , a r g i l l i t e ; medium-bedded to laminated, graded bedding, ss: 50$ s t : 35$ arg: 15% A r g i l l i t e , s i l t y , massive. L i t h i c sandstone, f i n e - to medium-grained, massive. L i t h i c sandstone, fine-grained, s i l t s t o n e , a r g i l l i t e ; medium-bedded to laminated, graded bedding penecontemporaneous deformations, ss: 50% s t : 30$ arg: 20$ Covered  interval.  L i t h i c sandstone, medium- to coarse-grained, thickbedded. L i t h i c sandstone, medium- to fine-grained, s i l t s t o n e , a r g i l l i t e ; thick-bedded to laminated, graded bedding, ss: 50$ s t : 40$ arg: 10$ L i t h i c sandstone, mostly medium-grained, mostly t h i n bedded, l o c a l l y massive. S i l t s t o n e , l i t h i c sandstone, fine-grained, a r g i l l i t e ; medium-bedded to laminated, pene-contemporaneous deformations. s t : 60$ ss: 20$ arg: 20$ L i t h i c sandstone, coarse-grained, with granules and pebbles of altered volcanic rock and fragments of a r g i l l i t e up to 2 i n . long; massive. S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, fine-grained; thin-bedded to laminated, st: 55$ arg: 25$ ss: 20$ Diabase  sill.  L i t h i c sandstone, fine-grained, s i l t s t o n e ; medium- to thin-bedded. ss: 80$ s t : 20$ S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, fine-grained; thin-bedded to laminated, st: 40$ arg: 40$ ss: 20$  67  Feet 3  L i t h i c sandstone, medium- t o f i n e - g r a i n e d , a r g i l l i t e ; thin-bedded t o l a m i n a t e d , s s : 80$ s t : 10$ a r g : 10$  siltstone,  20  A r g i l l i t e , l i t h i c sandstone, c o a r s e - t o f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; t h i n bedded t o l a m i n a t e d , graded bedding, a r g : 40$ s s : 30$ s t : 30$  3  L i t h i c sandstone, medium- t o c o a r s e - g r a i n e d , m a s s i v e .  15 5  20  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, mostly f i n e g r a i n e d ; t h i n - b e d d e d t o l a m i n a t e d , upper p a r t c a r b o n a t e d . L i t h i c sandstone, mostly f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; t h i c k - b e d d e d t o l a m i n a t e d , graded b e d d i n g , s s : 80$ a r g : 10$ s t : 10$ L i t h i c sandstone, m o s t l y f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; m o s t l y thin-bedded t o l a m i n a t e d , a few beds one f o o t t h i c k , s s : 40$^ a r g : 30$ s t : 30$  5.5  L i t h i c sandstone, c o a r s e - g r a i n e d , grades downward i n t o p e b b l e - c o n g l o m e r a t e , i n c l u d e s fragments o f l a m i n a t e d s i l t s t o n e and a r g i l l i t e ; m a s s i v e .  6.5  L i t h i c sandstone, medium- t o f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; medium-bedded t o l a m i n a t e d , pene-contemporaneous d e f o r m a t i o n s , graded b e d d i n g , s s : 50$ a r g : 30$ s t : 20$  6  L i t h i c sandstone, f i n e - g r a i n e d , p a r t l y t h i c k - b e d d e d , s i l t s t o n e , a r g i l l i t e ; thin-bedded to laminated, a l l s t r o n g l y carbonated. s s : 70$ s t : 20$ a r g : 30$  5.5  S i l t s t o n e , l i t h i c sandstone, f i n e - g r a i n e d , thin-bedded t o l a m i n a t e d , c a r b o n a t e d , s t : 40$ s s : 30$ a r g : 30$  4  L i t h i c sandstone, f i n e - g r a i n e d , t h i c k - b e d d e d t o l a m i n a t e d , s i l t s t o n e , a r g i l l i t e ; thin-bedded t o l a m i n a t e d , a l l carbonated. s s : 70$ s t : 20$ a r g : 10$  5.5  L i t h i c sandstone, f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; t h i n - b e d d e d t o l a m i n a t e d , graded b e d d i n g , c a r b o n a t e d , s s : 40$ s t : 40$ a r g : 20$  2  L i t h i c sandstone, f i n e - g r a i n e d , m a s s i v e ,  argillite;  carbonated.  68  Feet 1.5  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, thin-bedded to laminated, carbonated, s t : 50$ a r g : 30$ s s : 20$  fine-grained;  4  L i t h i c sandstone, f i n e - g r a i n e d , m a s s i v e ,  4  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, f i n e g r a i n e d ; thin-bedded t o m a s s i v e , c a r b o n a t e d , s t : 50$ a r g : 30$ s s : 20$  carbonated.  10  L i t h i c sandstone, c o a r s e - g r a i n e d , l o c a l l y g r a d i n g i n t o g r a n u l e conglomerate, s i l t s t o n e , a r g i l l i t e ; l i t h i c sandstone m o s t l y m a s s i v e ; s i l t s t o n e and a r g i l l i t e thin-bedded t o laminated.  20  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, f i n e - g r a i n e d ; t h i n - b e d d e d t o l a m i n a t e d , graded b e d d i n g , penecontemporaneous d e f o r m a t i o n s .  3  16  3.5 15  L i t h i c sandstone, c o a r s e - t o f i n e - g r a i n e d , a r g i l l i t e ; medium-bedded t o l a m i n a t e d , s s : 90$ s t : 5$ a r g : 5$  siltstone,  L i t h i c sandstone, mostly f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; thin-bedded t o l a m i n a t e d ; one bed o f a r g i l l i t e w i t h strong p r e - l i t h i f i c a t i o n contortions, s s : 40$ s t : 40$ a r g : 20$ L i t h i c sandstone, medium- t o f i n e - g r a i n e d , medium- t o thin-bedded. S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, m o s t l y f i n e g r a i n e d ; medium-bedded t o l a m i n a t e d , pene-contemporaneous d e f o r m a t i o n s , graded bedding, s t : 60$ a r g : 30$ s s : 10$ Fault.  Bottom o f measured s e c t i o n .  685  The l i t h i c sandstones a r e b l u e grey.  S i x specimens  a n a l y z e d c o n t a i n 10 t o 40$ o f f e l d s p a r and 1 t o 5$ o f q u a r t z . The b a l a n c e c o n s i s t s d o m i n a n t l y o f v o l c a n i c f r a g m e n t s , a s m a l l p r o p o r t i o n o f c h l o r i t e , and a c l a y m a t r i x . I n u n a l t e r e d specimens t h e m a t r i x c o n s t i t u t e s o n l y a  few p e r c e n t o f t h e r o c k s ; i n many a l t e r e d specimens t h e c l a y c o n t e n t seems t o be h i g h e r .  But i n these rocks the m a t r i x  cannot be d i s t i n g u i s h e d from t h e margins o f a l t e r e d v o l c a n i c f r a g m e n t s , and t h e r e s u l t s o f p o i n t c o u n t e r a n a l y s e s t h a t range up t o 20$ o f c l a y c o n t e n t a r e p r o b a b l y t o o h i g h . The l i t h i c fragments a r e m o s t l y v o l c a n i c but i n c l u d e particles of argillite  r a n g i n g from sand t o pebble  size,  p r o b a b l y d e r i v e d from contemporaneous sediments. The v o l c a n i c fragments a r e f i n e - g r a i n e d and h i g h l y altered.  They c o n s i s t l a r g e l y o f p l a g i o c l a s e and c h l o r i t e but  a l s o c o n t a i n p o t a s s i c f e l d s p a r , q u a r t z , 'Iron o r e " , and secondary m i n e r a l s such as c a r b o n a t e , s e r i c i t e , e p i d o t e , c h l o r i t e and zeolites.  The l a r g e s t number o f fragments resemble  original  a n d e s i t e s o r k e r a t o p h y r e s ; s m a l l e r p r o p o r t i o n s seem t o be der i v e d from b a s a l t s o r s p i l i t e s , from d a c i t e s o r q u a r t z k e r a t o p h y r e s , and from f e l s i t i c  rocks.  Some c o m p l e t e l y c h l o r -  i t i z e d fragments may be a l t e r e d v o l c a n i c g l a s s .  Some o f t h e de-  t r i t a l f e l d s p a r and q u a r t z may have formed p h e n o c r y s t s i n such rocks.  The fragments a r e m o s t l y s u b a n g u l a r .  The s o r t i n g i s  b e t t e r t h a n i n t y p i c a l greywackes but poorer than i n t y p i c a l quartz a r e n i t e s . The conglomerates a r e made up o f g r a n u l e s o r p e b b l e s . many l o c a l i t i e s t h e fragments a r e r a t h e r a n g u l a r .  They seem t o  have been d e r i v e d from t h e same source as t h e sandstones but a r e r i c h e r i n l i t h i c fragments and poorer i n f e l d s p a r and q u a r t z .  In  70 Division C D i v i s i o n C s e p a r a t e d from B by a f a u l t , i s made up e s s e n t i a l l y o f t h e same r o c k types as B but c o n t a i n s a l a r g e r p r o p o r t i o n o f t h e c o a r s e r grades and i s m o s t l y m a s s i v e . sandstone  Lithic  i s t h e dominant r o c k - t y p e and g r a n u l e and p e b b l e -  conglomerates composed o f r a t h e r a n g u l a r fragments common i n t h e lower p a r t o f t h e D i v i s i o n .  a r e n o t un-  S i l t s t o n e and a r g i -  l l i t e w h i c h form o n l y a s m a l l f r a c t i o n o f t h e exposed r o c k s a r e p r e s e n t i n laminae and t h i n beds.  A covered i n t e r v a l o f 350  f e e t i n t h e upper p a r t o f t h e D i v i s i o n may c o n t a i n a h i g h e r p r o p o r t i o n o f these r o c k s . The  f o l l o w i n g s t r a t i g r a p h i c s e c t i o n was measured on  the west s i d e o f t h e F r a s e r R i v e r , a p p r o x i m a t e l y one m i l e n o r t h o f t h e mouth o f B r i d g e R i v e r . a r e based on r a p i d e s t i m a t e s .  P e r c e n t a g e s o f r o c k types  71  Top o f Measured S e c t i o n : Member A I I I , J a c k a s s M o u n t a i n Group Feet 61  L i t h i c sandstone, l i g h t b l u i s h g r e y , g r e e n i s h g r e y , l o c a l l y b r o w n i s h grey w e a t h e r i n g , medium- t o f i n e - g r a i n e d , m o s t l y massive w i t h a few t h i n i n t e r beds o f s i l t s t o n e , l i g h t g r e y , g r e e n i s h grey w e a t h e r i n g , and a r g i l l i t e , dark b l u i s h g r e y , dark b l u i s h grey w e a t h e r i n g . Fault.  23  L i t h i c sandstone as above, upper 3 f e e t  carbonated.  1  L i t h i c sandstone, f i n e - g r a i n e d , s i l t s t o n e , medium-bedded t o l a m i n a t e d . s s : 70% s t : 20$ a r g : 10$  9  L i t h i c sandstone, c o a r s e - t o f i n e - g r a i n e d , p a r t l y m a s s i v e , p a r t l y thin-bedded t o l a m i n a t e d , I n c l u d e s a 1 f o o t l e n s o f v o l c a n i c pebble conglomerate.  3  S i l t s t o n e , a r g i l l i t e , l i t h i c sandstone, c o a r s e - t o f i n e - g r a i n e d ; thin-bedded t o l a m i n a t e d , s t r o n g l y sheared. s t : 50$ a r g : 30$ s s : 20$  16  370 38  4 44  L i t h i c sandstone, v e r y c o a r s e - g r a i n e d , g r a n u l e cong l o m e r a t e , one i n c h fragments o f a r g i l l i t e , some pebbles o f v o l c a n i c r o c k s , p o o r l y s o r t e d , m a s s i v e . Covered  interval.  L i t h i c sandstone, f i n e - to c o a r s e - g r a i n e d , massive; t h i n i n t e r b e d s o f s i l t s t o n e and a r g i l l i t e . s s : 98$ s t : a r g : 2$ Covered i n t e r v a l ,  recessive.  L i t h i c sandstone, f i n e - to c o a r s e - g r a i n e d , massive.  2  L i t h i c sandstone, f i n e - g r a i n e d , s i l t s t o n e , thin-bedded t o laminated.  8  Covered i n t e r v a l , r e c e s s i v e .  33  argillite;  argillite;  L i t h i c sandstone, f i n e - t o c o a r s e - g r a i n e d , m a s s i v e , t h i n i n t e r b e d s o f s i l t s t o n e and a r g i l l i t e f o r m i n g l e s s than 1$ o f t h e u n i t .  L i t h i c s a n d s t o n e , c o a r s e - t o f i n e - g r a i n e d , w i t h some g r a n u l e s and pebbles o f v o l c a n i c r o c k and fragments of a r g i l l i t e , mostly massive, p a r t l y thin-bedded, a few t h i n i n t e r b e d s o f s i l t s t o n e and a r g i l l i t e . s s : 95$ s t : a r g : 5$ L i t h i c s a n d s t o n e , s i l t s t o n e ; medium- t o t h i n - b e d d e d , recessive. s s : 60$ s t : 40$ L i t h i c s a n d s t o n e , c o a r s e - t o f i n e - g r a i n e d , upper p a r t f i n e - g r a i n e d , m a s s i v e , some g r a n u l e s and p e b b l e s o f volcanic rocks, poorly sorted. L i t h i c sandstone, coarse- t o f i n e - g r a i n e d , grading upward i n t o s i l t s t o n e , s i l t s t o n e grades upwards i n t o a r g i l l i t e ; m o s t l y m a s s i v e , t h i n - b e d d e d i n upper p a r t , s s : 60$ s t : 30$ a r g : 10% L i t h i c sandstone, coarse- t o f i n e - g r a i n e d , coarser i n lower p a r t , m a s s i v e . L i t h i c sandstone, coarse- t o f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e , t h i n - b e d d e d t o l a m i n a t e d , graded b e d d i n g , s s : 40$ s t : 30$ a r g : 30$ Conglomerate, v o l c a n i c pebbles and g r a n u l e s , rounded t o s u b - a n g u l a r , m a t r i x o f l i t h i c sandstone and s i l t s t o n e , w i t h fragments o f s i l t s t o n e and a r g i l l i t e 2 inches to 5 feet long; p o o r l y s o r t e d , massive. L i t h i c sandstone, f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; t h i n - b e d d e d t o l a m i n a t e d , upper p a r t f i s s i l e , pene-contemporaneous d e f o r m a t i o n s . s s : 40$ s t : 30$ a r g : 30$ L i t h i c sandstone, c o a r s e - t o f i n e - g r a i n e d , t h i n - b e d d e d t o l a m i n a t e d , graded bedding. L i t h i c sandstone, f i n e - g r a i n e d , s i l t s t o n e , thin-bedded t o laminated, s s : 60$ s t : 30$ a r g : 10$  argillite,  L i t h i c sandstone, lower p a r t v e r y c o a r s e - g r a i n e d , w i t h g r a n u l e s , m a s s i v e , upper p a r t medium- t o f i n e - g r a i n e d , p a r t l y m a s s i v e , p a r t l y medium-bedded t o l a m i n a t e d . A r g i l l i t e , f i s s i l e , siltstone; a r g ; 70$ s t : 30$  thin-bedded,  73  Feet 1.5 .5  Sandstone, medium- t o f i n e - g r a i n e d , grades upward i n t o s i l t s t o n e and a r g i l l i t e ; medium-bedded to laminated. Siltstone, argillite, lithic thin-bedded to laminated, s t : 40$ a r g : 40$ s s : 20$  sandstone,  fine-grained;  2  L i t h i c sandstone, f i n e - g r a i n e d , medium-bedded to laminated, ss: 98$ s t : 2$  1  Covered  8  L i t h i c sandstone, f i n e - g r a i n e d , grades upward i n t o s i l t s t o n e ; mostly massive, p a r t l y thin-bedded to laminated.  1  Argillite, siltstone, lithic thin-bedded to laminated, arg: 40$ s t : 40$ s s : 20$  20  i n t e r v a l , road.  sandstone,  fine-grained;  L i t h i c sandstone, lower part c o a r s e - g r a i n e d , upper p a r t medium- to f i n e - g r a i n e d , mostly massive, upper part thin-bedded; l e n s o f l i m e s t o n e 3X 0.5 f e e t , l i g h t grey, brownish weathering, f i n e - g r a i n e d .  1.5  S i l t s t o n e , l i t h i c sandstone, medium- to f i n e - g r a i n e d , a r g i l l i t e ; thin-bedded to laminated, s t : 50$ s s : 30$ a r g : 20$  4  L i t h i c sandstone, mostly f i n e - g r a i n e d , mostly t h i n bedded to laminated, p a r t l y medium-bedded; some i n t e r laminated s i l t s t o n e .  2.5  L i t h i c sandstone, c o a r s e - to f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; thin-bedded to l a m i n a t e d , graded bedding, pene-icontemporaneous deformations, ss: 55$ s t : 30$ a r g : 15$  4  L i t h i c sandstone, medium- to f i n e - g r a i n e d , thin-bedded to laminated.  1  Limestone, l i g h t grey, g r e y i s h b u f f weathering, grains of s i l t - s i z e .  74 Feet 27.5  L i t h i c sandstone, m o s t l y f i n e - to medium-grained, p a r t l y coarse-grained, mostly massive, p a r t l y t h i n bedded, s i l t s t o n e , a r g i l l i t e , b o t h thin-bedded t o laminated. At 20 f e e t from bottom l e n s o f l i m e s t o n e 7X 0.75 f e e t , medium g r e y , l i g h t g r e e n i s h - g r e y w e a t h e r i n g , very fine m i c r o - c r y s t a l l i n e , p y r i t e . ss: 99$ s t : a r g : 1$  881  Bottom:  w a t e r - l e v e l of Fraser River  A t y p i c a l granule-conglomerate  contains  approximately  10$ o f f e l d s p a r , l a r g e l y a l b i t e , 40$ o f v o l c a n i c r o c k  fragments,  and 10$ o f c h l o r i t e ; the c l a y m a t r i x makes up about 40$ o f the rock.  Some o f the sandstones  and conglomerates  carry highly  altered tuffaceous m a t e r i a l . T h i s u n i t shows a h i g h degree o f a l t e r a t i o n to a l b i t e , c h l o r i t e , and c a r b o n a t e , the a l t e r a t i o n a p p a r e n t l y b e i n g r e l a t e d to s e v e r a l branches o f the F r a s e r R i v e r f a u l t zone. F i g u r e 2 shows the r e l a t i v e p r o p o r t i o n o f t h r e e components o f t h e s e r o c k s :  f e l d s p a r , q u a r t z , and l i t h i c  t o g e t h e r w i t h c h l o r i t e and m i c a .  I n the framework o f G i l b e r t s  c l a s s i f i c a t i o n ( W i l l i a m s , T u r n e r , G i l b e r t , 1955,  p. 293)  r o c k s would be c l a s s i f i e d as v o l c a n i c a r e n i t e s . A few c a n i c greywackes may  fragments  the vol-  be r e p r e s e n t e d , but the content o f o r i g i n a l  c l a y m a t r i x i n these r o c k s i s u n c e r t a i n . 3.  The Problem o f A l b i t i z a t i o n  As p o i n t e d out by D u f f e l l and McTaggart (1952, p.  37)  most o f the f e l d s p a r i s p l a g i o c l a s e and has t h e c o m p o s i t i o n o f  75  QUARTZ  FELDSPARS  COMPOSITION  ROCK FRAGMENTS, CHLORITE,EPIDOTE, MICAS OF F R A G M E N T S , S A N D S T O N E S , L I L L O O E T  CLASSIFICATION  ADAPTED  FROM  FIGURE 2  Gl L B E RT, ( 1 9 5 5 )  GP  76 s o d i c a l b i t e , a l t h o u g h one g r a i n o b s e r v e d by t h e a u t h o r i n 1 out o f 17 t h i n - s e c t i o n s i s zoned from An^ t o A n  1 0  .  i n c l u s i o n s o f e p i d o t e , and t h e z o n a l d i s t r i b u t i o n  Abundant  of sericite  i n some g r a i n s i n d i c a t e t h a t t h e a l b i t e was d e r i v e d more c a l c i c p l a g i o c l a s e by The periods:  from  alteration.  a l b i t i z a t i o n may have o c c u r r e d i n any o f t h r e e  as a l t e r a t i o n  the f o r m a t i o n  by h y d r o t h e r m a l s o l u t i o n s soon  after  o f t h e l a v a s from w h i c h t h e a r e n i t e s a r e d e r i v e d ,  by metamorphism o f t h e s e v o l c a n i c r o c k s , o r by a l b i t i z a t i o n o f . the d e r i v e d  sedimentary  rocks.  L a t e magmatic a l b i t i z a t i o n i s suggested by t h e f o l l o w ing observation.  I n one t h i n - s e c t i o n an amygdule i n a s c o r -  i a c e o u s v o l c a n i c fragment i s f i l l e d w i t h w a t e r - c l e a r  plagio-  c l a s e w h i c h i s p r o b a b l y a l b i t e ; but no such p l a g i o c l a s e c a n be seen i n f r a c t u r e s o r c a v i t i e s  o f the sedimentary  Another t h i n - s e c t i o n c o n t a i n s  rock.  b o t h a l b i t e and zoned  c a l c i c p l a g i o c l a s e which i n d i c a t e s that the a l b i t e  i n this  rock i s d e t r i t a l . On t h e o t h e r hand, a s i l l i n t r u d i n g t h e L i l l o o e t  group  near a major f a u l t has been p r e h n i t i z e d ( D u f f e l l and McTaggart, 1952,  p. 9 2 ) , and t h e gabbros west o f L i l l o o e t w h i c h a r e  spatially  c l o s e t o t h e s t r a t a o f t h e L i l l o o e t group have been  a l b i t i z e d and p r e h n i t i z e d .  P r o b a b l y t h e sedimentary r o c k s were  exposed l o c a l l y t o t h e same a l t e r i n g The periods  relative  of alteration  solutions.  importance o f each o f t h e t h r e e remains  uncertain.  possible  77  4.  Structure  The beds o f D i v i s i o n s A and B s t r i k e n o r t h w e s t e r l y and dip steeply.  J u d g i n g from t h e d i s t r i b u t i o n o f r o c k t y p e s and a  few d e t e r m i n a t i o n s o f s t r a t i g r a p h i c t o p s t h e i r major s t r u c t u r e i s an i s o c l i n a l a n t i c l i n e w h i c h i s i n p a r t o v e r t u r n e d t o t h e southwest.  I n D i v i s i o n A t h e major a n t i c l i n e i s m o d i f i e d by a  g r e a t e r number o f minor f o l d s t h a t a r e i n d i c a t e d by t h e r e l a t ive d i r e c t i o n s o f the s t r a t i g r a p h i c tops.  A few f o l d s near t h e  lower p a r t o f D i c k e y Creek a r e shown on t h e map.  The t h i c k n e s s  o f t h e i r l i m b s p r o b a b l y i s o f t h e o r d e r o f a few hundred f e e t . The more competent beds o f D i v i s i o n B do n o t show t h i s p a t t e r n o f t i g h t secondary  folding.  To t h e west t h e r o c k s a r e p r o b a b l y i n f a u l t c o n t a c t w i t h b a s i c and u l t r a b a s i c i n t r u s i o n s . exposed.  The c o n t a c t i s n o t  To t h e east they a r e i n f a u l t c o n t a c t w i t h f l a t  lying  o r g e n t l y d i p p i n g s t r a t a o f D i v i s i o n C and o f t h e J a c k a s s M o u n t a i n group. D i v i s i o n C, p r o b a b l y o f marine o r i g i n , i s o v e r l a i n by the c o n t i n e n t a l member A l o f t h e J a c k a s s Mountain group.  The  t r a n s i t i o n from marine t o c o n t i n e n t a l d e p o s i t s suggests an u n c o n f o r m i t y but an a n g u l a r d i s c o r d a n c e between t h e two groups has n o t been observed. 5.  Mode o f O r i g i n  The presence o f A u c e l l a i n d i c a t e s t h a t D i v i s i o n A was d e p o s i t e d i n a marine environment,  and t h e a s s o c i a t i o n o f  78 carbonaceous  m a t t e r w i t h the sediments shows t h a t i t was  at  times o f the r e s t r i c t e d type i n which reducing c o n d i t i o n s prevail.  As most o f the r o c k s show graded bedding the  were p r o b a b l y d e p o s i t e d by t u r b i d i t y c u r r e n t s . of  u n i f o r m l y laminated rocks i s remarkable.  sediments  The t h i c k n e s s  C o n t o r t i o n s and  c r e n u l a t i o n s i n the r o c k s a p p a r e n t l y formed b e f o r e the  lithi-  f i c a t i o n o f the sediments suggest t h a t some o f t h e s e t u r b i d i t y c u r r e n t s a r e r e l a t e d t o submarine s l u m p i n g . slumping may  The causes o f such  be t e c t o n i c d i s t u r b a n c e s o f the b a s i n .  The same c o n d i t i o n s a p p a r e n t l y p e r s i s t e d d u r i n g the d e p o s i t i o n o f D i v i s i o n B.  The g r a d u a l t r a n s i t i o n i n t h i s  unit  from a r g i l l i t e to sandstone and conglomerate however, suggests an u p l i f t o f b a s i n o r s o u r c e a r e a .  A s m a l l seam o f c o a l i n  D i v i s i o n B probably o r i g i n a t e d i n a c o n t i n e n t a l or near-shore mar ine  env ironment. D i v i s i o n s A and B a r e t i g h t l y f o l d e d and i n t r u d e d by  numerous dykes and s i l l s whereas D i v i s i o n C and the o v e r l y i n g s t r a t a o f the J a c k a s s Mountain Group l i e almost and a r e c u t by v e r y few i n t r u s i v e r o c k s .  horizontally  These r e l a t i o n s  suggest t h a t the f o l d i n g and the i n t r u s i o n took p l a c e s h o r t l y a f t e r t h e d e p o s i t i o n o f D i v i s i o n B, and t h a t B and C a r e s e p a r a t e d by an a n g u l a r u n c o n f o r m i t y .  But as B and C a r e i n  f a u l t c o n t a c t , and the s t r a t a between them are not  exposed  such an u n c o n f o r m i t y can o n l y be i n f e r r e d and not o b s e r v e d . A f t e r a p e r i o d o f u p l i f t and e r o s i o n t h e a r e a was submerged; the b e l e m n i t e s i n D i v i s i o n C i n d i c a t e a marine onment.  again envir-  As t h i s u n i t c o n s i s t s m o s t l y o f sandstone and some  conglomerate,  t h e sediments were p r o b a b l y d e p o s i t e d not f a r  from t h e shore.  The t u f f a c e o u s m a t e r i a l i n t h e s e r o c k s  suggests  contemporaneous v o l c a n i s m . At t h e end o f t h e time r e p r e s e n t e d by t h e L i l l o o e t group t h e a r e a a g a i n r o s e above sea l e v e l . glomerate  The b a s a l con-  o f t h e J a c k a s s M o u n t a i n group p r o b a b l y was l a i d down  i n a c o n t i n e n t a l environment. 6.  Age and C o r r e l a t i o n  The L i l l o o e t group was f i r s t d e f i n e d and d e s c r i b e d by D u f f e l l and McTaggart.  Specimens found by these a u t h o r s i n  the lower p a r t o f t h e group were i d e n t i f i e d by J.A. J e l e t z k y a s  " A u c e l l a sp. i n d . ( e x a f f . c r a s s i c o l l i s ) K e y s e r l i n g " and  c o n s i d e r e d t o be e a r l y Lower Cretaceous age.  (Lower Neocomian) i n  ( D u f f e l l and McTaggart, 1952, p. 3 9 ) . Some&ssils  found d u r i n g t h e p r e s e n t  investigation  i n D i v i s i o n B (F13) a r e a c c o r d i n g t o J e l e t z k y " i n d e t e r m i n a t e t r u e belemnoids o f g e n e r a l J u r a s s i c o r Cretaceous  age".  Sim-  i l a r but v e r y p o o r l y p r e s e r v e d specimens were n o t i c e d i n D i v i s i o n C. D u f f e l l and McTaggart have c o r r e l a t e d t h e L i l l o o e t group w i t h D i v i s i o n A o f t h e m o d i f i e d Dewdney Creek group o f the P r i n c e t o n a r e a and w i t h t h e Dewdney Creek group o f t h e Coquihalla<, a r e a .  The c o r r e l a t i o n i s based m a i n l y on l i t h o l o g y  and s t r a t i g r a p h i c p o s i t i o n o f t h e r e s p e c t i v e u n i t s . I f the unconformity  between D i v i s i o n s B and C were  proved D i v i s i o n C s h o u l d be t r e a t e d as a s e p a r a t e u n i t o r  i n c l u d e d w i t h t h e J a c k a s s Mountain group.  However, s i n c e  a t t h i s time i t s presence can o n l y be i n f e r r e d , these f o l l o w i n g e a r l i e r workers,  rocks,  have been l e f t i n t h e L i l l o o e t  group.  JACKASS MOUNTAIN GROUP 1.  D i s t r i b u t i o n and T h i c k n e s s  D u f f e l l and McTaggart have s u b d i v i d e d t h e J a c k a s s M o u n t a i n group i n t o t h r e e s t r a t i g r a p h i c u n i t s c a l l e d A, D i v i s i o n B, and D i v i s i o n C.  Division  I n t h e p r e s e n t work t h r e e  l i t h o l o g i c a l u n i t s , members A I , A l l , and A I I I a r e d i s t i n g u i s h e d i n D i v i s i o n A. D i v i s i o n A u n d e r l i e s t h e lower and i n t e r m e d i a t e l e v e l s o f F o u n t a i n R i d g e and o f t h e n o r t h s i d e o f t h e F r a s e r R i v e r between F o u n t a i n and t h e mouth o f B r i d g e R i v e r . forms conspicuous  Division B  c l i f f s on t h e h i g h e r l e v e l s o f t h e same a r e a .  D i v i s i o n C, u n d e r l i e s l a r g e p a r t s o f F o u n t a i n R i d g e and o f t h e C a m e l s f o o t Range. Member A I has an approximate t h i c k n e s s o f 150 f e e t . On t h e n o r t h s l o p e o f F o u n t a i n Ridge A l l i s about 2500 f e e t t h i c k b u t p o s s i b l y r e p e a t e d by f a u l t i n g .  On t h e s o u t h  slope  o f t h e C a m e l s f o o t Range, 1-1/2 m i l e s n o r t h e a s t o f t h e mouth o f B r i d g e R i v e r , A I I I comprises a p p r o x i m a t e l y  1000 f e e t o f s t r a t a .  About 1-1/2 m i l e s n o r t h o f F o u n t a i n on t h e n o r t h side;: o f t h e F r a s e r R i v e r D i v i s i o n B i s about 1000 f e e t t h i c k and on F o u n t a i n Ridge a p p r o x i m a t e l y  1500 f e e t .  D u f f e l l and McTaggart  s t a t e ( p . 40) t h a t t h e D i v i s i o n i s 1750 f e e t t h i c k on t h e west s l o p e o f t h e Camelsfoot Range near t h e n o r t h w e s t e r n edge o f t h e A s h c r o f t map a r e a o u t s i d e o f t h e p r e s e n t The  map a r e a .  t o p o f D i v i s i o n C i s removed by e r o s i o n .  Accord-  i n g t o D u f f e l l and McTaggart a t l e a s t 5000 f e e t o f s t r a t a a r e represented  (p. 91). 2.  Lithology  Division A Member A I Member A l comprises conglomerate and l i t h i c t h a t c a r r i e s some p l a n t r e m a i n s .  sandstone  The conglomerate i s exposed  o n l y f o r one m i l e a l o n g t h e shores o f t h e F r a s e r R i v e r i n t h e w e s t e r n p a r t o f t h e a r e a u n d e r l a i n by D i v i s i o n A. appears f u r t h e r e a s t , p r o b a b l y east.  I t dis-  because o f a g e n t l e d i p t o t h e  The sandstone w i t h p l a n t remains extends t o t h e e a s t e r n  boundary o f D i v i s i o n A . but where t h e conglomerate i s l a c k i n g Member A l i s d i f f i c u l t t o d i s t i n g u i s h from A H . The  f o l l o w i n g s t r a t i g r a p h i c s e c t i o n o f A l was measured  on t h e n o r t h s i d e o f t h e F r a s e r R i v e r about 1 m i l e o f t h e mouth o f B r i d g e based on r a p i d  River.  estimates.  northeast  Percentages o f rock types a r e  82 Feet  Top  of  section  8  Conglomerate, brownish green weathering, v o l c a n i c p e b b l e s , 1-3 i n . , w e l l r o u n d e d , m a t r i x o f l i t h i c sandstone, massive.  9  C o n g l o m e r a t e , g r a n u l e s and f i n e p e b b l e s , w e l l rounded to subrounded, m a s s i v e .  16  C o n g l o m e r a t e , v o l c a n i c p e b b l e s , m o s t l y 1-4 i n . , w e l l r o u n d e d , abundant m a t r i x o f l i t h i c s a n d s t o n e , strongly carbonated.  8  L i t h i c sandstone, l i g h t b l u i s h grey, g r e e n i s h grey to brownish grey weathering, s c a t t e r e d lenses o f pebble conglomerate; massive, s t r o n g l y carbonated.  2  C o n g l o m e r a t e , 15 f e e t l e n s , v o l c a n i c m o s t l y 1-3 i n . , w e l l r o u n d e d .  2  L i t h i c sandstone, medium-grained, c o m p a r a t i v e l y l o o s e l y cemented, l e n s e s o f p e b b l e - c o n g l o m e r a t e , t h i n beds o f a r g i l l i t e ; s t r o n g l y c a r b o n a t e d .  3  L i t h i c sandstone, medium-grained, c o m p a r a t i v e l y l o o s e l y cemented.  1  L i t h i c sandstone, s i l t s t o n e , l i g h t b l u i s h grey, greenish-grey weathering, a r g i l l i t e , dark b l u i s h grey, dark b l u i s h grey weakening, thin-bedded t o l a m i n a t e d , s t r o n g l y s h e a r e d and l a m i n a t e d .  8  Lithic  1  Conglomerate, v o l c a n i c m o s t l y .5-2 i n .  4  Lithic lenses  2  Conglomerate, v o l c a n i c m o s t l y .5-2 i n .  1  Lithic  3  Conglomerate  1  Lens  12  pebbles,  thin-bedded,  s a n d s t o n e , medium- t o f i n e - g r a i n e d , pebbles, well  massive.  rounded,  sandstone, f i n e - to medium-grained, massive, o f v o l c a n i c p e b b l e and g r a n u l e c o n g l o m e r a t e . pebbles, w e l l  sandstone, medium-grained, as  of l i t h i c  Conglomerate  as  above. s a n d s t o n e as above.  above.  rounded,  massive.  4 15  Conglomerate, g r a n u l e s and p e b b l e s o f v o l c a n i c r o c k s , c o m p a r a t i v e l y l o o s e l y cemented, m a s s i v e . L i t h i c sandstone, medium- t o f i n e - g r a i n e d , m o s t l y m a s s i v e , a few t h i n beds v e r y l o o s e l y cemented, p r o b a b l y t u f f a c e o u s , a few t h i n i n t e r b e d s o f s i l t s t o n e and a r g i l l i t e ; s t r o n g l y c a r b o n a t e d . Fault, continuity of section uncertain.  15  L i t h i c s a n d s t o n e , medium- t o c o a r s e - g r a i n e d , m a s s i v e , a few t h i n i n t e r b e d s o f a r g i l l i t e and s i l t s t o n e , s t r o n g l y sheared.  10?  L i t h i c s a n d s t o n e , medium- t o f i n e - g r a i n e d , m a s s i v e ; t h i c k n e s s u n c e r t a i n because o f f a u l t i n g . Fault.  5?  L i t h i c s a n d s t o n e , medium- t o f i n e - g r a i n e d , m a s s i v e , w i t h a few t h i n i n t e r b e d s o f s i l t s t o n e and a r g i l l i t e ; t h i c k n e s s u n c e r t a i n because o f f a u l t i n g .  4  L i t h i c sandstone, f i n e - g r a i n e d , s i l t s t o n e , a r g i l l i t e ; medium- t o t h i n - b e d d e d , ss: s t : 80$ a r g : 20$  11  L i t h i c s a n d s t o n e , medium- t o c o a r s e - g r a i n e d , t u f f a c eous, w i t h fragments o f p l a n t - m a t t e r , some c o a l y wood, a few g r a n u l e s and pebbles o f v o l c a n i c r o c k s , l o o s e l y cemented, m o s t l y t h i n - b e d d e d , p a r t l y m a s s i v e ; recessive. Bottom o f s e c t i o n : t o p o f D i v . C., L i l l o o e t Group.  145 The s t r a t a change c o n s i d e r a b l y over d i s t a n c e s as s h o r t as one hundred  feet.  The round-stones o f t h e conglomerate a r e m o s t l y made up o f l i g h t grey w e a t h e r i n g massive a p h a n i t i c r o c k s some o f w h i c h show a few f i n e - g r a i n e d p h e n o c r y s t s . specimens  Two t y p i c a l  examined i n t h i n - s e c t i o n a r e q u a r t z - k e r a t o p h y r e s .  84 They c o n t a i n m i c r o - p h e n o c r y s t s o f a l b i t e and c h l o r i t e a s s o c i a t e d w i t h " i r o n o r e " pseudomorphous a f t e r a p y r i b o l e .  The  groundmass c o n s i s t s d o m i n a n t l y o f p l a g i o c l a s e m i c r o l i t e s , some quartz, and m i n e r a l s t o o f i n e - g r a i n e d f o r i d e n t i f i c a t i o n .  The  p l a g i o c l a s e i s a l t e r e d by s e r i c i t e and c a r b o n a t e . R e l a t i v e l y weak c e m e n t a t i o n and t h e presence o f p l a n t m a t t e r , m o s t l y remnants o f stems, a r e c h a r a c t e r i s t i c o f some o f t h e l i t h i c sandstones a s s o c i a t e d w i t h t h e c o n g l o m e r a t e . lithic  The  sandstones c o n t a i n l i t t l e q u a r t z (1% o r l e s s ) and  feldspar  (3$ o r l e s s ) and a r e composed m a i n l y o f v o l c a n i c  fragments and c h l o r i t e .  Some o f t h e fragments show s h a r d - l i k e  o u t l i n e s , o t h e r s appear t o be v e s i c u l a r and p r o b a b l y many o f them a r e o f t u f f a c e o u s  origin.  As t h e v o l c a n i c fragments a r e  h i g h l y a l t e r e d they cannot be d i s t i n g u i s h e d e a s i l y from t h e original clay The  matrix.  fragments a r e subrounded t o subangular and. moderate-  ly w e l l sorted. resemble v o l c a n i c  I n t h e i r roundness and s o r t i n g t h e sandstones arenites.  A c a r b o n a t i z e d l i t h i c sandstone from t h e v i c i n i t y o f F o u n t a i n s t a t i o n i s o f v e r y f i n e sand g r a d e , f a i r l y w e l l s o r t e d and c o n t a i n s fragments t h a t a r e subrounded t o s u b a n g u l a r i n shape but r e p l a c e d a t t h e margins by c h l o r i t e . The r o c k cont a i n s a p p r o x i m a t e l y 2,0% o f f e l d s p a r , 15% o f q u a r t z , and 7% o f r e c o g n i z a b l e r o c k fragments. C h l o r i t e , m i c a , e p i d o t e , and c l a y make up about 20% o f t h e rock. The b a l a n c e c o n s i s t s o f c a r b o n a t e and der i v e d " i r o n o r e " w h i c h has r e p l a c e d t h e o r i g i n a l c l a y matrix to a large extent. The f e l d s p a r , mostly plagioclase i s p a r t l y c l e a r , p a r t l y a l t e r e d and r i c h i n e p i d o t e . A l l grains of plagioclase determined have t h e c o m p o s i t i o n o f a l b i t e .  85  Member A H Member A H  s t r o n g l y a l t e r e d , f a u l t e d , and p o o r l y ex-  posed c o n s i s t s l a r g e l y o f l i t h i c sandstone but c o n t a i n s beds of  conglomerate t h a t a r e a few f e e t t h i c k , seams o f p l a n t  m a t t e r i n t h e lower p a r t o f t h e s e c t i o n , and an i n c r e a s i n g p r o p o r t i o n o f i n t e r b e d d e d s i l t s t o n e i n t h e upper p a r t .  On t h e  west s l o p e o f F o u n t a i n R i d g e , e a s t o f t h e r a i l r o a d b r i d g e near L i l l o o e t t h e t y p i c a l g r e e n i s h w e a t h e r i n g massive l i t h i c  sand-  stone i s u n d e r l a i n by dark s i l t s t o n e o f c o n s i d e r a b l e t h i c k n e s s . The t y p i c a l l i t h i c sandstone i s m a s s i v e , b l u e grey on f r e s h s u r f a c e s , and g r e e n i s h on weathered  faces.  S i x speci-  mens a n a l y z e d c o n t a i n 3 t o 10$ o f f e l d s p a r , m o s t l y a l b i t e , 2 to  5$ o f q u a r t z , and a few per cent o f e p i d o t e and m i c a ; t h e  b a l a n c e c o n s i s t s d o m i n a n t l y o f v o l c a n i c fragments. ments a r e f a i r l y c l o s e l y packed. chlorite.  The f r a g -  I n t e r s t i c e s a r e f i l l e d by  The fragments a r e a l t e r e d on t h e o u t s i d e t o " c l a y " .  M i n o r c o n s t i t u e n t s a r e " i r o n o r e " and carbonaceous  matter.  Some o f t h e l o w e s t beds o f t h e member show g r e y i s h laminae about one m i l l i m e t e r t h i c k and spaced a f r a c t i o n o f a c e n t i meter a p a r t .  M i c r o s c o p i c e x a m i n a t i o n shows t h a t they a r e l a y e r s  rich i n pyrite.  As t h e m i n e r a l i s m o d e r a t e l y w e l l rounded i t  probably i s of d e t r i t a l  origin.  The p a r t i c l e s a r e m o s t l y subrounded, o f f i n e  grade,  and b e t t e r s o r t e d t h a n i n any o t h e r u n i t o f t h e J a c k a s s Mountain group.  The l i t h i c sandstone o f Member A H  c l a s s i f i e d as " v o l c a n i c a r e n i t e " ( G i l b e r t , 1955).  c a n be  86  Member A I I I Member A I I I c o n s i s t s o f a r g i l l a c e o u s s i l t s t o n e , l a m i n a t e d a r g i l l i t e , l i t h i c sandstone and l e n s e s and beds o f l i m e stone t h a t a r e a few f e e t  thick.  A s e c t i o n measured on t h e s o u t h s l o p e o f t h e Camelsf o o t Range can be summarized as f o l l o w s : Feet 520  S i l t s t o n e , dark b l u e g r e y , dark b l u e grey w e a t h e r i n g , p a r t l y c o n c r e t i o n a r y , l i t h i c sandstone, grey, greeni s h weathering, f i n e - to coarse-grained, a r g i l l i t e , d a r k b l u e g r e y , dark b l u e grey w e a t h e r i n g , l e n s e s and beds o f l i m e s t o n e , l i g h t g r e y , l i g h t grey w e a t h e r i n g ; massive t o l a m i n a t e d , s t : 50$ s s : 35$ a r g : 10$ 1ms: 5$  450  S i l t s t o n e , as above w i t h a r g i l l i t e f r a g m e n t s , f o s s i l i f e r o u s , belemnites, pelecypods, mostly massive, w i t h a few l e n s e s and beds o f l i m e s t o n e as above.  970  The s t r a t a v a r y c o n s i d e r a b l y over d i s t a n c e s o f a few m i l e s , and l i t h i c sandstone and l i m e s t o n e a r e n o t p r e s e n t i n every s e c t i o n . A t y p i c a l massive a r g i l l a c e o u s s i l t s t o n e i s made up o f about 50$ o f s i l t s i z e d m i n e r a l s , m o s t l y f e l d s p a r , q u a r t z , e p i d o t e , m i c a , and c h l o r i t e . The m a t r i x c o n s i s t s l a r g e l y o f c l a y but i n c l u d e s a few p e r c e n t o f carbonaceous m a t t e r . The specimen cont a i n s a p p r o x i m a t e l y 40$ o f s p h e r i c a l o r e l l i p t i c a l p e l l e t s o f a r g i l l i t e t h a t a r e d a r k e r c o l o r e d and r i c h e r i n carbonaceous m a t t e r than t h e s i l t s t o n e . A t y p i c a l l a m i n a t e d specimen i s composed m a i n l y o f l a y e r s o f dark a r g i l l i t e r a n g i n g from a few m i l l i m e t e r s t o one c e n t i m e t e r i n t h i c k n e s s and a s m a l l e r f r a c t i o n o f laminae o f g r e y i s h s i l t y a r g i l l i t e t h a t a r e one m i l l i m e t e r o r a few m i l l i meters t h i c k . The dark a r g i l l i t e c o n t a i n s about 8$ o f s i l t s i z e d m i n e r a l s and 5$ o f carbonaceous m a t t e r ,  and the b a l a n c e c o n s i s t s o f c l a y - s i z e d m a t e r i a l . The g r e y i s h a r g i l l i t e comprises a p p r o x i m a t e l y 4-5$ of s i l t , 3$ o f carbonaceous m a t t e r and 52$ o f c l a y . The s i l t f r a c t i o n c o n s i s t s o f f e l d s p a r , m i c a , e p i d o t e , c h l o r i t e , and c a r b o n a t e . The specimen i s w e l l s i z e - s o r t e d and shows graded bedding. The d a r k c o l o r i s produced by t h e carbonaceous m a t t e r . Division B In  t h e p r e s e n t i n v e s t i g a t i o n D i v i s i o n B o f the J a c k a s s  M o u n t a i n group was  examined o n l y b r i e f l y .  Few a d d i t i o n s can  be made t o the account g i v e n by D u f f e l l and  McTaggart.  The D i v i s i o n c o n s i s t s , i n the o r d e r o f abundance, o f conglomerate, l i t h i c  sandstone, a r g i l l i t e ,  and  siltstone.  The conglomerate i s made up m o s t l y o f c o b b l e s and p a r t l y o f b o u l d e r s and p e b b l e s . paratively rare.  G r a n u l e conglomerate i s com-  Most o f the roundstones a r e d e r i v e d from  g r a n i t i c r o c k s o t h e r s from v o l c a n i c r o c k s , c h e r t and They a r e embedded i n an abundant m a t r i x o f l i t h i c and f a i r l y  w e l l sorted w i t h respect to s i z e .  ures a r e v e r y r a r e .  argillite  sandstone  Imbricate struct  I n some l o c a l i t i e s the l o n g axes o f t h e  roundstones seem t o l i e i n t h e p l a n e o f b e d d i n g , but exact bedding a t t i t u d e s cannot be measured i n t h e s e r o c k s .  In a  s e c t i o n measured by D u f f e l l and McTaggart on J a c k a s s M o u n t a i n the  conglomerate beds range i n t h i c k n e s s from 5 t o 100  most o f them b e i n g 8 to 20 f e e t t h i c k .  feet,  They a r e not con-  s p i c u o u s l y l e n t i c u l a r but can be t r a c e d f o r s c o r e s o f f e e t . The l i t h i c sandstone weathers g r e e n i s h , i s medium- t o f i n e - g r a i n e d , and resembles the sandstone o f D i v i s i o n C. r o c k s show no i n t e r n a l s t r a t i f i c a t i o n .  The  On J a c k a s s M o u n t a i n  t h e sandstone beds a r e from 1 f o o t t o 50 f e e t t h i c k and have an approximate  t h i c k n e s s o f 10 f e e t .  The to  i n t e r b e d d e d s i l t s t o n e s and a r g i l l i t e s  the ones i n member A H .  p o o r l y exposed  I n t h e p r e s e n t map  are s i m i l a r  a r e a o n l y a few  s t r a t a were seen.  In the p r e s e n t map  a r e a the l o w e s t beds o f  conglomerate  i n most p l a c e s r e s t conformably on 200 t o 300 f e e t o f l i t h i c sandstone. localities  Only at t h e r o a d - c u t west o f F o u n t a i n and a t two on F o u n t a i n Ridge were t h e y seen t o o v e r l i e dark  silt-  stone and a r g i l l i t e , a t l e a s t t e n f e e t t h i c k , w i t h e r o s i o n a l unconformity. L i t h i c sandstone makes up perhaps one q u a r t e r o f the m i d d l e and upper p a r t o f D i v i s i o n B.  I t becomes more abundant  i n t h e upward d i r e c t i o n and i s dominant i n t h e b a s a l p a r t o f D i v i s i o n C. of  The l i t h i c sandstone  i s c o n t i n u o u s w i t h the m a t r i x  the conglomerate, and the r e l a t i o n between t h e two r o c k types  i n most l o c a l i t i e s and-fill  i s conformable.  The o n l y example o f a c u t -  s t r u c t u r e i n the p r e s e n t map  a r e a was n o t i c e d on the  s o u t h s l o p e o f t h e Camelsfoot Range where conglomerate  overlies  a bed o f a r g i l l i t e w i t h e r o s i o n a l u n c o n f o r m i t y . Division C A c c o r d i n g t o D u f f e l l and McTaggart (p. 43) D i v i s i o n C of  t h e J a c k a s s Mountain group has a p p r o x i m a t e l y the f o l l o w i n g  composition: greywacke, i . e . l i t h i c sandstone argillite conglomerate  60-70$ 25-35$ 4$  89  The f o l l o w i n g s t r a t i g r a p h i c s e c t i o n o f a p a r t o f D i v i s i o n C was measured by the a u t h o r on the east s l o p e o f F o u n t a i n R i d g e , about 1 m i l e southwest o f t h e I n d i a n s e t t l e m e n t of  Fountain Valley.  Feet 100  Top o f s e c t i o n . L i t h i c sandstone, weathering, f i n e stone, a r g i l l i t e ; ss: 98% st,; a r g :  l i g h t b l u i s h g r e y , g r e e n i s h grey to c o a r s e - g r a i n e d , massive, s i l t laminated to thin-bedded,  2%  215  Covered i n v e r v a l , s l i g h t l y  recessive.  500  L i t h i c s a n d s t o n e , as above, m o s t l y m a s s i v e . At 430 f e e t from t h e bottom l i t h i c sandstone f i n e t o v e r y f i n e - g r a i n e d , l a m i n a t e d ; 80-85 f e e t l i t h i c sandstone w i t h s c a t t e r e d , p o o r l y s o r t e d pebbles and c o b b l e s , w e l l rounded, m o s t l y g r a n i t i c , p a r t l y v o l c a n i c ; at 45 f e e t from bottom o f u n i t a few l a m i n a e o f s i l t s t o n e and a r g i l l i t e .  80  L i t h i c s a n d s t o n e , as above, g r a d i n g upwards i n t o s i l t s t o n e and a r g i l l i t e , s c a t t e r e d c o b b l e s and p e b b l e s , w e l l rounded, m o s t l y g r a n i t i c .  850  L i t h i c s a n d s t o n e , as above, m o s t l y m a s s i v e . At 700 f e e t from t h e bottom a few l a m i n a e o f l i t h i c sandstone f i n e to v e r y f i n e - g r a i n e d ; a t 650 f e e t a 5 f e e t l e n s o f c o n g l o m e r a t e , pebbles m o s t l y o f v o l c a n i c r o c k s , w e l l rounded; a t 330 f e e t a few l a m i n a e o f s i l t s t o n e and a r g i l l i t e ; a t 140 f e e t from the bottom laminae o f l i t h i c sandstone f i n e to v e r y f i n e - g r a i n e d and s i l t s t o n e .  1745  The t y p i c a l l i t h i c sandstone i s m a s s i v e , l i g h t g r e y , and weathers g r e e n i s h .  bluish  Four specimens a n a l y z e d c o n t a i n  feldspar quartz mica epidote r o c k fragments and chlorite " i r o n o r e " , carbonaceous m a t t e r , a p a t i t e , sphene  10 3 4 1  -  15  -  trace  90 As the l i t h i c fragments are m o s t l y a l t e r e d around t h e i r margins the c o n t e n t o f o r i g i n a l c l a y m a t r i x i s v e r y d i f f i c u l t to determine. A l l f e l d s p a r c r y s t a l s examined a r e o f s o d i c  albite.  Most o f t h e r o c k fragments a r e v o l c a n i c and some a r e metamorphic.  A n g u l a r fragments o f a r g i l l i t e  r a n g i n g up t o p e b b l e s i z e  and p e b b l e s o f o t h e r r o c k s a r e p r e s e n t i n some beds i n s m a l l amounts.  The fragments a r e subrounded t o s u b a n g u l a r .  s o r t i n g i s poorer t h a n i n Member A H t h a n i n t y p i c a l h i g h rank greywackes. are  o f D i v i s i o n A but b e t t e r A l l specimens  examined  o f f i n e - o r medium sand grade. In  of  The  s e c t i o n s measured by D u f f e l l and McTaggart  the beds  l i t h i c sandstone average 60 f e e t i n t h i c k n e s s . A r g i l l i t e i s i n t e r b e d d e d w i t h the l i t h i c  sandstone  i n d i s c o n t i n u o u s s t r i n g e r s , up t o t h r e e f e e t l o n g , o r i n more e x t e n s i v e laminae t h a t a r e one t o two i n c h e s t h i c k . argillite  The  commonly c o n t a i n s a r e l a t i v e l y l a r g e f r a c t i o n o f  sand and s i l t w h i c h i n one specimen s t u d i e d c o n s i s t s o f f e l d s p a r , q u a r t z and e p i d o t e . In  c o m p o s i t i o n the conglomerate o f D i v i s i o n C c l o s e l y  resembles the conglomerate o f D i v i s i o n B. the  I n most l o c a l i t i e s  beds a r e not t h i c k e r t h a n t h i r t y f e e t ; but a conglomerate  u n d e r l y i n g the s l o p e s soutlraest o f Ward Creek may be s e v e r a l hundred f e e t t h i c k . Near t h e mouth o f F o u n t a i n Creek a few hundred f e e t o f c o n t i n e n t a l beds a r e exposed. lithic  The r o c k s c o n s i s t m o s t l y o f  sandstone but a l s o comprise beds o f pebble and c o b b l e  conglomerate t h a t a r e a few f e e t t h i c k and s e v e r a l seams o f f o s s i l plant matter.  Three c h a r a c t e r i s t i c specimens o f a  f i n e - g r a i n e d l i t h i c sandstone c o n t a i n 4 t o 18$ o f f e l d s p a r , m o s t l y a l b i t e , and 3 t o 7$ o f q u a r t z .  The b a l a n c e c o n s i s t s  mostly of f i n e - g r a i n e d , h i g h l y a l t e r e d v o l c a n i c fragments, l e s s c h l o r i t e , and s m a l l amounts o f e p i d o t e and m i c a . p a r t i c l e s a r e subrounded t o a n g u l a r .  The  The p r o p o r t i o n o f o r i g -  i n a l c l a y m a t r i x cannot be d e t e r m i n e d . A specimen o f v o l c a n i c a r e n i t e has approxi m a t e l y the f o l l o w i n g c o m p o s i t i o n : f e l d s p a r (mostly a l b i t e ) quartz m i c a , e p i d o t e , and c h l o r i t e l i t h i c , dominantly v o l c a n i c fragments c a r b o n a t e and " i r o n o x i d e "  36$ 19$ 4$ 31$ 10$  The g r a i n s a r e o f f i n e sand grade and a n g u l a r to sub-rounded. The cement c o n s i s t s o f c a r b o n a t e and " i r o n o x i d e " w h i c h may have been i n t r o d u c e d by h y d r o t h e r m a l s o l u t i o n s as t h e s e beds a r e near a major f a u l t zone. Seams o f p l a n t m a t t e r i n t e r b e d d e d w i t h l i t h i c  sand-  stone a r e a l s o exposed on t h e w e s t e r n banks o f the F r a s e r R i v e r , near F o u n t a i n .  S t r a t a c o n t a i n i n g a small percentage o f plant  remains were found near t h e mouth o f S a l l u s Creek a t a few l o c a l i t i e s i n the v i c i n i t y o f Lee Creek and B l a c k h i l l Creek. F i g u r e 3 shows the r e l a t i v e p r o p o r t i o n o f q u a r t z , f e l d s p a r , and l i t h i c fragments w i t h t h e i r a l t e r a t i o n pro-. d u c t s i n 12 specimens from t h e J a c k a s s M o u n t a i n group. A l l specimens a r e i n the range a s s i g n e d by G i l b e r t t o v o l c a n i c a r e n i t e , v o l c a n i c wacke, o r v o l c a n i c greywacke. the  According to  f a i r s o r t i n g and r e l a t i v e l y c l o s e p a c k i n g most o f t h e  9.2  QUARTZ  FELDSPARS COMPOSITION JACKASS  OF F R A G M E N T S ,  MOUNTAIN  CLASSIFICATION  GROUP  ADAPTED  FROM  FIGURE 3  SANDSTONES,  G I L B E R T,( 1955)  ROCKFRAGMENTS, CHLORITE,EPIDOTE, MICAS  100  •  >  s  75 / /  50  / i  co < cr o cr LU co cr < o o  / /  '  /  •  •  25  f  •*  / *  •  LL  o  r  I GRAIN SIZE SIZE DISTRIBUTION  1/2  IN  THIN-SECTION ANALYSIS 1) Dl V. C , MD= . 23MM  —  ••• — i — • —  1 —  1/4  1/8  SAND- AND COARSE SILT-GRADE, OF 3 * 400 GRAINS,AFTER  PACKH AM , ( 19 55 )  S0= 3.2  2) DIV. C , MD = . I 7MM  S0= 2.8  3) MEMBER All, MD= .12MM  S0=22  FIGURE 4  ••  1  T  1/16  MM  —  94 r o c k s a r e a r e n i t e s r a t h e r t h a n wackes o r greywackes. I n F i g u r e 4 t h e s i z e d i s t r i b u t i o n i n t h e sand and coarse s i l t  grades o f t h r e e c h a r a c t e r i s t i c specimens  Member A l l and D i v i s i o n C i s shown. ( P l a t e X I V ) .  from  The maximum  s e c t i o n a l d i a m e t e r o f 400 g r a i n s was measured and t h e cumula t i v e s i z e d i s t r i b u t i o n c u r v e o b t a i n e d was r e c o n s t r u c t e d w i t h the a i d o f t a b l e s g i v e n by Packham  (1955).  The s o r t i n g c o e f f i c i e n t o f t h e specimen from A l l i s 2.2; t h e two specimens o f D i v i s i o n C have s o r t i n g c o e f f i c i e n t s o f 2.8 and 3.2 r e s p e c t i v e l y . On t h e b a s i s o f 170 sediments from many d i f f e r e n t types o f environments T r a s k (1932, pp. 71-72) o b t a i n e d t h e following  d i s t r i b u t i o n o f s o r t i n g c o e f f i c i e n t s (So): So " " "  l e s s t h a n 1.9 " "2.5 " "4.5 " " 5.0  The extremes a r e 1.26 and 9.4. concludes:  - 10$  - 25$ - 75%  - 90$ The mode i s 2.9.  I f So i s l e s s t h a n 2.5 t h e sample i s w e l l  He  sorted;  i f i t i s g r e a t e r t h a n 4.5 t h e sediment i s p o o r l y s o r t e d ; and i f i t i s about 3.0 t h e d e p o s i t i s n o r m a l l y s o r t e d . A c c o r d i n g t o T r a s k s c l a s s i f i c a t i o n t h e specimen from 1  member A l l would be w e l l s o r t e d and t h e specimens from D i v i s i o n C are normally sorted.  However, compared w i t h s t u d i e s by Krum-  b e i n and T i s d e l ( 1 9 4 0 ) , and Hough (1942) t h e r e s u l t s o b t a i n e d are t o o h i g h .  Krumbein and T i s d e l found t h a t c r y s t a l l i n e r o c k s  w h i c h have d i s i n t e g r a t e d  i n p l a c e have a c o e f f i c i e n t o f s o r t i n g  95 t h a t p l a c e s them i n t o t h e range o f T r a s k ' s w e l l s o r t e d s e d i m e n t s . Hough p o i n t s out t h a t most n e a r - s h o r e marine sediments have s o r t i n g c o e f f i c i e n t s between 1.0 and 2.0. The s u b j e c t s o f s i z e a n a l y s i s from t h i n s e c t i o n and s o r t i n g c o e f f i c i e n t s o f greywackes and r e l a t e d r o c k s need more investigation.  (Compare a l s o Greenman, (1951)j Krumbein (1953),  R o s e n f e l d , J a c o b s e n , and F e r n (1953)). 3. The Problem o f A l b i t i z a t i o n The p l a g i o c l a s e i n the J a c k a s s Mountain group c o n s i s t s d o m i n a n t l y o f a l b i t e a l t h o u g h a few g r a i n s o f o l i g o c l a s e were noted.  As a d j a c e n t s t r a t a o f t h e younger Spences B r i d g e and  K i n g s v a l e groups and the o l d e r P a v i l i o n group a r e not a l b i t i z e d t h e a l b i t e o f the J a c k a s s Mountain group appears t o be detrital.  From d i f f e r e n t o b s e r v a t i o n s D u f f e l l and  a r r i v e d a t the same c o n c l u s i o n (p. 92f).  McTaggart  The problem r e m a i n s ,  however, whether the a l b i t e was produced by s p i l i t i z a t i o n o r by r e g i o n a l metamorphism o f the s o u r c e r o c k s . 4.  Structure  The s t r a t a o f t h e J a c k a s s Mountain Group l i e m o s t l y f l a t o r d i p at low a n g l e s .  I n the v i c i n i t y o f major  however, they have been t i l t e d  i n t o almost v e r t i c a l  faults, positions.  On t h e n o r t h e r n p a r t o f F o u n t a i n Ridge t h e t h r e e d i v i s i o n s form a s h a l l o w s y n c l i n e .  As the c o n t a c t s here a r e a l l  a l t e r e d and sheared t h e f o l d i n g p r o b a b l y was accompanied  strongly by  much d i f f e r e n t i a l s l i p p a g e on bedding p l a n e s .  The group i s  broken by s e v e r a l l o n g i t u d i n a l and t r a n s v e r s e f a u l t s t h a t  will  be d i s c u s s e d i n a l a t e r c h a p t e r . 5.  Mode o f O r i g i n  I n f o r m a t i o n about t h e mode o f o r i g i n o f t h e J a c k a s s M o u n t a i n group can be o b t a i n e d from t h r e e s o u r c e s : from t h e t e x t u r e and c o m p o s i t i o n o f t h e s e d i m e n t a r y r o c k s , from t h e i n c l u d e d f o s s i l s , and from t h e h i s t o r y o f t h e F r a s e r R i v e r fault  zone. Member A I c o n t a i n i n g c o n g l o m e r a t e , much p l a n t m a t t e r ,  and no marine f o s s i l s p r o b a b l y was l a i d down i n a c o n t i n e n t a l environment.  Volcanic eruptions r e s u l t i n g i n the deposition  o f t u f f p r o b a b l y took p l a c e a t t h e same t i m e . F o s s i l s i n d i c a t e a marine environment f o r members A l l and A I I I , and a s s o c i a t e d carbonaceous m a t t e r shows t h a t t h e b a s i n was " r e s t r i c t e d " .  As t h e g r a i n s i z e i n t h e s e members i s  c o m p a r a t i v e l y f i n e t h e sediments were l a i d down r e l a t i v e l y f a r from t h e shore o r were d e r i v e d from a s o u r c e a r e a w i t h o u t pronounced  relief.  The r e l a t i v e l y c o a r s e g r a i n s i z e i n t h e beds o f t h e lower p a r t o f D i v i s i o n B i s s u g g e s t i v e o f a n e a r - s h o r e e n v i r o n ment o f d e p o s i t i o n o r u p l i f t o f t h e s o u r c e a r e a . The o r i g i n o f t h e conglomerate i n D i v i s i o n B poses s e v e r a l problems. The g r e a t t h i c k n e s s o f t h e conglomerate suggests a r a p i d u p l i f t o f t h e s o u r c e a r e a and may have been caused, as  97  D u f f e l l and McTaggart s u g g e s t e d , the F r a s e r R i v e r f a u l t zone.  ( p . 4 7 ) by e a r l y movements o f  The p r e s e n t study o f t h i s  fault  zone i n d i c a t e s t h a t b e f o r e t h e d e p o s i t i o n o f t h e Spences B r i d g e group a graben had formed w h i c h c o n t r o l l e d t h e s e d i m e n t a t i o n o f D i v i s i o n C and perhaps a l s o o f D i v i s i o n B o f t h e J a c k a s s Mount a i n group.  The p r e s e n t f a u l t zone i s complex and comprises a t  l e a s t f o u r major l o n g i t u d i n a l f a u l t s w i t h r e l a t i v e downward movement o f t h e e a s t e r n f a u l t b l o c k and one f a u l t w i t h r e l a t i v e downward movement o f t h e w e s t e r n b l o c k .  I n the southern part o f  t h e a r e a t h e f a u l t - z o n e has a w i d t h o f a p p r o x i m a t e l y 7 m i l e s and t h e graben i t s e l f o f a p p r o x i m a t e l y one m i l e . t r a c e d throughout  The graben has been  t h e whole map a r e a and p r o b a b l y extends much  f a r t h e r t o t h e northwest  and t o t h e s o u t h e a s t .  The l a t e s t move-  ments on one o f t h e f a u l t s took p l a c e i n e a r l y o r m i d d l e The of  Tertiary.  f a u l t s v i s i b l e now may n o t c o i n c i d e w i t h t h e f a u l t s  t h e e a r l y Lower C r e t a c e o u s .  But t h e p r e s e n t s i t u a t i o n p e r -  haps g i v e s a p i c t u r e o f t h e c o n d i t i o n s i n t h e p a s t .  There may  have e x i s t e d a narrow, e l o n g a t e t r o u g h w h i c h was perhaps i n the o r d e r o f t e n m i l e s wide and more than one hundred m i l e s l o n g . The conglomerate  o f D i v i s i o n B i s found i n t h e w e s t e r n p a r t o f  the p r e s e n t f a u l t zone and perhaps was l a i d down a l o n g t h e western margin o f the i n f e r r e d trough. l e n t s o f t h e conglomerate t h e a r e a a r e not exposed.  The s t r a t i g r a p h i c  equiva-  i n t h e m i d d l e and e a s t e r n p a r t o f Because o f t h e s c a r c i t y o f bedding  a t t i t u d e s and c o m p l i c a t i o n s by f a u l t i n g not enough i n f o r m a t i o n c o u l d be o b t a i n e d about t h e v a r i a t i o n s i n t h e t h i c k n e s s o f t h e  conglomerate.  But  the n o r t h w e s t e r n  i t was  mentioned t h a t the conglomerate on  edge o f the A s h c r o f t map  feet t h i c k e r than opposite Fountain. an i n c r e a s e i n t h i c k n e s s to the  a r e a i s perhaps  750  These s c a n t y d a t a suggest  northeast.  D i v i s i o n B i s the o l d e s t known s t r a t i g r a p h i c u n i t i n t h e p r e s e n t map  a r e a t h a t c o n t a i n s a major p r o p o r t i o n o f  gran-  i t i c material. Some a r g i l l i t e i n t e r b e d d e d w i t h conglomerate c o n t a i n s marine f o s s i l s , but i t i s u n c e r t a i n whether the b a s i n permanently or o n l y t e m p o r a r i l y f l o o d e d by the sea. o f p l a n t m a t t e r perhaps s u p p o r t s  was The  lack  the t h e o r y o f a permanently  marine environment. I f the environment was marine the d e t r i t a l m a t e r i a l may  i n p a r t have been rounded by t r a n s p o r t - i o n i n streams w h i c h  descended from the b o r d e r i n g mountains w i t h a steep and  i n p a r t by wave a c t i o n on beaches.  gradient  A problem i s the  mechanism o f d i s t r i b u t i o n i n the b a s i n over a w i d t h o f more t h a n one m i l e . The  I t may  be assumed t h a t c u r r e n t s were a c t i v e .  e r o s i o n s u r f a c e s l o c a l l y observed may  by such a g e n t s .  have been produced  The n a t u r e and o r i g i n o f the p o s t u l a t e d  c u r r e n t s , however, are u n c e r t a i n .  The  sediments o f D i v i s i o n B  do not resemble the t u r b i d i t y c u r r e n t d e p o s i t s o f the group o r the Cache Creek group.  Laminations,  Lillooet  graded b e d d i n g ,  slump s t r u c t u r e s , and  i n t r a f o r m a t i o n a l b r e c c i a s are  spicuous  Perhaps the d i s t r i b u t i o n o f the g r a v e l  was  or l a c k i n g .  incon-  g r e a t l y a i d e d by r e l a t i v e l y steep submarine s l o p e s produced  by f a u l t i n g .  The  areas o f g r e a t e s t d e p r e s s i o n a l s o may  have  s h i f t e d l a t e r a l l y i n the basin. I n o r d e r t o e x p l a i n t h e g r e a t w i d t h o f t h e conglomerate D u f f e l l and McTaggart suggested d e p o s i t i o n on a f l o o d p l a i n t h a t was o n l y a t t i m e s inundated  by t h e s e a . They m e n t i o n ,  however, t h a t such c h a r a c t e r i s t i c f e a t u r e s o f a f l o o d p l a i n as c u t - a n d - f i l l s t r u c t u r e and l e n t i c u l a r shape o f t h e d e p o s i t s are uncommon. Some o f t h e s t r a t a o f D i v i s i o n C c o n t a i n i n g conglomerat and  p l a n t m a t t e r were d e p o s i t e d  marine environment. are o f marine o r i g i n .  i n a c o n t i n e n t a l o r near shore  Others, including invertebrate  fossils,  Carbonaceous m a t t e r a s s o c i a t e d w i t h t h e  a r g i l l i t e i n d i c a t e s t h a t t h e environment a t times v/as r e d u c i n g . The  r o c k s r a r e l y show s t r u c t u r e s s u g g e s t i v e o f c u r r e n t a c t i o n .  A f a i r l y continuous u p l i f t of the borderland  can be i n f e r r e d  from t h e g e n e r a l l y c o a r s e - g r a i n s i z e o f t h e s e d i m e n t s .  The  source a r e a was u n d e r l a i n d o m i n a n t l y by v o l c a n i c r o c k s and a s m a l l e r p r o p o r t i o n o f Coast I n t r u s i o n s . I n summary i t can be s t a t e d t h a t D i v i s i o n C and p r o b a b l y a l s o D i v i s i o n B were d e p o s i t e d trough that subsided  i n a narrow  elongate  r a p i d l y with respect to bordering  l a n d s but f l u c t u a t e d w i t h r e s p e c t t o s e a l e v e l .  high-  At times i t  may have been connected w i t h t h e open s e a , more o f t e n i t formed a r e s t r i c t e d marine environment and t e m p o r a r i l y i t may have been a c o n t i n e n t a l v a l l e y t h a t was p o s s i b l y o c c u p i e d large  river.  by a  6.  Age and C o r r e l a t i o n  The name " J a c k a s s M o u n t a i n Conglomerate Group" was g i v e n by Selwyn t o t h e sandstone.,, q u a r t z i t e , s h a l e , and p e b b l e conglomerate o f J a c k a s s M o u n t a i n . the  He r e c o g n i z e d t h a t  r o c k s a r e younger than t h e Cache Creek group. Dawson r e f e r s t o t h e r o c k s as "Queen C h a r l o t t e  I s l a n d " group w h i c h he a s s i g n e d t o t h e C r e t a c e o u s . D u f f e l l and McTaggart a p p l i e d t h e name J a c k a s s M o u n t a i n Group and e s t a b l i s h e d a mid-Lower C r e t a c e o u s age. On ground o f l i t h o l o g i c a l and p a l e o n t o l o g i c a l correspondences t h e y c o r r e l a t e D i v i s i o n s A, B, and C o f t h e J a c k a s s M o u n t a i n group w i t h D i v i s i o n s B, C, and D o f t h e Dewdney Creek group o f t h e P r i n c e t o n a r e a , t h e P a s a y t e n group o f t h e S i m i l k a m e e n R i v e r d i s t r i c t , and "Lower C r e t a c e o u s " r o c k s o f t h e C o q u i h a l l a map area. F o s s i l s found d u r i n g t h e p r e s e n t mapping and i d e n t i f i e d by J.A. J e l e t z k y c o n f i r m t h e mid-Lower.Cretaceous age o f t h e J a c k a s s M o u n t a i n group. I n Member A l l on t h e n o r t h w e s t e r n s l o p e o f F o u n t a i n R i d g e about 1/2 m i l e east o f t h e mouth o f t h e B r i d g e R i v e r t h e f o l l o w i n g f o s s i l s , i d e n t i f i e d by J.A. J e l e t z k y , were found (F14): Pseudomelanla ? s p . i n d e t . (a g a s t r o p o d ) "Pterocera"? sp. indet. (a g a s t r o p o d ) Ostrea sp. i n d e t .  101  P e c t e n ( E n t o l i u m ) sp. i n d e t . M y t i l u s sp. i n d e t . A s t a r t e ? sp. i n d e t . A c c o r d i n g t o J e l e t z k y the c o l l e c t i o n "cannot be beyond a t e n t a t i v e s u g g e s t i o n t h a t i t s gastropods and  dated  pelecy-  pods show some s i m i l a r i t y w i t h those o f the u n d e s c r i b e d Lower C r e t a c e o u s  mid-  (Earremian, o r ? A p t i a n ) faunas o f the Quat-  s i n o Sound, Vancouver I s l a n d . J e l e t z k y i d e n t i f i e d a f o s s i l found a p p r o x i m a t e l y  1-1/2  m i l e s due n o r t h o f the mouth o f B r i d g e R i v e r i n Member A I I I as:  (F15)  Ancyloceras  ( H e l i c a n c y l u s ) c f . aequicostatum  Gabb  T h i s ammonite " i s c h a r a c t e r i s t i c o f t h e A p t i a n r o c k s (so c a l l e d A l d e r s o n and Argonaut zones o f Anderson, 1938, Sp. Paper 16, p. 65-66, t a b l e 2 ) .  The  G.S.  state of preservation  o f t h e o n l y specimen a v a i l a b l e i s , however, too poor t o  ex-  c l u d e i t s r e f e r e n c e t o o t h e r a l l i e d forms o f A n c y l o c e r a s , w h i c h range down i n t o Upper B a r r e m i a n where.  r o c k s i n C a l i f o r n i a and  else-  The w r i t e r p r e f e r s t h e r e f o r e t o date the l o t here  d i s c u s s e d as o f Upper B a r r e m i a n  (?) o r A p t i a n age i n terms o f  the i n t e r n a t i o n a l standard stages. I n B r i t i s h Columbia, o l d e r mid-Lower C r e t a c e o u s  faunas o f s i m i l a r and  slightly  age have been known f o r some time  from t h e r o c k s o f t h e J a c k a s s M o u n t a i n group o f t h e A s h c r o f t a r e a (see D u f f e l l and McTaggart, 1 9 5 2 ,  pp. 4 8 - 5 2 ) and  from  the Dewdney Creek group o f t h e P r i n c e t o n a r e a (see R i c e , p.  18-19)".  1947,  A.  102 A f o s s i l c o l l e c t e d on the s o u t h s l o p e o f the Camelsf o o t Range, at an e l e v a t i o n o f 1700  f e e t , approximately  1-1/2  m i l e s n o r t h e a s t o f the mouth o f the B r i d g e R i v e r ( F l 6 ) was i d e n t i f i e d by J e l e t z k y as A c r o t e u t h i s sp. i n d e t . He s t a t e s :  " T h i s b e l e m n i t e genus i s r e s t r i c t e d to t h e  e a r l y mid-Lower Cretaceous  r o c k s not o l d e r than the B e r r i a s i a n  (= I n f r a v a l a n g i h i a h ) and not younger t h a n the B a r r e m i a n o f the i n t e r n a t i o n a l s t a n d a r d .  stages  I t i s not known t o range i n t o  the A p t i a n stage e i t h e r i n N o r t h A m e r i c a o r i n E u r a s i a . " An " i n d e t e r m i n a t e ( p h y l l o c e r a t i d ? ) ammonite" found on the n o r t h s'id:e.: o f the F r a s e r R i v e r o p p o s i t e the mouth o f !  F o u n t a i n Creek (F17) "can o n l y be dated as o f the g e n e r a l J u r a s s i c o r Cretaceous  age" but i n d i c a t e s a marine environment.  SPENCES BRIDGE GROUP Introduction A b e l t o f i n t e r c a l a t e d v o l c a n i c and sedimentary  rocks  i s exposed between t h e s o u t h e a s t e r n e x t r e m i t y o f the map and the s l o p e s n o r t h o f McKay Creek.  area  Dawson i n c l u d e d these  r o c k s w i t h h i s "Lower V o l c a n i c Group" w h i c h he c o n s i d e r e d t o be M i o c e n e .  Drysdale  group, and F.K.  (1914) renamed t h i s group Spences B r i d g e  Knowlton regarded p l a n t f o s s i l s found  D r y s d a l e t o be Lower Cretaceous  but w i t h J u r a s s i c  B e l l r e f e r r e d the same f o s s i l s and new  by  affinities.  c o l l e c t i o n s made by  D u f f e l l and McTaggart to the e a r l y Upper Lower  Cretaceous  (Aptian stage).  New  f o s s i l s found d u r i n g the p r e s e n t  g a t i o n show t h a t some o f the r o c k s a r e l a t e Lower  investi-  Cretaceous  ( A l b i a n ) and t h e r e f o r e c o r r e l a t i v e w i t h t h e K i n g s v a l e group. C o n s e q u e n t l y the v o l c a n i c r o c k s have been s u b d i v i d e d several units.  into  Some u n i t s have been c o r r e l a t e d w i t h t h e Spences  B r i d g e g r o u p , o t h e r s w i t h the K i n g s v a l e group.  The  age  and  c o r r e l a t i o n o f s e v e r a l u n i t s I s o l a t e d by f a u l t i n g a r e unknown. LOWER DIVISION A. B a s a l Member Between S a l l u s Creek and Gibbs Creek a r e two  isolated  s m a l l a r e a s u n d e r l a i n by v o l c a n i c r o c k s . The n o r t h e r n o u t c r o p s , l o c a t e d a p p r o x i m a t e l y  1 mile  n o r t h o f Gibbs C r e e k , c o n s i s t o f a p h a n i t i c and a p h a n i t i c p o r p h y r i t i c andesite, of a n d e s i t i c flow-breccia, t u f f dacite. The  and  A l a y e r o f t u f f c o n t a i n s remnants o f p l a n t stems.  c o n t a c t s between two f l o w s d i p 70°  t o the n o r t h e a s t .  The o t h e r a r e a , s i t u a t e d about 1/2 e a s t , i s made up o f p o r p h y r i t i c d a c i t e .  m i l e to the  south-  In the eastern h a l f  o f the a r e a the d a c i t e weathers r e d d i s h brown and  locally  shows f i n e f l o w l a y e r i n g and p a r a l l e l o r i e n t a t i o n o f p l a g i o clase phenocrysts. contortions.  Some o f these f l o w l a y e r s show s t r o n g  I n the w e s t e r n h a l f the d a c i t e i s u n i f o r m l y  g r e e n i s h grey and c o n t a i n s c o a r s e p h e n o c r y s t s . l o c a l i t i e s the p l a g i o c l a s e p h e n o c r y s t s  In a  few  form f l o w l a y e r s t h a t  g e n e r a l l y have c o n s t a n t a t t i t u d e s over s e v e r a l hundred f e e t ; but i n one p l a c e a t i g h t a n t i c l i n e o f f l o w l a y e r s , about 2 f e e t a c r o s s was  seen.  The  cdips o f the f l o w l a y e r s range  104 from 80° t o 25  and t h e s t r i k e s from n o r t h e a s t t o n o r t h w e s t .  A specimen o f t h e grey p o r p h y r i t i c d a c i t e cons i s t s d o m i n a n t l y o f p l a g i o c l a s e , and c h l o r i t i z e d p a l a g o n i t e o r c h l o r o p h a e i t e , and c o n t a i n s a p p r o x i m a t e l y 10$ o f q u a r t z , 15$ o f c h l o r i t e , and s m a l l p r o p o r t i o n s o f " i r o n o r e " , b i o t i t e , and a p a t i t e . Most o f t h e p h e n o c r y s t s a r e p l a g i o c l a s e , but a few c o n s i s t o f q u a r t z o r b i o t i t e . A g r a i n of p l a g i o c l a s e showing o s c i l l a t o r y normal z o n i n g has an approximate c o m p o s i t i o n o f A1142 i n t h e c o r e and An30 a t t h e margin. B o t h p l a g i o c l a s e and q u a r t z phenocrysts i n c l u d e f i n e - g r a i n e d minerals o f the groundmass. The q u a r t z p h e n o c r y s t s a r e surrounded by r i m s o f f e l d s p a t h i c m a t e r i a l , and some i n c l u d e p l a g i o c l a s e c r y s t a l s o f i n t e r m e d i a t e s i z e . No f l o w s t r u c t u r e s a r e apparent i n t h e r o c k . The c o n t a c t s o f t h e s e v o l c a n i c r o c k s a r e n o t exposed but topography  and s t r u c t u r e suggest t h a t they o v e r l i e D i v i s i o n  I o f t h e P a v i l i o n group unconformably.  Near t h e m a r g i n o f  t h e s o u t h e r n o u t c r o p a r e a remnants o f a b r e c c i a , one o r a few i n c h e s t h i c k were seen t o o v e r l i e bed-rock o f c h e r t and a r g i l l ite.  The b r e c c i a i s composed o f t h e same r o c k t y p e s  and a r g i l l i t e ) , l e t s of quartz.  (chert  cemented by c a r b o n a t e , and t r a v e r s e d by v e i n I t p r o b a b l y o r i g i n a t e d on t h e Lower Cretaceous  e r o s i o n s u r f a c e and l o c a l l y u n d e r l i e s t h e v o l c a n i c f l o w s . A c c o r d i n g t o D u f f e l l and McTaggart t h e Spences B r i d g e group l o c a l l y r e s t s unconformably (p.  on t h e Cache Creek  group,  54). T h e r e f o r e t h e s e r o c k s a r e thought t o r e p r e s e n t t h e  b a s a l u n i t o f t h e Spences B r i d g e group. B.  Gibbs Creek Assemblage 1.  D i s t r i b u t i o n and T h i c k n e s s The u n i t u n d e r l i e s t h e r i d g e s o u t h o f Gibbs Creek and  small areas n o r t h o f that creek.  I t has been s u b d i v i d e d i n t o  105  t h r e e members.  The base o f A, t h e lower member, i s n o t exposed.  I t has a minimum t h i c k n e s s o f 200 f e e t .  On t h e s l o p e  immediate-  l y s o u t h o f Gibbs Creek member B i s a p p r o x i m a t e l y 700 f e e t t h i c k but i t t h i n s t o t h e s o u t h and d i s a p p e a r s about one m i l e s o u t h o f Gibbs Creek.  The t o p o f member C has been removed  by e r o s i o n ; i t s minimum t h i c k n e s s i s 500 f e e t . LIthology Member A Member A i s v e r y u n i f o r m c o n s i s t i n g o n l y o f dark g r e y o r g r e e n i s h w e a t h e r i n g p o r p h y r i t i c a n d e s i t e w i t h medium- t o c o a r s e - g r a i n e d p h e n o c r y s t s o f p l a g i o c l a s e and medium- t o f i n e grained phenocrysts o f a u g i t e .  No d i r e c t i o n a l t e x t u r e s were  seen. About 50$ o f a t y p i c a l specimen c o n s i s t s o f p l a g i o c l a s e p h e n o c r y s t s , r a n g i n g a p p r o x i m a t e l y from 2 mm t o .1 mm i n s i z e . The p l a g i o c l a s e , c o m p l e x l y twinned and z o n e d , ranges from i n t e r m e d i a t e o l i g o c l a s e t o c a l c i c a n d e s i n e . The m i n e r a l i s much a l t e r e d and has i n c l u s i o n s o f s e r i c i t e , c a r b o n a t e and c h l o r i t e . C r y s t a l s o f a u g i t e form a s m a l l e r f r a c t i o n o f t h e p h e n o c r y s t s . The a u g i t e has an approximate c o m p o s i t i o n o f C a 4 ] M g 4 8 F e n . (ny - 1.684). The m i n e r a l i s p a r t l y t o c o m p l e t e l y r e p l a c e d by c h l o r i t e . The groundmass c o n s i s t s m o s t l y o f v e r y f i n e - g r a i n e d p l a g i o c l a s e m i c r o l i t e s and s m a l l amounts o f c h l o r i t e , " i r o n o r e " , a u g i t e and q u a r t z . C a v i t i e s a r e l i n e d by c h l o r i t e and f i l l e d by q u a r t z and c a r b o n a t e . C l o t s o f an e x t r e m e l y f i n e - g r a i n e d m i n e r a l o f h i g h b i r e f r i n g e n c e and h i g h r e l i e f a r e d i s p e r s e d t h r o u g h t h e r o c k . The m i n e r a l i s p o s s i b l y a carbonate. Member B Member B i s composed o f sedimentary and p y r o c l a s t i c beds and o f v o l c a n i c f l o w s .  I t s composition v a r i e s w i t h i n  106 s m a l l a r e a s and t h e c o n t a c t s w i t h t h e u n d e r l y i n g and o v e r l y i n g rocks are mostly g r a d a t i o n a l . The of  sedimentary  r o c k s a r e most abundant i n t h e v i c i n i t y  Gibbs Creek, p a r t i c u l a r l y i n t h e n o r t h e a s t e r n p a r t o f t h e  area.  A s e c t i o n here c o n t a i n s a p p r o x i m a t e l y 450 f e e t o f sand-  s t o n e , s i l t s t o n e , s i l t y a r g i l l i t e , and conglomerate. I n t e r c a l a t e d v o l c a n i c f l o w r o c k s range from a n d e s i t e to  r h y o l i t e i n composition.  conspicuous  Light colored flow rocks  form  c l i f f s around t h e r i d g e s o u t h o f Gibbs Creek and  mark t h e upper boundary o f member B.  A few specimens examined  i n t h i n - s e c t i o n have t h e c o m p o s i t i o n o f d a c i t e , q u a r t z - l a t i t e , and r h y o l i t e .  They a l l a r e v e r y poor i n b i o t i t e ,  chlorite,  and " i r o n o r e " and c o n t a i n 10$ o r more o f q u a r t z w h i c h i n some specimens forms p h e n o c r y s t s o r m i c r o p h e n o c r y s t s .  Significant  m i n e r a l o g i c a l d i f f e r e n c e s exist only i n the composition o f the feldspar.  The d a c i t e c o n t a i n s o n l y p l a g i o c l a s e w h i c h  zoned p h e n o c r y s t s r a n g i n g from o l i g o c l a s e t o c a l c i c and m i c r o l i t e s o f o l i g o c l a s e .  forms  andesine  The q u a r t z - l a t i t e c o n t a i n s s o d i c  o l i g o c l a s e and p o t a s s i c f e l d s p a r w h i c h b o t h form  microphenocrysts.  The r h y o l i t e has p h e n o c r y s t s o f s o d i c andesine and a groundmass c o n s i s t i n g dominantly o f p o t a s s i c f e l d s p a r . f l o w b r e c c i a and shows under t h e m i c r o s c o p e  The r o c k forms a a spherulitic texture.  Most o f t h e s p h e r u l i t e s a r e made up o f r a d i a t i n g f i b r e s but one shows c o n c e n t r i c d i f f e r e n t i a t i o n . The a n d e s i t e s o f member B resemble t h e members A and C.  t h e ones found i n  107  P y r o c l a s t i c r o c k s a r e w i d e l y d i s t r i b u t e d but form o n l y a s m a l l p r o p o r t i o n o f t h e t o t a l assemblage. A t u f f from t h e n o r t h s i d e o f t h e lower p a r t o f Gibbs Creek weathers l i g h t g r e y i s h green but c o n t a i n s dark fragments t h a t a r e up t o f i v e m i l l i m e t e r s long. I t c o n s i s t s o f approximately 50% o f l a r g e p a r t l y broken c r y s t a l s o f p l a g i o c l a s e t h a t have t h e appearance o f p h e n o c r y s t s . They show complex t w i n n i n g and i n many i n s t a n c e s f i n e z o n i n g . ( P l a t e XV) A g r a i n e x h i b i t i n g t h e t y p i c a l o s c i l l a t o r y z o n i n g i s s o d i c l a b r a d o r i t e i n t h e c o r e and s o d i c a n d e s i n e a t t h e o u t e r m a r g i n . Some g r a i n s have abundant i n c l u s i o n s o f r e l a t i v e l y c o a r s e - g r a i n e d a p a t i t e and o f " i r o n o r e " . A s m a l l number o f c r y s t a l s are of clinopyroxene. L i t h i c fragments cons t i t u t e a l i t t l e l e s s t h a n h a l f o f t h e r o c k . Most o f them a r e from v o l c a n i c r o c k s o f i n t e r m e d i a t e c o m p o s i t i o n but some a r e from metamorphic r o c k s , i n c l u d i n g carbonaceous s i l t s t o n e and f i n e - g r a i n e d meta-quartzite. C r y s t a l s and l i t h i c fragments a r e embedded i n a m a t r i x o f g l a s s shards and d u s t - l i k e g l a s s y m a t t e r . C a v i t i e s are f i l l e d w i t h r a d i a t i n g o r f e l t e d aggregates o f c h l o r i t e and c a r b o n a t e . Member C Member C c o n s i s t s m o s t l y o f p o r p h y r i t i c a n d e s i t e , l e s s d a c i t e , and a s m a l l p r o p o r t i o n o f i n t e r c a l a t e d sandstone and siltstone. The  andesite i s uniform  i n composition  and t e x t u r e .  I t i s d a r k g r e y , p o r p h y r i t i c , and l a c k i n g i n f l o w - s t r u c t u r e s . The  p h e n o c r y s t s i n t h e o r d e r o f t h e i r abundance a r e o f p l a g i o -  clase, clino-pyroxene,  and h o r n b l e n d e .  The p l a g i o c l a s e i s  t w i n n e d and zoned and ranges i n c o m p o s i t i o n o l i g o c l a s e to c a l c i c andesine.  from  intermediate  Some g r a i n s have a spongy o r  s k e l e t a l s t r u c t u r e and c o n t a i n i n c l u s i o n s o f s e r i c i t e , c a r b o n a t e , c h l o r i t e , and v o l c a n i c g l a s s . r e p l a c e d by c h l o r i t e , i s t w i n n e d .  The c l i n o p y r o x e n e , p a r t l y  Some g r a i n s have a lower  b i r e f r i n g e n c e around t h e m a r g i n s .  The c o m p o s i t i o n o f t h e  m i n e r a l s l i e i n t h e boundary f i e l d o f a u g i t e , e n d i o p s i d e , and d i o p s i d e . (ny = 1.6875, 2v = 53.5°; F e n  y  =il.6755,  Ca  4 4  Mg^, augite;  2v = 4 9 ° , F e C a M g ^ , e n d i o p s i d e ; n 6  2v = 54°, F e i C a 0  The  1 3  4 4  Mg  4 6  3 8  6  = 1.683,  y  , augite).  groundmass i s v e r y f i n e - g r a i n e d and c o n s i s t s dom-  i n a n t l y o f o l i g o c l a s e m i c r o l i t e s w i t h minor " i r o n o r e " and chlorite.  Other m a f i c m i n e r a l s and g l a s s y m a t t e r may be  p r e s e n t but a r e d i f f i c u l t low p e r c e n t a g e The chlorite.  of quartz.  to i d e n t i f y .  Some r o c k s c o n t a i n a  A p a t i t e i s a common a c c e s s o r y .  rocks are dominantly  a l t e r e d by carbonate and  V e i n s a r e f i l l e d w i t h q u a r t z , c a r b o n a t e , and  z e o l i t e s , (too f i n e - g r a i n e d and t o o s c a r c e f o r f u r t h e r i d e n tification.) 3. The west.  S t r u c t u r e , C o r r e l a t i o n , Mode o f O r i g i n  r o c k s d i p u n i f o r m l y a t moderate a n g l e s t o t h e n o r t h  To t h e west they a r e i n f e r r e d t o be i n f a u l t  w i t h t h e F o u n t a i n V a l l e y assemblage ( s e e b e l o w ) .  contact  Unless t h e  u n i t i s s e p a r a t e d from t h e r o c k s t o t h e n o r t h by a c o n c e a l e d f a u l t , member A i s c o r r e l a t i v e w i t h t h e b a s a l member o f t h e Spences B r i d g e group w h i c h appears t o r e s t unconformably on a Lower C r e t a c e o u s not been s o l v e d .  land surface.  The problem o f c o r r e l a t i o n has  N e i t h e r has evidence f o r such a f a u l t been  o b t a i n e d n o r have u n d e r l y i n g r o c k s o f t h e P a v i l i o n group been observed  s o u t h o f Gibbs Creek.  Perhaps t h e Lower  e r o s i o n s u r f a c e s l o p e d down t o t h e s o u t h .  Cretaceous  The u n i t i s t e n t a t i v  l y r e f e r r e d t o t h e lower D i v i s i o n o f t h e Spences B r i d g e group.  109  Upper D i v i s i o n 1.  Distribution The r o c k s r e f e r r e d t o t h e uppermost p a r t o f t h e  Spences B r i d g e group a r e exposed on t h e west s i d e o f t h e F r a s e r R i v e r between t h e mouth o f Lee Creek and t h e s l o p e s n o r t h o f McKay Creek.  S o u t h o f Leon Creek t h e y a r e c o n c e a l e d by o v e r -  burden and o v e r l y i n g m i d d l e o r l a t e T e r t i a r y o l i v i n e  basalts.  As t h e s t r u c t u r e o f t h e s e r o c k s i s m o s t l y unknown t h e i r  thick-  ness i s u n c e r t a i n . 2.  Lithology The u n i t c o n s i s t s m o s t l y o f a n d e s i t e ; b a s a l t , r h y o l i t e  and t u f f a r e l e s s common. The a n d e s i t e s a r e grey o r r e d and a p a h a n i t i c o r aphanitict-porphyritic.  The p h e n o c r y s t s a r e o f f i n e r g r a i n t h a n  i n t h e Gibbs Creek assemblage.  Flow s t r u c t u r e s a r e r a r e .  The p h e n o c r y s t s c o n s i s t m o s t l y o f p l a g i o c l a s e but i n some t h i n - s e c t i o n s c r y s t a l s o r c l i n o p y r o x e n e , h o r n b l e n d e , o r b i o t i t e or t h e i r altered equivalents are present.  I n some  r o c k s t r a n s i t i o n a l t o d a c i t e , a few o f t h e p h e n o c r y s t s a r e o f quartz. The groundmass c o n s i s t s d o m i n a n t l y o f p l a g i o c l a s e m i c r o l i t e s , a few p e r c e n t o f " i r o n o r e " , and v a r y i n g amounts o f g l a s s . I n most specimens t h e p l a g i o c l a s e i s c a l c i c  andesine  o r a n d e s i n e - l a b r a d o r i t e zoned over a narrow range.  Plagio-  c l a s e p h e n o c r y s t s a r e m o s t l y twinned; t h e groundmass m i c r o -  110 l i t e s a r e i n p a r t untwinned. carbonate, phenocrysts  The m i n e r a l i s r e p l a c e d by  s e r i c i t e , and an u n i d e n t i f i e d z e o l i t e .  a r e p a r t l y o r c o m p l e t e l y r e p l a c e d by c h l o r i t e ,  " i r o n o r e " and chalcedony.  Other m i n e r a l s p r e s e n t as a l t e r -  a t i o n o r c a v i t y f i l l i n g a r e p r e h n i t e , chalcedony The phitic.  The m a f i c  and z e o l i t e s .  textures are intergranular, trachytic or hyalo-  Some specimens a r e f l o w b r e c c i a s . A t y p i c a l specimen o f b a s a l t i s b r o w n i s h g r e y , a p h a n i t i c , and v e s i c u l a r . M a c r o s c o p i c a l l y i t c a n h a r d l y be d i s t i n g u i s h e d from t h e a n d e s i t e s o f t h e u n i t . A t h i n - s e c t i o n c o n t a i n s a p p r o x i m a t e l y 80$ o f p l a g i o c l a s e ; t h e remainder c o n s i s t s d o m i n a n t l y o f c l i n o p y r o x e n e and some " i r o n o r e " . The p l a g i o c l a s e i s e u h e d r a l o r s u b h e d r a l and forms l a t h - l i k e crystals. I t i s twinned and shows f i n e z o n i n g , t h e c o m p o s i t i o n r a n g i n g from A1145 t o Anyo* clinopyroxene i s e u h e d r a l , s u b h e d r a l , o r a n h e d r a l and p a r t l y zoned. The c o m p o s i t i o n o f t h e l a r g e r g r a i n s was determined as Fey Ca4o M g e j Q , e n d i o p s i d e , T  n  e  (ny = 1.679, 2v - 53°).  A specimen o f r h y o l i t e i s l i g h t b u f f , p o r p h y r i t i c - a p h a n i t i c , and l a c k i n g i n f l o w s t r u c t u r e s . The p h e n o c r y s t s a r e up t o 2 m i l l i m e t e r s l o n g and c o n s i s t o f p l a g i o c l a s e , a n d e s i n e , q u a r t z , and a few s m a l l e r c r y s t a l s o f b i o t i t e . The andesine i s c l e a r , untwinned, f r a c t u r e d , and i n c l u d e s q u a r t z , b i o t i t e , and p l a g i o c l a s e c r y s t a l s o f f i n e t o i n t e r m e d i a t e s i z e . The p l a g i o c l a s e has an approximate composi t i o n o f A n ^ . Most g r a i n s a r e twinned. The p l a g i o c l a s e has i n c l u s i o n s o f s e r i c i t e and g l a s s and one g r a i n i s r e p l a c e d by a z e o l i t e w h i c h i s p o s s i b l y l a u m o n t i t e . Some g r a i n s have a spongy s t r u c t u r e . The q u a r t z i s rounded and embayed by m i n e r a l s o f t h e groundmass. The c r y s t a l s a r e rimmed by f i b r o u s i n t e r g r o w t h s o f f e l d s p a r and s i l i c a t h a t a r e o r i e n t e d a p p r o x i m a t e l y p e r p e n d i c u l a r t o t h e f a c e s . The groundmass c o n s i s t s dominantly o f f i b r o u s p a r t l y s p h e r u l i t l c i n t e r g r o w t h s o f s i l i c a and p o t a s s i c f e l d s p a r , o f q u a r t z , and s m a l l amounts o f b i o t i t e . A p a t i t e and " i r o n o r e " occur as a c c e s s o r i e s .  Ill 3.  S t r u c t u r e , Age, and C o r r e l a t i o n Near t h e mouth o f S l o k Creek t h e r o c k s d i p a t low  a n g l e s t o t h e s o u t h e a s t and seem t o u n d e r l i e t h e K i n g s v a l e group.  To t h e west they a r e i n f e r r e d t o be i n f a u l t  contact  w i t h t h e J a c k a s s M o u n t a i n group and t o t h e east w i t h t h e Cache Creek group. As t h e u n i t u n d e r l i e s sedimentary  rocks o f A l b i a n  age i t p r o b a b l y i s A p t i a n .  KINGSVALE GROUP 1.  D i s t r i b u t i o n and T h i c k n e s s  Sedimentary and v o l c a n i c r o c k s on t h e east s i d e o f t h e F r a s e r R i v e r about 1-1/2 m i l e s n o r t h o f G l e n F r a s e r f o r m e r l y i n c l u d e d w i t h t h e Spences B r i d g e group a r e now c o r r e l a t e d w i t h t h e K i n g s v a l e group. i n t o two D i v i s i o n s , A, and B. 700 f e e t t h i c k .  The r o c k s have been s u b d i v i d e d D i v i s i o n A i s approximately  A l t h o u g h t h e t o p o f B has been removed by  e r o s i o n , more t h a n 700 f e e t o f v o l c a n i c r o c k s a r e s t i l l  present.  ( R e i n e c k e , 1912, p. 12). 2.  Lithology  Division A D i v i s i o n A c o n s i s t s dominantly o f v o l c a n i c a r e n i t e t h a t grades i n t o b o t h pebble conglomerate,  and s i l t s t o n e .  Conglomerate forms perhaps one t h i r d o f t h e sequence, s i l t stone i s c o m p a r a t i v e l y r a r e .  112 Most o f t h e v o l c a n i c a r e n i t e i s grey but some beds are  red.  The r o c k s c o n s i s t d o m i n a n t l y o f v o l c a n i c  fragments,  o f l e s s t h a n $0% o f p l a g i o c l a s e and s m a l l amounts o f q u a r t z , " i r o n o r e " , and b i o t i t e .  The l i t h i c fragments a r e m o s t l y ande-  s i t i c i n c o m p o s i t i o n , some a r e b a s a l t i c and f e l s i t i c .  Where  the g r a i n s a r e not r e p l a c e d by t h e groundmass they a r e subrounded t o rounded.  I n one specimen n e i t h e r c a r b o n a t e nor  " i r o n o x i d e " n o r q u a r t z can be d e t e c t e d as cement.  Another  specimen c o n t a i n s a p p r o x i m a t e l y 50% o f r u s t y w e a t h e r i n g c a r bonate as m a t r i x .  Perhaps t h e c a r b o n a t e was i n t r o d u c e d by  h y d r o t h e r m a l s o l u t i o n s and has r e p l a c e d some o f t h e sedimentary material. Most r o c k s a r e w e l l bedded and s i z e - s o r t e d . the " i r o n o r e " i s concentrated i n t h i n laminae.  Locally  I n some l o c a l -  i t i e s graded bedding and c r o s s - b e d d i n g can be o b s e r v e d . A c o b b l e conglomerate on t h e e a s t s i d e o f t h e F r a s e r R i v e r , near t h e h i d d e n c o n t a c t w i t h t h e Spences B r i d g e group c o n s i s t s d o m i n a n t l y o f v o l c a n i c roundstones but a l s o c o n t a i n s some g r a n i t i c c o b b l e s . Division B D i v i s i o n B c o n s i s t s d o m i n a n t l y o f a n d e s i t e , a few f l o w s o f d a c i t e , and s e v e r a l t h i n l a y e r s o f t u f f a c e o u s and sedimentary r o c k s . The a n d e s i t e i s dark g r e y , l i g h t g r e y , o r r e d brown. Most o f t h e r o c k s a r e a p h a n i t i c - p o r p h y r i t i c but some a r e aphanitic.  Most o f t h e p h e n o c r y s t s a r e twinned and zoned p l a g i o c l a s e t h a t ranges i n c o m p o s i t i o n from i n t e r m e d i a t e andesine t o i n t e r m e d i a t e l a b r a d o r i t e ; t h e average c o m p o s i t i o n seems t o be c a l c i c andesine. oxyhornblende.  Some r o c k s a l s o c o n t a i n p h e n o c r y s t s o f I n t h e groundmass, w h i c h i s i n most specimens  v e r y f i n e - g r a i n e d , abundant m i c r o l i t e s o f p l a g i o c l a s e and a few p e r c e n t o f " i r o n o r e " can be r e c o g n i z e d .  Mafic  silicates,  too f i n e - g r a i n e d f o r i d e n t i f i c a t i o n and v o l c a n i c g l a s s a r e p r e s e n t i n s m a l l amounts.  A p a t i t e o c c u r s as an a c c e s s o r y .  Light c o l o r e d rocks that are t r a n s i t i o n a l t o d a c i t e c o n t a i n f i n e - g r a i n e d q u a r t z i n t h e groundmass.  The r o c k s a r e a l t e r e d  by s e r i c i t e , c h l o r i t e , and c a r b o n a t e . Some specimens have a t r a c h y t i c  texture.  A specimen o f d a c i t e i s p o r p h y r i t i c - a p h a n i t i c and c o n t a i n s e l o n g a t e prisms o f amphibole  i n a light greenish  grey groundmass. M i c r o s c o p i c e x a m i n a t i o n shows t h a t t h e amphib o l e i s oxyhornblende. I n t h e groundmass a few micro-phenocrysts o f p l a g i o c l a s e , l a t h - l i k e plagioclase m i c r o l i t e s , a small fraction of "iron o r e " , and v e r y f i n e - g r a i n e d i n t e r s t i t i a l q u a r t z can be i d e n t i f i e d . The m i c r o l i t e s a r e s o d i c a n d e s i n e ; t h e m i c r o - p h e n o c r y s t s a r e zoned and range i n c o m p o s i t i o n from s o d i c t o c a l c i c andesine. B.  Structure  The c o n t a c t o f D i v i s i o n A w i t h t h e Spences B r i d g e group i s n o t exposed.  The presence o f c o b b l e  conglomerate  near t h e base o f D i v i s i o n A suggests an u n c o n f o r m i t y . i s i o n B probably o v e r l i e s A conformably.  Div-  To t h e west t h e  K i n g s v a l e group i s i n f a u l t c o n t a c t w i t h t h e J a c k a s s M o u n t a i n group, t o t h e e a s t i n f a u l t c o n t a c t w i t h t h e P a v i l i o n group and p o s s i b l y w i t h , r o c k s o f t h e Spences B r i d g e group o v e r l y i n g t h e Cache Creek group.  In the v i c i n i t y o f the f a u l t contacts the  s t r a t a d i p s t e e p l y , elsewhere t h e d i p s a r e low t o moderate. 4.  Mode o f O r i g i n , Age, and C o r r e l a t i o n  The w e l l s o r t e d and g e n e r a l l y c o a r s e - g r a i n e d c h a r a c t e r o f t h e sediments o f D i v i s i o n A i n d i c a t e s d e p o s i t i o n by r u n n i n g w a t e r , and t h e abundance o f p l a n t m a t t e r a c o n t i n e n t a l e n v i r onment.  A p p a r e n t l y t h e y were l a i d down on t h e f l o o d  plain  o f a stream t h a t d r a i n e d a t e r r a i n u n d e r l a i n by v o l c a n i c r o c k s , mostly andesites. P l a n t f o s s i l s found i n t h e lower h a l f o f member A (F18) were i d e n t i f i e d by P r o f e s s o r G.E. Rouse as f o l l o w s : Menispermites ( c f . w i t h B e l l (1957), p. 130))  Upper Blaimore-Whitemud (Albian-Maestrichtian)  Celastrophyllum (celastrinites?)  ( A l b i a n - B a s a l Eocene)  Trochodendroides (Cercidiphyllum?) Ccf." po'tomacensis  Upper B l a i r m o r e (Albian)  Platanus sp.  (Albian through T e r t i a r y )  c f . Myrtophyllum boreale o r : c f . Magnoliaephyllum  (Albian-Tertiary) (Upper C r e t a c e o u s )  C i s s i t e s sp.  (Albian of Portugal) (Patapsco o f M a r y l a n d (Lower C r e t a c e o u s ) (Upper Cretaceous o f U.S.Rockies)  Tacutidens;  .  P r o f e s s o r Rouse s t a t e s i n h i s r e p o r t t h a t " f o u r and p o s s i b l y f i v e o f t h e s i x s p e c i e s have been r e c o r d e d  i n the  ( A l b i a n ) K i n g s v a l e by B e l l , b u t none o f these i s found i n t h e Spences B r i d g e  ( A p t i a n ) ... the m a t e r i a l ... i s younger t h a n  A p t i a n and hence younger than the Spences B r i d g e  group."  D u f f e l l and McTaggart s t a t e t h a t the K i n g s v a l e  group  i n the A s h c r o f t map a r e a has a s e d i m e n t a r y u n i t a t i t s base w h i c h i s l o c a l l y 800 t o 1000 f e e t t h i c k and c o n s i s t s o f a r k o s e , g r i t , mudstone, c o n g l o m e r a t e , and a r g i l l i t e .  Outcrops o f  t h e s e r o c k s extend f o r 16 m i l e s a l o n g N i c o l a R i v e r .  Many  o f t h e beds on N i c o l a R i v e r c o n t a i n fragments o f stems and l e a v e s , and the mudstones c a r r y w e l l p r e s e r v e d  plant  fossils.  One  o f t h e f o s s i l s c o l l e c t e d near G l e n F r a s e r , M e n i s p e r m i t e s ,  was  a l s o found i n t h e b e l t on N i c o l a R i v e r ( D u f f e l l and  McTaggart, 1952, p. 57-58).  These r e l a t i o n s suggest t h a t  D i v i s i o n A a t G l e n F r a s e r and t h e s e d i m e n t a r y b e l t on N i c o l a R i v e r a r e perhaps c o r r e l a t i v e and may r e p r e s e n t plain.  t h e same f l o o d -  However, as t h e s e a r e c o n t i n e n t a l d e p o s i t s o f p o s s i b l y  s m a l l e x t e n t t h e c o r r e l a t i o n i s not c e r t a i n .  SPENCES BRIDGE GROUP OR KINGSVALE GROUP Flows o f a n d e s i t e and d a c i t e w h i c h c o u l d be a s s i g n e d e i t h e r t o the Spences B r i d g e o r K i n g s v a l e groups a r e exposed immediately northeast road t o P a v i l i o n .  o f G l e n F r a s e r , on t h e east s i d e o f t h e  116 A specimen o f a n d e s i t e t r a n s i t i o n a l t o b a s a l t contains coarse phenocrysts of p l a g i o c l a s e and c o m p l e t e l y c h l o r i t i z e d p y r i b o l e s and a v e r y f i n e - g r a i n e d groundmass i n w h i c h p l a g i o c l a s e m i c r o l i t e s and " i r o n o r e " can be i d e n t i f i e d . The p l a g i o c l a s e o f the p h e n o c r y s t s has a spongy s t r u c t u r e , i s twinned and z o n e d , and ranges i n c o m p o s i t i o n from a n d e s i n e - l a b r a d o r i t e to l a b r a d o r i t e - b y t o w n i t e . The m i c r o l i t e s are o f a n d e s i n e - l a b r a d o r i t e . The r o c k shows carbonate and c h l o r i t e a l t e r a t i o n . The  d a c i t e weathers l i g h t grey and forms f l o w b r e c c i a s  w h i c h c o n t a i n fragments o f dark c o l o r e d v o l c a n i c r o c k s . A specimen has p h e n o c r y s t s o f c a l c i c andesine t h a t a r e t w i n n e d , zoned, and s t r o n g l y a l t e r e d , o f a p y r i b o l e t h a t i s c o m p l e t e l y r e p l a c e d by c h l o r i t e and " i r o n o r e " , and o f q u a r t z . The groundmass c o n t a i n s p l a g i o c l a s e , a r e l a t i v e l y h i g h p r o p o r t i o n o f q u a r t z and a low p r o p o r t i o n o f " i r o n o r e " and c h l o r i t e . A p a t i t e i s r e l a t i v e l y c o a r s e - g r a i n e d and abundant. Some o f the phenoc r y s t s a r e r e p l a c e d near c l e a v a g e s by a m i n e r a l w i t h a low n e g a t i v e r e l i e f and low b i r e f r i n g e n c e w h i c h i s e i t h e r o r t h o c l a s e o r a z e o l i t e . No o r t h o c l a s e c o u l d be i d e n t i f i e d i n the groundmass. The o u t c r o p s a r e s e p a r a t e d  from c l i f f s o f D i v i s i o n B  o f the K i n g s v a l e group by an expanse o f overburden about  one  h a l f m i l e wide. The  s t r a t i g r a p h i c p o s i t i o n o f these r o c k s i s u n c e r t a i n  because t h e l o c a t i o n o f the boundary f a u l t between the  Pav-"  i l i o n group and the K i n g s v a l e group i n t h i s a r e a i s unknown. I f t h i s l o n g i t u d i n a l f a u l t i s not o f f s e t by a t r a n s v e r s e f a u l t i t c o n t i n u e s under the o v e r b u r d e n i n the v i c i n i t y o f the P a v i l i o n road and the r o c k s belong t o t h e lower D i v i s i o n o f the Spences B r i d g e group w h i c h o v e r l i e s the P a v i l i o n group. However, the r o c k s i n the v i c i n i t y o f the road show no o f a l t e r a t i o n and s h e a r i n g .  The  l o n g i t u d i n a l f a u l t may  signs be  OUTCROP BOUNDARY 0 YY y  2  A T T I T U D E , SCHISTOSITY,  \  30 Q  .5  LAYERING OF VOLCANIC  MILES ROCKS  Q U A R T Z - DIORITE K I N G S V A L E GP, DIV. B, OR S P E N C E S BRIDGE GR, LOWER DIV.  19  KINGSVALE  4  PAVILION GROUP,DIVISION 11  GROUP, DIVISION B  FIG. 5= G E O L O G Y  ROAD +-+  OF G L E N F R A S E R  RAILROAD  AREA  I  o f f s e t by a t r a n s v e r s e f a u l t a l o n g t h e s o u t h e r n b o r d e r o f t h e s t o c k s o u t h o f P a v i l i o n i n w h i c h case t h e v o l c a n i c r o c k s would be p a r t o f D i v i s i o n B o f t h e K i n g s v a l e group.  The  a l t e r n a t i v e s a r e shown on F i g u r e 5.  FOUNTAIN VALLEY ASSEMBLAGE 1.  D i s t r i b u t i o n and T h i c k n e s s The F o u n t a i n V a l l e y assemblage made up l a r g e l y o f  v o l c a n i c r o c k s , i s exposed on b o t h s i d e s o f t h e F r a s e r R i v e r east o f F o u n t a i n Creek. members, A, B, and C.  I t has been s u b d i v i d e d i n t o  three  The base o f Member A, w h i c h i s i n  f a u l t c o n t a c t w i t h t h e J a c k a s s Mountain group, i s n o t exposed. Member A has a minimum t h i c k n e s s o f 1200 f e e t .  Member B i s  l e n t i c u l a r ; i t s t h i c k n e s s ranges from 600 f e e t t o 2500 f e e t . The upper p a r t o f Member C w h i c h i s i n i n f e r r e d f a u l t w i t h t h e Gibbs Creek assemblage i s n o t exposed.  contact  The member i s  about 1000 f e e t t h i c k . 2.  Lithology Member A Member A c o n s i s t s m o s t l y o f i n t e r l a y e r e d f e l s i t i c and  andesitic rocks.  About 1000 f e e t southwest o f t h e l o n g  rail-  road t u n n e l near Gibbs Creek a s h o r t l e n s o f conglomerate i s i n t e r c a l a t e d w i t h the v o l c a n i c flows. Successions  o f a n d e s i t i c r o c k s form u n i t s about one  hundred f e e t t h i c k , and i n d i v i d u a l f e l s i t i c f l o w s range up t o 20 f e e t i n t h i c k n e s s .  119 The and  f e l s i t i c r o c k s are l i g h t grey to b u f f , a p h a n i t i c ,  l a c k i n g i n flow structures. A t h i n - s e c t i o n of a dacite o f andesine m i c r o l i t e s , 10 t o 15 and s m a l l amounts o f " i r o n o r e " The m i c r o l i t e s show s u b p a r a l l e l r o c k i s a l t e r e d by c a r b o n a t e and  consists mainly percent of quartz and v o l c a n i c g l a s s . orientation. The chlorite.  Other specimens examined are p r o b a b l y l a t i t e  or  q u a r t z l a t i t e and r h y o l i t e ; but the exact c o m p o s i t i o n o f t h e s e r o c k s cannot be determined because o f t h e i r e x t r e m e l y f i n e grain  size. A t y p i c a l specimen o f a n d e s i t e i s r e d d i s h brownVaphanitic and forms a f l o w - b r e c c i a . In t h i n - s e c t i o n a few m i c r o - p h e n o c r y s t s o f p l a g i o c l a s e are v i s i b l e i n a groundmass t h a t c o n s i s t s mostly of m i c r o l i t e s of andesine. W i t h i n small a r e a s o f the t h i n - s e c t i o n the m i c r o l i t e s show p a r a l l e l a l i g n m e n t . I n c o r p o r a t e d fragments have the same m i n e r a l c o m p o s i t i o n as the m a t r i x but d i f f e r i n g r a i n s i z e and i n the o r i e n t a t i o n o f the m i c r o l i t e s . C a v i t i e s a r e f i l l e d by v e r y f i n e - g r a i n e d q u a r t z and c h l o r i t e . The s e c t i o n i s s t a i n e d by " i r o n o x i d e " .  Member B Member B, a c o n s p i c u o u s , c l i f f - f o r m i n g u n i t , i s made up o f a c i d i c v o l c a n i c f l o w s r a n g i n g I t seems to c o n s i s t o f a m u l t i t u d e  from d a c i t e t o r h y o l i t e . o f f l o w s but the bound-  a r i e s between i n d i v i d u a l f l o w s are d i f f i c u l t to d e t e r m i n e . The  r o c k s a r e l i g h t grey on f r e s h s u r f a c e s  b r o w n i s h b u f f on weathered s u r f a c e s aphanitic-porphyritic.  and  and  reddish  aphanitic  I n some l o c a l i t i e s the  or  or  plagioclase  p h e n o c r y s t s are a l i g n e d and p r o b a b l y o r i e n t e d p a r a l l e l t o the l a y e r i n g o f the  flows.  120 A thin-section of a porphyritic-aphanitic d a c i t e c o n s i s t s o f about 30$ o f p h e n o c r y s t s , and 70$ o f groundmass. Most o f t h e p h e n o c r y s t s a r e o f p l a g i o c l a s e ; a few c o n s i s t o f b i o t i t e , " i r o n o r e " t h a t has r e p l a c e d b i o t i t e , and q u a r t z . The p l a g i o c l a s e , w h i c h has t h e c o m p o s i t i o n o f c a l c i c a n d e s i n e , i s twinned and zoned. The p l a g i o c l a s e p h e n o c r y s t s show a spongy s t r u c t u r e w h i c h i s due t o replacement by m i n e r a l s o f t h e groundmass and c a r b o n a t e . The b i o t i t e i s r e p l a c e d inwards from i t s margins and c l e a v a g e s . The groundmass c o n s i s t s d o m i n a n t l y o f l a t h - l i k e s o d i c o l i g o c l a s e . About 10 t o 15$ o f t h e groundmass i s made up o f a n h e d r a l q u a r t z . S m a l l e r f r a c t i o n s a r e formed by " i r o n o r e " , b i o t i t e and v o l c a n i c g l a s s . P o t a s s i c f e l d s p a r i s r a r e o r a b s e n t . A p a t i t e o c c u r s as an a c c e s s o r y m i n e r a l . A specimen o f r h y o l i t e weathers b r o w n i s h b u f f and i s l i g h t g r e y i s h b u f f on f r e s h s u r f a c e s . Under the microscope f i n e - g r a i n e d phenocrysts o f andesine and q u a r t z a r e v i s i b l e i n a m i c r o f e l s i t i c groundmass. The m i n e r a l s o f t h e groundmass, p r o b a b l y i n t e r growths o f p o t a s s i c f e l d s p a r and c r i s t o b a l i t e ( ? ) a r e f i b r o u s and form a g g r e g a t e s most o f w h i c h show a r a d i a t i n g structure. Undulating, brecciated flow l a y e r s made up o f r e l a t i v e l y f i n e - g r a i n e d a g g r e g a t e s a l t e r n a t e w i t h l a y e r s o f c o a r s e r aggregate s i z e . F r a c t u r e s i n t h e specimen a r e f i l l e d w i t h " i r o n oxide". Member C O n l y t h e l o w e s t p a r t o f Member C i s exposed.  I t con-  s i s t s o f a n d e s i t e , a n d e s i t i c f l o w b r e c c i a , and a few f e e t o f l i t h i c sandstone t h a t c o n t a i n s  seams o f p l a n t m a t t e r .  A t y p i c a l a n d e s i t e specimen from t h e east shore o f t h e F r a s e r R i v e r weathers p u r p l e t o g r e y i s h green. The r o c k i s a p h a n i t i c - p o r p h y r i t i c and c o n t a i n s a s m a l l percentage o f p l a g i o c l a s e phenoc r y s t s t h a t a r e l a r g e l y r e p l a c e d by c a r b o n a t e . The groundmass i s made up d o m i n a n t l y o f m i c r o l i t e s o f s o d i c a n d e s i n e , and a few p e r c e n t o f " i r o n o r e " and c h l o r i t e . The m i c r o l i t e s show s u b - p a r a l l e l o r i e n t a t i o n . The r o c k c o n t a i n s v e i n l e t s o f c a r b o n a t e , q u a r t z , and c h l o r i t e .  121 3.  S t r u c t u r e , Mode o f O r i g i n , Age The v o l c a n i c flows s t r i k e approximately N 20° W and  d i p at moderate to steep angles to the n o r t h e a s t .  At one  l o c a l i t y near the contact o f the members A and B a f e l s i t i c flow o f B i n c l u d e s fragments  o f a more b a s i c rock probably  from member A; the s t r a t i g r a p h i c tops t h e r e f o r e probably f a c e to the n o r t h e a s t . The u n i t seems to occupy a graben between o l d e r rocks to the west and to the e a s t .  The f a u l t contact w i t h the  Jackass Mountain group to the west i s exposed at s e v e r a l l o c a l i t i e s on both s i d e s o f the F r a s e r R i v e r .  The contact  w i t h the lower p a r t o f the Spences B r i d g e group i s covered by an expanse o f overburden;  a f a u l t between these two u n i t s i s  suggested by c r o s s s e c t i o n B-B' ( F i g u r e 1 ) . f a u l t perhaps  This i n f e r r e d  i s connected w i t h the normal f a u l t that forms  the western boundary o f the Cache Creek group i n the c e n t r a l and n o r t h e r n p a r t s o f the map a r e a . The a s s o c i a t i o n o f these v o l c a n i c rocks w i t h conglomerate  and w i t h sandstone  c a r r y i n g seams o f p l a n t  matter  indicates a continental o r i g i n . The  s t r u c t u r e suggests that the F o u n t a i n V a l l e y assem-  blage i s younger than the Gibbs Creek assemblage.  I t s age may  l i e anywhere between the A p t i a n stage o f the Lower Cretaceous and the e a r l y or middle  Tertiary.  122 WARD CREEK ASSEMBLAGE 1.  D i s t r i b u t i o n and T h i c k n e s s  V o l c a n i c r o c k s o f Cretaceous  o r e a r l y T e r t i a r y age  form a narrow e l o n g a t e b e l t on t h e west s i d e o f t h e F r a s e r R i v e r between Leon Creek and t h e n o r t h w e s t e r n the map a r e a .  extremity of  As t h e b e l t i s i n f a u l t c o n t a c t w i t h o t h e r u n i t s  on two s i d e s , and as i t s i n t e r n a l s t r u c t u r e i s l a r g e l y unknown no a c c u r a t e statement  o f i t s t h i c k n e s s can be g i v e n ;  s e v e r a l thousand f e e t o f v o l c a n i c r o c k s may be p r e s e n t . 2. The  Lithology  u n i t i s made up d o m i n a n t l y  of andesite, less  d a c i t e and f e l s i t i c r o c k s and minor t u f f , b a s a l t , l i t h i c  sand-  s t o n e , and c o a l . The a n d e s i t e weathers dark grey o r p u r p l e and i s mostly massive. rarely  Flow-banding and p o r p h y r i t i c t e x t u r e s were  seen. A thin-section of a t y p i c a l andesite-flow b r e c c i a i s made up d o m i n a n t l y o f m i c r o l i t e s o f c a l c i c a n d e s i n e , about . 0 5 mm l o n g , and a few c r y s t a l s o f b i o t i t e i n an e x t r e m e l y f i n e - g r a i n e d , p a r t l y g l a s s y groundmass. A l t h o u g h t h e m i n e r a l c o m p o s i t i o n i s u n i f o r m throughout t h e s l i d e i n d i v i d u a l b r e c c i a - f r a g m e n t s c a n be d i s t i n g u i s h e d by t h e v a r i a t i o n i n t h e o r i e n t a t i o n o f t h e m i c r o l i t e s . The s e c t i o n i s v e i n e d by chalcedony. In  a few l o c a l i t i e s flow-banded d a c i t e ( ? ) was  observed.  M a c r o s c o p i c a l l y t h e r o c k s a r e f i n e l y l a y e r e d and p o r p h y r i t i c . The  f l o w l a y e r s range from p u r p l e t o cream i n c o l o r and a r e  123  a few m i l l i m e t e r s t h i c k .  They show s m a l l f l o w f o l d s one o r a  few f e e t a c r o s s and f i n e c r e n u l a t i o n s . Under t h e m i c r o s c o p e p h e n o c r y s t s a r e seen t o c o n s i s t o f p l a g i o c l a s e , q u a r t z , and b i o t i t e . The p l a g i o c l a s e , m o s t l y s o d i c a n d e s i n e , i s t w i n n e d , zoned and has i n c l u s i o n s o f g l a s s . The q u a r t z p h e n o c r y s t s a r e p a r t l y embayed and c o r r o d e d by m i n e r a l s o f t h e groundmass. The groundmass c o n s i s t s o f minute m i c r o l i t e s o f p l a g i o c l a s e , and v e r y s m a l l c r y s t a l s o f q u a r t z and b i o t i t e embedded i n a m a t r i x o f g l a s s . The m i c r o l i t e s form f l o w - l a y e r s t h a t curve around the phenocrysts. Some f l o w l a y e r s , more c o a r s e g r a i n e d than most o f t h e groundmass, a r e r e l a t i v e l y r i c h i n quartz. A specimen o f b a s a l t from t h e upper p a r t o f T r i m b l e Creek i s v e r y dark on f r e s h s u r f a c e s , weathers dark g r e e n and i s a p h a n i t i c . I t c o n t a i n s m i c r o p h e n o c r y s t s o f p l a g i o c l a s e and c l i n o - p y r o x e n e . The p l a g i o c l a s e , s o d i c b y t o w n i t e i n c o m p o s i t i o n , i s l a t h - l i k e , twinned and f i n e l y zoned. Some o f the c l i n o - p y r o x e n e , d i o p s i d e - a u g i t e , (ny=1.6835» 2v-55°, Ca45Mg4^Feo) shows t w i n n i n g , and a few g r a i n s have rims o f lower b i r e f r i n g e n c e . Some o f t h e c r y s t a l s a r e r e p l a c e d by c h l o r i t e . The groundmass c o n s i s t s d o m i n a n t l y o f minute p l a g i o c l a s e m i c r o l i t e s , some " i r o n o r e " , c h l o r i t e and other mafic minerals too f i n e - g r a i n e d f o r ident i f i c a t i o n , and v o l c a n i c g l a s s . The  r o c k s o f t h i s u n i t show no s i g n s o f metamorphism  but a r e l o c a l l y a l t e r e d . by c a r b o n a t e ,  Some a r e v e i n e d o r p a r t l y r e p l a c e d  c h l o r i t e , chalcedony o r e p i d o t e .  Felsitic  r o c k s i n t h e shear zone southwest o f t h e B i g B a r f e r r y  contain  c r y s t a l s o f p y r i t e , t h e amygdules i n an a n d e s i t e f l o w a r e f i l l e d w i t h q u a r t z and p i s t a c i t e . 3.  Structure  The Ward Creek assemblage l i e s a p p r o x i m a t e l y w i t h p a r t s o f t h e K i n g s v a l e group, t h e Spences B r i d g e  on s t r i k e group,  124  and the F o u n t a i n V a l l e y assemblage, and l i k e these i t i s bel i e v e d t o occupy a graben.  Between Leon Creek and B i g Bar  Creek t h e u n i t i s i n f a u l t c o n t a c t w i t h the P a v i l i o n group to northeast.  N o r t h o f B i g Bar Creek i t i s unconformably  l a i n by t h e F r e n c h Bar f o r m a t i o n .  To t h e southwest  over-  the r o c k s  a r e i n f e r r e d to be i n f a u l t c o n t a c t w i t h D i v i s i o n C o f t h e J a c k a s s M o u n t a i n Group. of  They a r e s e p a r a t e d from t h e DIVISION  the Spences B r i d g e group by overburden  and  overlying  middle or l a t e T e r t i a r y o l i v i n e b a s a l t . About one m i l e southwest of  s h e a r i n g and a l t e r a t i o n i s exposed f o r a p p r o x i m a t e l y  feet. The  The  1000  s c h i s t o s i t y o f t h i s zone d i p s s t e e p l y t o the west.  shear zone p o s s i b l y i s p a r t o f a more e x t e n s i v e f a u l t  t h a t may of  o f t h e B i g Bar f e r r y a zone  t e r m i n a t e t h e F r e n c h Bar f o r m a t i o n on the east s i d e  the F r a s e r R i v e r .  However, the p o s s i b l e c o n t i n u a t i o n s o f  the shear zone t o t h e n o r t h as w e l l as t o t h e s o u t h are c o v e r ed by expanses o f  overburden.  L i t t l e i s known about t h e i n t e r n a l s t r u c t u r e o f the Ward Creek assemblage because d e t e r m i n a t i o n s o f a t t i t u d e s s t r a t i g r a p h i c tops i n most l o c a l i t i e s  and  are d i f f i c u l t to o b t a i n .  Between Watson B a r Creek and B i g Bar Canyon the r o c k s i n the w e s t e r n p a r t o f the v o l c a n i c b e l t d i p s t e e p l y and a p p r o x i m a t e l y N 3 5 ° W. northeast.  strike  The s t r a t i g r a p h i c tops f a c e t o the  At s e v e r a l l o c a l i t i e s northwest o f B i g Bar Canyon  moderate n o r t h e a s t e r l y d i p s were o b s e r v e d .  4.  Mode of O r i g i n , Age and Correlation  The presence of coal seams indicates a continental environment. The unit i s older than the unconformably overlying French Bar formation.  I t may be c o r r e l a t i v e with the upper  D i v i s i o n of the Spences Bridge group, with parts of the Kingsvale group or Early Tertiary volcanic rocks of the Quesnel map-area.  I t s age may l i e anywhere between the Aptian  stage of the Lower Cretaceous and the Oligocene. McKenzie (1920) referred these rocks to his Oligocene Taseko formation.  However, as this formation also includes  o l i v i n e basalts i t probably comprises rocks ranging from Early to Middle or Late Tertiary and may have to be redefined. FRENCH BAR FORMATION The French Bar formation extends from Big Bar Creek to the northwestern extremity of the map area near French Bar Canyon.  Near Big Bar Creek i t i s at least 2100 feet thick.  The formation consists mostly of cobble-pebble- and granuleconglomerate,  less volcanic arenite, and small amounts of  s i l t s t o n e . (Plates XVI, XVII). Beds of arenite and conglomerate  are mostly from one  to twenty feet thick, and i n d i v i d u a l beds of arenite and conglomerate can be traced for several hundred feet.  A unit  composed dominantly of volcanic arenite and some interbedded conglomerate  i s exposed for about 1-1/2 miles.  126 The  r o c k s weather y e l l o w i s h o r b r o w n i s h and con-  glomerate s t r a t a a r e darker colored than a r e n i t e .  The s e d i -  ments a l l seem t o have been d e r i v e d from v o l c a n i c r o c k s were m o s t l y o f a n d e s i t i c c o m p o s i t i o n .  that  The conglomerates con-  s i s t almost e n t i r e l y o f v o l c a n i c f r a g m e n t s .  The a r e n i t e s i n  a d d i t i o n t o t h e v o l c a n i c f r a g m e n t s , c o n t a i n a s m a l l amount o f f e l d s p a r , q u a r t z , b i o t i t e , and " i r o n o r e " .  The s i l t s t o n e s  a r e made up o f t h e same m i n e r a l s and c h l o r i t e .  Rounding and  s o r t i n g v a r y c o n s i d e r a b l y , but i n g e n e r a l t h e beds a r e modera t e l y w e l l s i z e - s o r t e d and t h e fragments subrounded.  Con-  g l o m e r a t e s and a r e n i t e s have a m a t r i x o f s i l t - s i z e d r o c k - f l o u r and a r e p a r t l y cemented by " i r o n o x i d e " and r a r e l y Some a r e n i t e s a r e v e r y p o o r l y c o n s o l i d a t e d .  carbonate.  L o c a l l y the aren-  i t e c o n t a i n s seams o f f o s s i l p l a n t s . Graded bedding and c r o s s bedding a r e r a r e and were observed o n l y where t h e sandstone i s i n t e r l a m i n a t e d w i t h silt-stone. The F r e n c h B a r f o r m a t i o n o v e r l i e s t h e Ward Creek assemblage unconformably.  I t i s o v e r l a i n by a v o l c a n i c s e -  quence t h a t i s i n f a u l t c o n t a c t w i t h t h e P a v i l i o n group.  The  s t r a t a s t r i k e u n i f o r m l y about N 25° W and d i p s t e e p l y o r moderately to the northeast.  I n the southeastern  p a r t near  the boundary f a u l t o f t h e P a v i l i o n group t h e d i p s a r e approxi m a t e l y 80° and i n t h e northwest they a r e c l o s e t o 45°i  Near  B i g B a r Creek exposures o f t h e conglomerate end a b r u p t l y . P o s s i b l y t h e f o r m a t i o n here i s c u t o f f by a f a u l t ; a s t r o n g  s h e a r zone t h a t may be p a r t o f s u c h a f a u l t i s exposed i n t h e v o l c a n i c r o c k s on t h e west s i d e o f t h e r i v e r . t h e b a s i n o f d e p o s i t i o n may have ended h e r e .  Alternatively, The f o r m a t i o n  i s i n t r u d e d by numerous b a s a l t i c dykes and s i l l s . The a s s o c i a t e d p l a n t m a t t e r i n d i c a t e s a c o n t i n e n t a l environment f o r t h e f o r m a t i o n .  The g e n e r a l l y rounded n a t u r e  o f t h e fragments and l o c a l l a m i n a t i o n s suggest d e p o s i t i o n by running water.  Beds t h a t show poor s o r t i n g and r o u n d i n g may  have been d e p o s i t e d as mudflows.  The c o a r s e s i z e o f t h e  fragments i s i n d i c a t i v e o f s t e e p g r a d i e n t s . may be r e l a t e d t o contemporaneous  These  gradients  volcanism or tectonism.  P l a n t f o s s i l s found i n t h e upper p a r t o f t h e f o r m a t i o n , near B i g B a r Creek were i d e n t i f i e d by P r o f e s s o r G.E. Rouse as f o l l o w s : DIVISION Class Order  SPERMATOPHYTA GYMNOSPERMAE CONIFERALES  1.  M e t a s e q u o i a o c c i d e n t a l i s (Newb.) Chaney. Paleocene-Miocene  »  ? S e q u o i a n o r d e n s k i o l d i Heer.  2  Class Sub-Class  Paleocene-Eocene  ANGIOSPERMAE DICOTYLEDONAE  3»  Cinnamomum s p . - c f . a f f i n e Lg  Upper C r e t a c e o u s Eocene.  «  C a r p i n u s g r a n d i s Unger.  Tertiary  5«  ? S a l i x s p . - c f . S. wyomingensis Kn. and Cock  Paleocene-Miocene  6.  ? L a u r o p h y l l u m s p . <- c f . L. laraminum (DN) B e l l  Paleocene  7*  T e t r a c e r a s p . - c f . T. c a s t a n e a f o l l a Mac G.  Eocene  4  128  8.  Hamamelis ? c l a r u s H o l l i c k  9.  A l n u s sp. c f . A. cremastogynoides  Paleocene-Eocene Berry  Eocene-Oligocene  Rouse s t a t e s i n h i s r e p o r t : "As can be n o t e d , the d e t e r m i n a t i o n s i n d i c a t e a d e f i n i t e T e r t i a r y age f o r the s t r a t a , w i t h a p r e f e r e n c e towards an Eocene d a t i n g .  However, i t i s p o s s i b l e t h a t the beds a r e  e i t h e r e a r l i e r T e r t i a r y or O l i g o c e n e ; a more d e f i n i t e  age  d e t e r m i n a t i o n cannot be based on the r e l a t i v e l y p o o r l y p r e s e r v e d fragmentary  remains.  I t i s the w r i t e r ' s considered  o p i n i o n t h a t the B i g Bar f l o r a i s c l o s e l y contemporaneous w i t h those from o t h e r T e r t i a r y b a s i n s i n B.C. and P r i n c e t o n .  e.g. Chu-Chua,  The ages o f t h e s e l a t t e r sediments have been  v a r i o u s l y a s c r i b e d as Eocene to Miocene.  The c l o s e s t more p r o -  b a b l e age would seem t o be Upper-Eocene o r O l i g o c e n e f o r the B i g Bar  flora." I n 1920  McKenzie d e s c r i b e d and d e f i n e d the F r e n c h  f o r m a t i o n as f o l l o w s :  (p. 76 A - 77  Bar  A)  " T h i s f o r m a t i o n i s w e l l exposed on upper F r e n c h  Bar  C r e e k , and u n d e r l i e s the c o u n t r y westward a c r o s s the r i d g e s i n w h i c h Yalakom r i v e r heads as f a r as upper Churn/Creek drainage basin.  I t may  have a c o n s i d e r a b l e e x t e n s i o n i n the  area southeast of that j u s t d e s c r i b e d . " "The conglomerates amounts.  F r e n c h Bar f o r m a t i o n i s made up o f v e r y  coarse  w i t h l e n t i c u l a r sandstone beds i n s u b o r d i n a t e  The r o c k s a r e much l e s s i n d u r a t e d than any o f the  sediments o f those i n c l u d e d i n the E l d o r a d o  series"  (Lower  Cretaceous), and the pebbles and boulders easily weather out of their sandy matrix.  The formation i s characterized by a  high percentage of large, well rounded boulders of the plutonic rocks of the Coast Mountains .... The conglomerate  beds range  from 10 to 100 feet thick, and the formation as a whole gives the impression of being of f l u v i a t i l e o r i g i n . " ... "The thickness of the French Bar formation as exposed near the creek of that name i s approximately 2000 feet." "On l i t h o l o g i c and s t r u c t u r a l grounds, this formation i s tentatively correlated with the Coldwater supposedly of Oligocene  group of Dawson,  age".  As the conglomerate  and arenite on the Fraser River  l i e only approximately 6 miles to the east of the French Bar formation and as they have a comparable l i t h o l o g y , s e d i mentary structure and thickness they are tentatively c o r r e l ated with that formation.  The g r a n i t i c boulders reported by  McKenzie are probably of l o c a l o r i g i n and were not transported into the Big Bar area.  The deposits appear to be older than  the T e r t i a r y sedimentary rocks on Big Bar Creek, on Leon Creek, and near P a v i l i o n because they are much stronger deformed. VOLCANIC ROCKS OVERLYING THE FRENCH BAR  FORMATION  The French Bar formation i s overlain by a minimum of 2000 feet of t u f f , andesite, basalt, f e l s i t e , and minor seams of coal. The andesite i s generally greyish brown, aphanitic, and mostly massive.  A specimen of basalt weathers greyish brown and  has a v e s i c u l a r , aphanitic texture.  130  I t c o n s i s t s o f abundant m i c r o p h e n o c r y s t s o f p l a g i o c l a s e and a u g i t e i n a groundmass o f v e r y fine-grained plagioclase, clino-pyroxene, "iron o r e " , and v o l c a n i c g l a s s and i t s a l t e r a t i o n products. The p l a g i o c l a s e m i c r o p h e n o c r y s t s , intermediate to sodic l a b r a d o r i t e , are l a t h l i k e , t w i n n e d , and show o s c i l l a t o r y normal z o n i n g . They have a s u b - p a r a l l e l o r i e n t a t i o n . Some o f t h e a u g i t e p h e n o c r y s t s (ny=1.6905 2v-52°; C a ^ M g ^ F e - ^ ) a l s o show t w i n n i n g . A thin-section of a whitish relatively l i g h t f e l s i t i c r o c k c o n t a i n s a few c o r r o d e d p h e n o c r y s t s o f p l a g i o c l a s e and q u a r t z i n a v e s i c u l a r g l a s s y groundmass. To t h e n o r t h e a s t t h e v o l c a n i c r o c k s a r e i n f a u l t c o n t a c t w i t h t h e P a v i l i o n group.  T h i s c o n t a c t i s n o t ex-  posed but a f a u l t can be i n f e r r e d from t h e f a c t t h a t t h e P a v i l i o n group s t r i k e s i n t o t h e T e r t i a r y v o l c a n i c s , from t h e s t e e p d i p s near t h e c o n t a c t s , and from s h e a r i n g and a l t e r a t i o n . MIDDLE OR LATE TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 1. A.  S e d i m e n t a r y Rocks n e a r P a v i l i o n  D i s t r i b u t i o n and T h i c k n e s s M i d d l e o r L a t e T e r t i a r y o u t c r o p s near P a v i l i o n l i e i n  a n o r t h e a s t e r l y t r e n d i n g zone t h a t i s a p p r o x i m a t e l y l o n g and 1-1/2 m i l e s w i d e .  The exposures a r e c o n f i n e d t o  narrow zones a l o n g h i l l s i d e s . outcrops  5 miles  The e l e v a t i o n o f t h e l o w e s t  i s 3200 f e e t a t t h e n o r t h e a s t e r n e x t r e m i t y and  n e a r l y 4000 f e e t a t t h e s o u t h w e s t e r n e x t r e m i t y .  Individual  exposures do n o t exceed 200 f e e t i n t h i c k n e s s but t h e v e r t i c a l range o f t h e d e p o s i t s on t h e s l o p e s o u t h o f P a v i l i o n Creek i s g r e a t e r than 500 f e e t .  On t h e n o r t h s i d e o f t h e same v a l l e y  131  however, the r o c k s are l e s s than one hundred f e e t  thick.  A s m a l l o u t c r o p o f s i m i l a r r o c k was noted at approxi m a t e l y 4000 f e e t e l e v a t i o n on the s l o p e above Moran, and a n o t h e r one l i e s  i m m e d i a t e l y n o r t h e a s t o f the r a i l r o a d  ing  near G l e n F r a s e r .  B.  Lithology The r o c k s c o n s i s t o f l i t h i c a r e n i t e ,  and a s m a l l p r o p o r t i o n o f carbonaceous  shale.  cross-  conglomerate, The c o n t a c t s  between t h e s e r o c k t y p e s are w e l l d e f i n e d , but the r o c k s show no pronounced  internal stratification.  The r o c k s and t h e  soil  d e r i v e d from them a r e b r i c k - r e d .  I n hand-specimens o f con-  glomerate and a r e n i t e , a r g i l l i t e ,  c h e r t , q u a r t z , and  c h l o r i t e fragments can be r e c o g n i z e d . from sand t o c o b b l e s .  rarely  These p a r t i c l e s  range  The weakness o f t h e i r cement has r e -  s u l t e d i n the f o r m a t i o n o f numerous c a v e s , and i n a major l a n d s l i d e about one m i l e east o f P a v i l i o n . Three specimens  o f l i t h i c a r e n i t e examined under the  m i c r o s c o p e c o n t a i n 10-35$ q u a r t z , 0-9$  f e l d s p a r , 11-35$ c h e r t ,  and 2 0 - 5 0 $ l i t h i c f r a g m e n t s , m o s t l y o f a r g i l l i t e  and a s m a l l  p r o p o r t i o n o f o t h e r sedimentary and metamorphic r o c k s .  Minor  d e t r i t a l c o n s t i t u e n t s a r e c a r b o n a t e , m u s c o v i t e , and t o u r m a l i n e . The fragments i n most specimens O r i g i n a l l y they were subrounded  are w e l l s i z e - s o r t e d .  t o rounded  but they have p a r t l y  been r e p l a c e d by the m a t r i x w h i c h c o n s i s t s o f c a r b o n a t e and "iron oxide".  C.  Structure The  u n i t o v e r l i e s unconformably s t r a t a o f t h e P a v i l i o n  group and s m a l l bodies o f igneous r o c k s a s s i g n e d t o t h e Coast Intrusions.  The beds l i e h o r i z o n t a l l y o r d i p a t a n g l e s o f  l e s s t h a n t e n degrees and appear n e a r l y everywhere disturbed.  little  An i s o l a t e d o u t c r o p by t h e P a v i l i o n M o u n t a i n r o a d ,  however, has pronounced j o i n t i n g , p o s s i b l y p a r a l l e l t o b e d d i n g , t h a t d i p s 55 degrees e a s t . A l t h o u g h t h e exposures o f t h e T e r t i a r y r o c k s on t h e s l o p e n o r t h o f P a v i l i o n Creek t e r m i n a t e a t t h e f a u l t  contact  between D i v i s i o n I and I I o f t h e Cache Creek feroup, t h e r e i s no evidence t h a t t h e T e r t i a r y sedimentary p l a c e d by t h a t f a u l t .  r o c k s were d i s -  I t i s more l i k e l y t h a t t h e c o n t a c t  formed a t o p o g r a p h i c c o n t r o l o f d e p o s i t i o n .  The a m p h i b o l i t e s  to t h e west o f t h a t c o n t a c t w h i c h a r e i n d u r a t e d by a d i o r i t i c i n t r u s i o n a r e p r o b a b l y more r e s i s t a n t t o w e a t h e r i n g ribbon cherts to the east.  I n T e r t i a r y time they may have  formed t h e m a r g i n o f a b a s i n and r e c e i v e d no D.  than t h e  sediments.  Mode o f O r i g i n The  sediments appear t o be d e r i v e d m o s t l y from r o c k s  o f t h e Cache Creek and P a v i l i o n groups and t o minor e x t e n t from Coast I n t r u s i o n s . As they c o n s i s t o f r e l a t i v e l y c o a r s e , w e l l s o r t e d m a t e r i a l they p r o b a b l y r e p r e s e n t a f l o o d p l a i n .  The r e d  c o l o r o f the rocks i n d i c a t e s o x i d i z i n g c o n d i t i o n s which p r e v a i l only i n w e l l drained areas.  The b l a c k s h a l e , however, shows  t h a t l o c a l l y swamp c o n d i t i o n s e x i s t e d .  133 The o r i g i n a l l i m i t s o f the d e p o s i t s are o n l y p a r t l y known.  On the n o r t h e a s t they l a p a g a i n s t a p l u t o n which r i s e s  above the T e r t i a r y beds, and n o r t h o f P a v i l i o n Creek they come t h i n and probably d i s a p p e a r . i n a v a l l e y that was  They may  be-  have been l a i d down  connected w i t h the a r e a south o f Leon  Creek and p a r t l y c o i n c i d e d w i t h the present F r a s e r R i v e r v a l l e y . E.  Age Dawson c o r r e l a t e d the sediments  w i t h the  sandstones  u n d e r l y i n g the b a s a l t p l a t e a u on Leon Creek and p l a c e d them i n the middle Miocene. (Dawson, 1895, Taggart  p. 212B).  i n c l u d e them w i t h the Coldwater  D u f f e l l and  Mc-  Beds (?) o f the Kam-  loops group which i s c o n s i d e r e d to be Miocene or e a r l i e r ,  (p.66)  Although the rocks near P a v i l i o n are s i m i l a r i n l i t h o l o g y to those on Hat Creek they d i f f e r i n s t r u c t u r e . The  s t r a t a on Hat Creek d i p at angles up to 60° whereas the  beds near P a v i l i o n l i e almost  horizontally.  Dawson's c o r r e l a t i o n o f the sediments  near  Pavilion  w i t h those south o f Leon Creek i s supported by s e v e r a l f e a t u r e s . Both s t r a t a are approximately at the same e l e v a t i o n , both seem to be undisturbed and both appear to be o l d e r than the l a t e s t v o l c a n i c rocks o f the a r e a .  I t w i l l be mentioned that  the  s t r a t a south of Leon Creek probably u n d e r l i e Middle to Late Tertiary olivine basalts.  The sediments  on P a v i l i o n Creek are  at a s l i g h t l y lower e l e v a t i o n than an i s o l a t e d remnant o f T e r t i a r y a n d e s i t e s i t u a t e d about  1-1/2  oh the p l a t e a u on P a v i l i o n Mountain.  m i l e s to the n o r t h e a s t D u f f e l l and McTaggart  134 p o i n t e d out t h a t the s e d i m e n t a r y o u t c r o p near G l e n F r a s e r i s cut by two dykes, (p. 65p). to the l a t e s t v o l c a n i c  Such dykes may w e l l be r e l a t e d  activity.  The upper s u r f a c e o f t h e s e d i m e n t a r y r o c k s near P a v i l i o n i s c o n t i n u o u s w i t h a w e l l p r e s e r v e d e r o s i o n p l a i n on P a v i l i o n M o u n t a i n o f a p p r o x i m a t e l y 20 square m i l e s .  I t i s believed  t h a t s u r f a c e s o f t h i s type a r e not o l d e r than Miocene. ( T h o r n b u r y , 1954, 2.  p. 26).  S e d i m e n t a r y Rocks A s s o c i a t e d w i t h the O l i v i n e B a s a l t s near Leon Creek and B i g Bar Creek About two m i l e s s o u t h o f Leon Creek and one m i l e west  o f the F r a s e r R i v e r p o o r l y c o n s o l i d a t e d sediments a r e exposed f o r about one m i l e a l o n g the s t e e p l y s l o p i n g margin o f a p l a t e a u at an e l e v a t i o n o f a p p r o x i m a t e l y 3500 f e e t .  The  t h i c k n e s s o f t h e exposed s t r a t a i s l e s s t h a n one hundred but the u n i t may  be much t h i c k e r .  feet,  The r o c k s , m o s t l y b r o w n i s h  and r e d d i s h , range from sandstone t o b o u l d e r conglomerate and a r e i n p a r t w e l l bedded. by c o l o r o r g r a i n s i z e . thick.  D i f f e r e n t l a y e r s can be d i s t i n g u i s h e d The beds a r e from one t o t e n f e e t  The d e t r i t a l m a t e r i a l c o n s i s t s m a i n l y o f c h e r t and  a r g i l l i t e , and some g r a n i t i c fragments. a r e p o o r l y rounded.  The cement c o n s i s t i n g o f c a r b o n a t e and  " i r o n o x i d e " i s m o s t l y weak. quartz d i o r i t e . slumping.  P e b b l e s and sand g r a i n s  The beds r e s t unconformably  on  A low d i p has p r o b a b l y been produced by r e c e n t  The sediments seem t o have been d e r i v e d from r o c k s  o f t h e immediate v i c i n i t y .  They p r o b a b l y u n d e r l i e o l i v i n e  b a s a l t but may o n l y be s l i g h t l y o l d e r t h a n t h a t v o l c a n i c r o c k . At many l o c a l i t i e s around t h e margins o f t h e T e r t i a r y b a s a l t t h e s o i l c o n t a i n s u n u s u a l l y w e l l rounded pebbles and cobbles.  These roundstones a r e p r o b a b l y d e r i v e d from con-  g l o m e r a t e s w h i c h u n d e r l i e t h e b a s a l t s but a r e h i d d e n by t h e abundant t a l u s t h a t surrounds t h e i r c l i f f s a t t h e m a r g i n s . Such conglomerates would be c o r r e l a t i v e w i t h t h e o u t c r o p des c r i b e d above and w i t h t h e s e d i m e n t a r y r o c k s near P a v i l i o n . F l a t l y i n g sedimentary r o c k s , 200 t o 300 f e e t are of  thick  exposed f o r a p p r o x i m a t e l y one m i l e a l o n g t h e upper t h e p l a t e a u n o r t h o f B i g B a r Creek.  margin  To t h e e a s t t h e y  i n t e r f i n g e r w i t h o l i v i n e b a s a l t , and t o t h e west t h e i r c o n t a c t i s covered.  The r o c k s a r e m o s t l y p e b b l e - o r c o b b l e - c o n g l o m e r a t e  but i n c l u d e b o u l d e r - c o n g l o m e r a t e , s a n d s t o n e , and minor amounts of mudstone.  The roundstones a r e made up o f c h e r t , a r g i l l i t e ,  l i m e s t o n e , and g r e e n s t o n e , a l l d e r i v e d from t h e Cache Creek or  P a v i l i o n groups and from g r a n i t i c r o c k s , and h i g h l y v e s i c -  ular Tertiary basalts.  The fragments a r e w e l l rounded and  f a i r l y w e l l s o r t e d and cemented by c a r b o n a t e . the  The s t r e n g t h o f  cement v a r i e s i r r e g u l a r l y throughout t h e r o c k .  The s e d i -  ments seem t o have been d e p o s i t e d by r u n n i n g water and appare n t l y a r e contemporaneous w i t h t h e o l i v i n e b a s a l t s . p r o b a b l y s l i g h t l y younger  They a r e  than t h e T e r t i a r y sedimentary r o c k s  near Leon Creek and near P a v i l i o n .  136  3. A.  D i s t r i b u t i o n and  Olivine Basalt  Thickness  The o u t c r o p s o f M i d d l e or L a t e T e r t i a r y b a s a l t s a r e c o n f i n e d t o two narrow zones.  One  olivine i s situated  t h e west s i d e o f the F r a s e r R i v e r between McKay Creek Watson Bar Creek;  on  and  ( P l a t e X V I I I ) , the o t h e r one, l o c a t e d  approx-  i m a t e l y 10 m i l e s t o t h e n o r t h , extends a l o n g t h e lower p a r t o f B i g Bar Creek.  The e l e v a t i o n o f the upper s u r f a c e o f t h e  first  zone g r a d u a l l y drops from 4400 f e e t i n t h e s o u t h t o 3900 f e e t i n t h e n o r t h over a d i s t a n c e o f a p p r o x i m a t e l y 10 m i l e s ; the upper s u r f a c e o f the second zone drops from 3900 f e e t i n t h e west t o 3600 f e e t i n the east over a d i s t a n c e o f a p p r o x i m a t e l y 5 m i l e s . These upper s u r f a c e s seem t o r e p r e s e n t t h e o r i g i n a l top o f t h e v o l c a n i c f l o w s because t h e y a r e o f g r e a t r e g u l a r i t y and marked by c o a r s e v e s i c l e s .  They a r e o v e r l a i n o n l y by a t h i n  veneer  o f s o i l and form p l a t e a u s w h i c h a r e w e l l expressed on t o p o g r a p h i c maps.  The e l e v a t i o n s o f t h e lower c o n t a c t s a r e known  w i t h l e s s a c c u r a c y because they a r e h i d d e n by t a l u s and because t h e o u t e r margins o f the v o l c a n i c p l a t e a u s have slumped almost everywhere. feet.  The  P r o b a b l y the b a s a l t s a r e nowhere t h i c k e r than  200  sheet s o u t h o f Leon Creek seems t o t h i n out t o the  west; the f l o w s on B i g Bar Creek appear t o be t h i c k e r I n the west t h a n i n t h e east where they i n t e r f i n g e r w i t h sediments. I n d i v i d u a l f l o w s are from 10 t o 50 f e e t t h i c k .  Some o f them  were t r a c e d a l o n g the margin o f t h e p l a t e a u s f o r s e v e r a l hundred f e e t but they may  be much more e x t e n s i v e .  137  B.  Lithology The r o c k s a r e red-brown and some o f them a r e r e l a t i v e l y  coarse-grained.  Dark green c r y s t a l s o f o l i v i n e about one t o  two m i l l i m e t e r s l o n g can be d e t e c t e d w i t h t h e unaided upper p a r t s o f t h e f l o w s a r e h i g h l y v e s i c u l a r . i n g i s a common f e a t u r e .  eye.  Columnar  The  joint-  N o r t h o f B i g B a r Creek e l l i p s o i d a l  s t r u c t u r e s about one f o o t or a few f e e t t h i c k t h a t resemble p i l l o w s were seen. Seven specimens s t u d i e d i n t h i n - s e c t i o n c o n s i s t a p p r o x i m a t e l y o f 50-60$ p l a g i o c l a s e , 7-22$ o l i v i n e , and 3-5$ "iron oxide". pyroxene.  The b a l a n c e i s made up d o m i n a n t l y o f c l i n o -  Orthopyroxene,  not i d e n t i f i e d i n a l l o f t h e specimens,  forms l e s s than 1$ o f t h e r o c k .  A p a t i t e , z i r c o n ( ? ) , and an  unknown m i n e r a l o c c u r r i n g as v e r y f i n e - g r a i n e d n e e d l e - l i k e i n c l u s i o n s i n t h e p l a g i o c l a s e a r e p r e s e n t o n l y i n minute p r o portions. (Plate XIX). The p l a g i o c l a s e forms e u h e d r a l t o s u b h e d r a l m i c r o l i t e s t h a t e x h i b i t C a r l s b a d and a l b i t e t w i n n i n g . laws a r e l e s s commonly r e p r e s e n t e d .  The o t h e r t w i n  The m i n e r a l shows z o n i n g ,  m o s t l y o f t h e normal t y p e , and has an average c o m p o s i t i o n An^Q'  It is little  near  altered.  Some c r y s t a l s o f o l i v i n e a r e s u b h e d r a l , but most o f the g r a i n s are anhedral.  The c o m p o s i t i o n o f t h e m i n e r a l ranges  from F034 t o F072 and averages  Fo8o»  l  n  s e v e r a l specimens t h e  o l i v i n e i s p a r t l y a l t e r e d to brownish " i r o n oxide".  The a l t e r -  a t i o n i s s t r o n g e s t around t h e o u t e r margins o f t h e g r a i n s and near f r a c t u r e s but a l s o o c c u r s i n t h e i r  interior.  138  The ortho-pyroxene altered. En^  i s s u b h e d r a l and c o l o r l e s s  unless  I n one specimen i t s c o m p o s i t i o n was determined  (ny=1.685> - 2 v ) .  as  I n some specimens t h e m i n e r a l i s  altered by"iron oxide." The c l i n o p y r o x e n e forms v e r y f i n e - g r a i n e d s u b h e d r a l o r anhedral grains the composition o f which i s d i f f i c u l t to identify.  Most o f t h e c l i n o p y r o x e n e seems t o be a u g i t e but  some p i g e o n i t e may be p r e s e n t . an approximate  I n one specimen t h e a u g i t e has  c o m p o s i t i o n o f Ca^Mg^Fe-^^ (ny=1.689).  Of t h e " i r o n o r e " m i n e r a l s i l m e n i t e i s much more abundant than  magnetite.  The t e x t u r e o f t h e r o c k s i s s e r i a t e and i n t e r g r a n u l a r . I n some specimens t h e p l a g i o c l a s e m i c r o l i t e s show s u b p a r a l l e l alignment.  The s i z e o f t h e e s s e n t i a l m i n e r a l s i n a r e l a t i v e l y  c o a r s e - g r a i n e d specimen ranges a p p r o x i m a t e l y from 2mm mm and i n a f i n e - g r a i n e d r o c k from 1 mm t o .015 mm. o f t e x t u r e may be d i s t i n g u i s h e d :  t o .02 Two  types  e i t h e r o l i v i n e a l o n e forms  the l a r g e g r a i n s (type I ) or the l a r g e g r a i n s c o n s i s t o f p l a g i o c l a s e and o r t h o p y r o x e n e  as w e l l as o l i v i n e ( t y p e I I ) .  The i n t e r m e d i a t e range i s dominated by p l a g i o c l a s e but a l s o c o n t a i n s some o l i v i n e and c l i n o p y r o x e n e .  The f i n e s t grade  i s made up o f m o s t l y c l i n o p y r o x e n e and s m a l l amounts o f plagioclase.  TABLE 3 MINERAL COMPOSITION OF 7 SPECIMENS OF OLIVINE BASALT  %  %  lc  51  lb  Specimen  2  %  %  nx" o f Composn o f Comp. (001) c l i t i o n i n o l i v i n e ±n% eavage f r a g - % o f An ments o f t 1% plagioclase  3  1.5587 + .001  61  1.5584 + .001  60  1.5584 .001  60  olivine  17  0  16  59  22  1  14  4  la  60  20  0  15  5  2c  57  32  trace  8  3  1.5585 i .001  60  2b  50  25  0  15  6  4  1.5586 t .001  2a  50  25  0  8  14  3  3  49  40  0  7  4  A  R.M. Crump and N.B.Kettner, (1953)  Iron iron oxide ore alter-  y  orthopyroxene  #  plagio- clinoclase pyroxene  %  13  (3)  '  Texture  1.6855 .002  84  II  1.6893 .002  82  II  1.6900 .002  81.5  II  1.6991 .001  77.5  II  61  1.7100 t .001  1.5590 t .002  62  1.6900 i .001  1.5581 t .001  59  1.6910 t .002  I pilotaxitic I 81.5 trachytic 81 I  i  t t  t t  72.5  A. P o l d e r v a a r t , (1950)  Specimen l a , b, and c, a r e t a k e n from t h r e e s u c c e s s i v e f l o w s o f t h e p l a t e a u s o u t h o f Leon Creek, and specimen 2 a , b, and c , a r e from t h r e e s u c c e s s i v e f l o w s from t h e p l a t e a u n o r t h o f Leon Creek. The two l o c a l i t i e s a r e a p p r o x i m a t e l y 2 m i l e s a p a r t . Specimen 3 i s from n o r t h o f B i g B a r Creek.  140 The  p r e s e n t sampling  i n composition.  The  i n d i c a t e s no s y s t e m a t i c v a r i a t i o n  presence o f orthopyroxene  i n some f l o w s  p r o b a b l y i s not s i g n i f i c a n t because the m i n e r a l o c c u r s o n l y i n small quantities.  The one  f l o w (2b) t h a t c o n t a i n s an o l i v i n e  c o m p a r a t i v e l y r i c h i n i r o n shows no d e v i a t i o n from the average i n the c o m p o s i t i o n o f i t s p l a g i o c l a s e . T h i s l a c k o f c o r r e l a t i o n between o l i v i n e and p l a g i o c l a s e may  perhaps be  explained  by the f a c t t h a t the t e x t u r e o f the r o c k i s o f type ( I ) and approaches t h a t o f an o l i v i n e  porphyry.  C. S t r u c t u r e The  b a s a l t s r e s t unconformably on r o c k s o f the P a v i l i o n  group and on p o o r l y c o n s o l i d a t e d T e r t i a r y sediments.  Their  upper s u r f a c e s l o p e s about 50 f e e t per m i l e to the n o r t h c o r r esponding t o a d i p o f l e s s than one degree.  They o v e r l i e  the  F r a s e r R i v e r f a u l t zone w i t h o u t any s i g n s o f d i s t u r b a n c e . B e i n g r e l a t i v e l y r e s i s t a n t to w e a t h e r i n g  the b a s a l t s  form c l i f f s and have produced uncommonly steep p r o f i l e s i n the u n d e r l y i n g r o c k s w h i c h they p r o t e c t . r o c k s a r e not a b l e to support s l o p e s and y i e l d by s l u m p i n g .  A p p a r e n t l y t h e s e weaker  the l o a d o f the b a s a l t s at such The margins o f the b a s a l t  p l a t e a u s a r e a l s o c h a r a c t e r i z e d by numerous f r a c t u r e s a l o n g w h i c h openings from a few f e e t to tens o f f e e t wide The  develop.  t e r r a c e - l i k e f a u l t b l o c k s around the b a s a l t p l a t -  eaus near Leon Creek a r e v i s i b l e on a i r - p h o t o g r a p h s .  ( P l a t e XX)  141 D.  Mode o f O r i g i n There can be l i t t l e doubt t h a t t h e f o u r o u t c r o p  areas  between McKay Creek and Watson B a r Creek a r e remnants o f a continuous valley.  sheet o f v o l c a n i c f l o w s w h i c h o r i g i n a l l y f i l l e d a  Some o f t h e mountain s l o p e s t h a t bounded t h i s v a l l e y  on t h e west a r e s t i l l p r e s e r v e d .  The s l o p e s a r e u n d e r l a i n by  r o c k s o f t h e J a c k a s s M o u n t a i n group and o f t h e Ward Creek assemblage.  The v a l l e y i n w h i c h t h e b a s a l t s were l a i d down  a p p a r e n t l y c o n t a i n e d sands and g r a v e l s t h a t may have been partly of f l u v i a t i l e  origin.  The d i s t r i b u t i o n o f t h e b a s a l t s on B i g B a r C r e e k , t h e i r a s s o c i a t i o n w i t h f l u v i a t i l e sediments,  and t h e presence o f  p o s s i b l e p i l l o w s t r u c t u r e s s u g g e s t i n g submerged d e p o s i t i o n i n d i c a t e t h a t these f l o w s l i k e t h e u n d e r l y i n g T e r t i a r y  sediments,  also occupied a v a l l e y . Because o f t h e u n i f o r m i t y o f l i t h o l o g y and e l e v a t i o n and t h e s i m i l a r i t y o f environment i t i s p r o b a b l e t h a t t h e b a s a l t s a l o n g B i g B a r Creek were connected  w i t h those s o u t h o f  Watson B a r Creek. As no b a s a l t s a r e p r e s e r v e d between Watson B a r Creek and B i g B a r Creek such a c o n n e c t i o n must have u n d e r l a i n areas t h a t have s u b s e q u e n t l y  been eroded down t o e l e v a t i o n s lower  t h a n 3900 f e e t ; t h e r e f o r e i t must have o c c u p i e d a narrow zone along the l i n e o f the present v a l l e y o f the Fraser R i v e r . I t was mentioned t h a t t h e upper s u r f a c e o f t h e n o r t h e r n o u t c r o p zone d i p s a t a g r a d i e n t o f a p p r o x i m a t e l y  50 f e e t per  m i l e t o t h e n o r t h and t h a t t h e upper s u r f a c e o f t h e f l o w s on  B i g Bar Creek s l o p e w i t h a s i m i l a r g r a d i e n t to the e a s t . i s tempted to conclude was  t h a t the source o f the v o l c a n i c f l o w s  l o c a t e d not f a r from the s o u t h e r n  present outcrops  One  extremity of  their  and t h a t t h e y f l o w e d northward and  eastward  a l o n g v a l l e y s t h a t c o i n c i d e i n p a r t w i t h the p r e s e n t v a l l e y s o f F r a s e r R i v e r and B i g Bar Creek.  The  f a c t , however, t h a t  the upper s u r f a c e s o f the b a s a l t s s o u t h o f V/atson Bar  Creek  and n o r t h o f B i g Bar Creek have the same e l e v a t i o n o f 3900 feet t  50 f e e t and  t h a t no g r a d i e n t i s n o t i c e a b l e i n d i c a t e s  t h a t some t i l t i n g has o c c u r r e d s i n c e the d e p o s i t i o n o f the flows.  The  d i r e c t i o n of t i l t  and t h e r e f o r e the o r i g i n a l  slope  o f the a n c i e n t v a l l e y s a r e unknown. These b a s a l t s a r e the o l d e s t v o l c a n i c r o c k s i n the p r e s e n t map-area t h a t c o n t a i n o l i v i n e .  T h e i r appearance marks  the end o f the phase dominated by a n d e s i t e .  It i s generally  thought t h a t such f l o w s a r e d e r i v e d from a b a s a l t i c l a y e r i n the e a r t h ' s c r u s t and r i s e t h r o u g h deep r e a c h i n g f r a c t u r e s . As the f l o w s o v e r l i e one o r two major f a u l t s they may ascended t h r o u g h  w e l l have  f r a c t u r e s a s s o c i a t e d w i t h the F r a s e r R i v e r  f a u l t zone but a f t e r they ceased to be  active.  T h i s c o n c l u s i o n conforms i n a g e n e r a l way  w i t h Dawson's  concept t h a t the f l o w s a r e o f l o c a l o r i g i n (Dawson, 1895»p.216B). E.  Age Dawson i n c l u d e d the b a s a l t s i n h i s "Upper V o l c a n i c  Group" w h i c h he p l a c e d i n the Upper Miocene.  D u f f e l l and  Taggart c o r r e l a t e d them w i t h the Kamloops group c o n s i d e r e d  Mcas  143 Miocene or e a r l i e r . basalts personal  rest  However, i n the Kamloops a r e a  the o l i v i n e  uneonformably on the Kamloops group (W.H.Mathews,  communication). As Dawson r e m a r k e d " t h e i r , p r e s e n t  a very great formation."  amount o f r i v e r e r o s i o n s i n c e  (1895, p . 2 1 6 B ) .  deposits  it  are younger than e a r l y On t h e o t h e r conglomerate  is  because u n l i k e that  erosion since  the v o l c a n i c  River f a u l t zone.  from Oligocene to  s p a n a r e l a t i v e l y y o u n g age an o r i g i n a l s u r f a c e  conditions of rapid  erosion.  l a t e M i o c e n e age i s  suggested.  rocks  of f a i r  is  early  Pleistocene.  probable  because  extent preserved  For these reasons  under  a Pliocene  or  (Compare T h o r n b u r y , 1954 p .  c l o s e l y resemble  basalts  of the Quesnel map-area assigned  ( T i p p e r 1959)  the M i o c e n e , P l i o c e n e ,  2.  been  Their  l i t h o l o g y and g e o m o r p h i c e n v i r o n m e n t t h e  to  their contains  f o r m a t i o n t h e y have not  age t h e n r a n g e s  to  their  hand, they are younger than the French Bar  possible  With respect  date o f  Pleistocene.  by movements o f t h e F r a s e r  they present  represents  As the F r a s e r R i v e r  improbable that  affected  Within that  the  The d e p t h o f  d e p o s i t i o n i s more t h a n 3000 f e e t . Pleistocene  appearance  and p o s s i b l y  rocks by  Pleistocene.  INTRUSIVE ROCKS  ULTRABASIC INTRUSIONS ULTRABASIC ROCKS NEAR LILLOOET 1.  Distribution A belt  of ultrabasic  rocks l i e s  26).  between T r i a s s i c  or  144  older  r o c k s t o t h e west and t h e L i l l o o e t  the v i c i n i t y pentinites extends be  2.  of Lillooet.  outcrops  a p p e a r t o be one h a l f m i l e w i d e .  beyond  linked  Although  group t o t h e e a s t I n a r e scarce the s e r The b e l t  t h e p r e s e n t map a r e a t o t h e n o r t h e a s t  with the ultrabasic  rocks o f the Shulaps  probably and may  Range.  Lithology All  specimens  examined a r e s e r p e n t i n i z e d h a r z b u r g i t e .  I n most o f them m e d i u m - t o - c o a r s e - g r a i n e d or b a s t i t e  i s s e t i n a b l a c k o r dark  light  green  enstatite  o l i v e - g r e e n groundmass  A p a r t l y s e r p e n t i n i z e d s p e c i m e n has approximately the following composition o f primary m i n e r a l s : 66$ 30$ 2fo 1$  olivine enstatite clinopyroxene chromite The seriate.  texture o f the rock  i s allotriomorphic-  The o l i v i n e i s a n h e d r a l and r e l a t i v e l y f i n e g r a i n e d , r a n g i n g a p p r o x i m a t e l y f r o m . 5 t o . 2 mm i n s e c t i o n a l diameter. The c o m p o s i t i o n o f t h e m i n e r a l i s Fa^o ( y - 1 . 6 7 4 ) . Some g r a i n s c o n t a i n i n c l u s i o n s o f chromite. n  The e n s t a t i t e E n c ^ ( n - 1 . 6 7 0 ) i s s u b h e d r a l o r a n h e d r a l and r a n g e s i n g r a i n s i z e a p p r o x i m a t e l y f r o m one c e n t i m e t e r t o one h a l f m i l l i m e t e r . I t has i n c l u s i o n s o f c l i n o p y r o x e n e t h a t a r e o r i e n t e d p a r a l l e l to the o p t i c plane o f the host. Two t y p e s o f i n c l u s i o n s c a n be r e c o g n i z e d : l a m e l l a e o f u n i f o r m w i d t h ( . 0 2 5 mm x . 5 mm) and s p i n d l e s h a p e d o r i r r e g u l a r p a t c h e s ( e . g . .4 x . 8 mm). A l l i n c l u s i o n s w i t h i n a s i n g l e g r a i n have t h e same c r y s t a l l o g r a p h l c o r i e n t a t i o n . The o r i e n t a t i o n o f t h e i n c l u s i o n s I s n o t t h e same as t h a t o f t h e host but i n c e r t a i n s e c t i o n s t h e e x t i n c t i o n p o s i t i o n o f g u e s t and h o s t c o i n c i d e . The b i r e f r i n g e n c e o f the i n c l u s i o n s d e c r e a s e s from t h e i r c e n t r e toward y  145 t h e i r o u t e r m a r g i n ; as many as t e n d i f f e r e n t zones o f d i s t i n c t i n t e r f e r e n c e c o l o r can be o b s e r v e d . C l i n o p y r o x e n e a l s o o c c u r s as i n d i v i d u a l g r a i n s t h a t p r o b a b l y have t h e c o m p o s i t i o n o f d i o p s i d e , (ny = 1.678). The g r a i n s a r e s u b h e d r a l t o a n h e d r a l and o f s m a l l e r s i z e than t h e o r t h o p y r o x e n e . Their s e c t i o n a l diameter l i e s between one and one h a l f millimeter. The c h r o m i t e i s opaque on b r o w n i s h t r a n s l u c e n t and a n h e d r a l . I t i s r e l a t i v e l y f i n e - g r a i n e d , r a n g i n g from about one q u a r t e r t o one e i g h t h o f a m i l l i m e t e r i n s e c t i o n a l diameter. 3.  Serpentinization Most o f t h e u l t r a b a s i c r o c k s a r e s t r o n g l y o r c o m p l e t e l y  serpentinized;  t h e l e a s t a l t e r e d specimen seen c o n s i s t s o f  about 65$ s e r p e n t i n e . The  t h r e e main s i l i c a t e s a r e a f f e c t e d d i f f e r e n t l y by  the s e r p e n t i n i z a t i o n .  The d i o p s i d e  completely serpentinized  i s l i t t l e altered.  Some  c r y s t a l s o f e n s t a t i t e c o n t a i n un-  altered inclusions of diopside. Most o f t h e e n s t a t i t e i s p a r t l y o r c o m p l e t e l y r e p l a c e d by a n t i g o r i t e .  The s e r p e n t i n i z a t i o n has p r o g r e s s e d from t h e  m a r g i n and from c l e a v a g e s and t h e b l a d e s o f a n t i g o r i t e l i e approximately p a r a l l e l to the cleavage o f the host. The  o l i v i n e i s s t r o n g l y a f f e c t e d by t h e s e r p e n t i n i z a t i o n .  Replacement from t h e m a r g i n and from f r a c t u r e s has produced two  t y p e s o f mesh s t r u c t u r e s .  I n the f i r s t type "serpophite"  i s surrounded by a few b l a d e s o f a n t i g o r i t e .  I n some specimens  the a n t i g o r i t e shows v e r y r o u g h l y a p r e f e r r e d  o r i e n t a t i o n which  may be t h e r e s u l t o f s t r e s s , (Leech, 1953» p. 3 2 ) .  I n others  the s e r p o p h i t e i s surrounded by one o r s e v e r a l l a y e r s o f v e r y  146 f i n e f i b r e s t h a t grow p e r p e n d i c u l a r l y to the w a l l s o f serpophite core.  The  fibres  are p o s s i b l y " c h r y s o t i l e " .  the  ( l e n g t h s l o w , low b i r e f r i n g e n c e ) The  i n t e r s t i c e s between c h r y s o t i l e  l a y e r s c o n t a i n m a t e r i a l t h a t i s i s o t r o p i c or has low  bire-  f r i n g e n c e t o g e t h e r w i t h g r a i n s o f an opaque m i n e r a l w h i c h i s probably  secondary m a g n e t i t e .  These g r a i n s range from a  f r a c t i o n o f a m i c r o n i n s i z e to l a r g e r , v e i n - l i k e a g g r e g a t e s r a n g i n g up to .4 mm The  i n l e n g t h and  " s e r p o p h i t e " and  .02 mm  i n width.  some o f the f i b r o u s s e r p e n t i n e  c o n t a i n minute a c i c u l a r i n c l u s i o n s w h i c h range from .005 .03 mm  i n l e n g t h and a r e a p p r o x i m a t e l y  .001 mm  thick.  to The  i n c l u s i o n s are a l s o found i n the m a r g i n a l zones o f o l i v i n e g r a i n s but never i n the core o f t h a t m i n e r a l .  These o u t e r  zones a p p a r e n t l y have been a l t e r e d as t h e y show a lower b i r e f r i n g e n c e t h a n the i n n e r p a r t o f the g r a i n s . The and 1.53.  r e f r a c t i v e i n d i c e s o f t h e m i n e r a l l i e between I t may  serpentine.  be s e p i o l i t e , a m i n e r a l w h i c h o c c u r s  S e p i o l i t e a s s o c i a t e d w i t h t a l c was  4.  (Bowen and T u t t l e 1949,  p.  in  synthesized  Bowen and T u t t l e at temperatures around 350° C and a o f 15,000 l b s . / i n .  1.51  by  pressure  443).  Carbonate-Silica-Alteration On  the r i d g e n o r t h e a s t  o f Town Creek the s e r p e n t i n i z e d  u l t r a b a s i c r o c k s have been r e p l a c e d by c a r b o n a t e and  quartz.  The  cliffs.  a l t e r e d r o c k s form c o n s p i c u o u s ,  r u s t y weathering  I n some specimens from these o u t c r o p s are preserved  remnants o f  serpentine  but i n o t h e r s o n l y the presence o f c h r o m i t e i n -  d i c a t e s t h a t the r o c k s o r i g i n a l l y were u l t r a b a s i c .  147 The c o m p o s i t i o n o f the carbonate l i e s near the boundary o f magnesian d o l o m i t e and p a r a n k e r i t e (ng-1.699).  It is  p r e s e n t i n a network o f v e i n l e t s t h a t e n c l o s e s q u a r t z and nodules o f carbonate some o f w h i c h i n c l u d e a few f i n e g r a i n s of " i r o n ore".  The c e n t r e o f the v e i n l e t s c o n t a i n much secon-  dary " i r o n o x i d e " .  I n some specimens the carbonate i s cut by  v e i n l e t s of quartz. (Plate X X I ) . 5.  Age and O r i g i n Because o f i n s u f f i c i e n t exposure  the n a t u r e o f the  c o n t a c t s and the i n t e r n a l s t r u c t u r e o f the u l t r a b a s i c r o c k s are unknown.  However, the f o l l o w i n g o b s e r v a t i o n s may  b e a r i n g on t h e i r age and (1)  have some  origin.  The u l t r a b a s i c r o c k s occupy a zone between  T r i a s s i c o r e a r l i e r r o c k s t o the west and the L i l l o o e t group t o the east w h i c h s o u t h o f the p r e s e n t map c o n t a c t . ( D u f f e l l and McTaggart, 1953, (2)  27).  Other u l t r a b a s i c i n t r u s i o n s i n the map  o n l y i n r o c k s o f the P a v i l i o n (3)  p.  area are i n f a u l t  area occur  group.  The s e r p e n t i n i t e s a r e on s t r i k e and p o s s i b l y  con-  t i n u o u s w i t h the u l t r a m a f i c complex o f the Shulaps Range to w h i c h they bear a c l o s e l i t h o l o g i c a l resemblance.  Leech  found  t h a t the main mass o f the i n t r u s i o n s i n the Shulaps Range c u t s Upper T r i a s s i c s t r a t a , and he observed c h r o m i t e , p r o b a b l y d e r i v e d from these i n t r u s i o n s , i n Lower J u r a s s i c (p.39).  sediments,  He i n f e r r e d t h a t the u l t r a b a s i c r o c k s were emplaced  i n the Upper T r i a s s i c .  148 (4)  I n t r u s i o n s o f s i m i l a r l i t h o l o g y a r e wide  spread  i n B r i t i s h Columbia and a t t r i b u t e d by W h i t e t o the Upper T r i a s s i c C a s s i a r orogeny (White, 1959). Because o f the l a s t t h r e e p o i n t s i t i s thought t h a t the s e r p e n t i n i t e s west o f L i l l o o e t a r e o f an o r i g i n a l Upper T r i a s s i c age.  T h e i r a s s o c i a t i o n w i t h the r e g i o n a l f a u l t  be e x p l a i n e d i n two ways.  E i t h e r they a r e i n i n t r u s i v e  w i t h Cache C r e e k - t y p e o f r o c k s to t h e west and  the  o r t h e u l t r a b a s i c r o c k s , o r i g i n a l l y emplaced i n the  Taliaferro  Triassic,  concept was  "Cold i n t r u s i o n s " have been d e s c r i b e d  (1943, p. 205)  squeezed by  and Thayer, (1948, p. 64-65), and  r e f e r r e d to the F r a s e r R i v e r f a u l t zone by  and McTaggart (1953, p. 76), and (1953, p.  contact  faulting,  were r e m o b i l i z e d i n o r a f t e r the Lower C r e t a c e o u s and i n t o the f a u l t .  contact  in fault  w i t h the L i l l o o e t group to the east and a n t e d a t e  can  Duffell  to the S h u l a p s Range by Leech,  39).  PERIDOTITE INTRUDING THE  PAVILION GROUP  At a few l o c a l i t i e s s e r p e n t i n i z e d dykes were seen to i n t r u d e D i v i s i o n s I and  the  I I o f the Cache Creek group.  A hand specimen from a dyke exposed on the east bank o f t h e F r a s e r R i v e r , a p p r o x i m a t e l y one m i l e n o r t h o f the mouth o f S i w a s h C r e e k , i s r e d d i s h brown on weathered s u r f a c e s , b l a c k to o l i v e green on f r e s h s u r f a c e s , and f i n e - g r a i n e d . About 15$ o f the p r i m a r y m i n e r a l s are c l i n o pyroxene ( e n d i o p s i d e ? ny - 1.675), t h e balance c o n s i s t s o f f o r s t e r i t e (+2v l a r g e r t h a n 87°) and a s m a l l amount o f a b r o w n i s h opaque m i n e r a l w h i c h i s probably chromite. The e n d i o p s i d e i s s u b h e d r a l and the o l i v i n e and the c h r o m i t e a r e a n h e d r a l . The g r a i n s i z e i s near .5 mm.  S e r p e n t i n i z a t i o n has produced  a mesh s t r u c t u r e  s i s t i n g o f o l i v i n e o r s e r p o p h i t e cores surrounded  by  con-  relative-  l y broad b l a d e s o f a n t i g o r i t e t h a t l i e i n s u b p a r a l l e l o r i e n tation.  The c l i n o p y r o x e n e has been a f f e c t e d by the  t i n i z a t i o n t o a much l e s s e r e x t e n t t h a n the o l i v i n e . i s a l s o some carbonate  serpenThere  replacement.  As these dykes cut r o c k s t h a t a r e p o s s i b l y o f Lower T r i a s s i c age but have not been seen i n t h e a d j a c e n t Lower Cretaceous limits.  s t r a t a t h e i r age may  l i e anywhere between t h o s e  L i t h o l o g i c a l l y they a r e not i d e n t i c a l w i t h t h e  b a s i c r o c k s west o f L i l l o o e t .  ultra-  But as the emplacement o f u l t r a -  b a s i c r o c k s i s a r a r e event i n the h i s t o r y o f a s m a l l a r e a i t i s l i k e l y t h a t t h e s e dykes a r e contemporaneous w i t h the masses near L i l l o o e t and i n t h e Shulaps Range.  T h e r e f o r e they a r e  t e n t a t i v e l y r e f e r r e d t o t h e Upper T r i a s s i c .  COAST INTRUSIONS 1. 1.  EARLY LOWER CRETACEOUS OR OLDER  Distribution I n the p r e s e n t a r e a d i o r i t i c r o c k s c o n s i d e r e d t o be  e a r l y Lower Cretaceous o r o l d e r a r e t h e most abundant o f the igneous r o c k s a s s i g n e d to Coast  Intrusions.  A s t o c k u n d e r l i e s Mount M a r t l e y on the s o u t h e a s t e r n edge o f t h e map  a r e a , (see F i g u r e 6)  A n o t h e r , about 5 m i l e s  l o n g and up t o 2 m i l e s w i d e , extends from t h e mouth o f KellyCreek t o Leon Creek. of P a v i l i o n .  P a r t s o f a s m a l l s t o c k a r e exposed  The p r e s e n t map ( F i g u r e 1) suggests  south  that i t i s  l e s s e x t e n s i v e than i n d i c a t e d on p r e v i o u s maps, and i n s t e a d o f one l a r g e mass a number o f s m a l l i n t r u s i o n s a r e shown.  Some o f  these may be o f f - s h o o t s o f a s t o c k o r b a t h o l i t h h i d d e n a t depth. A zone o f s m a l l i n t r u s i o n s extends from P a v i l i o n t o K e l l y Creek. A r e l a t i v e l y s m a l l p l u g u n d e r l i e s t h e s l o p e s a t t h e n o r t h end o f P a v i l i o n Lake.  I n t h e n o r t h e r n p a r t o f t h e a r e a t h e Coast  I n t r u s i o n s a r e r e p r e s e n t e d o n l y by a d y k e - l i k e mass on t h e lowest p a r t o f B i g B a r Creek w h i c h i s about one m i l e l o n g and a few hundred f e e t w i d e . 2.  Lithology The  i n t r u s i o n s a r e composed o f d i o r i t e , q u a r t z  g r a n o d i o r i t e , and d a c i t e . type.  diorite,  Quartz d i o r i t e i s t h e commonest r o c k  The p l u t o n i c r o c k s have a h y p i d i o m o r p h i c  t e x t u r e and a r e m o s t l y medium-grained.  equigranular  Many o f t h e dyke  rocks are p o r p h y r i t i c . The hornblende, men.  e s s e n t i a l minerals present a r e p l a g i o c l a s e , quartz, and b i o t i t e ; a u g i t e was n o t i c e d o n l y i n one s p e c i -  " I r o n o r e " c o n s t i t u t e s up t o 2% o f t h e r o c k .  Apatite i s  c o m p a r a t i v e l y common as an a c c e s s o r y m i n e r a l , and z i r c o n and sphene a r e r a r e . mafic  silicates.  One dyke r o c k c o n t a i n s m u s c o v i t e but no  The p l a g i o c l a s e i s m o s t l y s u b h e d r a l , zoned, and twinned; the z o n i n g i s most commonly o f t h e normal o s c i l l a t o r y  type.  The m i n e r a l c o n t a i n s i n c l u s i o n s o f s e r i c i t e , e p i d o t e , and carbonate.  P o t a s s i c f e l d s p a r , i f p r e s e n t a t a l l , forms l e s s  t h a n one per cent o f t h e r o c k s . The hornblende  i s s u b h e d r a l and some g r a i n s a r e twinned.  I t shows pronounced p l e o c h r o i s m being dark green i n t h e zd i r e c t i o n and p a l e b r o w n i s h green i n t h e x - d i r e c t i o n .  The  b i o t i t e i s a n h e d r a l o r s u b h e d r a l and brown o r green i n c o l o r . B o t h hornblende  and b i o t i t e c o n t a i n i n c l u s i o n s o f  " i r o n o r e " and a p a t i t e and a r e i n many specimens p a r t l y o r c o m p l e t e l y r e p l a c e d by  chlorite.  The q u a r t z i s a n h e d r a l and most g r a i n s a r e f r e e from inclusions. T a b l e 4 shows t h e range i n t h e c o m p o s i t i o n o f the rocks.  I t seems t o be t r u e i n a g e n e r a l way t h a t t h e p l a g i o -  c l a s e becomes more s o d i c and t h a t t h e percentage  of mafic  m i n e r a l s decreases as t h e content o f q u a r t a i n c r e a s e s ; but there are exceptions. Near t h e c o n t a c t s w i t h r o c k s o f t h e P a v ' l l i o n . g r o u p „ the Coast i n t r u s i o n s a r e l o c a l l y contaminated r e l a t i v e l y h i g h p r o p o r t i o n o f hornblende.  and c o n t a i n a  "TABLE 4 MINERAL COMPOSITION OF 8 SPECIMENS FROM COAST INTR' IONS, EARLY LOWER CRETACEOUS OR OLDER Locality  Composition o f plagioclase  % of Quartz  f of mafic minerals 0  Classification o f rock  Dyke on lower B i g Bar Creek  C a l c i c andesine, zoned  6  35  diorite  S o u t h o f mouth o f K e l l y Creek  Zoned from c a l c i c o l i g o c l a s e to sodic l a b r a d o r i t e  5  26  diorite  P l u t o n , southeast of P a v i l i o n , east side  altered to a l b i t e  8  27  d i o r i t e , transi t i o n a l to quartz-diorite  Dyke near Moran  C a l c i c andesine, zoned  11  25  quartz-diorite  P l u t o n between Leon Creek and K e l l y Creek  Intermediate a n d e s i n e , zoned  23  12  quartz-diorite  Stack., s o u t h e a s t o f P a v i l i o n , west s i d e  Zoned from s o d i c to i n t e r m e d i a t e andesine  33  22  quartz-diorite  Mount M a r t l e y S t o c k  Zoned from c a l c i c o l i g o c l a s e to sodic andesine  30  19  quartz-diorite, t r a n s i t i o n a l to granodiorite  Stack.: a t n o r t h end o f P a v i l i o n Lake  Zoned from c a l c i c o l i g o c l a s e to sodic andesine  32  13  quartz-diorite t r a n s i t i o n a l to granodiorite  153  3.  Associated M i n e r a l i z a t i o n S m a l l s u l f i d e d e p o s i t s are a s s o c i a t e d w i t h  i n t r u s i o n s i n many l o c a l i t i e s  but o n l y the B i g S l i d e Mine  (Ml) near the mouth o f K e l l y Creek w h i c h operated months i n 1887 p r o p e r t y was  for a  has been o f some economic i m p o r t a n c e .  i n s p e c t e d by G.M.  Dawson i n 1887  and by  Richmond o f the B.C.D epartment o f Mines i n 1932. a t i o n o f a l l p r e v i o u s r e p o r t s was (p. 103  these  A  few  The A.M. compil-  g i v e n by D u f f e l l and McTaggart  f . ) . The m i n e r a l i z a t i o n here c o n s i s t s o f p y r i t e ,  pyrrhotite, arsenopyrite, chalcopyrite, marcasite, l i m o n i t e , n a t i v e gold, and c a r b o n a t e i n two p i n c h i n g and  s w e l l i n g quartz  v e i n s t h a t are up to 4 f e e t wide and have an average t h i c k n e s s of eight inches.  The  host r o c k i s a s m a l l d i o r i t i c mass t h a t  i n t r u d e s c h e r t , a r g i l l i t e , and minor v o l c a n i c r o c k s o f D i v i s i o n I o f the P a v i l i o n group. vicinity,  S o u t h o f K e l l y Creek, i n the same  another s m a l l d e p o s i t was  short l e v e l s .  e x p l o r e d by a s h a f t and  two  The w r i t e r noted some p y r i t e , b o r n i t e , m a l a c h i t e  and a z u r i t e i n an abundant gangue o f q u a r t z and c a r b o n a t e on a s u r f a c e dump. Disseminated  p y r i t e and a r s e n o p y r i t e form r u s t y zones  i n the d i o r i t e o u t c r o p s i t e , and  on T i f f i n Creek and  i n chert, a r g i l l -  d i o r i t e on the upper p a r t o f S a l l u s Creek. A specimen o f b o r n i t e shown to the w r i t e r was  s a i d to  have been c o l l e c t e d on the upper p a r t o f S i w a s h Creek near the c o n t a c t between g r a n i t i c dykes and  limestone.  S m a l l amounts o f  copper m i n e r a l s have been found i n the p l u t o n south o f Leon Creek.  4.  S t r u c t u r e , Mode o f O r i g i n A l t h o u g h e l o n g a t e masses are p a r a l l e l to the  strike  o f the host r o c k s the i n t r u s i o n s l o c a l l y cut a c r o s s the p r e e x i s t i n g s t r u c t u r e s . F o l i a t i o n s and l i n e a t i o n s a r e r a r e l y apparent.  The major r e g i o n a l f a u l t s pass around the p l u t o n i c  masses, but minor zones o f s h e a r i n g and a l t e r a t i o n a r e present  locally. That the q u a r t z - d i o r i t e has been emplaced by  and not by p r o c e s s e s o f g r a n i t i z a t i o n i s suggested  intrusion  by  the  c r o s s c u t t i n g r e l a t i o n o f the g r a n i t i c r o c k s and the v e r y grade o f r e g i o n a l metamorphism i n the c o u n t r y r o c k s s h a l l o w depth o f emplacement.  low  suggesting  C r y s t a l l i z a t i o n from a magma i s  a l s o i n d i c a t e d by the o s c i l l a t o r y normal z o n i n g o f the p l a g i o clase. 5.  Age The r o c k s i n t r u d e D i v i s i o n s I and I I o f the Cache  Creek group and t h e r e f o r e they a r e not o l d e r than T r i a s s i c . They were not observed  i n i n t r u s i v e c o n t a c t w i t h the Spences  B r i d g e group or the K i n g s v a l e group o f mid-Lower Cretaceous I t i s a l s o p r o b a b l e t h a t they were emplaced b e f o r e the  age  earliest  movement on f a u l t "e" o f the F r a s e r R i v e r f a u l t zone, (see F i g ure 6, p.168) w h i c h i s thought e a r l y Lower  to have t a k e n p l a c e i n the  Cretaceous.  I n the present map-area t h i s group o f Coast I n t r u s i o n s cannot be d i s t i n g u i s h e d l i t h o l o g i c a l l y from the e a r l y Lower Cretaceous  q u a r t z - d i o r i t e t h a t i n t r u d e s the L i l l o o e t  group.  McTaggart and D u f f e l l , however, c o r r e l a t e them w i t h the Mount  L y t t o n b a t h o l i t h and p r e s e n t c o r r e l a t i o n (see page 176).  s t r u c t u r a l s t u d i e s support  this  D u f f e l l and McTaggart suggest  t h a t t h e Mount L y t t o n b a t h o l i t h i s o l d e r than t h e i n t r u s i o n s west o f t h e F r a s e r R i v e r and perhaps contemporaneous w i t h t h e Guichon Creek b a t h o l i t h , and r e f e r i t t o t h e J u r a s s i c ( p . 81).  II. 1.  EARLY LOWER CRETACEOUS  Distribution The  Coast I n t r u s i o n s known t o be e a r l y Lower C r e -  taceous o c c u r as dykes and s i l l s  i n t h e L i l l o o e t group.  The  l a r g e s t o f these i n t r u s i o n s i s a l e n t i c u l a r p l u t o n about 1/2 m i l e l o n g and s e v e r a l hundred f e e t wide w h i c h i s exposed on t h e east s i d e o f t h e F r a s e r R i v e r near t h e r a i l r o a d b r i d g e i n t h e v i c inity of Lillooet. 2.  Lithology All  specimens examined a r e q u a r t z - d i o r i t e o r d a c i t e .  Coarse o r medium-grained r o c k s have a h y p i d i o m o r p h i c  granular  t e x t u r e but p o r p h y r i t i c types c o n s i s t o f medium- t o c o a r s e grained phenocrysts  i n a f i n e - g r a i n e d o r a p h a n i t i c groundmass.  Some r o c k s a r e e n t i r e l y a p h a n i t i c . A specimen from t h e l e n t i c u l a r s i l l - l i k e p l u t o n near the r a i l r o a d b r i d g e n o r t h e a s t o f L i l l o o e t i s composed o f t h e f o l l o w i n g primary  minerals:  156  Feldspar quartz hornblende biotite "iron ore", apatite, sphene  70$ 21$  8$ 1$  trace  The f e l d s p a r c o n s i s t s d o m i n a n t l y o f subh e d r a l s o d i c a n d e s i n e t h a t i s twinned and shows normal or o s c i l l a t o r y normal z o n i n g . O r t h o c l a s e w h i c h i s s u b h e d r a l or a n h e d r a l makes up o n l y a s m a l l f r a c t i o n o f the t o t a l f e l d s p a r . Some o f the f e l d s p a r i s s t r o n g l y s e r i c i t i z e d . Most o f the hornblende i s s u b h e d r a l . The m i n e r a l i s dark green i n the z - d i r e c t i o n . The b i o t i t e i s s u b h e d r a l or a n h e d r a l and p l e o c h r o i c i n browns. The q u a r t z i s a n h e d r a l and r e l a t i v e l y f r e e from i n c l u s i o n s . As a l t e r a t i o n m i n e r a l s s e r i c i t e , and c h l o r i t e a r e f a i r l y abundant.  carbonate,  The t e x t u r e o f the r o c k i s g r a n i t i c and t h e s i z e o f the e s s e n t i a l m i n e r a l s ranges from 2.5 mm t o 1 mm. The p h e n o c r y s t s o f dyke r o c k s c o n s i s t o f p l a g i o c l a s e w h i c h commonly i s zoned a n d e s i n e . as p h e n o c r y s t s .  Hornblende  and q u a r t z a r e r a r e  The groundmess o f t h e p o r p h y r i e s c o n t a i n s i n  a d d i t i o n t o t h e s e m i n e r a l s b i o t i t e , and i n some specimens muscovite. H i g h l y a l t e r e d r o c k s found i n the v i c i n i t y o f major f a u l t s a r e r i c h i n c h l o r i t e , m u s c o v i t e , c a r b o n a t e , and p r e h n i t e . 3.  Age G r a n i t i c dykes a r e abundant i n the lower and  middle  p a r t o f t h e L i l l o o e t group w h i c h are t i g h t l y f o l d e d but  lacking  i n t h e f l a t l y i n g upper p a r t , D i v i s i o n C, and v e r y s c a r c e i n the J a c k a s s Mountain group.  I t i s p o s s i b l e t h a t the  intrusion  t o o k p l a c e s h o r t l y a f t e r the d e p o s i t i o n o f the sediments  and  was  157  n e a r l y contemporaneous w i t h the main p e r i o d o f f o l d i n g .  The  age o f t h e s e q u a r t z - d i o r i t e s p r o b a b l y i s e a r l y Lower C r e t a c e o u s .  III. 1.  LATE BARREMIAN  Distribution The Coast I n t r u s i o n s o f t h i s group occur o n l y as dykes o r  s m a l l p l u g s i n the J a c k a s s Mountain c e n t r a l p a r t s o f the map exposed  group.  a r e a they a r e r a r e .  I n the s o u t h e r n and A few dykes a r e  on the n o r t h s i d e o f t h e F r a s e r R i v e r o p p o s i t e the mouth  o f F o u n t a i n Creek.  Between F o u n t a i n and the mouth o f B r i d g e  R i v e r s e v e r a l zones o f carbonate a l t e r a t i o n a r e v i s i b l e on the shores o f the F r a s e r R i v e r some o f w h i c h are a s s o c i a t e d w i t h s m a l l g r a n i t i c dykes.  S i m i l a r zones o f a l t e r a t i o n i n t h e v i c i n -  i t y o f Lee Creek and B l a c k h i l l Creek t h a t a p p a r e n t l y are not r e l a t e d t o major f a u l t s may depth.  i n d i c a t e i n t r u s i v e bodies a t g r e a t e r  I n the n o r t h e r n p a r t o f the map-area, i n the v i c i n i t y o f  Watson Bar Creek, g r a n i t i c r o c k s a r e more abundant.  The  largest  o f t h e s e i n t r u s i o n s i s shown on F i g u r e 1. 2.  Lithology L i t h o l o g i c a l l y t h e s e dykes do not d i f f e r from the  two  o t h e r groups o f Coast i n t r u s i o n s i n the a r e a ; they a r e p o r phyritic quartz-diorites.  A t y p i c a l specimen has  coarse  p h e n o c r y s t s o f zoned andesine and a f i n e - g r a i n e d groundmass cons i s t i n g o f p l a g i o c l a s e , q u a r t z , h o r n b l e n d e , b i o t i t e , and minor orthoclase.  " I r o n o r e " and a p a t i t e were noted as a c c e s s o r i e s .  158 Secondary m i n e r a l s p r e s e n t are s e r i c i t e , e p i d o t e , c h l o r i t e , and  carbonate. A dyke w h i c h p r o b a b l y l i e s i n the immediate v i c i n i t y  o f f a u l t "d" o f the F r a s e r R i v e r f a u l t zone has been a l t e r e d completely.  The p l a g i o c l a s e has been a l t e r e d to a l b i t e  e p i d o t e and the m a f i c m i n e r a l s to c h l o r i t e . e x t e n s i v e l y r e p l a c e d by 3.  and  The r o c k i s  carbonate.  Associated Mineralization On the upper p a r t o f S t i r r u p Creek f o u r s m a l l ( e p i t h e r -  mal?) d e p o s i t s o f s t i b n i t e , c i n n a b a r , g o l d , w e h r l i t e ,  and  b a r i t e ( P r o f e s s o r H.V.Warren, p e r s o n a l communication) i s a s s o c i a t e d w i t h p o r p h y r i t i c q u a r t z d i o r i t e t h a t has i n t r u d e d l i t h i c sandstone o f D i v i s i o n C o f the J a c k a s s Mountain group The m i n e r a l s o c c u r i n q u a r t z v e i n s t h a t cut b l e a c h e d ritic  porphy-  q u a r t z - d i o r i t e and s t r o n g l y c a r b o n a t i z e d c o u n t r y r o c k .  Occurrences  o f t h i s type a r e p r o b a b l y the source o f the numerous  g o l d p l a c e r s on S t i r r u p Creek ( o u t s i d e the map 4.  (M2).  area).  Age As these dykes i n t r u d e D i v i s i o n C o f the  M o u n t a i n group but have not been found  Jackass  i n the Spences B r i d g e  group o r K i n g s v a l e group they p r o b a b l y were emplaced i n the l a t e Barremian.  They are the youngest Coast I n t r u s i o n s known  i n the g e n e r a l a r e a .  159  GABBRO AND DIABASE NEAR LILLOOET 1.  Distribution, Structure  Gabbros and d i a b a s e s a r e exposed f o r about 6 m i l e s between a p o i n t on t h e west bank o f t h e F r a s e r R i v e r about 2 m i l e s s o u t h e a s t o f L i l l o o e t and t h e head o f Town Creek on t h e r i d g e northwest o f L i l l o o e t . separated  The o u t c r o p s a r e m o s t l y  s m a l l and  by expanses o f overburden; l a r g e r masses a r e ex-  posed o n l y i n t h e v i c i n i t y o f t h e power house on S e t o n Creek. I t i s n o t known whether t h e o u t c r o p s a r e connected and thus form one l a r g e i n t r u s i o n o r whether they r e p r e s e n t numerous s m a l l i n t r u s i o n s . The  b e l t as a whole s t r i k e s a p p r o x i m a t e l y  N 30° W and  forms t h e e a s t e r n m a r g i n o f a zone o c c u p i e d d o m i n a n t l y by ultrabasic rocks.  To t h e east t h e i n t r u s i o n s a r e p o s s i b l y i n  f a u l t c o n t a c t w i t h t h e L i l l o o e t group, but t h i s c o n t a c t i s nowhere exposed. 2. The  Lithology  r o c k s on t h e east shore o f t h e F r a s e r R i v e r , o u t -  s i d e o f t h e map-area have n o t been s t u d i e d d u r i n g t h e p r e s e n t investigation.  According  t o B r o c k (1956) they a r e hypersthene  gabbros t h a t show d i f f e r e n t i a t i o n . The  i n t r u s i o n s on t h e west s i d e a r e g r e y i s h g r e e n , med-  ium- t o f i n e - g r a i n e d , and show no s t r a t i f i c a t i o n . l y a l t e r e d , and t h e i r o r i g i n a l c o m p o s i t i o n  They a r e h i g h -  i s recognizable only  i n a few specimens t h a t range from b r o n z i t e gabbro t o a u g i t e diorite.  160  A l l specimens c o n t a i n a u g i t e w h i c h shows no v a r i a t i o n i n composition. "hour g l a s s " s t r u c t u r e . pyroxene was  I n one t h i n - s e c t i o n the a u g i t e has I n two out o f n i n e t e e n specimens o r t h o -  recognized.  o t h e r one h y p e r s t h e n e ,  systematic  I n one specimen i t was  b r o n z i t e i n the  but the two m i n e r a l s p r o b a b l y do  d i f f e r i n c o m p o s i t i o n by more than 5$ o f the e n s t a t i t e I n some o f the o t h e r r o c k s o r t h o p y r o x e n e  may  not molecule.  have been p r e s e n t  o r i g i n a l l y but p r o b a b l y has been r e p l a c e d by m i n e r a l s o f the chlorite  group.  Only i n two specimens the o r i g i n a l p l a g i o c l a s e  appears to be p r e s e r v e d . l i e s near A n g o andesine  I n the b r o n z i t e gabbro i t s c o m p o s i t i o n  I n the a u g i t e d i o r i t e i t i s zoned from c a l c i c  to c a l c i c o l i g o c l a s e .  But as the cores o f many p l a g i o -  c l a s e c r y s t a l s i n t h i s r o c k are h i g h l y a l t e r e d they may a more c a l c i c c o m p o s i t i o n o r i g i n a l l y . r o c k s c o n t a i n hornblende t h i s m i n e r a l of primary  A l t h o u g h most o f the  perhaps o n l y i n the a u g i t e d i o r i t e i s origin.  The d i f f e r e n c e s between the b a s i c and a c i d i c apparent  i n the f o l l o w i n g  table:  b ronzite-gabbro plagioclase augite bronzite c h l o r i t e group, r e p l a c i n g ( b r o n z i t e ?) "iron ore" augite  have had  50% 37%  5%  6% 2%  diorite  plagioclase augite hornblende c h l o r i t e group "iron ore"  60$  30$ 8$  1$ 1$  types i s  161  T a b l e 5 shows t h e d e t e r m i n a t i o n s o f the main primarym i n e r a l s i n 4 c h a r a c t e r i s t i c specimens. I t i s apparent  t h a t t h e s e gabbros are not u n i f o r m i n  c o m p o s i t i o n but owing t o t h e l a c k o f exposure  and the h i g h  degree o f a l t e r a t i o n the t r e n d s and mechanisms o f d i f f e r e n t i a t i o n c o u l d not be worked o u t . The o u t c r o p s n o r t h o f L i l l o o e t a r e o f medium- t o f i n e g r a i n e d gabbro and have a h y p i d i o m o r p h i c g r a n u l a r t e x t u r e . Most o f them a r e e q u i g r a n u l a r , but some a r e s e r i a t e . some o f t h e specimens the a u g i t e appears s t r a i n e d .  In The  o r i g i n a l t e x t u r e o f t h e r o c k s has been o b l i t e r a t e d t o a l a r g e e x t e n t by  alteration.  I n the o u t c r o p s on S e t o n Creek the degree o f a l t e r a t i o n i s even h i g h e r .  Some r o c k s seem t o have been f i n e -  g r a i n e d gabbros w i t h a h y p i d i o m o r p h i c g r a n u l a r t e x t u r e . specimens resemble v a r i o l i t i c texture.  o r i g i n a l d i a b a s e s ; one o f them shows a  Two  TABLE 5 MINERAL COMPOSITION OF 5 SPECIMENS OF ALTERED GABBROIC AND DIORITIC ROCKS Spec.  Qrtho-pyroxene, comp. x  Augite Composition  Measurements  Measurements  Hornblende  +  Plagioclase 'Composition H  14  En 89 t 1% bronzite  (+) h i g h 2v Ca Mg Fe 5 ny=1.6721.001 +2%  ny=1.684t .002 2v=49°  Absent  16  Magnesiam hvnershypersthene  t n Qf)0  (-)2v c l o s e  CaoyMgAoFe-j^  n =1.685t * .002 2v=44°  present A 40 but probably probably altered secondary  13  absent o r completely altered  Ca oMg 6Fe  n =1.6861  absent  12  4 1  absent o r altered  4  4 4  1 (  4  14  Measurement  v  y  y  .003  A 6lt n  n  nx  = 1.5591 .001 1  nx' 1.54721 .001  completely altered  2v=48° C a  4iyg4| 12  x  H.H.Hess and H . A . P h i l l i p s , (1940)  +  H.H.Hess, (1949)  4  R.M. Crump and K.H.Kettner, (1953)  F e  ny=1.685l  *  .002  present Zoned kxi2$replacing An^ augite  nx' =  1.5541.540  CN  ro  3.  Metamorphism and  I n 17 out o f 19  Alteration  specimens t h e p l a g i o c l a s e has been  a l t e r e d to a l b i t e and m i n e r a l s o f the e p i d o t e group among w h i c h p i s t a c i t e seems to be abundant.  The o r t h o p y r o x e n e  been r e p l a c e d p a r t l y o r c o m p l e t e l y by m i n e r a l s o f the group.  has  chlorite  A m i n e r a l o f t h a t group showing b l a d e d h a b i t , low  b i r e f r i n g e n c e , and p o s i t i v e e l o n g a t i o n p r o b a b l y i s a n t i g o r i t e . The a u g i t e i s b e t t e r p r e s e r v e d than the o t h e r m i n e r a l s but p a r t l y r e p l a c e d by m i n e r a l s o f the c h l o r i t e group, by  horn-  blende, or " i r o n ore". The r o c k s a r e r e p l a c e d by p r e h n i t e , c a r b o n a t e ,  and  l e s s commonly by t r e m o l i t e and p o s s i b l y the amphibole n e p h r i t e . As v e i n f i l l i n g p r e h n i t e , carbonate One  specimen i s m y l o n i t i z e d ; i n o t h e r s the a u g i t e  appears to be s t r a i n e d and  bent. 4.  The  and a l b i t e o c c u r .  Age  c o n t a c t s o f the gabbros were not seen.  An  indi-  c a t i o n o f t h e i r age i s g i v e n by the f o l l o w i n g o b s e r v a t i o n . E a s t o f F o u n t a i n C r e e k , i n the v i c i n i t y o f f a u l t "d" a specimen was  c o l l e c t e d t h a t i s composed o f c h l o r i t i z e d  pyroxene and hornblende strong s c h i s t o s i t y .  i n a m a t r i x o f p r e h n i t e and shows a  I t resembles the h i g h l y a l t e r e d gabbros  o r d i o r i t e s west o f L i l l o o e t . suggests  clino-  The o c c u r r e n c e o f these  rocks  t h a t they were i n t r u d e d i n t o major f a u l t zones and  164  therefore  a r e e a r l y Lower Cretaceous o r younger.  a l t e r a t i o n may have been produced by l a t e magmatic  Their solutions.  ANDESITIC AND BASIC DYKES A l l r o c k u n i t s , except f o r t h e M i d d l e o r L a t e T e r t i a r y o l i v i n e basalts are intruded b a s a l t i c dykes.  by a n d e s i t i c , d i a b a s i c o r  These dykes may range i n age from e a r l y  Mesozoic to Late T e r t i a r y . the accompanying map.  They a r e too s m a l l t o be shown on  165  CHAPTER I I THE FRASER RIVER FAULT ZONE 1.  Introduction A l t h o u g h Dawson (1895) c o n s i d e r e d  the s t r u c t u r e o f  the F r a s e r R i v e r a r e a as a s e r i e s o f t i g h t f o l d s he n o t i c e d the s h a t t e r e d and a l t e r e d n a t u r e o f t h e r o c k s i n many  local-  i t i e s and suggested t h a t some o f t h e major c o n t a c t s a r e f a u l t s . He d e s c r i b e d , f o r example, t h e s t r u c t u r e i n t h e v i c i n i t y o f S t e i n Creek as f o l l o w s : "but  i n t h i s v i c i n i t y , on b o t h s i d e s o f t h e r i v e r e n t i r e  masses o f t h e r o c k s have become reddened and decomposed by a c t i o n subsequent t o t h e i r d e p o s i t i o n .  The beds a r e a l l much  s h a t t e r e d , and l i n e s o f f a u l t i n g i n t h i s p l a c e undoubtedly r u n a l o n g t h e v a l l e y one o f w h i c h a p p a r e n t l y  bounds t h e C r e t a c e o u s  t r o u g h on the east s i d e o f t h e v a l l e y . " (p. 147 B, f . ) He s t a t e d o f t h e c o n t a c t o f t h e Jackass M o u n t a i n group w i t h t h e r o c k s o f t h e Spences B r i d g e group (which he  considered  t o be T e r t i a r y ) between McKay Creek and Leon Creek: "The  boundary between t h e C r e t a c e o u s r o c k s on t h e west  and v o l c a n i c T e r t i a r y r o c k s , i s here remarkably d i s t i n c t and s t r a i g h t , and f o l l o w s a well-marked v a l l e y w h i c h i s n e a r l y p a r a l l e l to that of the Fraser.  There i s some r e a s o n t o  suppose t h a t t h i s boundary may be a f a u l t e d one, but t h i s i s not so c e r t a i n . " ( p . 2 1 5 B . )  166 I n 1912 N.L.Bowen i n a r e c o n n a i s s a n c e survey o f t h e Fraser River valley  from L y t t o n t o Vancouver observed t h a t the  C r e t a c e o u s s t r a t a s o u t h o f L y t t o n occupy a grabben between g r a n i t i c rocks: "The  average s t r i k e o f t h e Cretaceous beds i s about N  15° W and t h e beds a r e commonly a t low a n g l e s , but c l o s e t o the g r a n i t e s the a t t i t u d e  may be n e a r l y o r q u i t e v e r t i c a l .  The g r a n i t e does n o t , however, g i v e any e v i d e n c e o f b e i n g i n trusive.  The r e l a t i o n shown i s due t o t h e down f a u l t i n g o f  the C r e t a c e o u s beds.  This part of the Fraser V a l l e y i s , i n  f a c t , excavated a l o n g a b e l t o f c o m p a r a t i v e l y s o f t i e s themselves  p r e s e r v e d by graben f a u l t i n g .  sedimentar-  The s t r i p s o f  P a l e o z o i c r o c k s , t o o , p r o b a b l y owe t h e i r p r e s e n t p o s i t i o n t o t h i s f a u l t i n g , f o r t h e s t r i k e o f t h e i r beds makes a sharp angle w i t h the e l o n g a t i o n o f the s t r i p s . " D u f f e l l and McTaggart c o r r o b o r a t e d Bowen's o b s e r v a t i o n t h a t i n t h e s o u t h e r n p a r t o f t h e A s h c r o f t a r e a the F r a s e r R i v e r C r e t a c e o u s b e l t o c c u p i e s a graben.  North o f  C i n q u e f o i l Creek however, they noted a s e r i e s o f f a u l t s i n w h i c h t h e r o c k s t o t h e west have been e l e v a t e d r e l a t i v e t o those i n the east.  They gave evidence o f i n t e r m i t t e n t  i t y from Lower Cretaceous to post-Eocene  activ-  time and showed t h a t  c a r b o n a t e , p r e h n i t e , and a l b i t e a l t e r a t i o n a r e a s s o c i a t e d w i t h the f a u l t zone.  As t h e p r o b a b l e cause o f t h e f a u l t i n g  suggested u p l i f t and t i l t i n g o f t h e Coast  they  Mountains.  Leech (1953) mapped a f a u l t zone i n t h e Yalakom a r e a  167  that i s probably  connected w i t h a major f a u l t d i s c o v e r e d  by  D u f f e l l and McTaggart near L i l l o o e t . McCammon and Wasmith (1956) d u r i n g a study o f p o s s i b l e dam  s i t e s on the F r a s e r R i v e r observed s e v e r a l f a u l t s i n the  n o r t h e r n p a r t s o f the p r e s e n t map-area w h i c h they c o n s i d e r e d be p o s s i b l e e x t e n s i o n s o f the F r a s e r R i v e r f a u l t zone o f Ashcroft  1953)  the  area. The  (1)  to  present  study has added the f o l l o w i n g i n f o r m a t i o n :  Those f a u l t s o f the A s h c r o f t sheet ( D u f f e l l and McTaggart t h a t are s i t u a t e d i n the p r e s e n t map  a r e a have been  mapped i n g r e a t e r d e t a i l but w i t h o u t major changes. (2)  I t i s shown t h a t the w e s t e r n c o n t a c t o f the  Pavilion  group i s another f a u l t o f the F r a s e r R i v e r f a u l t zone.  The  movement on t h i s f a u l t i s i n the o p p o s i t e sense t o t h a t o f  the  o t h e r f a u l t s o f the zone, showing a r e l a t i v e downward movement o f the w e s t e r n b l o c k .  The  s t r u c t u r e o f the p r e s e n t  map  a r e a t h e r e f o r e appears to be a complex graben.  I t i s suggested  t h a t f a u l t movements on t h i s graben c o n t r o l l e d  the d e p o s i t i o n o f  D i v i s i o n s B and C o f the J a c k a s s M o u n t a i n group. (3)  Another l o n g i t u d i n a l  f a u l t , the n a t u r e o f i t s movement  unknown, has been mapped w i t h i n the P a v i l i o n (4)  group.  I t i s shown t h a t the l a t e s t movement on one o f  longitudinal 2.  f a u l t s probably  the  took p l a c e i n M i d d l e T e r t i a r y  time.  D e s c r i p t i o n o f the F r a s e r R i v e r F a u l t Zone  The main branches o f the F r a s e r R i v e r f a u l t zone are shown on F i g u r e 6.  The main f a u l t s o f the zone t r e n d n o r t h -  LILLI  169 w e s t e r l y to n o r t h e r l y and a r e r e f e r r e d to as faults.  longitudinal  Faults trending w e s t e r l y , i n part apparently o f f s e t t -  i n g the l o n g i t u d i n a l f a u l t s , are r e f e r r e d to as c r o s s - f a u l t s . S i x major l o n g i t u d i n a l f a u l t s have been r e c o g n i z e d i n the map  area.  At l e a s t two o f them a r e c o n t i n u o u s  through-  out the a r e a and some o f them have been shown to extend f a r t o the s o u t h .  I t i s assumed t h a t o t h e r f a u l t s e x i s t but have not  been r e c o g n i z e d because o f t h i c k o v e r b u r d e n and l a c k o f o f f s e t i n the f o r m a t i o n s t r a n s e c t e d .  The  s t r i k e n o r t h w e s t e r l y to n o r t h e r l y , and, d e f l e c t i o n on the map  obvious  longitudinal faults  judged by t h e i r l a c k o f  i n c r o s s i n g r i d g e s or v a l l e y s , d i p  steeply. F a u l t " a " (see F i g u r e 6)  s e p a r a t e s the L i l l o o e t group  on the east from T r i a s s i c o r o l d e r r o c k s to the west.  The  f a u l t i s not exposed i n the map-area but has been seen f a r t h e r s o u t h ( D u f f e l l and McTaggart, 1953)  and i s p r o b a b l y  t o the n o r t h w i t h a major f a u l t i n the Yalokom a r e a 1953).  continuous (Leech,  I n the p r e s e n t map-area i t has a s s o c i a t e d w i t h i t s e r -  p e n t i n i z e d u l t r a b a s i c i n t r u s i o n s ^ gabbros and d i a b a s e w h i c h e i t h e r l o c a l i z e d the break o r i n t r u d e d the f a u l t zone. Fault  11  b" b r i n g s the L i l l o o e t group i n t o c o n t a c t w i t h  the J a c k a s s M o u n t a i n group.  I t has s e v e r a l branches near the  mouth o f B r i d g e R i v e r t h a t seem to converge t o a s i n g l e break to; ,the s o u t h and to the n o r t h .  The  f a u l t i s p o o r l y exposed  i , V  and- has no t o p o g r a p h i c e x p r e s s i o n on the w e s t e r n the Camelsfoot  Range and o f F o u n t a i n R i d g e .  slopes of  Where the  indiv-  i d u a l branches c r o s s F r a s e r R i v e r , the s t r a t a are d i s t u r b e d  over w i d t h s up to s e v e r a l hundred f e e t . F a u l t " c " d i v i d e s the J a c k a s s Mountain group i n t o main b l o c k s .  two  A l l t h r e e d i v i s i o n s o f the group a r e exposed i n  the w e s t e r n b l o c k but o n l y D i v i s i o n C i n the e a s t e r n b l o c k . Near F o u n t a i n S t a t i o n t h r e e c l o s e l y spaced branches were observed The  or i n f e r r e d but elsewhere o n l y one c o u l d be e s t a b l i s h e d .  e a s t e r n b r a n c h i s i n d i c a t e d by a narrow b e l t o f s t e e p l y  d i p p i n g and d i s t o r t e d s t r a t a east and n o r t h e a s t o f  Fountain  S t a t i o n a l o n g the west shore o f the F r a s e r R i v e r .  The  e r n b r a n c h i s marked by i n t e n s e l y s t a i n e d and sheared  westcliffs  few hundred f e e t above the road west o f F o u n t a i n S t a t i o n . c e n t r a l b r a n c h i s exposed o n l y on the shore o f the r i v e r p r o b a b l y c o n t i n u e s t o the s o u t h .  The but  I t truncates D i v i s i o n B  brings i t into contact w i t h a f a u l t s l i c e of D i v i s i o n  a  and  C.  F a u l t "d" forms the c o n t a c t o f D i v i s i o n C o f the J a c k a s s M o u n t a i n group w i t h v o l c a n i c r o c k s o f the  Fountain  V a l l e y assemblage, the upper D i v i s i o n o f the Spences B r i d g e group, and the Ward Creek assemblage.  The  f a u l t zone i s exposed  east o f F o u n t a i n Creek a t the s o u t h shore o f the F r a s e r R i v e r , and a g a i n n o r t h e a s t o f the mouth o f B l a c k h i l l Creek.  Several  minor f a u l t s p a r a l l e l w i t h f a u l t "d" occur near t h e mouth o f F o u n t a i n Creek.  Between the mouths o f Gibbs Creek and  Black-  h i l l C r e e k , on the west s i d e ' o f the F r a s e r R i v e r , the  strata  o f D i v i s i o n C, commonly f l a t - l y i n g or g e n t l y d i p p i n g , have been t i l t e d i n t o almost v e r t i c a l a t t i t u d e s f o r d i s t a n c e s o f at l e a s t o n e - h a l f m i l e west o f the f a u l t zone ( P l a t e X X I I ) .  Minor  es o f the zone a r e exposed at the mouths o f S a l l u s and  branch-  Blackhill  Creeks.  I n t h i s v i c i n i t y , the main f a u l t seems t o have con-  t r o l l e d the course o f the F r a s e r R i v e r .  Between the upper  p a r t o f McKay Creek and Leon Creek the f a u l t i s covered about 2-1/2  m i l e s by f l a t - l y i n g Miocene or P l i o c e n e  b a s a l t s t h a t a p p a r e n t l y have not been o f f s e t by the  for  (?) fault.  To the n o r t h , on Watson Bar C r e e k , the f a u l t i s marked by intense'carbonate  a l t e r a t i o n i n the l i t h i c sandstones  and  the v o l c a n i c r o c k s . F a u l t "e" the w e s t e r n boundary f a u l t o f the P a v i l i o n group i s w e l l exposed on a c l i f f f a u l t d i p s about 75°  to the southwest. ( P l a t e XXTV)  o f the f a u l t p l a n e on the c l i f f variation i n dip.  i n B i g Bar Canyon, where the  The  that l i e s approximately  The  i s s t r a i g h t , suggesting  trace little  f o o t - w a l l here c o n s i s t s o f r i b b o n c h e r t p a r a l l e l to the f a u l t p l a n e and  t a i n s numerous v e i n l e t s o f q u a r t z and c a r b o n a t e . w a l l i s a n d e s i t e t h a t has been converted  The  con-  hanging  i n t o a l a y e r o f gouge  about 40 f e e t t h i c k . Between Watson Bar Creek and F r e n c h Bar Canyon the e x i s t e n c e o f a f a u l t c o n t a c t i s i n d i c a t e d by the steep d i p s o f the o t h e r w i s e  f l a t l y i n g or m o d e r a t e l y d i p p i n g v o l c a n i c r o c k s .  From Watson Bar Creek to McKay Creek the r o c k s a d j a c e n t the c o n t a c t are p o o r l y exposed.  to  Between McKay Creek and  a  l o c a l i t y about one m i l e northwest o f G l e n F r a s e r the f a u l t i s not exposed but i n d i c a t e d by anomalous d i p s ( P l a t e X X I I I ) s i g n s o f s h a t t e r i n g and a l t e r a t i o n .  and  Immediately n o r t h o f G l e n  F r a s e r the l o c a t i o n o f the f a u l t i s u n c e r t a i n .  From G l e n  F r a s e r t o t h e mouth o f Gibbs Creek t h e e a s t e r n c o n t a c t o f t h e Pavilion.:'  group i s covered by o v e r b u r d e n .  Southwest o f t h e  mouth o f Gibbs Creek a f a u l t between t h e lower D i v i s i o n  of the  Spences B r i d g e group and t h e F o u n t a i n V a l l e y assemblage was i n f e r r e d from a c r o s s s e c t i o n ( B - B ' ) . T h i s i n f e r r e d  f a u l t pro-  b a b l y i s c o n t i n u o u s w i t h t h e e a s t e r n boundary f a u l t o f t h e P a v i l i o n group t r a c e d from northwest o f G l e n F r a s e r t o n o r t h o f B i g B a r Creek. F a u l t "e" l i e s c l o s e t o t h e w e s t e r n margin o f s e v e r a l g r a n i t i c masses. are  No major p l u t o n s i n t h e p r e s e n t map a r e a  exposed t o t h e east o f t h i s  fault.  F a u l t " f " forms t h e c o n t a c t between D i v i s i o n Division the  I I o f the P a v i l i o n  I and  group.. The f a u l t I s exposed on  s l o p e n o r t h o f P a v i l i o n Creek and i n d i c a t e d by s h e a r i n g  and a l t e r a t i o n s o u t h o f Moran.  The n o r t h w e s t e r n c o n t i n u a t i o n  o f t h e c o n t a c t i s obscured by l a c k o f o u t c r o p and metamorphism (see  p. 5 8 ) . S o u t h o f P a v i l i o n Creek t h e c o n t a c t i s v e r y p o o r l y  exposed.  On K e a t l e y Creek a f a u l t r e l a t i o n was i n f e r r e d  from  an a b r u p t l i t h o l o g i c a l change, from t h e u n u s u a l narrowness o f Division  I and an anomalous s t r a t i g r a p h i c  t o p near t h e c o n t a c t .  The f a u l t s " a " , "b", " c " , and "d" appear t o be'normal f a u l t s w i t h r e l a t i v e downward movement o f t h e e a s t e r n b l o c k ; f a u l t "e" i s a normal f a u l t w i t h r e l a t i v e downward movement of the western block. complex graben. certain.  These f i v e l o n g i t u d i n a l  f a u l t s form a  The sense o f movement on f a u l t " f " i s un-  173 Cross-faults,  a p p r o x i m a t e l y normal t o t h e l o n g i t u d i n a l  f a u l t s , seem t o be c o m p a r a t i v e l y s h o r t and t o show s m a l l offsets.  A l t h o u g h h o r i z o n t a l and v e r t i c a l d i s p l a c e m e n t s can  be e s t a b l i s h e d  i n some p l a c e s , i n o t h e r s o f f s e t s cannot be  r e c o g n i z e d a t a l l and f a u l t i n g i s i n d i c a t e d o n l y by abrupt changes i n a t t i t u d e .  The c r o s s - f a u l t zones c o n s i s t o f s i n g l e  breaks o r , as on F o u n t a i n R i d g e , o f a s e r i e s o f c l o s e l y faults.  spaced  One o f t h e c r o s s f a u l t s o f f s e t s a l o n g i t u d i n a l f a u l t  but o t h e r s appear t o s t o p a t them. 3.  Associated A l t e r a t i o n  The most common a l t e r a t i o n a s s o c i a t e d w i t h t h e F r a s e r R i v e r f a u l t zone i s c a r b o n a t i z a t i o n . r u s t y brown.  The carbonate  weathers  I n an a l t e r e d r o c k from B i g B a r Canyon i t has  the c o m p o s i t i o n o f magnesiodolomite (n =1.6795). 0  I n con-  g l o m e r a t e s , sandstones, and s i l t s t o n e s t h e carbonate r e p l a c e s m o s t l y t h e m a t r i x , but i n t h e o t h e r r o c k s i t o c c u r s i n v e i n l e t s and i r r e g u l a r p a t c h e s .  I n many l o c a l i t i e s v e i n l e t s o f  quartz a r e a s s o c i a t e d w i t h the carbonate. Igneous r o c k s and l i t h i c sandstones show s i g n s o f low grade o r r e t r o g r e s s i v e and i n t e r m e d i a t e p l a g i o c l a s e  near major f a u l t s  metamorphism.  Calcic  have been c o n v e r t e d t o a l b i t e and  e p i d o t e and t h e m a f i c m i n e r a l s t o c h l o r i t e .  C h l o r i t e and  e p i d o t e i n many o f these r o c k s form v e i n l e t s and a p p a r e n t l y have been r e d i s t r i b u t e d by s o l u t i o n s .  D u f f e l l and McTaggart  have p o i n t e d out t h a t i n many l o c a l i t i e s t h e a l b i t i z a t i o n i s accompanied by p r e h n i t i z a t i o n .  The p r e h n i t e appears i n v e i n l e t s  o r r e p l a c e s the p l a g i o c l a s e o f the h o s t . a r e a the m i n e r a l was  I n the p r e s e n t  map  found i n the g a b b r o i c b e l t west o f  L i l l o o e t , i n a d i o r i t i c dyke near the mouth o f B r i d g e R i v e r , i n a g a b b r o i c or d i o r i t i c dyke and a l i t h i c sandstone  east o f  F o u n t a i n Creek and i n the d i o r i t e mass southeast o f P a v i l i o n . A l l t h e s e l o c a l i t i e s are i n the v i c i n i t y o f major f a u l t  zones.  I t i s p o s s i b l e t h a t the a l t e r i n g s o l u t i o n s and the g a b b r o i c dykes ascended t h r o u g h such f r a c t u r e s and t h a t dykes and s o l u t i o n s are r e l a t e d i n o r i g i n .  West o f L i l l o o e t the gabbros  a r e a l s o v e i n e d by t r e m o l i t e and p o s s i b l y the amphibole nephrite. 4.  H i s t o r y o f the F r a s e r R i v e r F a u l t Zone  The h i s t o r y o f the F r a s e r R i v e r f a u l t zone p r o b a b l y i s a l o n g and complex sequence o f i n t e r m i t t e n t movements. e v i d e n c e f o r the e a r l i e r movements i s i n c o m p l e t e , and l i e s m o s t l y i n the s t r a t i g r a p h i c r e c o r d .  indirect,  Only the l a t e s t  movements can be e s t a b l i s h e d d i r e c t l y from the p r e s e n t Cross s e c t i o n C-C  1  The  structure.  shows t h a t the f a u l t i n g i s younger  t h a n t h e f o l d i n g o f the L i l l o o e t group w h i c h p r o b a b l y  took  p l a c e i n the Neocomian. The  e a r l i e s t i n d i c a t i o n o f the e x i s t e n c e o f the f a u l t  zone i s the conglomerate  o f D i v i s i o n B (Barremian) o f the  J a c k a s s M o u n t a i n group.  The g r e a t t h i c k n e s s o f c o a r s e  sedi-  ments i n t h i s u n i t suggests r a p i d u p l i f t o f the source a r e a w h i c h may  have been accomplished  by normal f a u l t i n g .  175  There i s a l s o some evidence t h a t the f a u l t zone a c t i v e d u r i n g the d e p o s i t i o n o f D i v i s i o n C (Barremian) at  was or  the end o f t h a t t i m e . About one m i l e n o r t h o f the mouth o f Gibbs Creek  v o l c a n i c r o c k s o f the Spences B r i d g e group a p p a r e n t l y o v e r l i e the P a v i l i o n group w i t h u n c o n f o r m i t y .  About one m i l e to the  west s t r a t a o f D i v i s i o n C, s e v e r a l thousand f e e t t h i c k a r e exposed.  The  u n i t s are p r o b a b l y s e p a r a t e d by two f a u l t s  l a t e s t movement on w h i c h took p l a c e i n the m i d d l e (Cross-section C-C). ways.  The  the  (?) T e r t i a r y .  s i t u a t i o n can be e x p l a i n e d i n two  E i t h e r the s t r a t a o f the J a c k a s s Mountain group never  extended to the l o c a l i t y where the Spences B r i d g e group l a i d down l a t e r ; o r the e a s t e r n p a r t o f D i v i s i o n C was  was removed  by u p l i f t and e r o s i o n b e f o r e the d e p o s i t i o n o f the Spences B r i d g e group.  I n the f i r s t case the sediments o f D i v i s i o n C  must have been d e p o s i t e d i n a r a p i d l y s u b s i d i n g t r o u g h whose e a s t e r n boundary a p p r o x i m a t e l y c o i n c i d e d w i t h the p r e s e n t The  fault.  second e x p l a n a t i o n i m p l i e s a r a p i d u p l i f t o f g r e a t magni-  tude i m m e d i a t e l y  to the east o f the present f a u l t zone.  Both  e x p l a n a t i o n s suggest movements o f the p r e s e n t f a u l t zone; i n the f i r s t case i t would have t a k e n p l a c e i n the mid-Lower  Cretaceous  ( B a r r e m i a n ) ; i n the second case s l i g h t l y l a t e r ( e a r l y A p t i a n ? ) . I f the r o c k s n o r t h o f Gibbs Creek a r e not c o r r e l a t i v e w i t h the b a s a l u n i t o f the Spences B r i d g e Group i n the type a r e a , but y o u n g e r , the f a u l t i n g might be m i d d l e o r l a t e A p t i a n . M i d d l e and Upper Cretaceous  and e a r l y T e r t i a r y move-  176 merits c a n n o t this  be e s t a b l i s h e d ,  time i s r e l a t e d  (Compare C l o o s ,  but perhaps  to the F r a s e r  that  (Eocene-Oligocene).  The M i d d l e o r L a t e  basalts overlie fault  " d " without signs of or Recent  a,  b,  c,  blocks,  i n the west.  faulting  and d , w h i c h show r e l a t i v e to  uplift  and t i l t i n g  By analogy f a u l t  "e",  t h e movement  the p l u t o n i c masses s i t u a t e d  showing r e l a t i v e to  i m m e d i a t e l y to the  the g r e a t e s t  grabens  hand Hans C l o o s  uplift  east.  of  Perhaps  greater  depth  the Fraser  River area  gradual s h i f t Perhaps  (1930)  has  suggested  that  o f t h e w o r l d p r o b a b l y w e r e p r o d u c e d by  b r o a d d o m a l u p l i f t s and a r e  by t h e  de-  c o n n e c t e d w i t h t h e Mount L y t t o n b a t h o l i t h . On t h e o t h e r  of  the  of the Coast Mountains  t h e s e p l u t o n s a r e p a r t o f a l a r g e r mass h i d d e n a t is  on  depression of  p r e s s i o n o f t h e w e s t e r n b l o c k c o u l d be r e l a t e d  that  disturbance,  Causes o f F a u l t i n g  D u f f e l l and M c T a g g a r t have r e l a t e d  eastern  Tertiary  been f o u n d . 5.  faults  are  o v e r l i e the French Bar  and t o p o g r a p h i c e v i d e n c e o f P l e i s t o c e n e has n o t  zone.  r o c k s d i s t u r b e d by f a u l t movements  t h e v o l c a n i c f l o w s and t u f f s  olivine  River fault  1939).  The y o u n g e s t  formation  the v o l c a n i s m o f  the r e s u l t  of t e n s i o n .  i n t h e Lower C r e t a c e o u s  from marine to  both processes are  continental related.  is  An u p l i f t indicated  conditions.  177  CHAPTER I I I  Geological H i s t o r y o f the Area I n t h e Permian and T r i a s s i c t h e area was p a r t o f a somewhat r e s t r i c t e d marine b a s i n i n w h i c h carbonaceous m a t t e r was n o t o x i d i z e d .  I n t h e Upper Permian a r e e f zone extended  t h r o u g h t h e p r e s e n t Bowman Range and P a v i l i o n M o u n t a i n s .  To  the west o f t h e r e e f s a l t e r n a t i n g l a y e r s o f mud and r a d i o l a r i a n d e b r i s were l a i d down.  The c o n d i t i o n s were m o d e r a t e l y  s t a b l e but some v o l c a n i c e r u p t i o n s t o o k p l a c e . T r i a s s i c t h e a r e a became t e c t o n i c a l l y a c t i v e .  In the T e c t o n i c move-  ments r e s u l t i n g i n sub-marine slumping and t u r b i d i t y were accompanied by s t r o n g v o l c a n i s m .  currents  The d e p o s i t s o f t h i s  epoch c o n s i s t e d o f l i t h i c sand, t u f f , v o l c a n i c f l o w s , aceous mud, r a d i o l a r i a n d e b r i s , l i m e , and s i l t . a c t i v i t y may have c u l m i n a t e d 1959).  argill-  The t e c t o n i c  i n t h e C a s s i a r orogeny (White,  However, i n t h e present map a r e a t h e o n l y i n t r u s i o n s  marking t h a t event a r e Upper T r i a s s i c ( ? ) u l t r a b a s i c i n t r u s i o n s west o f L i l l o o e t and east o f t h e F r a s e r R i v e r . No sedimentary o r v o l c a n i c r o c k s o f t h e time i n t e r v a l between T r i a s s i c and Lower C r e t a c e o u s a r e exposed.  The  Lower C r e t a c e o u s s e d i m e n t s , however, were d e r i v e d from v o l c a n i c r o c k s t h a t p r o b a b l y were d e p o s i t e d  during t h i s i n t e r v a l .  v o l c a n i c r o c k s were r i c h i n a l b i t e and p r o b a b l y  These  belong to the  178 spilite-keratophyre suite.  They were p o s s i b l y J u r a s s i c and  exposed t o t h e n o r t h e a s t and/or southwest o f t h e F r a s e r R i v e r f a u l t zone.  The s o u r c e r o c k s may have been r e l a t e d t o t h e  M i d d l e J u r a s s i c k e r a t o p h y r e s exposed near H a r r i s o n M i l l s , B.C. ( B u r l e y , 1954). I n t r u s i o n o f g r a n i t i c r o c k s i n t o t h e P a v i l i o n group may have t a k e n p l a c e i n t h e J u r a s s i c . I n t h e e a r l i e s t Lower C r e t a c e o u s d u r i n g t h e d e p o s i t i o n o f D i v i s i o n s A and B o f t h e L i l l o o e t group t h e a r e a was p a r t o f a r e s t r i c t e d marine b a s i n w h i c h was t e c t o n i c a l l y u n s t a b l e .  The  mud o f D i v i s i o n s A and B and an i n c r e a s i n g p r o p o r t i o n o f l i t h i c sand i n D i v i s i o n B were d e p o s i t e d by t u r b i d i t y c u r r e n t s t h a t were accompanied by submarine s l u m p i n g .  During the d e p o s i t i o n  o f D i v i s i o n B t h e a r e a g r a d u a l l y r o s e and then was f o l d e d , i n t r u d e d by d i o r i t i c d y k e s , e l e v a t e d above sea l e v e l , and eroded. The uppermost  p a r t o f t h e L i l l o o e t group, D i v i s i o n C, con-  s i s t i n g o f t u f f a c e o u s l i t h i c s a n d s t o n e , g r a n u l e conglomerate and a s m a l l p r o p o r t i o n o f a r g i l l i t e was d e p o s i t e d i n a marine environment perhaps under n e a r - s h o r e c o n d i t i o n s .  A t t h e end o f  t h a t t i m e (Neocomian?) t h e a r e a a g a i n r o s e above s e a - l e v e l , and the b a s a l conglomerate o f t h e J a c k a s s Mountain group was l a i d down i n a c o n t i n e n t a l environment.  Associated tuffaceous  m a t t e r i n d i c a t e s contemporaneous v o l c a n i s m . D u r i n g t h e d e p o s i t i o n o f t h e members A H  and A I I I o f  D i v i s i o n A and o f t h e b a s a l p a r t o f D i v i s i o n B o f t h e J a c k a s s M o u n t a i n group (Barremian) t h e a r e a was p a r t o f a r e s t r i c t e d  179  marine b a s i n .  The sediments o f A I c o n s i s t e d d o m i n a n t l y o f  f i n e sand, t h o s e o f A l l o f mud,  silt  and f i n e sand, and t h e  b a s a l p a r t o f D i v i s i o n B was composed o f medium-grained T h i s change i n g r a i n s i z e may  sand.  r e f l e c t a r e l a t i v e depression of  t h e b a s i n f o l l o w e d by a g r a d u a l r i s e . The t h i c k conglomerate o f D i v i s i o n B i s the e a r l i e s t e v i d e n c e o f a c t i v i t y on the F r a s e r R i v e r f a u l t zone w h i c h cont i n u e d i n t e r m i t t e n t l y to the M i d d l e T e r t i a r y . may  The  faulting  be r e l a t e d t o the i s o s t a t i c r i s e o f Coast I n t r u s i o n s to  the e a s t and t o the west o r an u p l i f t o f the whole a r e a .  A  complex graben s t r u c t u r e was produced w h i c h p r o b a b l y c o n t r o l l e d the s e d i m e n t a t i o n o f D i v i s i o n s B and C o f t h e J a c k a s s Mountain group.  D i v i s i o n s B and C c o n s i s t i n g o f c o n g l o m e r a t e , l i t h i c  s a n d s t o n e , and minor a r g i l l i t e p r o b a b l y were l a i d down i n a narrow e l o n g a t e t r o u g h w h i c h s u b s i d e d r a p i d l y w i t h r e s p e c t t o the b o r d e r i n g mountains but f l u c t u a t e d w i t h r e s p e c t t o sea level.  At times i t may  have been connected w i t h the open s e a ,  more o f t e n i t formed a r e s t r i c t e d marine b a s i n , and t e m p o r a r i l y i t may river.  have been a c o n t i n e n t a l v a l l e y o c c u p i e d by a l a r g e Graded bedding and slump s t r u c t u r e s a r e v e r y rare, and  i n t h i s r e s p e c t t h e s e "post t e c t o n i c " r o c k s d i f f e r from the o l d e r g e o s y n c l i n a l f a c i e s .  markedly  The sediments were m o s t l y  d e r i v e d from a l b i t e r i c h v o l c a n i c r o c k s and t o a l e s s e r e x t e n t from g r a n i t i c  intrusions.  Rocks younger t h a n the e a r l y Lower C r e t a c e o u s a r e o n l y found t o the east o f the Lower C r e t a c e o u s sedimentary b e l t , and a l l o f them a r e o f c o n t i n e n t a l o r i g i n .  180 I n t h e m i d d l e and of  great  thickness  posited  that  ments.  Perhaps the  of the  are  Fraser  Lower C r e t a c e o u s v o l c a n i c  c o n s i s t i n g dominantly of andesite  locally  intercalated with  v o l c a n i c flows  River  fault  Because o f the and  late  ascended  Probably  lack of  the  fossils  a  thickness  flood plain  The  river  canic  derived  rocks  Fraser  River  valley is  the  area  River  C r e e k and  from b a s a l t i c  These v o l c a n i c flows  and  tuffs  are  t h a t have b e e n d i s t u r b e d  fault  s a n d s were d e p o s i t e d L e o n C r e e k , and were c o n n e c t e d the  and  another  lithic  were l a i d  of  down  French Bar  on  Canyon.  series of  to f e l s i t i c the  sand  vol-  compositions.  youngest  rocks  by movements o f  found  the  in  Fraser  Fraser  by  olivine  fractures  associated  a p p e a r a n c e marks t h e  Creek.  i n a v a l l e y that  River  with end  valley.  the  Fraser  of a long  lithic of  deposits  partly coincided  T h e s e s e d i m e n t s were have r i s e n  River  fault  through zone.  period of volcanic  Their activity  rocks.  area  apparently  Pleistocene  P o s s i b l y these  b a s a l t s w h i c h may  andesitic  A l t h o u g h the  earliest  f l o o d p l a i n s near P a v i l i o n , south  formed  succeeded  Pleistocene  on  on B i g B a r  present  d o m i n a t e d by  the  continued.  zone.  B e t w e e n t h e M i o c e n e and  with  through f r a c t u r e s  Cretaceous  from v o l c a n i c rocks  were o v e r l a i n by  ranging  continental sedi-  Upper  volcanic activity  between B i g B a r  deposits  de-  the  I n E o c e n e - O l i g o c e n e t i m e g r a v e l and great  were  zone.  Paleocene-Eocene h i s t o r y of the  uncertain.  rocks  was  covered  by  glaciers in  little  glacial  erosion took  the  place.  181  Probably at the end of the l a s t g l a c i a t i o n the v a l l e y was occupied by braided streams and g l a c i a l lakes and more than 1000 feet of gravel, sand, s i l t , and mud flows were deposited. In Recent time the Fraser River has been rejuvenated and has cut  through the unconsolidated material into bed rock.  northwestern  and central part of the area received thin  deposits of volcanic ash.  The  182 BIBLIOGRAPHY Armstrong, J. E. (1949): Fort St. James map-area, B r i t i s h Columbia; Geol. Surv., Canada, Mem. 252. 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R e s o u r c e s , D i v . M i n e s , b u l l . 125.  184  van d e r Kaaden, G e r r i t (1951): O p t i c a l s t u d i e s on n a t u r a l p l a g i o c l a s e s w i t h h i g h and low-temperature o p t i c s ; Ph.D. t h e s i s , U n i v e r s i t y o f U t r e c h t . K r a u s k o p f , K.B. (1956): D i s s o l u t i o n and p r e c i p i t a t i o n o f s i l i c a a t l o w t e m p e r a t u r e s ; Geochim. et Cosmochim. A c t a . v o l . 10, pp. 1 - 2 6 . Krumbein, W.C. and G a r r e l s , . R.M. (1952): O r i g i n and c l a s s i f i c a t i o n o f c h e m i c a l sediments i n terms o f pH and o x i d a t i o n - r e d u c t i o n p o t e n t i a e ; J o u r . G e o l . , v o l . 60, pp. 1-33. Krumbein, W.C. and T i s d e l , F.W. (1940): S i z e d i s t r i b u t i o n o f s o u r c e r o c k s o f sediments: Am. J o u r . S c i . v o l . 2 3 8 , pp. 296-305. Krumbein, W.C. (1953) '• T h i n - s e c t i o n m e c h a n i c a l a n a l y s i s o f i n d u r a t e d sediments; J o u r . G e o l . , v o l . 4 3 , pp. 482-496. Lay, Douglas (1940): F r a s e r R i v e r T e r t i a r y d r a i n a g e - h i s t o r y i n r e l a t i o n t o p l a c e r - g o l d d e p o s i t s ; B r i t i s h Columbia Dept. M i n e s , B u l l . 3 . Leech, G.B. (1953): Geology and m i n e r a l d e p o s i t s o f t h e S h u l a p s Range, s o u t h w e s t e r n B r i t i s h C o l u m b i a , B.C. Dept. M i n e s , B u l l . 3 2 . Lowenstam, H.A. ( 1 9 5 0 ) : N i a g a r a n r e e f s o f t h e Great a r e a ; J o u r . G e o l . , v o l . 58, pp. 430-466.  Lakes  McCammon, J . and N a s m i t h , H. (1956): Geology o f low l e v e l damsites on t h e F r a s e r R i v e r ; B.C.Dept. M i n e s , unpubl. M c K e n z i e , J.P. (1921): A r e c o n n a i s s a n c e between Taseko Lake and F r a s e r R i v e r , B r i t i s h Columbia; G e o l . S u r v . , Canada, Sum. Rep., 1920, p t . A, pp. 70A-81A. Mathews, W.H. (1941): C l i m b s i n t h e L i l l o o e t Range; Can. A l p i n e J o u r . , pp. 60-64. (1944): G l a c i a l l a k e s and i c e r e t r e a t i n s o u t h c e n t r a l B r i t i s h Columbia; T r a n s . Roy. S o c , Canada, sec. N. pp. 3 9 - 5 7 . Paekham, G.H. (1955): Volume, - w e i g h t , - and number f r e q u e n c y a n a l y s i s o f sediments from t h i n - s e c t i o n d a t a : J o u r . G e o l . v o l . 6 3 , pp. 50-58. P o l d e r v a a r t , A r i e (1950): C o r r e l a t i o n o f p h y s i c a l p r o p e r t i e s and c h e m i c a l c o m p o s i t i o n i n t h e p l a g i o c l a s e , o l i v i n e , and o r t h o p y r o x e n e s e r i e s ; Am. M i n e r a l . , v o l . 3 5 , pp. 1 0 6 7 - 1 0 7 9 .  185  R e i n e c k e , L. (1920): M i n e r a l d e p o s i t s between L i l l o o e t and P r i n c e George, B r i t i s h C o l u m b i a : G e o l . S u r v . Canada, mem. 118. R e v e l l e , R. ( 1 9 3 4 ) : P h y s i c o - c h e m i c a l f a c t o r s a f f e c t i n g the s o l u b i l i t y o f C a l c i u m - c a r b o n a t e i n sea w a t e r ; J o u r . Sed., P e t r o g . , v o l . 4, pp. 1 0 3 - 1 1 0 . R i c e , H.M. A. (1947): Geology and m i n e r a l d e p o s i t s o f t h e P r i n c e t o n map-area, B r i t i s h Columbia; G e o l . S u r v . , Canada, Mem. 118. R o s e n f e l d , M.A., J a c o b s o n , L., and Ferm, J.C. ( 1 9 5 3 ) : A comparison o f s i e v e and t h i n - s e c t i o n t e c h n i q u e s f o r s i z e - a n a l y s i s ; J o u r . G e o l . , v o l . 6 1 , pp. 1 1 4 - 1 3 3 . S e l w y n , A.R.C. ( 1 8 7 2 ) : J o u r n a l and r e p o r t o f p r e l i m i n a r y e x p l o r a t i o n s i n B r i t i s h Columbia, Geol. Surv., Canada, Rept. o f P r o g . 1 8 7 1 - 7 2 , pp. 1 6 - 7 2 . T a l i a f e r r o , N.L. ( 1 9 4 3 ) : F r a n c i s c a n - K n o x v i l l e problem, B u l l . A.A.P.G., v o l . 26, pp. 1 0 - 2 1 9 . T h a y e r , T.P. (1948): R e l a t i o n o f s e r p e n t i n e to Upper T r i a s s i c o v e r t h r u s t i n g i n n o r t h e r n Oregon: G e o l . Soc. A m e r i c a , b u l l . v o l . 5 9 , pp. 1 3 5 8 - 1 3 5 9 . T i p p e r , W.H. ( 1 9 5 9 ) : Map 1 2 - 1 9 5 9 , Q u e s n e l , B r i t i s h C o l u m b i a , G e o l . S u r v . Canada. Thompson, M.L., and Wheeler, H.E. (1942): Permian f u s u l i n i d s from B r i t i s h C o l u m b i a , Washington, and Oregon; J o u r . P a l e o n t . , v o l . 1 6 , pp. 7 0 0 - 7 1 1 . T h o r n b u r y , W.D.  ( 1 9 5 4 ) : P r i n c i p l e s o f geomorphology.  Wiley  T r a s k , P.D., ( 1 9 3 2 ) : O r i g i n and environment o f source s e d i ments o f p e t r o l e u m . Houston, G u l f . P u b l . Co. Warren, H.V., ( 1 9 5 9 ) : The Moran Dam; March, 1 9 5 9 .  Canadian M i n . J o u r .  W h i t e , W.H. ( 1 9 5 9 ) : C o r d i l l e r a n t e c t o n i s m i n B r i t i s h Columbia; A.A.P.G. v o l . 4 3 , pp. 6 0 - 1 0 0 . W i l l i a m s , H., T u r n e r , F . J . and G i l b e r t , Ch.M. graphy, W.H.Freeman and Co.  (1955):  Petro-  W i n c h e l l , A.N. and W i n c h e l l , H. ( 1 9 5 D : Elements o f o p t i c a l mineralogy, Part I I , Wiley.  186  APPENDIX I : DETERMINATION OF MINERAL COMPOSITIONS The f o l l o w i n g o p t i c a l p r o p e r t i e s and r e f e r e n c e s have been used. High-temperature p l a g i o c l a s e ; e x t i n c t i o n a n g l e s i n zone normal t o (010); v a n der Kaaden, 1 9 5 l Where e x t i n c t i o n a n g l e s c o u l d not be measured, t h e T s u b o i - i n d e x , n_.' o f 001 - c l e a v a g e f r a g ments was used; Crump and K e t t n e r , 1*52. 5  The T s u b o i i n d i c e s have been worked o u t , so f a r , o n l y f o r l o w temperature p l a g i o c l a s e s . But i n t h e p r e s e n t study i t was found t h a t d e t e r m i n a t i o n s based on Crump and K e t t n e r s curves do not d e v i a t e f a r from those based on v a n d e r Kaaden's ext i n c t i o n angle curves. 1  Low-temperature p l a g i o c l a s e : T s u b o i - i n d i c e s ; Crump and K e t t n e r 19!?2, E x t i n c t i o n - a n g l e s ; W i n c h e l l and W i n c h e l l , 1951. Owing t o t h e u n c e r t a i n t y about t h e o p t i c a l p r o p e r t i e s o f p l a g i o c l a s e t h e d e t e r m i n a t i o n s p r o b a b l y have an a c c u r a c y o f t 2-5$.  only  However, t h e curves used have been i n t e r p r e t e d as  c l o s e l y as p o s s i b l e . C l i n o p y r o x e n e : ny, 2v; Hess, 194-9. Ort ho pyroxene: ny, o p t i c a l s i g n ; Hess and P h i l l i p s , 194-0, P o l d e r v a a r t , 1950. o p t i c a l s i g n ; P o l d e r v a a r t , 1950.  Olivine:  n  Carbonates:  no; W i n c h e l l and W i n c h e l l , 1951.  y  The T s u b o i - i n d i c e s have been determined  w i t h an a c c u r a c y o f  a p p r o x i m a t e l y t . 0 0 1 , o t h e r i n d i c e s w i t h an a c c u r a c y o f approximately 1 .002.  APPENDIX I I PLATES  PLATE I  PLATE I I  The F r a s e r R i v e r V a l l e y near Moran. View t o t h e n o r t h e a s t .  PLATE I I I  The F r a s e r R i v e r V a l l e y between S i w a s h Creek and Leon Creek. View t o t h e n o r t h w e s t .  PLATE IV  Unconsolidated P l e i s t o c e n e s e d i ments r e s t i n g on c h e r t and a r g i l l i t e o f the P a v i l i o n group, D i v i s i o n I , Upper Permian o r Triassic. Lower p a r t o f K e l l y Creek. View t o the n o r t h .  PLATE V  Mount Bowman.  View t o t h e s o u t h .  PLATE V I  C a l c a r e n i t e , thin-bedded t o laminated. At c l o s e i n s p e c t i o n the r o c k shows graded bedding and intraformational brecciation. Marble Canyon f o r m a t i o n , member I I I , Upper Permian. About two m i l e s northwest o f Mount Bowman.  PLATE V I I  Mount Soues.  View t o t h e n o r t h  S y n c l i n e on Mount K e r r . northwest.  View  to  the  PLATE IX  Interbedded l i m e s t o n e and c h e r t , showing box-type o f f o l d s . M a r b l e Canyon f o r m a t i o n , member I l i a , Upper Permian. About one m i l e west o f Mount K e r r . View to t h e n o r t h w e s t .  PLATE X  R a d i o l a r i a r i chert nodules i n argillaceous matrix. Argillaceous c h e r t from P a v i l i o n group, D i v i s i o n I , Upper Permian o r Triassic. Crossed n i c o l s x 2 5 .  PLATE X I  R a d i o l a r i a n c h e r t n o d u l e , showing r a d i a t i n g s p i n e s . P a v i l i o n group, D i v i s i o n I , Upper Permian o r T r i a s s i c . Left: ordinary l i g h t , r i g h t : crossed n i c o l s x ! 9 0 .  PLATE X I I  O o l i t i c l i m e s t o n e . O o l i t e s and p i s o l i t e s show e x t e r n a l concent r i c s t r u c t u r e and some r e l a t i v e l y c o a r s e twinned c r y s t a l s o f c a l c i t e i n t h e i n t e r i o r . P a v i l i o n group, D i v i s i o n I , Upper Permian o r Triassic. Crossed n i c o l s x35.  PLATE X I I I  M i g m a t i t e c o n s i s t i n g o f hornblende h o r n f e l s and d i o r i t i c i n t r u s i o n s . West shore o f F r a s e r R i v e r , o p p o s i t e the mouth o f K e l l y Creek. View t o the n o r t h w e s t .  PLATE XIV  Volcanic arenite, fine-grained. A few c l e a r g r a i n s a r e o f q u a r t z , the l i g h t grey g r a i n s a r e m o s t l y o f p l a g i o c l a s e . Specimen 2 o f f i g u r e 4. J a c k a s s M o u n t a i n group, D i v i s i o n C, B a r r e m i a n . o r d i n a r y l i g h t x32.  PLATS  XV  P l a g i o c l a s e c r y s t a l , showing t w i n n i n g and o s c i l l a t o r y normal z o n i n g , from t u f f , Spences B r i d g group, Gibbs Creek assemblage, member B, A p t i a n . Crossed n i c o l s x30.  PLATE XVI  The F r e n c h Bar f o r m a t i o n . Upper Eocene o r O l i g o c e n e , near F r e n c h Bar Canyon. Air-photograph.  PLATE X V I I  Conglomerate o f the F r e n c h Bar f o r m a t i o n , Upper Eocene o r O l i g o c e n e , near B i g Bar Creek.  PLATE X V I I I  O l i v i n e b a s a l t , Middle or Late T e r t i a r y . About 2 m i l e s n o r t h o f McKay Creek. View t o t h e n o r t h .  PLATE  XIX  O l i v i n e b a s a l t , showing l a r g e , corroded c r y s t a l s of o l i v i n e , l a t h l i k e , twinned p l a g i o c l a s e , and f i n e c r y s t a l s o f c l i n o p y r o x e n e and i r o n ore. The t e x t u r e i s s e r i a t e i n t e r granular. Crossed n i c o l s x32.  PLATE XX  S l i d e of Middle or L a t e Tertiary o l i v i n e b a s a l t near Leon Creek. Air-photograph.  PLATE XXI  Altered u l t r a b a s i c rock. A g r a i n o f c h r o m i t e , ( d a r k ) , some p a r a n k e r i t e , (medium grey t o d a r k ) , p a r t l y pseudomorphous a f t e r e n s t a t i t e and p a r t l y a l t e r e d t o l i m o n i t e , and v e i n s o f v e r y f i n e - g r a i n e d quartz, (mostly l i g h t g r e y ) . U l t r a b a s i c b e l t west o f Lillooet, Upper T r i a s s i c ( ? ) Crossed n i c o l s x32.  PLATE X X I I  S t e e p l y d i p p i n g s t r a t a o f the Jackass Mountain group, D i v i s i o n C, B a r r e m i a n , near f a u l t "d" on the east s i d e o f the F r a s e r R i v e r , between S a l l u s Creek and Gibbs Creek; v i e w t o the southwest.  PLATE X X I I I  A n d e s i t e and b a s a l t o f the Spences B r i d g e group, Upper D i v i s i o n , A p t i a n , d i p p i n g s t e e p l y t o the n o r t h e a s t near f a u l t c o n t a c t w i t h P a v i l i o n group, D i v i s i o n I I , T r i a s s i c , ( f a u l t "e"). Lower p a r t o f McKay Creek. View t o the n o r t h w e s t .  PLATE XXIV  F a u l t "e" i n B i g Bar Canyon. View to the s o u t h e a s t . On t h e n o r t h e a s t s i d e o f t h e f a u l t c h e r t and a r g i l l i t e o f the P a v i l i o n group, D i v i s i o n I , Upper Permian o r T r i a s s i c ; on t h e southwest s i d e b a s a l t and a n d e s i t e o f the Ward Creek assemblage, C r e t a c e o u s o r e a r l y T e r t i a r y . The f a u l t plane d i p s about 75° t o t h e southwest.  

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