@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Earth, Ocean and Atmospheric Sciences, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Trettin, Hans Peter"@en ; dcterms:issued "2012-01-09T23:33:10Z"@en, "1960"@en ; vivo:relatedDegree "Doctor of Philosophy - PhD"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """An area of 550 square miles between Lillooet and Big Bar, B.C. was mapped by the author using the scale of one mile to the inch. In the southern part of the Bowman Range four members are recognized in the Middle (?) and Upper Permian Marble Canyon formation which is partly composed of reefal limestone. This formation forms a northwesterly trending anticlinorium overturned to the northeast. The cherts, argillites, limestones, and volcanic rocks west of the Bowman Range, originally referred to the Permo-Pennsylvanian Cache Creek group are shown to be Permo-Triassic and are here assigned to the Pavilion group, a new group which is made up of two Divisions. Microscopic and stratigraphic evidence is given that the cherts of this group are of radiolarian origin. The Lower Cretaceous Lillooet group here is subdivided into three units. Divisions A and B are shown to form a northwesterly trending anticline. Three members are now recognized in Division A of the Lower Cretaceous Jackass Mountain group. The Lower Cretaceous Spences Bridge group is subdivided into several local and stratigraphic units. Two units previously assigned to the Spences Bridge group are correlated with the Kingsvale group on the basis of new fossil collections. Some volcanic and sedimentary rocks originally referred to the Miocene Kamloops group are here correlated with Miocene to Pleistocene rocks of the Quesnel map-area. West of Lillooet a belt of serpentinite was mapped that has structural and lithological similarities to the Upper Triassic ultrabasic intrusions of the Shulaps Range. Granitic rocks of three ages are recognized and range from early Lower Cretaceous or older to mid-Lower Cretaceous. It had earlier been shown that the Fraser River fault zone consists of several normal faults with relative downward movement to the east. East of these faults the author recognizes another fault with relative downward movement to the west. Lower Cretaceous and early Tertiary rocks thus occupy a graben between Permo-Triassic units to the northeast and to the southwest. This graben probably controlled the deposition of Divisions B and C of the Jackass Mountain group. The faulting may be related to the isostatic rise of adjacent granitic masses. Evidence is given that the latest movement on one of the faults took place in mid-Tertiary time."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/39967?expand=metadata"@en ; skos:note "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.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1957 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Doctor of Philosophy i n the Department of GEOLOGY We accept t h i s t h e s i s as conforming to the re q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA I960 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or 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 of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of G E O L O G Y The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada. Date J a n u a r y , 26, I 960 i i ABSTRACT An area of 550 square miles between L i l l o o e t and B i g B a r , B.C. was mapped by the author using the s c a l e of one mi l e to the i n c h . In the southern part of the Bowman Range four members are recognized i n the Middle (?) and Upper Permian Marble Canyon formation which i s p a r t l y composed of r e e f a l limestone. This formation forms a northwesterly trending 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 rocks west of the Bowman Range, o r i g i n a l l y r e -f e r r e d to the Permo-Pennsylvanian Cache Creek group are shown to be Permo-Triassic and are here assigned to the P a v i l i o n group, a new group which i s made up of two D i v i s i o n s . M i c r o -scopic and s t r a t i g r a p h i c evidence i s given that the cherts of t h i s group are of r a d i o l a r i a n o r i g i n . The Lower Cretaceous L i l l o o e t group here i s subdivided i n t o three u n i t s . D i v i s i o n s A and B are shown to form a northwesterly trending a n t i c l i n e . Three members are now recognized i n D i v i s i o n A of the Lower Cretaceous Jackass Mountain group. The Lower Cretaceous Spences Bridge group i s sub-d 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 assigned to the Spences Bridge group are c o r r e l a t e d w i t h the Kingsvale group on the basis of new f o s s i l c o l l e c t i o n s . i i i 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 to the Miocene Kamloops group are 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 rocks of the Quesnel map-area. West of L i l l o o e t a b e l t of s e r p e n t i n i t e was mapped that 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 to 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 of the Shulaps Range. G r a n i t i c rocks of three ages are recognized and range from e a r l y Lower Cretaceous or o l d e r to mid-Lower Cretaceous. I t had e a r l i e r been shown that the Fraser R i v e r f a u l t zone c o n s i s t s of 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 down-ward movement to the east. East of these f a u l t s the author recognizes another f a u l t w i t h r e l a t i v e downward movement to the west. Lower Cretaceous and e a r l y T e r t i a r y rocks thus occupy a graben between Permo-Triassic u n i t s to the northeast and to the southwest. This graben probably c o n t r o l l e d the d e p o s i t i o n of D i v i s i o n s B and C of the Jackass Mountain group. The f a u l t i n g may be r e l a t e d to the i s o s t a t i c r i s e of adjacent g r a n i t i c masses. Evidence i s given that the l a t e s t movement on one of the f a u l t s took place i n m i d - T e r t i a r y time. i v TABLE OF CONTENTS Page INTRODUCTION 1 1. Location and Access 1 2. Previous Geological Work 1 3 . F i e l d Work 2 4. Physiography and Pleistocene and Recent Geology 3 5. Climate, Vegetation, Wild L i f e 6 6. Industries 7 CHAPTER I GENERAL GEOLOGY 9 Introductory Statement 9 Table of Formations 10 1. SEDIMENTARY AND VOLCANIC ROCKS 17 CACHE CREEK GROUP 17 Introduction 17 MOUNT SOUES DIVISION 20 MARBLE CANYON FORMATION . 21 1. D i s t r i b u t i o n 21 2. Lithology and Thickness 21 3 . Structure 25 4. Mode of Origin 27 5. Age of Correlation 30 PAVILION GROUP 34 Introduction 34 DIVISION I 34 1. D i s t r i b u t i o n and Thickness 34 2. Lithology 34 3 . Metamorphism 38 4. Structure 40 5. Mode of Origin 42 6. Age 44 V DIVISION I I 44 1. D i s t r i b u t i o n and Thickness 44 2 . B i g Bar Assemblage 45 A. L i t h o l o g y 45 B. S t r u c t u r e 46 3. P a v i l i o n Assemblage 47 A. L i t h o l o g y 47 B. Met amor p h i snr and A l t e r a t i o n . . . . 53 C. S t r u c t u r e . 57 4 . Mode o f O r i g i n 59 5. Age and C o r r e l a t i o n 59 LILLOOET GROUP 60 1 . D i s t r i b u t i o n and Thickness 60 2 . L i t h o l o g y 61 D i v i s i o n A 61 D i v i s i o n B 62 D i v i s i o n C 70 3. The Problem of A l b i t i z a t i o n 74 4 . S t r u c t u r e . . . . . 77 5. Mode of O r i g i n 77 6 . Age and C o r r e l a t i o n 79 JACKASS MOUNTAIN GROUP 80 1 . D i s t r i b u t i o n and Thickness 80 2 . L i t h o l o g y 81 D i v i s i o n A 81 Member AI 81 Member A l l 85 Member A I I I 86 D i v i s i o n B 87 D i v i s i o n C 88 3. The Problem o f A l b i t i z a t i o n 95 4 . S t r u c t u r e 95 5 . Mode o f O r i g i n 96 6 . Age and C o r r e l a t i o n 100 SPENCES BRIDGE GROUP 102 I n t r o d u c t i o n 102 LOWER DIVISION . . . 103 1 . B a s a l Member 103 2 . Gibbs Creek Assemblage 104 A. D i s t r i b u t i o n and Thickness 104 B. L i t h o l o g y 105 Member A 105 Member B 105 Member C 107 C. S t r u c t u r e , 108 v i UPPER DIVISION 109 1. D i s t r i b u t i o n 109 2. L i t h o l o g y 109 3. S t r u c t u r e , Age, C o r r e l a t i o n I l l KINGSVALE GROUP I l l 1. D i s t r i b u t i o n and Thickness I l l 2. L i t h o l o g y I l l D i v i s i o n A I l l D i v i s i o n B 112 3. S t r u c t u r e 113 4. Mode of O r i g i n , Age, C o r r e l a t i o n 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 130 1. Sedimentary Rocks near P a v i l i o n 130 A. D i s t r i b u t i o n and Thickness 130 B. L i t h o l o g y 131 C. S t r u c t u r e 132 D. Mode of O r i g i n 132 E. Age 133 2. Sedimentary 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 on B i g Bar Creek 134 3. O l i v i n e B a s a l t 136 A. D i s t r i b u t i o n and Thickness 136 B. L i t h o l o g y 137 C. S t r u c t u r e 140 D. Mode of O r i g i n 141 E. Age 142 v i i 2. INTRUSIVE ROCKS 143 ULTRABASIC INTRUSIONS 143 ULTRABASIC ROCKS NEAR LILLOOET 143 1. Distribution 143 2. Lithology 144 3. Serpentinization 145 4. Carbonate-silica Alteration 146 5. Age and Origin 147 PERIDOTITE INTRUDING THE PAVILION GROUP 148 60AST INTRUSIONS 149 I. EARLY LOWER CRETACEOUS OR OLDER 149 1. Distribution 149 2. Lithology 150 3. Associated Mineralization 153 4. Structure, Mode of Origin 154 5. Age 154 II. EARLY LOWER CRETACEOUS 155 1. Distribution 155 2. Lithology 155 3. Age 156 III. LATE BARREMIAN (?) 157 1. Distribution 157 2. Lithology 157 3. Associated Mineralization 158 4. Age 158 GABBRO AND DIABASE NEAR LILLOOET 159 1. Distribution, Structure 159 2. Lithology 159 3. Metamorphism and Alteration 163 4. Age 163 ANDESITIC AND BASIC DYKES 164 v i i i CHAPTER I I THE FRASER RIVER FAULT ZONE 165 1. I n t r o d u c t i o n 165 2. D e s c r i p t i o n of the Fraser R i v e r F a u l t Zone . . 167 3. Associated A l t e r a t i o n 173 4. H i s t o r y 174 5. Causes of 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 i x LIST OF FIGURES Fig u r e Page 1. Geology of the Fraser 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. ] n ^ o h t (In pocket) 2. Composition of fragments, sandstones, L i l l o o e t group 75 3. Composition of fragments, sandstones, Jackass Mountain group 92 4. S i z e d i s t r i b u t i o n i n sand and coarse s i l t - g r a d e , t h i n - s e c t i o n a n a l y s i s . o f 2 specimens from D i v i s i o n C, one specimen from member A l l , Jackass Mountain group 93 5. Geology of Glen Fraser area 117 6. The Fraser R i v e r f a u l t zone 168 X LIST OF PHOTOGRAPHS (Appendix I I ) P l a t e I The Fraser R i v e r v a l l e y near Fountain. View to the southwest. I I The Fraser R i v e r v a l l e y near Moran. View to the northeast. I l l The Fraser R i v e r v a l l e y between Siwash Creek and Leon Creek. View to the Northwest. TV Unconsolidated P l e i s t o c e n e sediments r e s t i n g on chert and a r g i l l i t e of the P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c . Lower part of K e l l y Creek. View to the no r t h . V Mount Bowman. View to the south. VI C a l c a r e n i t e , thin-bedded to laminated. Marble Canyon formation, member I I I , Upper Permian. About two miles northwest of Mount Bowman. V I I Mount Soues. View to the no r t h . V I I I S y n c l i n e on Mount K e r r . View to the northwest. IX Interbedded limestone and c h e r t , showing box-type of f o l d s . Marble Canyon formation, member I l i a , Upper Permian. About one mile west of Mount Ke r r . View to the northwest. X R a d i o l a r i a n chert 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 chert from P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c . Photo-micrograph. Crossed n i c o l s x25. XI R a d i o l a r i a n chert nodule, showing r a d i a t i n g spines. P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c . Photo-micrograph. Ordinary l i g h t and crossed n i c o l s x 1 9 0 . X I I O o l i t i c limestone. P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c . Photo-micrograph. Crossed n i c o l s x35. X I I I Migmatite c o n s i s t i n g of 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 of Fraser R i v e r , opposite the mouth of K e l l y Creek. View to the northwest. P l a t e XIV 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 of f i g u r e 4. Jackass Mountain group. D i v i s i o n C. Barremian. Photo-micrograph. Ordinary l i g h t x32. XV P l a g i o c l a s e c r y s t a l , showing twinning and o s c i l l a t o r y normal zoning, from t u f f , Spences Bridge group, Gibbs Creek assemblage, member B, A p t i a n . Photo-micrograph. Crossed n i c o l s x30. XVI The French Bar formation, Upper Eocene or O l i g o -cene, near French Bar Canyon. Air-photograph. XVII Conglomerate of the French Bar formation, Upper Eocene or Oligocene, near B i g Bar Creek. 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 miles n o r t h of McKay Creek. View to the north. XIX O l i v i n e b a s a l t . Photo-micrograph. Crossed n i c o l s x 3 2 . XX 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. Air-photograph. XXI A l t e r e d u l t r a b a s i c rock. U l t r a b a s i c b e l t west of L i l l o o e t , Upper T r i a s s i c ( ? ) . Photo-micrograph. Crossed n i c o l s x 3 2 . XXII S t e e p l y dipping s t r a t a of the Jackass Mountain group, D i v i s i o n C, Barremian, near f a u l t \"d\" on the east side of the Fraser R i v e r , between S a l l u s Creek and Gibbs Creek; view to the southwest. X X I I I Andesite and b a s a l t of the Spences Bridge group, Upper D i v i s i o n , A p t i a n , dipping s t e e p l y to the northeast near f a u l t contact w i t h the 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 part of McKay Creek. View to the northwest. XXIV F a u l t \"e 1 1 i n B i g Bar Canyon. View to the south; '-. x i i ACKNOWLEDGMENTS The work was c a r r i e d out f o r the Fraser R i v e r Board of the Province of B r i t i s h Columbia under the s u p e r v i s i o n of the Department of Mines. The author i s indebted to Drs. H. Sargent and S.S.Holland f o r support and encouragement. During the seasons of 1957 and 1958 the author was very ably a s s i s t e d by Mr. L . V . H i l l s , and during one month of 1958 by Mr. D. Leeming. Pr o f e s s o r K.C.McTaggart v i s i t e d the author on s e v e r a l occasions i n the f i e l d , advised him i n the course of t h i n - s e c t i o n s t u d i e s , and read the manuscript. Help w i t h f i e l d - w o r k , laboratory-work, and manuscript was a l s o received 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 to 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. Stevenson, R.M. Thomson, and W.H. White f o r advice. The i d e n t i f i c a t i o n of f o s s i l s by Prof e s s o r W.H. Danner, Dr. J . J e l e t z k y , and Professor G.E. Rouse i s g r a t e f u l l y acknowledged. In the Fraser R i v e r area f r i e n d l y help was given by Mr. and Mrs. Ostensoe of L i l l o o e t , Mr, and Mrs. Hay and Mr. and Mrs. High of P a v i l i o n , and Mr. and Mrs. M a r r i o t of B i g Bar. 1 INTRODUCTION 1. L o c a t i o n and Access The area mapped, elongate and i r r e g u l a r , l i e s along the Fraser R i v e r between L i l l o o e t and French Bar Canyon and i n c l u d e s the adjacent Bowman Range and parts of the P a v i l i o n Mountains, the Camelsfoot Range, and Fountain Ridge. The eastern side of the Fraser R i v e r , and the west si d e i n the v i c i n i t y of L i l l o o e t , are served by highway, the P a c i f i c Great Eastern Railway, and secondary roads and t r a i l s . In the c e n t r a l and northern parts of the map area the west side i s a c c e s s i b l e by a cable car near P a v i l i o n and a f e r r y at the mouth of B i g Bar Creek. From these two c r o s s i n g s only pack t r a i l s and a few wagon roads provide f u r t h e r access to the western parts of the map area. 2. Previous G e o l o g i c a l Work The e a r l i e s t g e o l o g i c a l work i n the area was done i n 1871 by J . Richardson and A.R.C. Selwyn. The Cache Creek group and the Jackass Mountain group are named and described f o r the f i r s t time i n Selwyn's report (1872). In 1877 G.M. Dawson (1877-78) mapped the Kamloops area on a s c a l e of eight miles to the i n c h . Further s t u d i e s were c a r r i e d out i n the seasons of 1888, 1889} and 1890, and i n 1895 a report and a map on a s c a l e of 4 miles to the i n c h were published. Dawson e s t a b l i s h e d a l l of the major rock u n i t s 2 o f the present map area, and h i s map and report are s t i l l the o n l y source of in f o r m a t i o n f o r some of the northern parts of the Kamloops Area. In 1918 and 1919 Leopold Reinecke (1920) who examined the m i n e r a l deposits adjacent to the 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 described a few deposits i n the present map area. A reconnaissance survey from the Fraser R i v e r to Taseko Lake was c a r r i e d out i n 1920 by J.D.McKenzie whose map and report cover the west side of the Fraser R i v e r between Watson Bar Creek and French Bar Creek. From 1945 to 1947 S. D u f f e l l and K.C.McTaggart r e -mapped the Ashcroft area on a s c a l e of 4 miles to the i n c h . Their most important c o n t r i b u t i o n s to the geology o f the present map area concern the Lower Cretaceous sedimentary rocks, and the Fraser R i v e r f a u l t zone. In 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 the northern part of the map area. They discovered s e v e r a l f a u l t s which proved to be northern extensions of the Fraser R i v e r f a u l t zone. Some of the northwestern parts of the area mapped are here described f o r the f i r s t time. 3. 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 of 9 months during the summers of 1957 and 1958 and f o r one week i n 1959. 3 The dry cl i m a t e and good a c c e s s i b i l i t y of the area allowed uninterrupted work. In most of the area the geology was p l o t t e d on base maps on a sca l e of 1/2 m i l e to the i n c h . Near the Fraser R i v e r base maps on scales of 1000 feet and 500 feet to the i n c h were a v a i l a b l e . Locations were e s t a b l i s h e d by cross bearings, a l t i m e t e r readings, and pace and compass t r a v e r s e s . The geology of the Bowman Range was p l o t t e d on a i r photographs and, by means of 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 to base maps showing photo centers. 4. Physiography and P l e i s t o c e n e Geology Three major elements of the topography can be d i s t i n g u i s h e d : M i d - T e r t i a r y and o l d e r mountain ranges, Middle or Late T e r t i a r y upland surfaces 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 of the map area are the P a v i l i o n Mountains and the Bowman Range i n the east u n d e r l a i n by the Upper and (?) Middle Permian Marble Canyon formation, and the Camelsfoot Range and Fountain Ridge i n the west, u n d e r l a i n by Lower Cretaceous sedimentary rocks. The Bowman Range and the P a v i l i o n Mountains c o n s i s t mostly of p a r a l l e l r i d g e s formed by s t e e p l y dipping l i m e -stones. In the northern part of the Bowman Range a pla t e a u -l i k e topography has been produced by gently dipping limestone beds. As i n t h i s a r i d c l i m a t e limestone i s very r e s i s t a n t to weathering the highest mountains of the map-area are 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 moderately dipping l i t h i c sandstones and conglomerates that are h i g h l y r e s i s t a n t to weathering. I t has steep s l o p e s , and i s transected by numerous v a l l e y s , some of which are deeply i n c i s e d and narrow. Fountain Ridge i s a narrow remnant of the same mountain mass. In the present map area the e l e v a t i o n s of the Camelsfoot Range are mostly between 4500 and 5500 feet but r i s e up to 6900 f e e t . The a l t i t u d e s of Fountain Ridge range from 4200 to 5500 f e e t . Mount M a r t l e y , whose rounded top reaches an a l t i t u d e of 6700 f e e t at the southeastern edge of the present map area, i s formed by-highly 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 sedimentary and v o l c a n i c rocks of the P a v i l i o n group form h i l l y t r a c t s or mountains of l e s s e r height which r a r e l y r i s e above 5000 f e e t . Gently dipping Cretaceous 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 very r e s i s t a n t to weathering form a b e l t of low mountains that only i n the northern part of the area r i s e to e l e v a t i o n s of more than 6000 f e e t . F l a t l y i n g sedimentary and v o l c a n i c rocks of Middle or Late T e r t i a r y age form small plateaus at a l t i t u d e s ranging approximately from 3000 to 4000 feet near P a v i l i o n , between McKay Creek and Watson Bar Creek, and on B i g Bar Creek. North of P a v i l i o n , south of Watson Bar Creek, and i n the v i c i n i t y of B i g Bar Creek some of these d e p o s i t i o n a l surfaces are con-tinuous w i t h younger gently s l o p i n g e r o s i o n a l s u r f a c e s , which are covered only w i t h a t h i n veneer of unconsolidated P l e i s t -5 ocene and Recent d e p o s i t s . These Middle or Late T e r t i a r y surfaces are parts of the f l o o r of a v a l l e y that p o s s i b l y ex-tended from Glen Fraser to B i g Bar Mountain and was connected along B i g Bar Creek w i t h the extensive p l a t e a u east of the Bow-man 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 present Fraser R i v e r v a l l e y but has not been recognized south of Glen Fr a s e r . The present v a l l e y of the Fraser R i v e r i s younger than these Middle or Late T e r t i a r y surfaces and was probably developed i n P l e i s t o c e n e time. In most of the area i t i s approximately p a r a l l e l to the s t r i k e of the rocks and to the Fraser 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 that the R i v e r o r i g i n a l l y flowed along Fountain v a l l e y but was d i v e r t e d i n t o the Bridge R i v e r . The P l e i s t o c e n e v a l l e y bottom probably c o i n c i d e d approximately w i t h the present surface of the r i v e r which l i e s between 900 and 650 f e e t above sea l e v e l . This v a l l e y was f i l l e d , probably 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 than 1000 f e e t of unconsolidated m a t e r i a l s ranging from boulder g r a v e l to mud (See P l a t e I V ) . The s t r a t i g r a p h y of these de-p o s i t s changes over short distances and t h e i r h i s t o r y i s com-p l i c a t e d . Much of the m a t e r i a l showing d e l t a i c cross-bedding appears to have been deposited by braided streams. Some of the extensive s i l t d eposits between P a v i l i o n and B i g Bar Creek may have been l a i d down i n g l a c i a l l a k e s . Mudflows appear to have been deposited on a l l u v i a l fans of t r i b u t a r i e s . In Recent time the r i v e r has been rejuvenated and has cut through the unconsolidated sediments i n t o bedrock. This r e j u v e n a t i o n probably was caused by a decrease of the 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. 144). Although the area 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 r a r e . Probably no- r a p i d movements took place i n t h i s r e g i o n which l i e s only some 50 miles to the south of a major g l a c i a l d i v i d e (Geol. Assn. of Canada, 1958; W.H.Mathews, 1941, p. 64). A t h i n l a y e r of Recent v o l c a n i c ash has been found i n the v i c i n i t y of B i g Bar and Jesmond. W.H.Mathews ( o r a l communi ca t i o n ) suggests that the ash was ejected by a cinder cone on the upper Bridge R i v e r . H. Nasmith ( o r a l communication) re->/ ports Recent v o l c a n i c ash i n the v i c i n i t y of P a v i l i o n . y- v «• <.•> 5. Climate, V e g e t a t i o n , Wild L i f e The area l i e s i n the \"dry b e l t \" of the I n t e r i o r of B r i t i s h Columbia which i s sh e l t e r e d from r a i n and snow by the Coast Mountains. The average annual p r e c i p i t a t i o n at L i l l o o e t over 41 years was 12.35 inches. The summers are warm and the winters c o o l . The extremes at L y t t o n , some t h i r t y m iles south o f the map area i n 1956 were -9° i n January and 106° i n J u l y ; the extremes recorded w i t h i n 30 years are -25° and 1120. (Province of B. C. Dept. of 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 sparse. Some parts of the area are covered by f o r e s t s , some are p a r k - l i k e , and others open gr a s s - l a n d . The slopes of the western part are more densely f o r e s t e d than those of the eastern p a r t . Most of the trees are pines (lodge-pole pine, ponderosa p i n e ) ; white spruce balsam f i r and Douglas f i r , are common only i n the higher and c o o l e r areas that 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 which l i e s near 6500 f e e t . V a l l e y f l a t s are c h a r a c t e r i z e d by sage brush, bunch grass and cactus. The area i s noted f o r b i g game. Deer, moose, and black bears are common i n the Bowman Range and on the west side of the Fraser R i v e r ; goats were observed on the west side of the r i v e r , southwest of P a v i l i o n . 6. I n d u s t r i e s The main i n d u s t r y of the area i s c a t t l e ranching. The s o i l s of the Fraser 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 , which were seen i n many l o c a l i t i e s , are very f e r t i l e , but the r a i s i n g of c a t t l e feed depends on i r r i g a t i o n , and only a few creeks c a r r y water a l l summer. Logging i s second i n importance. In 1956 and 1957 only f o r e s t s on the east side of the Fraser R i v e r near P a v i l i o n K e l l y Lake, and Jesmond were logged but preparations f o r the e x p l o i t a t i o n of the west side were being made. Mining i s r e l a t i v e l y unimportant. In 1958 only two p l a c e r mines were o p e r a t i n g , one on the Fraser R i v e r , opposite Fountain (M3) and the other one on Watson Bar Creek. Some e x p l o r a t i o n work was done on the claims of the Monty group (M2), southwest of Ward Creek. 8 Tourism and b i g game hunting provide another source of income f o r l o c a l people. A power dam on the Fraser R i v e r would help the l o c a l 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 extensive 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 (Warren, 1959). 9 CHAPTER I GENERAL GEOLOGY Introductory Statement The general geology of the area i s summarized on the f o l l o w i n g t a b l e of 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 llowed here and the term i s a p p l i e d to other u n i t s that are roughly equivalent to formations but not w e l l enough known to 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 of 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 are termed \"assemblage\" and designated by the name of the area i n which they occur. TABLE OF FORMATIONS Succession System S e r i e s Stage Group Forma-t i o n or D i v i s i o n Assem-blage Mem-ber .Lithology and Contacts Quater-nary Recent and P l e i s t o -cene A l l u v i u m , 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 -Ceno-z o i c T e r t -i a r y 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 , minor andesite. - conformable contact -l i t h i c a r e n i t e , conglom-e r a t e , minor shale - angular unconformity -Eocene Oligocene or younger t u f f , f e l s i t e , a n d e s i t e , b a s a l t , minor c o a l . - conformable contact -Eocene-O l i g o -cene French Bar Formatior 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 , plant seams. - unconformity -Ceno-z o i c or Mesozoic Pre-Oligo-cene post e a r l y Lower Cretaceous Ward Creek assem-blage a n d e s i t e , d a c i t e , f e l s i t e , t u f f , minor b a s a l t , v o l c a n i c a r e n i t e , c o a l . - not i n contact -Succession System S e r i e s Stage Group Forma-t i o n or D i v i s i o n •Assem-blage Mem-ber L i t h o l o g y and Contacts Ceno-z o i c or Lower Cretac-eous or gabbro and diabase dykes Mesozoic younger / - not i n contact -A l b -ian? Spences Bridge Group ? Foun-t a i n V a l l e y C a n d e s i t e , minor v o l c a n i c a r e n i t e , v o l c a n i c bre-c c i a , plant seams or King- assem- B f e l s i t e or s v a l e Grp. ? blage A a n d e s i t e , f e l s i t e , minor conglomerate. - not i n contact -Apt-ian? Spences Bridge Grp. lower Div. or Kingsvale Grp. Div. B. Glen Fraser ass em. a n d e s i t e , d a c i t e . - contact not exposed -Div.B a n d e s i t e , d a c i t e , minor t u f f , v o l c a n i c a r e n i t e . Mesozoic Cre-taceous Lower Cre-taceous A l b -ian? Kings-v a l e Grp - conformable contact -Div. A v o l c a n i c a r e n i t e , con-glomerate, minor s i l t -stone, plant seams. - unconformity -Succession System S e r i e s Stage Group 'Form-a t i o n or D i v i s i o n Assem-blage 'Mem-ber L i t h o l o g y and Contacts Upper D i v i s i o n a n d e s i t e , minor d a c i t e , v o l c a n i c a r e n i t e , s i l t -stone. Spences Bridge Group Apt-ian? - not i n contact -Mesozoic Cret a -eous Lower C r e t a -eous Lower D i v i s i o n Gibbs Creek assem-C an d e s i t e , minor d a c i t e , v o l c a n i c a r e n i t e , s i l t -stone. blage B a n d e s i t e , 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 A - not i n contact -Lower D i v i s i o n Bas-a l mem. an d e s i t e , d a c i t e , t u f f , a n d e s i t i c b r e c c i a . - angular unconformity w i t h P a v i l i o n Group -ro Succession System S e r i e s Stage Group Form-a t i o n or D i v i s i o n Assem-blage Mem-ber L i t h o l o g y and Contacts Mesozoic Cre-baceous lower Cre-taceous Barre-miari(? p o r p h y r i t i c q u a r t z - d i o r i t e dykes and s i l l s . - i n t r u s i v e contact -) Jack-ass Mtn. Grp, Div. C v o l c a n i c a r e n i t e , a r g i l l -i t e , conglomerate; minor plant seams. - conformable contact -Div. B conglomerate, v o l c a n i c a r e n i t e , minor a r g i l l -i t e . - l o c a l unconformities -Div. A A I I I A l l AI s i l t s t o n e , v o l c a n i c aren-i t e a r g i l l i t e , minor limestone. 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 , a r g i l l i t e , conglomerate, conglomerate, tuffaceous sandstone, v o l c a n i c aren-i t e , minor plant seams. - unconformity -Succession System S e r i e s Stage Group Form-a t i o n or D i v i s i o n Assem-blage Mem-ber L i t h o l o g y and Contacts L i l l o -oet Grp.? Div. C v o l c a n i c a r e n i t e ( t u f f -aceous ), conglomerate, s i l t s t o n e , a r g i l l i t e . - f a u l t contact w i t h D i v i s i o n B, angular unconformity? -Mesozoic Cre-taceous Lower Cre-taceous Neoco-mian? p o r p h y r i t i c q u a r t z - d i o r -i 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. - i n t r u s i v e contact -L i l l o -oet Grp. Div. B v o l c a n i c a r e n i t e , s i l t -stone, a r g i l l i t e , con-glomerate. - g r a d a t i o n a l contact -Div. A a r g i l l i t e , s i l t s t o n e , v o l c a n i c a r e n i t e , minor c o a l . - not i n contact -Succession System S e r i e s Stage Group Form-a t i o n or D i v i s i o n Assem-blage Mem-ber L i t h o l o g y and Contacts Lower Cretaceous or older q u a r t z - d i o r i t e , d i o r i t e , g r a n o d i o r i t e stocks 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 w i t h P a v i l i o n group -Upper T r i a s -s i c (?) s e r p e n t i n i z e d p e r i d o t i t e and carbonate - s i l i c a a l t e r a t i o n . Mesozoic - i n t r u s i v e contact w i t h P a v i l i o n group -T r i a s s -i c (?) D i v . I I P a v i l -i o n assera. 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 , c h e r t , l i m e -stone; minor b r e c c i a , s i l t -stone, a m p h i b o l i t e , horn-f e l s , meta-quartzite. P a v i l -i o n Grp. - not i n contact -B i g Bar assem. t u f f , l i t h i c sandstone, a r g i l l i t e , c h e r t , v o l -canic flows. - g r a d a t i o n a l contact -Mesozoic and/ or P a l e o z o i c T r i a s s i c : and/ or Upper Per-mian P a v i l -i o n Grp. D i v . I c h e r t , a r g i l l i t e , minor t u f f , limestone, v o l c a n i c flows. - g r a d a t i o n a l contact -vn Succession System S e r i e s Stage Group Form-a t i o n or D i v i s i o n Assem-blage Mem-ber L i t h o l o g y and Contacts P a l e o z o i c Permian Upper Permian Upper Permian and/or Middle Permian Cache Creek Group Marble Canyon Form-a t i o n Southern Bowman Range IV I I I I I I c h e r t , a r g i l l i t e , l i m e -stone, t u f f , v o l c a n i c f l o w s . limestone c h e r t , a r g i l l i t e , l i m e -stone, t u f f , v o l c a n i c flows. limestone w i t h i n t e r -bedded ribbon c h e r t . - conformable contact -Middle Permian and/or Older ii Mt. Soues Div. 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 , l i m e -stone. ON 17 1K SEDIMENTARY AND VOLCANIC ROCKS CACHE CREEK GROUP I n t r o d u c t i o n The Cache Creek group was f i r s t described by Selwyn, 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 . The lower p a r t , s t u d i e d i n outcrops along the Cariboo Highway be-tween M a r t e l and C l i n t o n , was s a i d to contain limestone, black s h a l e , rocks r i c h i n epidote and c h l o r i t e a s s ociated 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 the o l d e s t Devonian and the 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 to co n t a i n l i m e -stone, marble, dolomite, 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 s h a l e s . F o r a m i n i f e r a from the Marble 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 considered to be Eocene or Cretaceous i n age. G.M. Dawson's report on the Kamloops area (1895) con-t a i n s the f i r s t comprehensive d e s c r i p t i o n of the Cache Creek . \"formation\" of the type area. Dawson described the d i s t r i b u t i o n of 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 : the Marble Canyon l i m e -stones, shown as a separate map u n i t , form a northwesterly t r e n d i n g b e l t , that extends from the Cornwall H i l l s to the northwestern extremity of the map area but i s concealed by T e r t i a r y rocks i n the v i c i n i t y of Hat Creek. Immediately to 18 the east of the limestone, i n the area of C a t t l e V a l l e y , McLean Lake, and Medicine Creek, v o l c a n i c rocks associated w i t h l i m e -stone are dominant. Farther east, on Bonaparte R i v e r and Thompson R i v e r , cherty q u a r t z i t e s and a r g i l l i t e s are most abundant. To the west of the limestone b e l t , i n the Edge H i l l s , i n the western part of the P a v i l i o n Mountains, and on Mount M a r t l e y , chert and a r g i l l i t e are dominant; f a r t h e r west, on P a v i l i o n Creek and Leon Creek, most of the rocks are v o l c a n i c . Dawson, as d i d Selwyn, considered the Marble Canyon limestones to be the upper part of the formation but str e s s e d t h e i r s t r a t i -graphic c o n t i n u i t y w i t h the underlying rocks. As the limestone b e l t i s flanked to the east and west by \" o l d e r \" rocks he thought that the 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 modified by numerous minor f o l d s . His summary of the s t r a t i g r a p h y of the Cache Creek group i s based on a composite s e c t i o n through the eastern limb of that \" s y n c l i n e \" (l895»p.46B): Feet 1. Massive limestones (Marble Canyon l i m e -stone) w i t h some minor i n t e r c a l a t i o n s of v o l c a n i c r o c k s , a r g i l l i t e s and eherty q u a r t z i t e s . At l e a s t 1000 feet seen i n some s i n g l e exposures. T o t a l thickness 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 limestones, w i t h some a r g i l l i t e s , cherty q u a r t z i t e s , e t c . , Minimum thickness 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 serpentines w i t h some l i m e -stone. The thickness of these beds, or of a part of them, was roughly estimated i n two places as between 4000 and 5000 f e e t . Minimum t o t a l thickness 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 of L o f t u s i a but because of accompanying f u s u l i n i d s r e f e r r e d i t to the Car-boniferous and defined the Cache Creek as an e s s e n t i a l l y Carbon-i f e r o u s 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 accumulated, Dawson's age determination was r e v i s e d . Dunbar (1932), Thompson and Wheeler (1942), and Wickenden ( D u f f e l l and McTaggart, 1952, p. 23) a l l agreed on a Permian age but disagreed on the s p e c i f i c p o s i t i o n i n that p e r i o d . D u f f e l l and McTaggart c a l l e d the Cache Creek a group and the Marble Canyon limestones 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 hy-potheses about the major s t r u c t u r e and s t r a t i g r a p h i c order w i t h -i n the group. The f i r s t i s Dawson's concept that two major u n i t s are arranged i n a s y n c l i n e ; the second that the \"group c o n s i s t s of two successions of a r g i l l i t e s , c h e r t s , greenstones, minor limestones, and q u a r t z i t e s , separated by the t h i c k s e r i e s of the Marble Canyon limestones.\" (p. 17). According to the f i r s t hypothesis the Cache Creek group i s approximately 10,000 feet t h i c k , according to the second hypothesis 20,000 f e e t . The l a t t e r thickness i s comparable, as D u f f e l l and McTaggart have pointed out, to a s e c t i o n of 24,000 fe e t measured by Armstrong i n the Fort S t . James area (1949) that includes three l i m e -stone u n i t s and four separate chert successions. In an attempt to solve the problems r e s u l t i n g from the e a r l i e r work the Marble Canyon Formation was studied i n some d e t a i l . F o s s i l s from the upper part of that formation are 20 assigned by W.R. Danner to the Upper and (?) Middle Permian. In the southern part o f the Bowman Range the Marble Canyon formation i s approximately 6000 feet t h i c k and contains 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 feet of l i m e -stone. I t here forms a northwesterly trending a n t i c l i n o r i u m that i s overturned to the northeast. In the core o f the a n t i -c l i n o r i u m , on the south slope of Mount Soues an ol 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 limestone i s exposed which i s here c a l l e d Mount Soues D i v i s i o n . The rocks to the west of Bowman Range and P a v i l i o n Mountains appear to o v e r l i e the Marble Canyon formation conformably. A f o s s i l found i n these rocks i s probably of T r i a s s i c age. As the Cache Creek group has been defined as a Permo-Pennsylvanian u n i t (Armstrong, 1949> p. 50) the Permo-Triassic rocks o v e r l y i n g the Marble Canyon formation are assigned to a new u n i t , the P a v i l i o n group. MOUNT SOUES DIVISION On the southeast slope of Mount Soues ribbon 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 of basic composition, t u f f , and limestone are exposed. The assemblage d i f f e r s from rocks of the P a v i l i o n group i n two respects: the presence of limestones that are i n t e r l a m i n a t e d w i t h ribbon c h e r t , and the r e l a t i v e abundance of bas i c v o l c a n i c f l o w s . The outcrop zone i s about two miles wide and pinches out to the northwest. The thick n e s s of the unit which i s o v e r l a i n conformably by the Marble Canyon formation i s estimated as approximately 1500 f e e t . The rocks are folded and f a u l t e d and seem to occupy the core of an 21 anticlinorium formed by the basal member of the Marble Canyon formation. As the Marble Canyon Formation is Middle (?) and Upper Permian the Mount Soues Division probably is Middle Permian and/or older. MARBLE CANYON FORMATION 1. Distribution In the present map area the Marble Canyon formation underlies the Bowman Range and the central part of the Pavilion Mountains. In the Bowman Range where the formation has been mapped in 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 faulting and folding, and the scarcity of marker beds, bedding attitudes, and stratigraphic top determinations i t has been almost im-possible 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 in the southern part of the Bowman Range. Four members I, II, III, IV are distinguished here, and a f i f t h I l i a is recognized in the central and northern parts of the area. The stratigraphy described on the following pages is valid only for the southern part of the Bowman Range; i t is impossible, for example, to recognize the same members in the Marble Canyon. 22 Member I , approximately 200 to 300 feet t h i c k i s com-posed of limestone and ribbon c h e r t . The limestone i s p a r t l y massive, 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 ribbon c h e r t . Laminae of chert are one to three inches t h i c k . Most of the laminae are extensive but at some l o c a l i t i e s they form short u n i t s one to s e v e r a l feet long. The limestone seems to be continuous over most of the area, but i n the v i c i n i t y of F i f t y - S e v e n Creek i t apparently forms discontinuous lenses that i n t e r f i n g e r w i t h c h e r t . No f o s s i l s were found i n the u n i t . Member I I , which o v e r l i e s I i s poorly 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 , small lenses and beds of lim e -stone, and v o l c a n i c flow rocks. Although the member appears to be 3200 f e e t t h i c k i t probably has been repeated by f o l d i n g , and the tru e thickness perhaps l i e s between 500 and 1000 f e e t . Member I I I , i s composed mainly of limestone but l o c a l l y contains small amounts of interbedded chert and a r g i l l i t e . The member forms a high r i d g e , about 13 miles l o n g , that culmin-ates i n Mount Bowman ( P l a t e V ) . South of Porcupine Creek the limestone i s approximately 1000 feet t h i c k ; south of Two-Mile Creek i t tapers and f i n a l l y disappears. North of Porcupine Creek the s t r u c t u r e probably i s complicated 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 the f u l l s t r i k e - l e n g t h nor the s t r a t i g r a p h i c thickness o f the limestone mass are c e r t a i n . The limestone masses on Mount Kerr (about 2500 to 3000 feet t h i c k ) are perhaps i n the same s t r a t i g r a p h i c p o s i t i o n as the ones on Mount Bowman but the two are not connected by outcrop; p o s s i b l y these bodies are 23 l e n t i c u l a r . Most of the limestone i s pure and massive and shows no bedding. In 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 grey and.; dark grey l a y e r s are v i s i b l e that are from a few m i l l i m e t e r s to one centimeter t h i c k . Under the microscope the l a y e r s are seen to d i f f e r i n g r a i n s i z e and i n the pr o p o r t i o n of minute i n c l u s i o n s i n the carbonate. Some of the rocks are c a l c a r e n i t e s and show graded bedding, r i p p l e marks, 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 . ( P l a t e V I ) . B r e c c i a s made up of fragments that range from a few m i l l i m e t e r s to one i n c h i n s i z e l o c a l l y occur w i t h i n the massive limestone. In the northern part of the map area some rocks that may be c o r r e l a t i v e w i t h member I I I con-t a i n o o l i t e s . F o s s i l s are r e l a t i v e l y r a r e ; remains of c o l o n i a l c o r a l s , of c r i n o i d s , e c h i n o i d s , algae, and f u s u l i n i d s have been found at a few l o c a l i t i e s . In the s y n c l i n e on Mount Kerr the t h i c k massive l i m e -stone of member I I I i s o v e r l a i n by a bed of limestone, approx-imately 500 f e e t t h i c k , that contains laminae of ch e r t . A sheet of i n t e r l a m i n a t e d limestone and chert forms the c r e s t of the Bowman Range between Mann Creek and Jesmond Creek. Scattered outcrops of a s i m i l a r type occur between Jesmond Creek and the northern extremity of the Bowman Range. These rocks are t e n t a -t i v e l y r e f e r r e d to member I l i a , but I t i s not c e r t a i n whether a l l of them are i n the 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 of chert from t h i s u n i t con-s i s t s of anhedral quartz grains showing undulose e x t i n c t i o n that range from a few microns to .2 mm i n diameter. Some s p h e r i c a l aggregates w i t h a diameter of .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 long and ,05 mm wide composed of very f i n e - g r a i n e d s i l i c a are v i s i b l e ; they are probably of r a d i o l a r i a n o r i g i n . 24 A hand specimen of limy chert c o n s i s t s of f i n e blue grey s t r i n g e r s , that are one to two centimeters long and a few m i l l i m e t e r s t h i c k , em-bedded i n a l i g h t grey groundmass. The s t r i n g e r s are crenulated and f r a c t u r e d . Under the micro-scope they are seen to c o n s i s t of f i n e - g r a i n e d s i l i c a , dominantly quartz w i t h undulose e x t i n c t -i o n , and small amounts of chalcedony. The l i g h t grey matrix comprises about 50% carbonate grains part of which, showing rhombohedral h a b i t , are pro-bably dolomite, and $0% quartz and chalcedony. S i l i c a and carbonate are uniformly 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 of f i n e - g r a i n e d s i l i c a i n the center and r e l a t i v e l y coarse-grained quartz 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 of a r g i l l i t e , c h e r t , limestone, t u f f , tuffaceous sandstone, and v o l c a n i c flow rocks, but only the limestones are w e l l exposed. The l a t t e r occur i n lenses and beds ranging from a few hundred feet to 8 miles i n s t r i k e l e n g t h . Some are of f a i r l y constant t h i c k n e s s , others vary considerably 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 Mountain, f o r example, that i s about 2 miles l o n g , ranges from 200 feet to about 2000 feet i n t h i c k n e s s . Most of the limestones do not show bedding. In 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 others f u s u l i n i d s , algae, c o r a l s , pelecypods, and.echinoderms ( ? ) . In the v i c i n i t y of i n t r u s i o n s the limestone 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 which l o c a l l y shows a f o l i a t i o n i n the form of f i n e dark l a y e r s r i c h i n carbonaceous matter. The thickness of t h i s member i s un c e r t a i n because i t s s t r u c t u r e could not be worked out. On the west s i d e of the Bowman Range i t occupies a b e l t one m i l e to 1-1/2 miles wide. The thickness of the u n i t i s perhaps between 3000 and 6000 f e e t . The succession i n the Marble Canyon formation i n the south-western part of the Bowman Range may be summarized as f o l l o w s : Member IV 3000-6000 f e e t . Chert, a r g i l l i t e , l imestone, t u f f , v o l c a n i c flows. \" I I I 1000 \" Limestone \" I I 500-1000 11 Chert, a r g i l l i t e , limestone, t u f f , v o l c a n i c f l o w s . 11 I 200- 300 11 Limestone w i t h interbedded ribbon c h e r t . 4700-8300 f e e t . The Marble Canyon formation i n t h i s area then i s approximately 6000 feet t h i c k and contains perhaps 2500 feet of limestone. As the limestone forms conspicuous c l i f f s and the other rocks are mostly concealed by overburden the pro-p o r t i o n of limestone i n the formation has been overestimated by previous workers. 3. S t r u c t u r e Because of f a c i e s changes, l a c k of marker beds, and the s c a r c i t y of bedding a t t i t u d e s and s t r a t i g r a p h i c top deter minations ( r e l a t e d to the r e e f a l character of the limestones) the whole s t r u c t u r a l p i c t u r e has not been worked out. Some success, however, was achieved i n the southern part of the Bowman Range, and the inf o r m a t i o n obtained i n t h i s area may b s u f f i c i e n t to e s t a b l i s h the age r e l a t i o n of the Marble Canyon formation to the P a v i l i o n group. The f o l l o w i n g three c r i t e r i a have been used f o r the r e c o g n i t i o n of f o l d s : 26 The most important c r i t e r i o n are bedding a t t i t u d e s . However, systematic changes i n s t r i k e and dip could not be observed i n a l l of the postulated f o l d s . A V-shaped or U-shaped limestone outcrop v i s i b l e on a i r photographs i s suggestive of the nose of a plunging f o l d because the limestones i n most l o c a l i t i e s form conspicuous out-crops whereas the other rock types, which are l e s s r e s i s t a n t to weathering, are mostly covered by overburden. However, t h i s c r i t e r i o n alone, i s not used to e s t a b l i s h a f o l d because the same outcrop s i t u a t i o n could be produced by the d i f f e r e n t i a l weathering of a s o l i d mass of limestone or 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 areas of a n t i c l i n e s or i n the troughs of s y n c l i n e s . Apparently the f o l d i n g was accomplished by very l i t t l e flowage and much f r a c t u r i n g of the s t r a t a . In the extreme case a box-type of f o l d i s produced w i t h s t e e p l y dipping 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 be-tween the c r e s t and the limbs. ( P l a t e IX) However, i n most l o c a l i t i e s the c r e s t s or troughs are c h a r a c t e r i z e d by i r r e g u l a r c o n t o r t i o n s . In the southern part of the Bowman Range Member I appears to form a northwesterly plunging a n t i c l i n o r i u m which i s overturned to the northeast and i s composed of at l e a s t f i v e a n t i c l i n e s and the corresponding s y n c l i n e s . ( C r o s s - s e c t i o n F - F 1 ) . ( P l a t e V I I ) A few f a u l t s , modifying the a n t i c l i n o r i u m are shown on the map; others are probably concealed by overburden. The only f o l d recognized w i t h assurance i n the c e n t r a l i part of the Bowman Range i s an u p r i g h t , broad, open s y n c l i n e on Mount K e r r , which plunges to the southeast and f i t s between two northwesterly plunging a n t i c l i n e s o u t l i n e d by Member I . ( P l a t e V I I I ) A change i n the d i r e c t i o n of dips and strong d i s t o r t i o n s are w e l l d i s p l a y e d i n the c e n t r a l part of the s y n c l i n e which i s formed by the i n t e r l a m i n a t e d limestone and chert of Member I l i a . In the northern part of the Bowman Range the dips of the s t r a t a are mostly moderate to low; t h e i r d i r e c t i o n s are uniform w i t h i n small areas but change a b r u p t l y from one area to another. No f o l d s could be o u t l i n e d . A few f a u l t s are shown on the map. I t i s b e l i e v e d that many others are hidden by overburden. I t seems that the s t r a t a here are broken i n t o numerous f a u l t blocks 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 of f a u l t i n g over f o l d i n g i n the northern part of the map area probably i s due to the great thickness of the s t r a t a , to t h e i r l e n t i c u l a r (?) shape and to low heat and pressure during the time of deformation. 4. Mode of O r i g i n The absence of coarse-grained c l a s t i c rocks and the dominance of b i o l o g i c a l , chemical, or 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 that the source area was of low r e l i e f or at a great distance from the basin of d e p o s i t i o n . Three types of limestone can be d i s t i n g u i s h e d . The f i r s t type 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 chert (member I and I l i a ) . These deposits are moderately t h i c k , ranging from 200 to 500 f e e t i n thickness and may cover as much as 100 square m i l e s . As they are as s o c i a t e d w i t h chert that i s p o s s i b l y of 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 the limestone: i t may have formed by the accumulation of 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 . However, no f o s s i l s have been found i n these rocks . Perhaps the s e d i -ments were deposited very s l o w l y and subjected to s o l u t i o n and r e c r y s t a l l i z a t i o n on the sea f l o o r . The a l t e r n a t i v e i s inorganic 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 the 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 of limestone deposit i s extremely t h i c k (up to 2500 f e e t ) but probably narrow. C o r a l s , algae, bryozoa and echinoids (together w i t h f u s u l i n i d s ) have been found i n these rocks. The f o s s i l s and the shapes of the deposits suggest that they are r e e f s . However, Lowenstam (1950) argues t h a t not any mass of f o s s i l i f e r o u s limestone showing r e e f l i k e dimensions should be c a l l e d a re e f and r e q u i r e s evidence that sediment binding organisms were present which were able to erect wave r e s i s t a n t s t r u c t u r e s . C e r t a i n c o l o n i a l c o r a l s such as Waagenophyllum (?) which are 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 of the type r e q u i r e d . The t h i c k limestone masses i n the v i c i n i t y of Mount Kerr are be l i e v e d to be r e e f s . A t h i r d type, o c c u r r i n g i n the members I I and IV i s l e n t i c u l a r or p o d - l i k e and ranges from one hundred feet to s e v e r a l miles i n s t r i k e l e n g t h . Many of these bodies have dimensions s i m i l a r to those of r e e f s but most of them are l a c k i n g i n f o s s i l s . Perhaps some were r e e f s composed of a l g a l s t r u c t u r e s that are no longer r e c o g n i z a b l e . The o r i g i n of these deposits i s u n c e r t a i n . 29 C a l c a r e n i t e s and b r e c c i a s i n the members I I I and I l i a i n d i c a t e l o c a l current a c t i v i t y . Some of the beds co n t a i n i n g o o l i t e s may have been deposited at shallow depth i n the zone of wave a c t i o n ( I l l i n g , 1954, pp. 35-44). The o r i g i n of the ribbon chert i s a c o n t r o v e r s i a l s u b j e c t . According to modern experimental work (Krauskopf, 1956) both fresh-water and sea-water are h i g h l y undersaturated w i t h respect to s i l i c a and n e i t h e r changes i n p.H. (below a p.H. of 9) nor i n s a l i n i t y a p p r e c i a b l y a f f e c t the s o l u b i l i t y of that substance. Only three of the va r i o u s hypotheses f o r the o r i g i n of chert seem reasonable i n view of the r e q u i r e d chemical c o n d i t i o n s e s t a b l i s h e d by Krauskopf: 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 that may be r e l a t e d to volcanlsm (Davis, 1918; C a i r n e s , 1924b, p. 41); the leac h i n g and r e d e p o s i t i o n of s i l i c a from v i t r i c t u f f , a m a t e r i a l that d i s s o l v e s much f a s t e r than m i n e r a l i c matter ( G o l d s t e i n and Hendricks, 1953) and the accumulation of debris from s i l i c e o u s organisms (Bramlette, 1946). Both v o l c a n i c f l o w s , and t u f f s are present i n the Marble Canyon formation. There i s however, no s t r i k i n g a s s o c i a t i o n of chert and v o l c a n i c flows and the r e l a t i v e l y small p r o p o r t i o n of t u f f appears i n s u f f i c i e n t as source of the much l a r g e r volume of c h e r t . However, t h i n -s e c t i o n s of chert show s p i n e - l i k e and nodular s t r u c t u r e s that could be of organic o r i g i n . B e t t e r preserved specimens of the same type have been found i n greater quantity i n the cherts of D i v i s i o n I of the P a v i l i o n group. Therefore i t i s b e l i e v e d that the chert of the Marble Canyon Formation i s l a r g e l y of organic o r i g i n . 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 at 11 l o c a l i t i e s i n the 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: F l L o c a l i t y : On r i d g e , about 1 mile east of Jesmond road, 1.25 miles northwest of Porcupine Creek, upper p a r t . Member IV Yabeina sp. Schwagerina sp. Verbeekina sp. Glomospira sp. Gy r o p o r e l l a sp. ass o c i a t e d : algae, c o r a l , s m a l l f u s u l i n i d s Age: Upper Permian. F2 L o c a l i t y : On r i d g e , about 1 mile east of Jesmond road, 2 miles southeast of Mt. Bowman. Member I I I Yabeina sp. one small Verbeekina 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 to Pachyploia T e t r a t a x i s sp. Gy r o p o r e l l a sp. ass o c i a t e d : echinoid d e b r i s , mollusc s h e l l s , and a c o r a l . Age: Upper Permian. The assemblage could be s l i g h t l y o l d e r than those from the other l o c a l i t i e s . L o c a l i t y : On r i d g e about 2 m i l e s east of Jesmond road, 2 m i l e s northeast of head of Porcupine 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. L o c a l i t y : Two miles southeast of Mt. K e r r , .7 miles northwest of F i f t y - s e v e n Creek. Member I I I Yabeina columbiana ?Neoschwagerina sp. ?Verbeekina sp. Ass o c i a t e d : other f o r a m i n i f e r a ( ? ) , c o r a l s , algae, coarse p l a t e s of echninoderms, c r i n o i d stems, a bryozoan fragment, and o o l i t e s . Age: Upper Permian. L o c a l i t y : 1.5 miles west of Mt. Kerr Member I I I Yabeina minuta Schwa^erina a c r i s Condonofusinella sp. Age: Upper Permian. 32 F6 L o c a l i t y : 3.2 miles east of Mt. Bowman, .2 miles n o r t h of Mann Creek Member I I I ? Yabeina sp. Condonofusinella sp. Glomospira sp. Age: Upper Permian F7 L o c a l i t y : 3.5 miles east-northeast of Mt. Bowman, .5 miles n o r t h of Mann Creek. Member I I I ? ?Waageno phy Hum sp. Associated: at l e a s t two Permian type f u s u l i n i d s . Age: Permian. F 8 L o c a l i t y : 2 miles east of Mt. Bowman, .5 miles south-west of head of Mann Creek Member I I I ? Yabeina sp. Age: Upper Permian F9 L o c a l i t y : about 5 miles east of Jesmond, 1 m i l e northeast of head of Jesmond Creek Member I I I ? 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: unknown but probably Upper P a l e o z o i c . F10 L o c a l i t y : About 1/2 m i l e n o r t h northwest of F 9 Member I I I ? C o r a l s , f o r a m i n i f e r a , echinoid stems. Age: unknown. 33 F l l L o c a l i t y : E astern bank of B i g Bar Creek, about 2.5 miles northwest of Jesmond. Member IV F u s u l i n i d s , pelecypods, c o r a l , algae or echinoderms. Age: Permian. W.R.Danner s t a t e s that most of the 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 to the American and A s i a t i c Tethys sea. \"The a s s o c i a t i o n of Yabeina-Schwa^erina-Condonofusinella i s t y p i c a l as f a r as i s known f o r the uppermost f u s u l i n i d zone i n North America and i s considered to 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 than the others but the f u s u l i n i d s are too r e c r y s t a l l i z e d to e s t a b l i s h whether they are Neoschwagerina and hence a zone lower i n the 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 the members I I I and IV or i n rocks that are b e l i e v e d to be c o r r e l a t i v e w i t h these members. Both members th e r e f o r e appear to be mostly Upper Permian; but the lower part of I I I may be Upper Middle Permian. The members I and I I are perhaps Middle Permian. PAVILION GROUP 34 I n t r o d u c t i o n The Permo-Triassic P a v i l i o n group i s composed of c h e r t , a r g i l l i t e , v o l c a n i c flow-rocks and t u f f , v o l c a n i c sand-stones, limestone, s i l t s t o n e , conglomerate, sedimentary b r e c c i a and the metamorphic equivalents of these rocks. Two D i v i s i o n s are d i s t i n g u i s h e d . Chert and a r g i l l i t e are dominant i n the lower part ( D i v i s i o n I) and v o l c a n i c rocks and sandstones i n the upper part ( D i v i s i o n I I ) . The top of the Upper Permian Marble Canyon limestone marks the boundary of the P a v i l i o n group w i t h the Permo-Pennsylvanian Cache Creek group. The rocks now assigned to the P a v i l i o n group were formerly included w i t h the Cache Creek group. DIVISION I 1. D i s t r i b u t i o n and Thickness D i v i s i o n I extends from the southeastern to the northern extremity of the map-area. On B i g Bar Creek, where the D i v i s i o n i s c ontinuously exposed and i t s boundaries w i t h the underlying and o v e r l y i n g formations are w e l l exposed, i t forms a zone about 5-1/2 m i l e s wide. I t s thickness may be anywhere between 1000 and 5000 f e e t and i s p o s s i b l y i n the v i c i n i t y of 3000 f e e t . 2. L i t h o l o g y D i v i s i o n I c o n s i s t s dominantly of chert and a r g i l l i t e 35 and t h e i r metamorphie equivalents and some limestone, 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 bodies of t u f f and limestone, l o c a l l y accompanied by l i t h i c sandstone, are found only i n the v i c i n i t y of the Fraser R i v e r between K e l l y and Butcher Creeks. They probably belong i n the upper part o f D i v i s i o n I . Small masses of t u f f , l imestone, and r a r e l y l i t h i c sandstone occur at v a r i o u s l o c a l -i t i e s and probably occupy d i f f e r e n t s t r a t i g r a p h i c p o s i t i o n s . The chert v a r i e s from l i g h t grey to b l u i s h black i n c o l o r . I t mostly occurs as \"ribbon c h e r t \" , that i s i n l a y e r s which are i n the order of one to three inches t h i c k and are separated by t h i n sheets of a r g i l l i t e or p h y l l i t e . The chert 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 pinching c r o s s -s e c t i o n . 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. Light grey chert i s composed dominantly of q u a r t z , and to a small p r o p o r t i o n of chalcedony and \" c l a y \" , that i s c l a y -s i z e d minerals of the c h l o r i t e - e p i d o t e - a n d mica-groups. Dark chert contains s m a l l amounts of carbonaceous matter. The quartz i s present i n anhedral g r a i n s which range from a few to approximately 30 microns i n diameter and show undulose e x t i n c t i o n . The quartz 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 are coarser grained than the \"mosaic\" and have a higher content of chalcedony and a lower con-tent of \" c l a y \" . The nodules are s p h e r i c a l or e l l i p t i c a l i n s e c t i o n and range from . 0 3 to . 3 mm i n diameter; the average diameter probably l i e s between .15 and .2 mm. A few nodules 36 show a r a d i a t i n g p a t t e r n around the margin; one has a spine-l i k e 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 to r a d i o l a r i a n cherts i n w e l l preserved specimens of C a l i f o r n i a ( J e n k i n s , 194-3, pp. 315, 319). Chert of t h i s type was seen i n 13 out of 18 t h i n - s e c t i o n s of specimens from v a r i o u s l o c a l i t i e s . 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 of quartz and carbonate. Carbonate a l s o occurs i n i s o l a t e d grains w i t h i n the c h e r t . The a r g i l l i t e i s b l u i s h black and laminated to massive. Under the microscope minute c r y s t a l s of mica, c h l o r i t e , c a r -bonate, and p a r t i c l e s of carbonaceous matter are seen to be embedded i n a groundmass of low b i r e f r i n g e n c e that i s 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 . The organic matter i s d i s -persed throughout the a r g i l l i t e but i n p h y l l i t i c specimens i t i s concentrated i n p a r a l l e l l a y e r s . Some o f the a r g i l l i t e contains massive or nodular aggregates of f i n e - g r a i n e d s i l i c a and grades i n t o c h e r t . Most of the 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 of f e l d s p a r fragments. The t u f f s do not form beds but l e n t i c u l a r masses which i n most l o c a l i t i e s are ass o c i a t e d w i t h limestone. A hand specimen of a l i t t l e a l t e r e d tuffaceous rock i s brownish green and composed of angular or l e n t i c u l a r fragments ranging from a f r a c t i o n of a m i l l i m e t e r to about 3 mm i n diameter. The s e c t i o n c o n s i s t s dominantly 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 grains of v o l c a n i c rocks some of which are v e s i c u l a r or amygdaloidal, a smaller pro-p o r t i o n of c h l o r i t e , which may represent a l t e r e d v o l c a n i c g l a s s , and a few percent of quartz, f e l d s p a r , hornblende, clino-pyroxene, and \" i r o n ore\". The tuffaceous o r i g i n of the rock i s appar-ent from two f e a t u r e s : the clino-pyroxene, a 37 mineral which has not been observed by the writer as a detrital mineral in 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 rhyolite or dacite. As the tuff was deposited in water i t may have incorporated some detrital material. A specimen from the slope north of the upper part of Siwash Greek probably represents a sheared and altered limy tuff. The hand specimen is bluish green and contains light to dark colored, rather angular fragments in a light green groundmass. The fragments range from one centimeter to about one m i l l i -meter in size. The thin section shows fragments of volcanic rocks embedded in an abundant matrix of chlorite and carbonate. The fragments are porphyritic and vitrophyric and mostly amygdaloidal. They show lath-like microlites and broad prisms of plagioclase in a groundmass that is altered to chlorite and very fine-grained deep brown carbonate. The carbonate of the cement is strongly twinned, in some places in a feathery fashion. The chlorite of the groundmass occurs in narrow stringers and large patches made up of radiating sheaves or felted masses. The limestones of Division I form pods and lenses. Short beds were observed in only a few l o c a l i t i e s . The largest of the lenticular masses is located on the slope north of the upper part of Siwash Creek and has been mapped as a separate unit. Except for gastropods, no fossils have been found in these lime-stones. Some of the limestones contain oolites and pisolites that range from a fraction of a millimeter to several millimeters in diameter. Most of them are ellipsoidal; less commonly they are spherical or spindle-shaped. The oolites are made up of concentric layers of very fine-grained carbonate. Radial struct-ures are rarely developed. The centre of the oolites is occupied by coarse-grained calcite, in some specimens by a single crystal or, less commonly, by chlorite and chert nodules (Plate XII). Most of the limestones are a s s o c i a t e d w i t h t u f f s , and near the contacts the two rocks are mixed. Some of the l i m e -stone near the contacts contains greenish or brownish weather-ing s t r i n g e r s of c h l o r i t e which i n some specimens are a s s o c i a t e d w i t h chalcedony. Angular fragments of limestone or i r r e g u l a r blebs w i t h rounded o u t l i n e s are incorporated i n the t u f f . The s i z e of these i n c l u s i o n s ranges from tens of f e e t to a f r a c t i o n of a centimeter. The 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 , and c h e r t . At some l o c a l i t i e s they show graded bedding and are s i m i l a r i n appearance to those of D i v i s i o n I I . 3. Metamorphism Where rocks of D i v i s i o n I are i n contact 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 of the meta-morphism i s r e l a t e d to the p l u t o n between K e l l y Creek and Leon Creek and the best exposures are on both banks of the Fraser R i v e r near the mouth of K e l l y Creek where a migmatite complex c o n s i s t i n g of d i o r i t i c dykes, amphibolites and banded horn-f e l s e s has been mapped as a separate u n i t . I t i s not c e r t a i n , however, i f a l l of the rocks belong to D i v i s i o n I ; some of the rocks on the west shore may be part of D i v i s i o n I I . Near the mouth of K e l l y Creek, a f a c i e s of D i v i s i o n I r i c h i n tuffaceous rocks has been i n t r u d e d by d i o r i t i c dykes. The contact between the dykes and the host rock 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 rock i s cut by numerous lenses and v e i n -l i k e s t r i n g e r s r i c h i n quartz 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 of the t r a n s i t i o n rock, 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 white quartz=feldspar v e i n l e t s that are from one to 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 rock contains approximately 75%> of hornblende ( g r a i n s i z e approximately .05-.5 mm) ass o c i a t e d w i t h \" i r o n ore\" and a t r a c e of b i o t i t e , and 25% of f i n e r grained (.005-.25 mm) quartz 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 ande-s i n e , i s p a r t l y anhedral, p a r t l y subhedral, and mostly twinned. A l a r g e p r o p o r t i o n of the f e l d s p a r i s w a t e r - c l e a r . A part of the rocks on the western bank of the Fraser R i v e r i n the same area are f i n e l y l a y e r e d amphibolites and h o r n f e l s e s . The rocks belong i n the hornblende-hornfels 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 or s t r o n g l y j o i n t e d a r g i l l i t e s . A specimen of these f o l i a t e d rocks i s com-posed of l i g h t grey and black l a y e r s ranging from one m i l l i m e t e r to 1.5 centimeter i n thickness that 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 mainly of subhedral hornblende c r y s t a l s , about .1 mm long that are 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: green, x: pale brownish green). The l i g h t c olored l a y e r s are made up of cloudy, 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 of approximately .05 mm, and a l i t t l e quartz. Horn-blende and p l a g i o c l a s e are present i n approximately equal p r o p o r t i o n s . A grey, massive, very f i n e - g r a i n e d specimen showing some medium-sized grains of 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 of rocks on the west side of the Fraser R i v e r , opposite the mouth of K e l l y Creek. The o r i g i n a l nature of the rock, which now belongs i n the e p i d o t e - a l b i t e h o r n f e l s 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 flow. 40 I t c o n s i s t s of approximately $0% of f e l d -spar, 42% of quartz, 5% of ep i d o t e , 2% of c h l o r i t e , 1% of carbonate and traces of sphene and \" i r o n ore\". The groundmass i s a t i g h t l y i n t e r l o c k e d aggregate of anhedral quartz, and subhedral to anhedral f e l d -spar, both ranging approximately from .05 to .5 mm i n s i z e , that i s cut by s t r i n g e r s of epidote, c h l o r i t e , and carbonate. The f e l d s p a r c o n s i s t s mostly of twinned sodic 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 are or absent. The a l b i t e of the groundmass i s cloudy w i t h i n c l u s i o n s of epidote; the l a r g e r c r y s t a l s , forming anhedral, twinned grains up to 1.5 mm long c o n t a i n i n c l u s i o n s of quartz, but not of epidote. The f i n e - g r a i n e d cloudy f e l d s p a r of the groundmass and some of the quartz are 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 the rocks; the 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 of the quartz may have been introduced. 4. S t r u c t u r e The contact between D i v i s i o n I and the Marble Canyon formation i s exposed only i n the v i c i n i t y of S a l l u s Creek and Kea t l e y Creek, north of P a v i l i o n Lake, and on B i g Bar Creek. In these l o c a l i t i e s n e i t h e r an unconformity nor a major f a u l t was observed although the contacts between limestone beds and a r g i l l i t e are l o c a l l y sheared. The contact i s g r a d a t i o n a l and the p r o p o r t i o n of interbedded limestone increases i n an east-ward d i r e c t i o n . As D i v i s i o n I i s i n contact w i t h the upper-most part of the Marble Canyon formation one might conclude that i t o v e r l i e s the limestones. However the westward t r a n s i t i o n from limestone to chert and a r g i l l i t e could represent 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 the upper Marble Canyon Formation. 41 In most l o c a l i t i e s the s t r a t a of 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 dip s t e e p l y . Marker beds are scarce and s t r a t i g r a p h i c tops could be determined only at a few l o c a l i t i e s . Judging from the w e l l s t r a t i f i e d and p l a s t i c nature of the rocks they are t i g h t l y f o l d e d ; the p a t t e r n of f o l d i n g may be s i m i l a r to that of the younger L i l l o o e t group, which has a comparable l i t h o l o g y . Dragfolds are developed only i n the v i c i n i t y of f a u l t s and are here of very v a r i e d plunge. In some l o c a l i t i e s the limestones show a l i n e a t i o n i n the form of grooves, but the plunges of 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 . D i v i s i o n 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 recognized. However, there are broad areas u n d e r l a i n by sheared rocks that are crossed by numerous minor i r r e g u l a r f a u l t s . The most extensive of these shear zones i s exposed between Moran and K e l l y Creek. Other shear zones of t h i s type were seen on the slope n o r t h of Gibbs Creek, i n High Bar Canyon, and on the slopes above B i g Bar Creek, near the mouth of S t a b l e Creek. In a d d i t i o n to these l a r g e zones shown on the map there are numerous small ones that have not been i n d i c a t e d . Almost a l l contacts between massive r o c k s , such as limestone, t u f f or l i t h i c sandstone on the one hand, and laminated a r g i l l i t e and chert on the other hand are sheared. Some of the d i s t o r t i o n s may have been caused by d i f f e r e n t i a l movements of sedimentary s t r a t a during f o l d i n g , others seem to be r e l a t e d to movements of Coast I n t r u s i o n s . 42 5. Mode of O r i g i n Remnants of r a d i o l a r i a n skeletons i n the chert suggest that D i v i s i o n I was l a i d down i n a marine environment. The presence of carbonaceous matter i n d i c a t e s a \" r e s t r i c t e d \" en-vironment (Krumbein and G a r r e l s , 1952). The s c a r c i t y of coarse-grained c l a s t i c sediments and the dominance o f f i n e -grained 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 that the source area was of low r e l i e f or at a great distance from the s i t e of d e p o s i t i o n . 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 the area. The environment of D i v i s i o n I appears s i m i l a r to that o f the Marble Canyon formation, except that c o n d i t i o n s f o r the growth of r e e f s were ra r e or l a c k i n g . I f D i v i s i o n I i s p a r t l y contemporaneous w i t h the Marble Canyon formation i t probably was deposited seaward from the re e f zone. The o r i g i n of the c h e r t , t u f f , and limestone, pose s p e c i a l problems. Mi c r o s c o p i c examination shows that the cherts are com-posed of a considerable p r o p o r t i o n o f nodules that resemble the r a d i o l a r i a n remains of r e l a t i v e l y w e l l preserved (Compare Je n k i n s , 194-3) pp. 315 } 319) rocks. A few of these nodules 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 the margins that are s t r o n g l y suggestive of an organic o r i g i n . Because of the microscopic evidence and the s c a r c i t y of v o l c a n i c centers i n the area i t i s b e l i e v e d that the chert i s of organic o r i g i n . The a l t e r n a t i o n s of chert and a r g i l l i t e may be due to seasonal changes that governed the l i f e of the s i l i c e o u s organisms or 43 the d e p o s i t i o n of the a s s o c i a t e d i n o r g a n i c matter. The l e n t i c u l a r shape of the t u f f bodies 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 that 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 de n s i t y currents that o r i g i n a t e d when the tuffaceous m a t e r i a l entered the water. The o r i g i n of the limestone i n D i v i s i o n I i s a d i f f i -c u l t problem. The b i g , p o d - l i k e mass north o f Siwash 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 . Regarding the smaller bodies two c o n s i s t e n t features may be of 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 of the limestone w i t h t u f f s , and the signs of current 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 . These r e l a t i o n s could be explained i n d i f f e r e n t ways. The limestones may be i n o r g a n i c and t h e i r p r e c i p i t a t i o n could have been caused by the currents that c a r r i e d the tuffaceous matter. The s o l u b i l i t y of calcium c a r -bonate i n sea water ( R e v e l l e , 1934) depends on the carbon d i o x i d e content of the water, on i t s temperature, pressure and pH. The currents descending from the surface may have warmed up the bottom waters and thus caused the p r e c i p i t a t i o n of some calcium carbonate. However, the amount of limestone produced by such a process would be r e l a t i v e l y s m a l l . I t i s a l s o p o s s i b l e that the currents c o l l e c t e d unconsolidated limy m a t e r i a l from the sea bottom and swept i t along together w i t h the tuffaceous m a t e r i a l . A t h i r d p o s s i b i l i t y i s that the d e p o s i t i o n of both t u f f and limestone was c o n t r o l l e d by de-p r e s s i o n s on the sea f l o o r . The limestone may have been de-p o s i t e d i n such depressions owing to b i o l o g i c a l or physico-chemical c o n d i t i o n s and the den s i t y currents may have dropped t h e i r load here because of 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 that D i v i s i o n I i s e i t h e r contemporaneous w i t h the upper part of the Marble Canyon f o r -mation or younger. I t i s o v e r l a i n by D i v i s i o n I I which i s pro-bably T r i a s s i c . 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 Thickness Rocks assigned to D i v i s i o n I I u n d e r l i e two separate areas. They have been c o r r e l a t e d because of t h e i r s i m i l a r l i t h o l o g y but they may not be e x a c t l y of the same age. The outcrops of the B i g Bar assemblage form a zone about 3 miles long and up to 1-1/2 miles wide i n the v i c i n i t y of the lower part of B i g Bar Creek. Their thickness i s of 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 area about 10 miles long and up to three miles wide s i t u a t e d mostly on the west s i d e o f the Fraser 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 that an accurate statement of the thickness cannot be given. S e v e r a l thousand feet of s t r a t a are probably present. 2. B i g Bar Assemblage A. L i t h o l o g y Because of f a c i e s changes and l a c k of outcrop the s t r a t i g r a p h y of the B i g Bar assemblage has not been worked out. A broad b e l t of 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 a r g i l l i t e extends from the west slope of Mount K o s t e r i n g across B i g Bar Creek to the south slope of B i g Bar Mountain. The contacts of t h i s b e l t are g r a d a t i o n a l . The rocks show graded bedding and abundant c o n t o r t i o n s that apparently were produced before the l i t h i f i c a t i o n of the sediments. To the east of t h i s b e l t i n the v i c i n i t y of B i g Bar Creek, flows of andesite and d a c i t e are exposed. The other p a r t s of the area are under-l a i n by t u f f , ribbon c h e r t , a r g i l l i t e , and limestone. The limestone occurs i n beds, not exceeding 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 lenses and pods associated w i t h t u f f , or i n t h i n l a y e r s 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 t y p i c a l specimen of i n t e r l a m i n a t e d a r g i l l i t e , s i l t -stone, and sandstone from the west-slope of Mount K o s t e r i n g weathers brownish green. I t s laminae o f a r g i l l i t e are from one centimeter to 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 con-s i s t i n g mostly of 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 . Approximately two t h i r d s of the a r g i l l i t e con-s i s t of c l a y - s i z e d m i n e r a l s , one t h i r d of s i l t - s i z e d carbonate, f e l d s p a r , and quartz, and a small f r a c t i o n of carbonaceous matter. The sandstone and the s i l t s t o n e are made up dominantly of carbonate, f e l d s p a r , and quartz, and a smaller p r o p o r t i o n of c l a y . The specimen shows graded bedding and some cross-bedding. 46 A graded u n i t ranges from very f i n e - g r a i n e d sandstone at the bottom through s i l t s t o n e to a r g i l l i t e . The contact 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 of carbonaceous matter 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 g r a i n - s i z e . The v o l c a n i c flow rocks weather greenish grey and are mostly p o r p h y r i t i c . Two specimens of a l t e r e d andesite con-s i s t dominantly of a l b i t e which forms m i c r o l i t e s and pheno-c r y s t s , and a smaller p r o p o r t i o n of epidote, ( l a r g e l y p i s t a c -i t e ) , c h l o r i t e , and carbonate; one specimen shows replacement by p r e h n i t e . The l a c k of zoning, the a l b i t i c composition, and the abundance of epidote, i n d i c a t e s that 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 of meta-dacite, pheno-c r y s t s of c a l c i c a l b i t e are embedded i n a f i n e -grained groundmass c o n s i s t i n g l a r g e l y of a l b i t e and quartz. 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 of the 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 rock i s veined by quartz and epidote. B. S t r u c t u r e The southwestern contact of the B i g Bar assemblage, ex-posed near the road to the High Bar f e r r y probably i s f a u l t e d . The rocks are s t r o n g l y sheared, and the t r a n s i t i o n from t u f f to chert and a r g i l l i t e i s abrupt. The northeastern contact i s g r a d a t i o n a l . No major f a u l t i s v i s i b l e here, but the contacts between masses of t u f f and chert and a r g i l l i t e are l o c a l l y sheared and a l t e r e d . In the southeast the un i t tapers and forms a nose. The northwestern contact i s not exposed. The s t r a t a s t r i k e approximately N 40° ¥ and d i p moderately to ste e p l y northeast. At many d i f f e r e n t l o c a l i t i e s i n the south-western h a l f of the u n i t the s t r a t i g r a p h i c tops were found to face the northeast. At three l o c a l i t i e s i n the northeastern h a l f they were seen to face the southwest. I t appears that the s t r a t a form a s y n c l i n e which i s overturned to the south-west and probably plunges to the northwest. In the c e n t r a l part of the u n i t on the slope n o r t h of B i g Bar Creek gently d i p p i n g s t r a t a were seen that appeared to l i e upside down. I t i s u n c e r t a i n whether these anomalous a t t i t u d e s were pro-duced by disturbances before or a f t e r the l i t h i f i c a t i o n of the rocks. The f o l d i n g of the u n i t probably 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 planes which 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 . A s c h i s t o s i t y which s t r i k e s n orthwesterly and dips s t e e p l y to the northeast was only observed i n the c e n t r a l parts of the B i g Bar assemblage, that i s near the a x i a l plane of the i n f e r r e d s y n c l i n e . 3. P a v i l i o n Assemblage A. L i t h o l o g y Approximately two t h i r d s of the P a v i l i o n assemblage are made up of v o l c a n i c r o c k s , mostly 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 of l i t h i c sandstone, a r g i l l i t e , l i m e -stone, s i l t s t o n e , b r e c c i a , and conglomerate. The t u f f s are greenish l e a t h e r i n g massive rocks which show f i n e , angular fragments only on f r e s h s u r f a c e s . T u f f s r i c h i n l i t h i c m a t e r i a l can hardly 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 are a l t e r e d to 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 ; s h a r d - l i k e o u t l i n e s 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 mostly of twinned p l a g i o c l a s e and a sm a l l p r o p o r t i o n of quartz; horn-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 are euhedral, others are broken; they are fre s h e r l o o k i n g and l e s s rounded than d e t r i t a l g r a i n s i n the sedimentary r o c k s . The v o l c a n i c rocks of the P a v i l i o n area range from b a s a l t to f e l s i t e . Many of them c o n t a i n phenocrysts of quartz. A g r e y i s h green weathering a p h a n i t i c ( t h o l e i t i c ) b a s a l t contains approximately 8% of quartz, 3% of endiopside (+2v moderate; ny 1.673) which forms micro-phenocrysts, and 10% of 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 minerals; the balance i s made up of twinned and zoned p l a g i o -c l a s e m i c r o l i t e s which range from c a l c i c l a b r a -d o r i t e to sodic bytownite i n composition. The rock i s crossed by narrow zones of mylonite and by veins of carbonate and c h l o r i t e . A blue grey p o r p h y r i t i c a p h a n i t i c flow rock of f e l s i t i c composition comprises about 4-0% of f r a c t u r e d and corroded phenocrysts ( g r a i n s i z e 2 mm - .5 mm) i n an extremely f i n e - g r a i n e d p a r t l y g lassy groundmass ( g r a i n s i z e approximately 1 - 5 microns). Most of the phenocrysts are of quartz; a smaller number c o n s i s t s of zoned and twinned andesine, and a few grains are of \" i r o n o r e \" , which probably has replaced a mafic m i n e r a l . The groundmass i s 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 . Besides quartz and f e l d s p a r minerals of the c h l o r i t e and mica groups are abundant. The s p e c i -men includes a few fragments of r e l a t i v e l y coarse-grained a c i d i c flow rocks. I t i s veined and replaced by quartz, carbonate, 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 apparently has been metamorphosed has about 30% of p l a g i o c l a s e phenocrysts ( 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 of anhedral quartz, 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 phenocrysts, unzoned but twinned a l b i t e are r e -placed around the margins by the groundmass and con t a i n numerous i n c l u s i o n s o f quartz, epidote, and minor f e l d s p a r . Some very 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 of quartz resemble myrmekitic i n t e r -growths. Quartz probably has been introduced i n t o the rock. The specimen i s veined by minerals of the epidote group, mostly p i s t a c i t e . A b e l t of laminated l i t h i c sandstone w i t h some a r g i l l i t e , conglomerate, 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 of the r a i l r o a d between P a v i l i o n and Moran. As the contacts of t h i s b e l t are g r a d a t i o n a l and poorly exposed i t could not be mapped as a separate u n i t . The rocks show graded bedding and c o n t o r t i o n s formed before the 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 brownish green and i s grey on f r e s h s u r f a c e s . Three specimens analyzed c o n t a i n approximately 10-40$ of f e l d s p a r , 1% of quartz, 45-85$ of l i t h i c fragments and c h l o r i t e , and l e s s than 1% of \" i r o n ore\" and epidote. The f e l d s p a r i s mostly twinned and zoned p l a g i o -c l a s e that has not been a l b i t i z e d . The l i t h i c fragments are mostly derived from v o l c a n i c rocks (dominantly of intermediate composition) and some from chert and a r g i l l i t e . Some spec-imens show graded bedding and are w e l l sorted but i n others the s o r t i n g i s poor. A comparatively unaltered rock has only a small content of c l a y m a t r i x ( l e s s than 10%), and i t s p a r t i c l e s are rounded or subrounded. Others are too h i g h l y a l t e r e d to determine the o r i g i n a l roundness and c l a y content. These rocks are 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 rock t r a n s i t i o n a l from coarse-grained grey-wacke to granule conglomerate has the f o l l o w i n g composition: p l a g i o c l a s e 10% quartz 1% c h l o r i t e and epidote 1% hornblende and \" i r o n ore\" -1% v o l c a n i c fragments 67% limestone 20% chert 1% The fragments are embedded i n a c l a y m a t r i x which probably makes up more than 10% of the rock. Both rounding and s i z e s o r t i n g are poor. The g r a i n s i z e ranges from 4 mm to .1 mm. Associated w i t h the l i t h i c sandstone and conglomerate are b r e c c i a s that are made up of 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 of limestone, c h e r t , and a r g i l l i t e . These b r e c c i a s are between 2 and 20 feet t h i c k and can be traced along s t r i k e f o r a few hundred f e e t . In most b r e c c i a s the fragments do not exceed a few centimeters i n diameter. However, on the r i d g e n o r t h of Keatley Creek, about 2 miles northeast of Glen F r a s e r , a s e c t i o n was measured that contains s e v e r a l very coarse b r e c c i a s or conglomerates. Thickness L i t h o l o g y i n Feet Top of measured s e c t i o n 4 L i t h i c sandstone w i t h granules and sand-s i z e d grains of limestone. 3 Laminated sandstone and s i l t s t o n e showing some cross-bedding. 12 L i t h i c sandstone w i t h fragments of limestone up to one i n c h long. 3 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 rix and a smaller p r o p o r t i o n of sand than normal. 51 Thickness i n Feet 24 2 2 2 1 2 2 8 12 4 6 6 5 16 L i t h o l o g y Limy conglomerate, c o n s i s t i n g mostly of limestone cobbles, about 4 inches i n diameter, some f r a g -ments of l i t h i c sandstone and c h e r t , and one lens of a r g i l l i t e , about 6 inches long. Laminated sandstone and s i l t s t o n e l o c a l l y show graded bedd-i n g . The conglomerate i s c l o s e l y packed and the fragments are w e l l rounded and s i z e - s o r t e d . Covered i n t e r v a l . C a l c a r e n i t e and granule conglomerate w i t h limy fragments i n a matrix of l i t h i c sandstone. C a l c a r e n i t e and granule conglomerate c o n s i s t i n g of limestone fragments i n a matrix of l i t h i c sandstone. Covered i n t e r v a l . L i t h i c sandstone. Fine-grained c a l c a r e n i t e . L i t h i c sandstone w i t h granules of limestone grading downward i n t o cobble conglomerate con-t a i n i n g dominantly fragments of limestone and minor a r g i l l i t e . Towards the top of the l a y e r the sand grains become scarcer and the matrix more a r g i l l a c e o u s . Dominantly a r g i l l i t e mixed w i t h marl and l i t h i c sandstone. The upper 6 f e e t c o ntain w e l l rounded cobbles of limestone and a r g i l l i t e about 6 inches i n diameter. L i t h i c sandstone. Granule conglomerate. One t h i r d of the fragments are of limestone and two t h i r d s of c h e r t . The matrix c o n s i s t s dominantly o f limestone. L i t h i c sandstone. Covered i n t e r v a l . B r e c c i a c o n s i s t i n g dominantly of limestone pebbles, approximately 1 i n c h i n diameter, and a few f r a g -ments of a r g i l l i t e about 6 inches long i n a m a t r i x of l i t h i c sandstone. 52 Thickness L i t h o l o g y i n Feet 6 Coarse limestone b r e c c i a . Most of the limestone i s blue grey, some brownish fragments may be d o l o m i t i c . Some boulders are angular others rounded. A small f r a c t i o n of the fragments ranging up to 6 inches i n l e n g t h are composed of che r t . The matrix c o n s i s t s of 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 granules of limestone. 6 L i t h i c sandstone. 6 A r g i l l i t e . 1 Covered i n t e r v a l : f a u l t ? 32 Coarse b r e c c i a composed mostly of limestone and some c h e r t . The s i z e of the limestone fragments ranges from pebbles 1/2 i n c h i n diameter to a boulder 8 feet l o n g , 4 fe e t wide. Most fragments are w e l l rounded, the l a r g e r ones mostly e l l i p -s o i d a l . The matrix i s l i t h i c sandstone; the granule grade i s poorly represented. 4 L i t h i c sandstone. 1 Fine b r e c c i a . Fragments dominantly of limestone 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 rocks are embedded i n a ma t r i x of l i t h i c sandstone. The fragments are up to one i n c h i n diameter and mostly w e l l rounded. F a u l t . 18 L i t h i c sandstone w i t h granule to pebble s i z e d fragments of limestone. 1 A r g i l l i t e . 48 L i t h i c sandstone that i s mostly massive but shows bedding i n the form of b l u i s h , s i l t y or a r g i l l a c -eous laminae near the contact w i t h the o v e r l y i n g a r g i l l i t e . Contains a few e l l i p s o i d a l fragments of a r g i l l i t e and some limestone pebbles. 68 Covered i n t e r v a l . 5 Fine-grained d i o r i t e s i l l . Thickness i n Feet L i t h o l o g y 3 F o s s i l i f e r o u s limestone c o n t a i n i n g c o r a l s , gastropods, brachiopods, gastropods, and echinoids and some o o l i t e s . The limestone 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 places l i t h i c sandstone and tuffaceous m a t e r i a l i s i n t e r l a m i n a t e d . 4 Ribbon c h e r t . Bottom of measured s e c t i o n 323 f e e t Limestone, a minor component of t h i s D i v i s i o n , occurs i n pods or lenses that do not exceed two hundred feet i n l e n g t h . The greatest c o n c e n t r a t i o n of such bodies occurs near P a v i l i o n Creek about 1/2 m i l e east of the Fraser R i v e r . At only two l o c a l -i t i e s f o s s i l s were found. C r i n o i d stems were c o l l e c t e d on the east side of the Fraser R i v e r about one m i l e south of the mouth of McKay Creek, and fragments of c o r a l s , pelecypods, gastropods and echinoids about two miles northeast of Glen Fraser (F12). B. Metamorphism and A l t e r a t i o n As the P a v i l i o n assemblage i s intruded by numerous d i o r i t i c bodies a considerable p r o p o r t i o n of the rocks show contact metamorphism. Both the hornblende-hornfels and the 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 represented. Some specimens are t r a n s i t i o n a l between these two groups. (See Table 1 ) . Most of the metamorphic rocks are dark green, f i n e -grained ( g r a i n - s i z e .01 - .15 mm) massive or weakly f o l i a t e d amphibolites which may have been deri v e d from t u f f s , l i t h i c sandstones, and b a s a l t s . In some of the specimens an o r i g i n a l fragmental character can s t i l l be detected under the microscope, but p y r o c l a s t i c rocks cannot be d i s t i n g u i s h e d from sedimentary rocks. A l l of these rocks c o n t a i n more than 40% of amphibole and most of them have 20-4-5% of p l a g i o c l a s e . In rocks of a moderate grade of metamorphism the amphibole i s represented by hornblende. The mineral v a r i e s i n hab i t from broad to slender 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: blue-green; y: green or greenish w i t h a brown t i n t ; x: pale brownish green or pale brown.) In a specimen showing r e t r o g r e s s i v e metamorphism the hornblende i s p a r t l y replaced by c h l o r i t e . A low-grade meta-morphic rock c o n s i s t s dominantly of a c i c u l a r , p l e o c h r o i c ( z : blue-green) a c t i n o l i t e . The p l a g i o c l a s e , ranging i n composition from c a l c i c andesine to a l b i t e , i s anhedral, f u l l of i n c l u s i o n s of epidote and amphibole, and p a r t l y twinned. Epidote appears i n appr e c i a b l e q u a n t i t y only i n rocks of intermediate to low grade of metamorphism. Quartz forms up to 30% of some specimens. As acc e s s o r i e s \"Iron ore\", sphene, and a p a t i t e are present. Some metamorphosed l i t h i c sandstones have the same min e r a l a s s o c i a t i o n s as these amphibolites but are 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 of hornblende-rich and f e l s i c l a y e r s are v i s i b l e which 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 , massive rocks c o n s i s t i n g dominantly of 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 orthoclase i n the other), quartz, and small amounts of c h l o r i t e , epidote, \"iron ore\", and carbonate apparently have been meta-morphosed under conditions of the albite-epidote hornfels f a c i e s . The porphyritic texture of one specimen and the f i n e -grained l a t h - l i k e habit of the plagioclase i n the other one indicate that they were (acidic) volcanic flow rocks. Near intrusions the ribbon cherts have been meta-morphosed to quartzite and the limestones to marble. As the unit i s bounded by major fa u l t s and broken i n t e r n a l l y by numerous minor ones, brecciation and myIon-i z a t i o n are common i n these rocks. Associated with the dynamic metamorphism i s a l t e r a t i o n by carbonate, epidote, c h l o r i t e , and quartz. TABLE 2 Mineral-composition of some metamorphic rocks, P a v i l i o n Group, D i v i s i o n II. Spec, -No. 58-MB r 58 M5 4 58 M3 57 Au-104 Determination of Plagioclase (+)2v,_010, x' A010 (maximum = 24 ) nx' on (001) 1.5485 (-)2v nx' on 001 = 1.538 (+)2v An 44 A n 2 0 010, x' A 010 =14 max. An3 a> CO a> cu CO -a rH •H CD O CD rH CD u o rH o o •H +3 X> c! o s / / / / / ' / • i • f •* • / * r — 1 — ••• —i— • — ••1 T — I 1/2 1/4 1/8 1/16 MM GRAIN SIZE SIZE DISTRIBUTION IN SAND- AND COARSE SILT-GRADE, THIN-SECTION ANALYSIS OF 3 * 400 GRAINS,AFTER PACKH AM , ( 19 55 ) 1) Dl V. C , MD= . 23MM S0= 3.2 2) DIV. C , MD = . I 7MM S0= 2.8 3) MEMBER All, MD= .12MM S0=22 FIGURE 4 94 rocks are a r e n i t e s r a t h e r than wackes or greywackes. In Figure 4 the s i z e d i s t r i b u t i o n i n the sand and coarse s i l t grades of three c h a r a c t e r i s t i c specimens from Member A l l and D i v i s i o n C i s shown. ( P l a t e XIV). The maximum s e c t i o n a l diameter of 400 grains was measured and the cumul-a t i v e s i z e d i s t r i b u t i o n curve obtained was reconstructed w i t h the a i d o f ta b l e s given by Packham (1955). The s o r t i n g c o e f f i c i e n t of the specimen from A l l i s 2.2; the two specimens of 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 of 2.8 and 3.2 r e s p e c t i v e l y . On the basis of 170 sediments from many d i f f e r e n t types of environments Trask (1932, pp. 71-72) obtained the f o l l o w i n g d i s t r i b u t i o n of 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 than 1.9 - 10$ \" \" \" 2 . 5 - 25$ \" \" \" 4 . 5 - 75% \" \" \" 5.0 - 90$ The extremes are 1.26 and 9.4. The mode i s 2.9. He concludes: I f So i s l e s s than 2.5 the sample i s w e l l s o r t e d ; i f i t i s greater than 4.5 the sediment i s poorly sort e d ; and i f i t i s about 3.0 the deposit i s normally sorted. According to T r a s k 1 s c l a s s i f i c a t i o n the specimen from member A l l would be w e l l sorted and the specimens from D i v i s i o n C are normally sorted. However, compared w i t h studies by Krum-bein and T i s d e l (1940), and Hough (1942) the r e s u l t s obtained are too hig h . Krumbein and T i s d e l found that c r y s t a l l i n e rocks which have d i s i n t e g r a t e d i n place have a c o e f f i c i e n t of s o r t i n g 95 that places them i n t o the range of Trask's w e l l sorted sediments. Hough p o i n t s out that most near-shore 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 subjects of 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 of greywackes and r e l a t e d rocks need more i n v e s t i g a t i o n . (Compare al s o Greenman, (1951)j Krumbein (1953), Rosenfeld, Jacobsen, and Fern (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 Jackass Mountain group c o n s i s t s dominantly of a l b i t e although a few grains of o l i g o c l a s e were noted. As adjacent s t r a t a of the younger Spences Bridge and Ki n g s v a l e groups and the older P a v i l i o n group are not a l b i -t i z e d the a l b i t e of the Jackass Mountain group appears to be d e t r i t a l . From d i f f e r e n t observations D u f f e l l and McTaggart a r r i v e d at the same co n c l u s i o n (p. 92f). The problem remains, 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 or by r e g i o n a l metamorphism of the source rocks. 4. S t r u c t u r e The s t r a t a of the Jackass Mountain Group l i e mostly f l a t or d i p at low angles. In the v i c i n i t y of major f a u l t s , however, they have been t i l t e d i n t o almost v e r t i c a l p o s i t i o n s . On the northern part of Fountain Ridge the three d i v i s i o n s form a shallow s y n c l i n e . As the contacts here are a l l s t r o n g l y a l t e r e d and sheared the f o l d i n g probably was accompanied by much d i f f e r e n t i a l slippage on bedding planes. 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 trans v e r s e f a u l t s that w i l l be discussed i n a l a t e r chapter. 5. Mode of O r i g i n Information about the mode of o r i g i n of the Jackass Mountain group can be obtained from three sources: from the te x t u r e and composition of the sedimentary r o c k s , from the included f o s s i l s , and from the h i s t o r y of the Fraser R i v e r f a u l t zone. Member AI co n t a i n i n g conglomerate, much plant matter, and no marine f o s s i l s probably was l a i d down i n a c o n t i n e n t a l environment. V o l c a n i c eruptions r e s u l t i n g i n the d e p o s i t i o n of t u f f probably took place at the same time. 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 associated carbonaceous matter shows that the basin was \" r e s t r i c t e d \" . As the g r a i n s i z e i n these members i s comparatively f i n e the sediments were l a i d down r e l a t i v e l y f a r from the shore or were derived from a source area without pronounced r e l i e f . The r e l a t i v e l y coarse g r a i n s i z e i n the beds of the lower part of D i v i s i o n B i s suggestive of a near-shore environ-ment of d e p o s i t i o n or u p l i f t of the source area. The o r i g i n of the conglomerate i n D i v i s i o n B poses s e v e r a l problems. The great thickness of the conglomerate suggests a r a p i d u p l i f t of the source area and may have been caused, as 97 D u f f e l l and McTaggart suggested, (p. 4 7 ) by e a r l y movements of the Fraser R i v e r f a u l t zone. The present study of t h i s f a u l t zone i n d i c a t e s that before the d e p o s i t i o n of the Spences Bridge group a graben had formed which c o n t r o l l e d the sedimentation of D i v i s i o n C and perhaps a l s o of D i v i s i o n B of the Jackass Moun-t a i n group. The present f a u l t zone i s complex and comprises at l e a s t four 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 move-ment of the eastern f a u l t block and one f a u l t w i t h r e l a t i v e down-ward movement of the western block. In the southern part of the area the f a u l t - z o n e has a width of approximately 7 miles and the graben i t s e l f of approximately one m i l e . The graben has been traced throughout the whole map area and probably extends much f a r t h e r to the northwest and to the southeast. The l a t e s t move-ments on one of the f a u l t s took place i n e a r l y or middle T e r t i a r y . The f a u l t s v i s i b l e now may not c o i n c i d e w i t h the f a u l t s of the e a r l y Lower Cretaceous. But the present s i t u a t i o n per-haps gives a p i c t u r e of the c o n d i t i o n s i n the past. There may have e x i s t e d a narrow, elongate trough which was perhaps i n the order of ten miles wide and more than one hundred miles long. The conglomerate of D i v i s i o n B i s found i n the western part of the present f a u l t zone and perhaps was l a i d down along the west-ern margin of the i n f e r r e d trough. The s t r a t i g r a p h i c equiva-l e n t s of the conglomerate i n the middle and eastern part of the area are not exposed. Because of the s c a r c i t y of bedding a t t i t u d e s and complications by f a u l t i n g not enough i n f o r m a t i o n could be obtained about the v a r i a t i o n s i n the thickness of the conglomerate. But i t was mentioned that the conglomerate on the northwestern edge of the Ashcroft map area i s perhaps 750 f e e t t h i c k e r than opposite Fountain. These scanty data suggest an increase i n thickness to the 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 the present map area that contains a major p r o p o r t i o n of gran-i t i c m a t e r i a l . Some a r g i l l i t e interbedded w i t h conglomerate contains 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 was permanently or only t e m p o r a r i l y flooded by the sea. The l a c k of p l a n t matter perhaps supports the theory of 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 part have been rounded by transport-ion i n streams which descended from the bordering mountains w i t h a steep gradient and i n part by wave a c t i o n on beaches. A problem i s the mechanism of d i s t r i b u t i o n i n the b a s i n over a width of more than one m i l e . I t may be assumed that currents were a c t i v e . The e r o s i o n surfaces l o c a l l y observed may have been produced by such agents. The nature and o r i g i n of 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 of D i v i s i o n B do not resemble the t u r b i d i t y current deposits of the L i l l o o e t group or the Cache Creek group. Laminations, graded bedding, 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 incon-spicuous or l a c k i n g . Perhaps the d i s t r i b u t i o n of the g r a v e l was g r e a t l y aided by r e l a t i v e l y steep submarine slopes produced by f a u l t i n g . The areas of greatest depression also may have s h i f t e d l a t e r a l l y i n the b a s i n . In order to e x p l a i n the great w i d t h of the 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 that was only at times inundated by the sea. They mention, however, that such c h a r a c t e r i s t i c features of 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 of the deposits are uncommon. Some of the s t r a t a of D i v i s i o n C co n t a i n i n g conglomerat and plant matter were deposited i n a c o n t i n e n t a l or near shore marine environment. Others, i n c l u d i n g i n v e r t e b r a t e f o s s i l s , are of marine o r i g i n . Carbonaceous matter associated w i t h the a r g i l l i t e i n d i c a t e s that the environment at times v/as reducing. The rocks r a r e l y show s t r u c t u r e s suggestive of current 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 the g e n e r a l l y coarse-grain s i z e of the sediments. The source area was u n d e r l a i n dominantly by v o l c a n i c rocks and a smaller p r o p o r t i o n of Coast I n t r u s i o n s . In summary i t can be stated that D i v i s i o n C and pro-bably a l s o D i v i s i o n B were deposited i n a narrow elongate trough that subsided r a p i d l y w i t h respect to bordering h i g h -lands but f l u c t u a t e d w i t h respect to sea l e v e l . At times i t may have been connected w i t h the open sea, more o f t e n i t formed a r e s t r i c t e d marine environment and tempor 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 that was p o s s i b l y occupied by a la r g e r i v e r . 6. Age and C o r r e l a t i o n The name \"Jackass Mountain Conglomerate Group\" was given by Selwyn to the sandstone.,, q u a r t z i t e , s h a l e , and pebble conglomerate of Jackass Mountain. He recognized that the rocks are younger than the Cache Creek group. Dawson r e f e r s to the rocks as \"Queen C h a r l o t t e I s l a n d \" group which he assigned to the Cretaceous. D u f f e l l and McTaggart a p p l i e d the name Jackass Mountain Group and e s t a b l i s h e d a mid-Lower Cretaceous age. On ground of 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 they c o r r e l a t e D i v i s i o n s A, B, and C of the Jackass Mountain group w i t h D i v i s i o n s B, C, and D of the Dewdney Creek group of the P r i n c e t o n area, the Pasayten group of the Similkameen R i v e r d i s t r i c t , and \"Lower Cretaceous\" rocks of the C o q u i h a l l a map area. F o s s i l s found during the present mapping and i d e n t i f i e d by J.A. J e l e t z k y confirm the mid-Lower.Cretaceous age of the Jackass Mountain group. In Member A l l on the northwestern slope of Fountain Ridge about 1/2 m i l e east of the mouth of the Bridge R i v e r the 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 ? sp. i n d e t . (a gastropod) \"Pterocera\"? sp. i n d e t . (a gastropod) Ostrea sp. i n d e t . 101 Pecten (Entolium) 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 . According to J e l e t z k y the c o l l e c t i o n \"cannot be dated beyond a t e n t a t i v e suggestion that i t s gastropods and pelecy-pods show some s i m i l a r i t y w i t h those of the undescribed mid-Lower Cretaceous (Earremian, or ? Aptian) faunas of the Quat-sino 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 approximately 1-1/2 m i l e s due n o r t h of the mouth of Bridge R i v e r i n Member A I I I (F15) as: Ancyloceras ( H e l i c a n c y l u s ) c f . aequicostatum Gabb This ammonite \" i s c h a r a c t e r i s t i c of the A p t i a n rocks (so c a l l e d Alderson and Argonaut zones of Anderson, 1938, G.S. A. Sp. Paper 16, p. 65-66, t a b l e 2 ) . The s t a t e of p r e s e r v a t i o n of the o n l y specimen a v a i l a b l e i s , however, too poor to ex-clude i t s reference to other a l l i e d forms of Ancyloceras, which range down i n t o Upper Barremian rocks i n C a l i f o r n i a and e l s e -where. The w r i t e r p r e f e r s t h e r e f o r e to date the l o t here discussed as of Upper Barremian (?) or A p t i a n age i n terms of the i n t e r n a t i o n a l standard stages. In B r i t i s h Columbia, faunas of s i m i l a r and s l i g h t l y o l d e r mid-Lower Cretaceous age have been known f o r some time from the rocks of the Jackass Mountain group of the Ashcroft area (see D u f f e l l and McTaggart, 1 9 5 2 , pp. 48 -52) and from the Dewdney Creek group of the P r i n c e t o n area (see R i c e , 1947, p. 18-19)\". 102 A f o s s i l c o l l e c t e d on the south slope of the Camels-foot Range, at an e l e v a t i o n o f 1700 f e e t , approximately 1-1/2 miles northeast of the mouth of the Bridge 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 : \"This belemnite genus i s r e s t r i c t e d to the e a r l y mid-Lower Cretaceous rocks 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 than the Barremian stages of the i n t e r n a t i o n a l standard. I t i s not known to range i n t o the A p t i a n stage e i t h e r i n North America or i n E u r a s i a . \" An \"indeterminate ( 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.:! of the Fraser R i v e r opposite the mouth of Fountain Creek (F17) \"can only be dated as of the general J u r a s s i c or Cretaceous age\" but i n d i c a t e s a marine environment. SPENCES BRIDGE GROUP I n t r o d u c t i o n A b e l t of 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 the southeastern extremity of the map area and the slopes n o r t h o f McKay Creek. Dawson included these rocks w i t h h i s \"Lower V o l c a n i c Group\" which he considered to be Miocene. Drysdale (1914) renamed t h i s group Spences Bridge group, and F.K. Knowlton regarded p l a n t f o s s i l s found by Drysdale to be Lower Cretaceous but w i t h J u r a s s i c a f f i n i t i e s . B e l l r e f e r r e d the same f o s s i l s and new 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 ( A p t i a n stage). New f o s s i l s found during the present i n v e s t i -g a t i o n show that some of the rocks are l a t e Lower 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 the K i n g s v a l e group. Consequently the v o l c a n i c rocks have been subdivided i n t o s e v e r a l u n i t s . Some u n i t s have been c o r r e l a t e d w i t h the Spences Bridge group, others w i t h the Kingsvale group. The age and c o r r e l a t i o n of 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 are unknown. LOWER DIVISION A. B a s a l Member Between S a l l u s Creek and Gibbs Creek are two i s o l a t e d s m a l l areas u n d e r l a i n by v o l c a n i c r o c k s . The northern outcrops, l o c a t e d approximately 1 m i l e n o r t h o f Gibbs Creek, c o n s i s t of 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 a n d e s i t e , of a n d e s i t i c f l o w - b r e c c i a , t u f f and d a c i t e . A l a y e r of t u f f contains remnants of p l a n t stems. The contacts between two flows dip 70° to the northeast. The other area, s i t u a t e d about 1/2 m i l e to the south-east, i s made up of p o r p h y r i t i c d a c i t e . In the eastern h a l f of the area the d a c i t e weathers r e d d i s h brown and l o c a l l y shows f i n e flow 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 of p l a g i o -c l a s e phenocrysts. Some of these flow l a y e r s show strong c o n t o r t i o n s . In the western h a l f the d a c i t e i s uniformly greenish grey and contains coarse phenocrysts. In a few l o c a l i t i e s the p l a g i o c l a s e phenocrysts form flow l a y e r s that g e n e r a l l y have constant 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 place a t i g h t a n t i c l i n e o f flow l a y e r s , about 2 f e e t across was seen. The cdips of the flow l a y e r s range 104 from 80° to 25 and the s t r i k e s from northeast to northwest. A specimen of the grey p o r p h y r i t i c d a c i t e con-s i s t s dominantly of 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 or c h l o r o p h a e i t e , and contains approximately 10$ of quartz, 15$ of c h l o r i t e , and sma l l proportions of \" i r o n o r e \" , b i o t i t e , and a p a t i t e . Most of the phenocrysts are p l a g i o c l a s e , but a few c o n s i s t of quartz or 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 zoning has an approximate composition of A1142 i n the core and An30 at the margin. Both p l a g i o c l a s e and quartz phenocrysts i n c l u d e f i n e - g r a i n e d minerals of the groundmass. The quartz phenocrysts are surrounded by rims of 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 of intermediate s i z e . No flow s t r u c t u r e s are apparent i n the rock. The contacts of these v o l c a n i c rocks are not exposed but topography and s t r u c t u r e suggest that they o v e r l i e D i v i s i o n I of the P a v i l i o n group unconformably. Near the margin of the southern outcrop area remnants of a b r e c c i a , one or a few inches t h i c k were seen to o v e r l i e bed-rock of chert and a r g i l l -i t e . The b r e c c i a i s composed of the same rock types (chert and a r g i l l i t e ) , cemented by carbonate, and traversed by v e i n -l e t s of quartz. I t probably o r i g i n a t e d on the Lower Cretaceous e r o s i o n surface and l o c a l l y u n d e r l i e s the v o l c a n i c f l o w s . According to D u f f e l l and McTaggart the Spences Bridge group l o c a l l y r e s t s unconformably on the Cache Creek group, (p. 54). Therefore these rocks are thought to represent the b a s a l u n i t of the Spences Bridge group. B. Gibbs Creek Assemblage 1. D i s t r i b u t i o n and Thickness The u n i t u n d e r l i e s the rid g e south of Gibbs Creek and small areas n o r t h of that creek. I t has been subdivided i n t o 105 three members. The base of A, the lower member, i s not exposed. I t has a minimum thic k n e s s of 200 f e e t . On the slope immediate-l y south of Gibbs Creek member B i s approximately 700 f e e t t h i c k but i t t h i n s to the south and disappears about one m i l e south of Gibbs Creek. The top of member C has been removed by e r o s i o n ; i t s minimum thic k n e s s i s 500 f e e t . LIthology Member A Member A i s very uniform c o n s i s t i n g only o f dark grey or greenish weathering p o r p h y r i t i c andesite w i t h medium- to coarse-grained phenocrysts of p l a g i o c l a s e and medium- to f i n e -grained phenocrysts of 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$ of a t y p i c a l specimen c o n s i s t s of p l a g i o c l a s e phenocrysts, ranging approximately from 2 mm to .1 mm i n s i z e . The p l a g i o c l a s e , complexly twinned and zoned, ranges from intermediate o l i g o -c l a s e to c a l c i c andesine. The mi 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 of s e r i c i t e , carbonate and c h l o r i t e . C r y s t a l s of au g i t e form a smaller-f r a c t i o n of the phenocrysts. The augite has an approximate composition of Ca4]Mg48Fen. (ny - 1.684). The m i n e r a l i s p a r t l y to completely replaced by c h l o r i t e . The groundmass c o n s i s t s mostly of very 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 sm a l l amounts o f c h l o r i t e , \" i r o n o r e \" , augite and quartz. C a v i t i e s are l i n e d by c h l o r i t e and f i l l e d by quartz and carbonate. C l o t s of an extremely f i n e - g r a i n e d m i n e r a l of high b i r e f r i n g e n c e and high r e l i e f are dispersed through the rock. The mi n e r a l i s p o s s i b l y a carbonate. Member B Member B i s composed of sedimentary and p y r o c l a s t i c beds and of 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 areas and the contacts w i t h the underlying 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 sedimentary rocks are most abundant i n the v i c i n i t y of Gibbs Creek, p a r t i c u l a r l y i n the northeastern part of the area. A s e c t i o n here contains approximately 450 feet of sand-stone, 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 flow rocks range from andesite to r h y o l i t e i n composition. L i g h t colored flow rocks form conspicuous c l i f f s around the r i d g e south of Gibbs Creek and mark the upper boundary of member B. A few specimens examined i n t h i n - s e c t i o n have the composition of 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 are very poor i n b i o t i t e , c h l o r i t e , and \" i r o n ore\" and co n t a i n 10$ or more of quartz which i n some specimens forms phenocrysts or microphenocrysts. S i g n i f i c a n t m i n e r a l o g i c a l d i f f e r e n c e s e x i s t only i n the composition of the f e l d s p a r . The d a c i t e contains only p l a g i o c l a s e which forms zoned phenocrysts ranging from o l i g o c l a s e to c a l c i c andesine and m i c r o l i t e s of o l i g o c l a s e . The q u a r t z - l a t i t e contains sodic 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 which both form microphenocrysts. The r h y o l i t e has phenocrysts of sodic andesine and a groundmass c o n s i s t i n g dominantly of p o t a s s i c f e l d s p a r . The rock forms a flow b r e c c i a and shows under the microscope a s p h e r u l i t i c t e x t u r e . Most o f the s p h e r u l i t e s are made up of 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 andesites of member B resemble the ones found i n the members A and C. 107 P y r o c l a s t i c rocks are widely d i s t r i b u t e d but form only a sm a l l p r o p o r t i o n o f the t o t a l assemblage. A t u f f from the no r t h s i d e of the lower part of Gibbs Creek weathers l i g h t g r e y i s h green but contains dark fragments that are up to 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% of l a r g e p a r t l y broken c r y s t a l s of p l a g i o c l a s e that have the appearance of phenocrysts. They show complex twinning and i n many instances f i n e zoning. ( P l a t e XV) A g r a i n e x h i b i t i n g the t y p i c a l o s c i l -l a t o r y zoning i s sodic l a b r a d o r i t e i n the core and sodic andesine at the outer margin. Some grai n s have abundant i n c l u s i o n s of r e l a t i v e l y coarse-grained a p a t i t e and of \" i r o n ore\". A sm a l l number of c r y -s t a l s are of clinopyroxene. L i t h i c fragments con-s t i t u t e a l i t t l e l e s s than h a l f of the rock. Most of them are from v o l c a n i c rocks of intermediate composition but some are 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 are embedded i n a matrix of glass shards and d u s t - l i k e g l a s s y matter. 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 or f e l t e d aggre-gates of c h l o r i t e and carbonate. Member C Member C c o n s i s t s mostly of 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 small p r o p o r t i o n of i n t e r c a l a t e d sandstone and s i l t s t o n e . The andesite i s uniform i n composition and t e x t u r e . I t i s dark grey, 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 phenocrysts i n the order of t h e i r abundance are of p l a g i o -c l a s e , clino-pyroxene, and hornblende. The p l a g i o c l a s e i s twinned and zoned and ranges i n composition from intermediate o l i g o c l a s e to c a l c i c andesine. Some grains have a spongy or s k e l e t a l s t r u c t u r e and con t a i n i n c l u s i o n s of s e r i c i t e , c a r -bonate, c h l o r i t e , and v o l c a n i c g l a s s . The clinopyroxene, p a r t l y replaced by c h l o r i t e , i s twinned. Some grains have a lower b i r e f r i n g e n c e around the margins. The composition of the minerals l i e i n the boundary f i e l d of a u g i t e , endiopside, and di o p s i d e . (ny = 1.6875, 2v = 53.5°; F e 1 3 C a 4 4 Mg^, a u g i t e ; n y =il.6755, 2v = 49°, Fe 6Ca 3 8Mg^ 6, endiopside; n y = 1.683, 2v = 54°, F e i 0 C a 4 4 M g 4 6 , a u g i t e ) . The groundmass i s very 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 of 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 ore\" and c h l o r i t e . Other mafic minerals and gla s s y matter may be present but are d i f f i c u l t to i d e n t i f y . Some rocks c o n t a i n a low percentage of quartz. A p a t i t e i s a common accessory. The rocks are dominantly a l t e r e d by carbonate and c h l o r i t e . Veins are f i l l e d w i t h q u a r t z , carbonate, and z e o l i t e s , (too f i n e - g r a i n e d and too scarce f o r f u r t h e r iden-t i f i c a t i o n . ) 3. S t r u c t u r e , C o r r e l a t i o n , Mode of O r i g i n The rocks dip uniformly at moderate angles to the n o r t h west. To the west they are i n f e r r e d to be i n f a u l t contact w i t h the Fountain V a l l e y assemblage (see below). Unless the un i t i s separated from the rocks to the nor t h by a concealed f a u l t , member A i s c o r r e l a t i v e w i t h the bas a l member of the Spences Bridge group which appears to r e s t unconformably on a Lower Cretaceous land s u r f a c e . The problem of c o r r e l a t i o n has not been solved. N e i t h e r has evidence f o r such a f a u l t been obtained nor have underlying rocks of the P a v i l i o n group been observed south of Gibbs Creek. Perhaps the Lower Cretaceous e r o s i o n surface sloped down to the south. 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 to the lower D i v i s i o n of the Spences Bridge group. 109 Upper D i v i s i o n 1. D i s t r i b u t i o n The rocks r e f e r r e d to the uppermost part o f the Spences Bridge group are exposed on the west side of the Fraser R i v e r between the mouth of Lee Creek and the slopes n o r t h o f McKay Creek. South of Leon Creek they are concealed by over-burden and o v e r l y i n g 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 s . As the s t r u c t u r e of these rocks i s mostly unknown t h e i r t h i c k -ness i s u n c e r t a i n . 2. L i t h o l o g y The u n i t c o n s i s t s mostly of andesite; b a s a l t , r h y o l i t e and t u f f are l e s s common. The andesites are grey or red and ap a h a n i t i c or aph-a n i t i c t - p o r p h y r i t i c . The phenocrysts are of f i n e r g r a i n than i n the Gibbs Creek assemblage. Flow s t r u c t u r e s are r a r e . The phenocrysts c o n s i s t mostly of 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 or clinopyroxene, hornblende, or b i o t i t e or t h e i r a l t e r e d equivalents are present. In some rocks t r a n s i t i o n a l to d a c i t e , a few of the phenocrysts are of quartz. The groundmass c o n s i s t s dominantly of p l a g i o c l a s e micro-l i t e s , a few percent of \" i r o n o re\", and v a r y i n g amounts of g l a s s . In most specimens the p l a g i o c l a s e i s c a l c i c andesine or a n d e s i n e - l a b r a d o r i t e zoned over a narrow range. P l a g i o -c l a s e phenocrysts are mostly twinned; the groundmass micro-110 l i t e s are i n part untwinned. The min e r a l i s replaced by carbonate, 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 . The mafic phenocrysts are p a r t l y or completely replaced by c h l o r i t e , \" i r o n ore\" and chalcedony. Other minerals present as a l t e r -a t i o n or c a v i t y f i l l i n g are p r e h n i t e , chalcedony and z e o l i t e s . The textures are i n t e r g r a n u l a r , t r a c h y t i c or hyalo-p h i t i c . Some specimens are flow b r e c c i a s . A t y p i c a l specimen of b a s a l t i s brownish grey, 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 can ha r d l y be d i s t i n g u i s h e d from the andesites of the u n i t . A t h i n - s e c t i o n contains approximately 80$ of p l a g i o c l a s e ; the remainder c o n s i s t s dominantly of clinopyroxene and some \" i r o n ore\". The p l a g i o -c l a s e i s euhedral or subhedral and forms l a t h - l i k e c r y s t a l s . I t i s twinned and shows f i n e zoning, the composition ranging from A1145 to Anyo* T n e c l i n o -pyroxene i s euhedral, subhedral, or anhedral and p a r t l y zoned. The composition of the l a r g e r grains was determined as Fey Ca4o M g e j Q , endiopside, (ny = 1.679, 2v - 53°). A specimen of r h y o l i t e i s l i g h t b u f f , por-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 flow s t r u c t u r e s . The phenocrysts are up to 2 m i l l i m e t e r s long and c o n s i s t of p l a g i o c l a s e , andesine, q u a r t z , and a few smaller c r y s t a l s of 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 inc l u d e s quartz, 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 of f i n e to intermediate s i z e . The p l a g i o c l a s e has an approximate compos-i t i o n of A n ^ . Most grains are twinned. The p l a g i o -c l a s e has i n c l u s i o n s of s e r i c i t e and glass and one g r a i n i s replaced by a z e o l i t e which i s p o s s i b l y laumontite. Some grains have a spongy s t r u c t u r e . The quartz i s rounded and embayed by minerals of the groundmass. The c r y s t a l s are rimmed by f i b r o u s intergrowths of f e l d s p a r and s i l i c a that are o r i e n t e d approximately perpendicular to the face s . The groundmass c o n s i s t s dominantly of f i b r o u s p a r t l y s p h e r u l i t l c intergrowths of s i l i c a and p o t a s s i c f e l d s p a r , of qua r t z , and sm a l l amounts of b i o t i t e . A p a t i t e and \" i r o n ore\" occur as a c c e s s o r i e s . I l l 3. S t r u c t u r e , Age, and C o r r e l a t i o n Near the mouth of Slok Creek the rocks d i p at low angles to the southeast and seem to u n d e r l i e the Kingsvale group. To the west they are i n f e r r e d to be i n f a u l t contact w i t h the Jackass Mountain group and to the east w i t h the Cache Creek group. As the u n i t u n d e r l i e s sedimentary rocks of A l b i a n age i t probably i s A p t i a n . KINGSVALE GROUP 1. D i s t r i b u t i o n and Thickness Sedimentary and v o l c a n i c rocks on the east s i d e of the Fraser R i v e r about 1-1/2 miles n o r t h of Glen Fraser formerly included w i t h the Spences Bridge group are now c o r r e -l a t e d w i t h the Ki n g s v a l e group. The rocks have been subdivided i n t o two D i v i s i o n s , A, and B. D i v i s i o n A i s approximately 700 fe e t t h i c k . Although the top of B has been removed by e r o s i o n , more than 700 fe e t of v o l c a n i c rocks are s t i l l present. (Reinecke, 1912, p. 12). 2. L i t h o l o g y D i v i s i o n A D i v i s i o n A c o n s i s t s dominantly of v o l c a n i c a r e n i t e that grades i n t o both pebble conglomerate, and s i l t s t o n e . Conglomerate forms perhaps one t h i r d of the sequence, s i l t -stone i s comparatively r a r e . 112 Most of the v o l c a n i c a r e n i t e i s grey but some beds are red. The rocks c o n s i s t dominantly of v o l c a n i c fragments, of l e s s than $0% of p l a g i o c l a s e and s m a l l amounts o f quartz, \" i r o n o r e \" , and b i o t i t e . The l i t h i c fragments are mostly ande-s i t i c i n composition, some are 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 are not replaced by the groundmass they are sub-rounded to rounded. In one specimen n e i t h e r carbonate nor \" i r o n oxide\"nor quartz can be detected as cement. Another specimen contains approximately 50% of r u s t y weathering c a r -bonate as m a t r i x . Perhaps the carbonate was introduced by hydrothermal s o l u t i o n s and has replaced some of the sedimen-t a r y m a t e r i a l . Most rocks are w e l l bedded and s i z e - s o r t e d . L o c a l l y the \" i r o n ore\" i s concentrated i n t h i n laminae. I n some l o c a l -i t i e s graded bedding and cross-bedding can be observed. A cobble conglomerate on the east side of the Fraser R i v e r , near the hidden contact w i t h the Spences Bridge group c o n s i s t s dominantly of v o l c a n i c roundstones but also contains some g r a n i t i c cobbles. D i v i s i o n B D i v i s i o n B c o n s i s t s dominantly of a n d e s i t e , a few flows of d a c i t e , and s e v e r a l t h i n l a y e r s of tuffaceous and sedimentary rocks. The andesite i s dark grey, l i g h t grey, or red brown. Most of the rocks are a p h a n i t i c - p o r p h y r i t i c but some are a p h a n i t i c . Most o f the phenocrysts are twinned and zoned p l a g i o -c l a s e that ranges i n composition from intermediate andesine to intermediate l a b r a d o r i t e ; the average composition seems to be c a l c i c andesine. Some rocks a l s o c o n t a i n phenocrysts o f oxyhornblende. In the groundmass, which i s i n most specimens very f i n e - g r a i n e d , abundant m i c r o l i t e s of p l a g i o c l a s e and a few percent of \" i r o n ore\" can be recognized. Mafic s i l i c a t e s , 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 are present i n small amounts. A p a t i t e occurs as an accessory. Light c o l o r e d rocks that are t r a n s i t i o n a l to d a c i t e c o n t a i n f i n e - g r a i n e d quartz i n the groundmass. The rocks are 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 carbonate. Some specimens have a t r a c h y t i c t e x t u r e . A specimen of 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 contains elongate prisms of amphibole i n a l i g h t greenish grey groundmass. Micr o s c o p i c examination shows that the amphi-bole i s oxyhornblende. In the groundmass a few micro-phenocrysts of p l a g i o c l a s e , l a t h - l i k e p l a g i o c l a s e m i c r o l i t e s , a small f r a c t i o n of \" i r o n o r e \" , and very f i n e - g r a i n e d i n t e r s t i t i a l quartz can be i d e n t i f i e d . The m i c r o l i t e s are sodic andesine; the micro-phenocrysts are zoned and range i n composition from sodic to c a l c i c andesine. B. S t r u c t u r e The contact of D i v i s i o n A w i t h the Spences Bridge group i s not exposed. The presence of cobble conglomerate near the base of D i v i s i o n A suggests an unconformity. Div-i s i o n B probably o v e r l i e s A conformably. To the west the K i n g s v a l e group i s i n f a u l t contact w i t h the Jackass Mountain group, to the east i n f a u l t contact w i t h the P a v i l i o n group and p o s s i b l y with,rocks of the Spences Bridge group o v e r l y i n g the Cache Creek group. In the v i c i n i t y of 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 the dips are low to moderate. 4. Mode of O r i g i n , Age, and C o r r e l a t i o n The w e l l sorted and g e n e r a l l y coarse-grained character of the sediments of 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 running water, and the abundance of plant matter a c o n t i n e n t a l e n v i r -onment. Apparently they were l a i d down on the f l o o d p l a i n o f a stream that drained 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 a n d e s i t e s . Plant f o s s i l s found i n the lower h a l f of member A (F18) were i d e n t i f i e d by Professor G.E. Rouse as f o l l o w s : Menispermites Upper Blaimore-Whitemud ( c f . w i t h B e l l (1957), p. 130)) ( A l b i a n - M a e s t r i c h t i a n ) C e l a s t r o p h y l l u m ( c e l a s t r i n i t e s ? ) ( A l b i a n - B a s a l Eocene) T a c u t i d e n s ; . Trochodendroides (Cercidiphyllum?) Upper Blairmore Ccf.\" po'tomacensis (Albian) Platanus sp. ( A l b i a n through T e r t i a r y ) c f . Myrtophyllum boreale ( A l b i a n - T e r t i a r y ) o r : c f . Magnoliaephyllum (Upper Cretaceous) C i s s i t e s sp. ( A l b i a n of Portugal) (Patapsco of Maryland (Lower Cretaceous) (Upper Cretaceous of U.S.Rockies) Professor Rouse s t a t e s i n h i s report that \"four and p o s s i b l y f i v e of the s i x species have been recorded i n the (Alb i a n ) Kingsvale by B e l l , but none of these i s found i n the Spences Bridge (Aptian) ... the m a t e r i a l ... i s younger than A p t i a n and hence younger than the Spences Bridge group.\" D u f f e l l and McTaggart s t a t e that the Kingsvale group i n the A s h c r o f t map area has a sedimentary u n i t at i t s base which i s l o c a l l y 800 to 1000 feet t h i c k and c o n s i s t s of arkose, g r i t , mudstone, conglomerate, and a r g i l l i t e . Outcrops o f these rocks extend f o r 16 miles along N i c o l a R i v e r . Many of the beds on N i c o l a R i v e r c o n t a i n fragments of stems and le a v e s , and the mudstones ca r r y w e l l preserved p l a n t f o s s i l s . One of the f o s s i l s c o l l e c t e d near Glen F r a s e r , Menispermites, was a l s o found i n the 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 that D i v i s i o n A at Glen Fraser and the sedimentary b e l t on N i c o l a R i v e r are perhaps c o r r e l a t i v e and may represent the same f l o o d -p l a i n . However, as these are c o n t i n e n t a l deposits of p o s s i b l y small extent the 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 of andesite and d a c i t e which could be assigned e i t h e r to the Spences Bridge or Kin g s v a l e groups are exposed immediately northeast of Glen F r a s e r , on the east side of the road to P a v i l i o n . 116 A specimen of andesite t r a n s i t i o n a l to b a s a l t contains coarse phenocrysts of p l a g i o -c l a s e and completely c h l o r i t i z e d p y r i b o l e s and a very f i n e - g r a i n e d groundmass i n which 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 ore\" can be i d e n t i f i e d . The p l a g i o c l a s e of the phenocrysts has a spongy s t r u c t u r e , i s twinned and zoned, and ranges i n composition 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 of a n d e s i n e - l a b r a d o r i t e . The rock 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 flow b r e c c i a s which c o n t a i n fragments of dark colored v o l c a n i c rocks. A specimen has phenocrysts of c a l c i c andesine that are twinned, zoned, and s t r o n g l y a l t e r e d , of a p y r i b o l e that i s completely replaced by c h l o r i t e and \" i r o n o re\", and of quartz. The groundmass contains 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 of quartz and a low p r o p o r t i o n of \" i r o n ore\" 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 coarse-grained and abundant. Some of the pheno-c r y s t s are replaced near cleavages by a m i n e r a l w i t h a low negative r e l i e f and low b i r e f r i n g e n c e which i s e i t h e r o r t h o c l a s e or a z e o l i t e . No o r t h o -c l a s e could be i d e n t i f i e d i n the groundmass. The outcrops are separated from c l i f f s of D i v i s i o n B of the Kingsvale group by an expanse of 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 rocks i s u n c e r t a i n because the l o c a t i o n of the boundary f a u l t between the Pav-\" i l i o n group and the Kingsvale group i n t h i s area 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 transverse f a u l t i t continues under the overburden i n the v i c i n i t y of the P a v i l i o n road and the rocks belong to the lower D i v i s i o n of the Spences Bridge group which o v e r l i e s the P a v i l i o n group. However, the rocks i n the v i c i n i t y of the road show no signs of a l t e r a t i o n and shearing. The l o n g i t u d i n a l f a u l t may be OUTCROP BOUNDARY 0 .5 I Y Y ATTITUDE , SCHISTOSITY, M I L E S y \\ LAYERING OF VOLCANIC ROCKS 30 Q U A R T Z - DIORITE 2 Q KINGSVALE GP, DIV. B, OR SPENCES BRIDGE GR, LOWER DIV. ROAD 19 KINGSVALE GROUP, DIVISION B +-+ RAILROAD 4 PAVILION GROUP,DIVISION 11 FIG. 5= G E O L O G Y OF G L E N F R A S E R A R E A o f f s e t by a transverse f a u l t along the southern border of the stock south of P a v i l i o n i n which case the v o l c a n i c rocks would be part of D i v i s i o n B of the Kingsvale group. The a l t e r n a t i v e s are shown on Figure 5. FOUNTAIN VALLEY ASSEMBLAGE 1. D i s t r i b u t i o n and Thickness The Fountain V a l l e y assemblage made up l a r g e l y of v o l c a n i c r o c k s , i s exposed on both side s of the Fraser R i v e r east of Fountain Creek. I t has been subdivided i n t o three members, A, B, and C. The base of Member A, which i s i n f a u l t contact w i t h the Jackass Mountain group, i s not exposed. Member A has a minimum thickness of 1200 f e e t . Member B i s l e n t i c u l a r ; i t s thickness ranges from 600 feet to 2500 f e e t . The upper part of Member C which i s i n i n f e r r e d f a u l t contact w i t h the Gibbs Creek assemblage i s not exposed. The member i s about 1000 feet t h i c k . 2. L i t h o l o g y Member A Member A c o n s i s t s mostly of i n t e r l a y e r e d f e l s i t i c and a n d e s i t i c rocks. About 1000 f e e t southwest of the long r a i l -road t u n n e l near Gibbs Creek a short lens of 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 of a n d e s i t i c rocks 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 flows range up to 20 f e e t i n t h i c k n e s s . 119 The f e l s i t i c rocks are l i g h t grey to b u f f , a p h a n i t i c , and l a c k i n g i n flow s t r u c t u r e s . A t h i n - s e c t i o n of a d a c i t e c o n s i s t s mainly of andesine m i c r o l i t e s , 10 to 15 percent of quartz and small amounts of \" i r o n ore\" and v o l c a n i c g l a s s . 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 rock i s a l t e r e d by carbonate and c h l o r i t e . Other specimens examined are probably l a t i t e or quartz l a t i t e and r h y o l i t e ; but the exact composition of these rocks cannot be determined because of t h e i r extremely f i n e g r a i n s i z e . A t y p i c a l specimen of andesite 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 micro-phenocrysts of p l a g i o -c l a s e are v i s i b l e i n a groundmass that 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 areas of 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 alignment. Incorporated fragments have the same mineral composition as the matrix 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 of the m i c r o l i t e s . C a v i t i e s are f i l l e d by very f i n e - g r a i n e d quartz 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 oxide\". Member B Member B, a conspicuous, c l i f f - f o r m i n g u n i t , i s made up of a c i d i c v o l c a n i c flows ranging from d a c i t e to r h y o l i t e . I t seems to c o n s i s t of a multitude of flows but the bound-a r i e s between i n d i v i d u a l flows are d i f f i c u l t to determine. The rocks are l i g h t grey on f r e s h surfaces and r e d d i s h or brownish b u f f on weathered surfaces and a p h a n i t i c or a p h a n i t i c - p o r p h y r i t i c . In some l o c a l i t i e s the p l a g i o c l a s e phenocrysts are a l i g n e d and probably o r i e n t e d p a r a l l e l to the l a y e r i n g of the f l o w s . 120 A t h i n - s e c t i o n of a p o r p h y r i t i c - a p h a n i t i c d a c i t e c o n s i s t s of about 30$ of phenocrysts, and 70$ of groundmass. Most of the phenocrysts are of p l a g i o c l a s e ; a few c o n s i s t of b i o t i t e , \" i r o n o r e \" that has replaced b i o t i t e , and quartz. The p l a g i o c l a s e , which has the composition of c a l c i c andesine, i s twinned and zoned. The p l a g i o c l a s e phenocrysts show a spongy s t r u c t u r e which i s due to replacement by minerals of the groundmass and carbonate. The b i o t i t e i s replaced inwards from i t s margins and cleavages. The groundmass c o n s i s t s dominantly o f l a t h - l i k e sodic o l i g o c l a s e . About 10 to 15$ of the groundmass i s made up of anhedral quartz. Smaller f r a c t i o n s are formed by \" i r o n ore\", 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 or absent. A p a t i t e occurs as an accessory m i n e r a l . A specimen of r h y o l i t e weathers brownish 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 of andesine and quartz are 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 minerals of the groundmass, probably i n t e r -growths of 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 (?) are f i b r o u s and form aggregates most of which show a r a d i a t i n g s t r u c t u r e . Undulating, b r e c c i a t e d flow l a y e r s made up of r e l a t i v e l y f i n e - g r a i n e d aggregates a l t e r n a t e w i t h l a y e r s of coarser aggregate s i z e . F ractures i n the specimen are f i l l e d w i t h \" i r o n oxide\". Member C Only the lowest part of Member C i s exposed. I t con-s i s t s of and e s i t e , a n d e s i t i c flow b r e c c i a , and a few fee t of l i t h i c sandstone that contains seams of plant matter. A t y p i c a l andesite specimen from the east shore of the Fraser R i v e r weathers purple to g r e y i s h green. The rock i s a p h a n i t i c - p o r p h y r i t i c and contains a small percentage of p l a g i o c l a s e pheno-c r y s t s that are l a r g e l y replaced by carbonate. The groundmass i s made up dominantly of micro-l i t e s of sodic andesine, and a few percent of \" i r o n ore\" 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 rock contains v e i n l e t s of ca r -bonate, quartz, and c h l o r i t e . 121 3. Structure, Mode of Ori g i n , Age The volcanic flows s t r i k e approximately N 20° W and dip at moderate to steep angles to the northeast. At one l o c a l i t y near the contact of the members A and B a f e l s i t i c flow of B includes fragments of a more basic rock probably from member A; the stratigraphic tops therefore probably face to the northeast. The unit seems to occupy a graben between older rocks to the west and to the east. The f a u l t contact with the Jackass Mountain group to the west i s exposed at several l o c a l i t i e s on both sides of the Fraser River. The contact with the lower part of the Spences Bridge group i s covered by an expanse of overburden; a f a u l t between these two units i s suggested by cross section B-B' (Figure 1 ) . This infe r r e d f a u l t perhaps i s connected with the normal fa u l t that forms the western boundary of the Cache Creek group i n the central and northern parts of the map area. The association of these volcanic rocks with con-glomerate and with sandstone carrying seams of plant matter indicates a continental o r i g i n . The structure suggests that the Fountain Valley assem-blage i s younger than the Gibbs Creek assemblage. Its age may l i e anywhere between the Aptian stage of the Lower Cretaceous and the early or middle T e r t i a r y . 122 WARD CREEK ASSEMBLAGE 1. D i s t r i b u t i o n and Thickness V o l c a n i c rocks of Cretaceous or e a r l y T e r t i a r y age form a narrow elongate b e l t on the west side of the Fraser R i v e r between Leon Creek and the northwestern extremity of the map area. As the b e l t i s i n f a u l t contact w i t h other 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 un-known no accurate statement of i t s t h i c k n e s s can be given; s e v e r a l thousand feet of v o l c a n i c rocks may be present. 2. L i t h o l o g y The u n i t i s made up dominantly of an d e s i t e , l e s s d a c i t e and f e l s i t i c rocks and minor t u f f , b a s a l t , l i t h i c sand-stone, and c o a l . The andesite weathers dark grey or purple and i s mostly massive. Flow-banding and p o r p h y r i t i c t e x t u r e s were r a r e l y seen. A t h i n - s e c t i o n of a t y p i c a l a ndesite-flow b r e c c i a i s made up dominantly of m i c r o l i t e s of c a l c i c andesine, about . 0 5 mm l o n g , and a few c r y s t a l s of b i o t i t e i n an extremely f i n e - g r a i n e d , p a r t l y g lassy groundmass. Although the mi n e r a l composition i s uniform throughout the s l i d e i n d i v i d u a l breccia-fragments can be d i s t i n g u i s h e d by the v a r i a t i o n i n the o r i e n t a t i o n of the m i c r o l i t e s . The s e c t i o n i s veined 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 the rocks are f i n e l y layered and p o r p h y r i t i c . The flow l a y e r s range from purple to cream i n c o l o r and are 123 a few m i l l i m e t e r s t h i c k . They show small flow f o l d s one or a few f e e t across and f i n e c r e n u l a t i o n s . Under the microscope phenocrysts are seen to c o n s i s t of p l a g i o c l a s e , quartz, and b i o t i t e . The p l a g i o c l a s e , mostly sodic andesine, i s twinned, zoned and has i n c l u s i o n s of g l a s s . The quartz phenocrysts are p a r t l y embayed and corroded by minerals of the groundmass. The groundmass c o n s i s t s of minute m i c r o l i t e s of p l a g i o c l a s e , and very small c r y s t a l s of quartz and b i o t i t e embedded i n a ma t r i x of 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 that curve around the phenocrysts. Some flow l a y e r s , more coarse-grained than most of the groundmass, are r e l a t i v e l y r i c h i n quartz. A specimen of b a s a l t from the upper part of Trimble Creek i s very dark on f r e s h s u r f a c e s , weathers dark green and i s a p h a n i t i c . I t contains microphenocrysts of p l a g i o c l a s e and clino-pyroxene. The p l a g i o c l a s e , sodic bytownite i n composition, i s l a t h - l i k e , twinned and f i n e l y zoned. Some of the clino-pyroxene, d i o p s i d e - a u g i t e , (ny=1.6835» 2v-55°, Ca45Mg4^Feo) shows twin n i n g , and a few grain s have rims of lower b i r e f r i n g e n c e . Some of the c r y s t a l s are replaced by c h l o r i t e . The groundmass c o n s i s t s dominantly of 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 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 . The rocks of t h i s u n i t show no signs of metamorphism but are l o c a l l y a l t e r e d . Some are veined or p a r t l y replaced by carbonate, c h l o r i t e , chalcedony or epidote. F e l s i t i c rocks i n the shear zone southwest of the B i g Bar f e r r y c o n tain c r y s t a l s of p y r i t e , the amygdules i n an andesite flow are f i l l e d w i t h quartz and p i s t a c i t e . 3. S t r u c t u r e The Ward Creek assemblage l i e s approximately on s t r i k e w i t h parts of the Kingsvale group, the Spences Bridge group, 124 and the Fountain V a l l e y assemblage, and l i k e these i t i s be-l i e v e d to occupy a graben. Between Leon Creek and B i g Bar Creek the u n i t i s i n f a u l t contact w i t h the P a v i l i o n group to n o r t h e a s t . North of B i g Bar Creek i t i s unconformably over-l a i n by the French Bar formation. To the southwest the rocks are i n f e r r e d to be i n f a u l t contact w i t h D i v i s i o n C of the Jackass Mountain Group. They are separated from the DIVISION of the Spences Bridge group by overburden and o v e r l y i n g 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 the B i g Bar f e r r y a zone of shearing and a l t e r a t i o n i s exposed f o r approximately 1000 f e e t . The s c h i s t o s i t y of t h i s zone dips s t e e p l y to the west. The shear zone p o s s i b l y i s part of a more extensive f a u l t that may terminate the French Bar formation on the east side of the Fraser 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 of the shear zone to the n o r t h as w e l l as to the south are cover-ed by expanses of overburden. L i t t l e i s known about the i n t e r n a l s t r u c t u r e of the Ward Creek assemblage because determinations of a t t i t u d e s and 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 are d i f f i c u l t to o b t a i n . Between Watson Bar Creek and B i g Bar Canyon the rocks i n the western part of the v o l c a n i c b e l t d i p s t e e p l y and s t r i k e approximately N 3 5 ° W. The s t r a t i g r a p h i c tops face to the northeast. At s e v e r a l l o c a l i t i e s northwest of B i g Bar Canyon moderate n o r t h e a s t e r l y dips were observed. 4. Mode of Origin, Age and Correlation The presence of coal seams indicates a continental environment. The unit is older than the unconformably overlying French Bar formation. It may be correlative with the upper Division of the Spences Bridge group, with parts of the Kingsvale group or Early Tertiary volcanic rocks of the Quesnel map-area. Its 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 olivine 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 is at least 2100 feet thick. The formation consists mostly of cobble-pebble- and granule-conglomerate, less volcanic arenite, and small amounts of siltstone. (Plates XVI, XVII). Beds of arenite and conglomerate are mostly from one to twenty feet thick, and individual beds of arenite and con-glomerate can be traced for several hundred feet. A unit composed dominantly of volcanic arenite and some interbedded conglomerate is exposed for about 1-1/2 miles. 126 The rocks weather y e l l o w i s h or brownish and con-glomerate s t r a t a are darker colored than a r e n i t e . The s e d i -ments a l l seem to have been derived from v o l c a n i c rocks that were mostly of a n d e s i t i c composition. The conglomerates con-s i s t almost e n t i r e l y of v o l c a n i c fragments. The a r e n i t e s i n a d d i t i o n to the v o l c a n i c fragments, c o n t a i n a small amount of f e l d s p a r , quartz, b i o t i t e , and \" i r o n ore\". The s i l t s t o n e s are made up of the same minerals and c h l o r i t e . Rounding and s o r t i n g vary c o n s i d e r a b l y , but i n general the beds are moder-a t e l y w e l l s i z e - s o r t e d and the fragments subrounded. Con-glomerates and a r e n i t e s have a ma t r i x of s i l t - s i z e d r o c k - f l o u r and are p a r t l y cemented by \" i r o n oxide\" and r a r e l y carbonate. Some a r e n i t e s are very poorly c o n s o l i d a t e d . L o c a l l y the aren-i t e contains seams of f o s s i l p l a n t s . Graded bedding and cross bedding are ra r e and were observed only where the sandstone i s i n t e r l a m i n a t e d w i t h s i l t - s t o n e . The French Bar formation o v e r l i e s the 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 se-quence that i s i n f a u l t contact w i t h the P a v i l i o n group. The s t r a t a s t r i k e uniformly about N 25° W and dip ste e p l y or moderately to the northeast. In the southeastern part near the boundary f a u l t of the P a v i l i o n group the dips are approx-imately 80° and i n the northwest they are c l o s e to 45°i Near B i g Bar Creek exposures of the conglomerate end a b r u p t l y . P o s s i b l y the formation here i s cut o f f by a f a u l t ; a strong shear zone that may be part of such a f a u l t i s exposed i n the v o l c a n i c rocks on the west s i d e of the r i v e r . A l t e r n a t i v e l y , the b a s i n of d e p o s i t i o n may have ended here. The formation 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 matter 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 the formation. The g e n e r a l l y rounded nature of the fragments and l o c a l laminations suggest d e p o s i t i o n by running water. Beds that show poor s o r t i n g and rounding may have been deposited as mudflows. The coarse s i z e of the fragments i s i n d i c a t i v e of steep g r a d i e n t s . These gradients may be r e l a t e d to contemporaneous volcanism or tectonism. P l a n t f o s s i l s found i n the upper part of the f o r -mation, near B i g Bar Creek were i d e n t i f i e d by Professor G.E. Rouse as f o l l o w s : DIVISION SPERMATOPHYTA Class GYMNOSPERMAE Order CONIFERALES 1. Metasequoia o c c i d e n t a l i s (Newb.) Chaney. Paleocene-Miocene 2» ? Sequoia n o r d e n s k i o l d i Heer. Paleocene-Eocene Class ANGIOSPERMAE Sub-Class DICOTYLEDONAE 3» Cinnamomum sp. - c f . a f f i n e Lg Upper Cretaceous-Eocene. 4« Carpinus grandis Unger. T e r t i a r y 5« ? S a l i x sp. - c f . S. wyomingensis Kn. Paleocene-Miocene and Cock 6. ? Laurophyllum sp. <- c f . L. laraminum Paleocene (DN) B e l l 7* T e t r a c e r a sp. - c f . T. c a s t a n e a f o l l a Eocene Mac G. 128 8. Hamamelis ? c l a r u s H o l l i c k Paleocene-Eocene 9. Alnus sp. c f . A. cremastogynoides Berry Eocene-Oligocene Rouse s t a t e s i n h i s r e p o r t : \"As can be noted, the determinations 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 preference towards an Eocene d a t i n g . However, i t i s p o s s i b l e that the beds are e i t h e r e a r l i e r T e r t i a r y or Oligocene; a more d e f i n i t e age determination cannot be based on the r e l a t i v e l y poorly pre-served fragmentary remains. I t i s the w r i t e r ' s considered o p i n i o n that 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 other T e r t i a r y basins i n B.C. e.g. Chu-Chua, and P r i n c e t o n . The ages of these 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 pro-bable age would seem to be Upper-Eocene or Oligocene f o r the B i g Bar f l o r a . \" In 1920 McKenzie described and defined the French Bar formation as f o l l o w s : (p. 76 A - 77 A) \"This formation i s w e l l exposed on upper French Bar Creek, and u n d e r l i e s the country westward across the ridges i n which Yalakom r i v e r heads as f a r as upper Churn/Creek drainage b a s i n . I t may have a considerable extension i n the area southeast of that j u s t d e s c r i b e d . \" \"The French Bar formation i s made up of very coarse conglomerates w i t h l e n t i c u l a r sandstone beds i n subordinate amounts. The rocks are much l e s s indurated than any of the sediments of those included i n the Eldorado s e r i e s \" (Lower Cretaceous), and the pebbles and boulders easily weather out of their sandy matrix. The formation is 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 origin.\" ... \"The thickness of the French Bar formation as exposed near the creek of that name is approximately 2000 feet.\" \"On lithologic and structural grounds, this formation is tentatively correlated with the Coldwater group of Dawson, supposedly of Oligocene 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 lithology, sedi-mentary structure and thickness they are tentatively correl-ated with that formation. The granitic boulders reported by McKenzie are probably of local origin and were not transported into the Big Bar area. The deposits appear to be older than the Tertiary sedimentary rocks on Big Bar Creek, on Leon Creek, and near Pavilion because they are much stronger deformed. VOLCANIC ROCKS OVERLYING THE FRENCH BAR FORMATION The French Bar formation is overlain by a minimum of 2000 feet of tuff, andesite, basalt, f e l s i t e , and minor seams of coal. The andesite is generally greyish brown, aphanitic, and mostly massive. A specimen of basalt weathers greyish brown and has a vesicular, aphanitic texture. 130 I t c o n s i s t s of abundant microphenocrysts of p l a g i o c l a s e and augite i n a groundmass of very f i n e - g r a i n e d p l a g i o c l a s e , clino-pyroxene, \" i r o n o r e \" , and v o l c a n i c glass 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 microphenocrysts, intermediate to sodic l a b r a d o r i t e , are l a t h -l i k e , twinned, and show o s c i l l a t o r y normal zoning. 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 of the augite phenocrysts (ny=1.6905 2v-52°; Ca^Mg^Fe-^) al s o show twinning. A t h i n - s e c t i o n of a w h i t i s h r e l a t i v e l y l i g h t f e l s i t i c rock contains a few corroded phenocrysts of p l a g i o c l a s e and quartz i n a v e s i c u l a r g l a s s y groundmass. To the northeast the v o l c a n i c rocks are i n f a u l t contact w i t h the P a v i l i o n group. This contact i s not ex-posed but a f a u l t can be i n f e r r e d from the f a c t that the P a v i l i o n group s t r i k e s i n t o the T e r t i a r y v o l c a n i c s , from the steep dips near the c o n t a c t s , and from shearing and a l t e r a t i o n . MIDDLE OR LATE TERTIARY SEDIMENTARY AND VOLCANIC ROCKS 1. Sedimentary Rocks near P a v i l i o n A. D i s t r i b u t i o n and Thickness Middle or Late T e r t i a r y outcrops 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 trending zone that i s approximately 5 miles long and 1-1/2 miles wide. The exposures are confined to narrow zones along h i l l s i d e s . The e l e v a t i o n of the lowest outcrops i s 3200 f e e t at the northeastern extremity and ne a r l y 4000 fe e t at the southwestern extremity. I n d i v i d u a l exposures do not exceed 200 f e e t i n thickness but the v e r t i c a l range of the deposits on the slope south of P a v i l i o n Creek i s greater than 500 f e e t . On the n o r t h side of the same v a l l e y 131 however, the rocks are l e s s than one hundred f e e t t h i c k . A s m all outcrop of s i m i l a r rock was noted at approx-imately 4000 f e e t e l e v a t i o n on the slope above Moran, and another one l i e s immediately northeast of the r a i l r o a d c r o s s -in g near Glen F r a s e r . B. L i t h o l o g y The rocks c o n s i s t of l i t h i c a r e n i t e , conglomerate, and a s m a l l p r o p o r t i o n of carbonaceous shale. The contacts between these rock types are w e l l d e f i n e d , but the rocks show no pronounced i n t e r n a l s t r a t i f i c a t i o n . The rocks and the s o i l d e r i v e d from them are b r i c k - r e d . In hand-specimens of 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 r a r e l y c h l o r i t e fragments can be recognized. These p a r t i c l e s range from sand to cobbles. The weakness of t h e i r cement has r e -s u l t e d i n the formation of numerous caves, and i n a major land s l i d e about one m i l e east of P a v i l i o n . Three specimens of l i t h i c a r e n i t e examined under the microscope c o n t a i n 10-35$ quartz, 0-9$ f e l d s p a r , 11-35$ c h e r t , and 20-50$ l i t h i c fragments, mostly of 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 of other sedimentary and metamorphic rocks. Minor d e t r i t a l c o n s t i t u e n t s are carbonate, muscovite, and tourmaline. The fragments i n most specimens are w e l l s i z e - s o r t e d . O r i g i n a l l y they were subrounded to rounded but they have p a r t l y been replaced by the m a t r i x which c o n s i s t s of carbonate and \" i r o n o xide\". C. S t r u c t u r e The u n i t o v e r l i e s unconformably s t r a t a of the P a v i l i o n group and small bodies of igneous rocks assigned to the Coast I n t r u s i o n s . The beds l i e h o r i z o n t a l l y or dip at angles of l e s s than ten degrees and appear n e a r l y everywhere l i t t l e d i s t u r b e d . An i s o l a t e d outcrop by the P a v i l i o n Mountain road, 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 to bedding, that dips 55 degrees east. Although the exposures of the T e r t i a r y rocks on the slope n o r t h of P a v i l i o n Creek terminate at the f a u l t contact between D i v i s i o n I and I I of the Cache Creek feroup, there i s no evidence that the T e r t i a r y sedimentary rocks were d i s -placed by that f a u l t . I t i s more l i k e l y that the contact formed a topographic c o n t r o l of d e p o s i t i o n . The amphibolites to the west of that contact which are indurated by a d i o r i t i c i n t r u s i o n are probably more r e s i s t a n t to weathering than the ribbon cherts to the east. In T e r t i a r y time they may have formed the margin of a basi n and received no sediments. D. Mode of O r i g i n The sediments appear to be derived mostly from rocks of the Cache Creek and P a v i l i o n groups and to minor extent from Coast I n t r u s i o n s . As they c o n s i s t of r e l a t i v e l y coarse, w e l l sorted m a t e r i a l they probably represent a f l o o d p l a i n . The red c o l o r of 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 black s h a l e , however, shows that 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 of the deposits are only partly known. On the northeast they lap against a pluton which r i s e s above the Te r t i a r y beds, and north of P a v i l i o n Creek they be-come t h i n and probably disappear. They may have been l a i d down i n a v a l l e y that was connected with the area south of Leon Creek and partly coincided with the present Fraser River v a l l e y . E. Age Dawson correlated the sediments with the sandstones underlying the basalt plateau on Leon Creek and placed them i n the middle Miocene. (Dawson, 1895, p. 212B). D u f f e l l and Mc-Taggart include them with the Coldwater Beds (?) of the Kam-loops group which i s considered 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 similar 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 structure. The s t r a t a on Hat Creek dip at angles up to 60° whereas the beds near P a v i l i o n l i e almost h o r i z o n t a l l y . Dawson's c o r r e l a t i o n of the sediments near P a v i l i o n with those south of Leon Creek i s supported by several features. Both s t r a t a are approximately at the same elevation, both seem to be undisturbed and both appear to be older than the l a t e s t volcanic rocks of the area. It w i l l be mentioned that the s t r a t a south of Leon Creek probably underlie Middle to Late T e r t i a r y o l i v i n e 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 elevation than an isolated remnant of T e r t i a r y andesite situated about 1-1/2 miles to the northeast oh the plateau on P a v i l i o n Mountain. D u f f e l l and McTaggart 134 pointed out that the sedimentary outcrop near Glen Fraser i s cut by two dykes, (p. 65p). Such dykes may w e l l be r e l a t e d to the l a t e s t v o l c a n i c a c t i v i t y . The upper surface of the sedimentary rocks near P a v i l i o n i s continuous w i t h a w e l l preserved e r o s i o n p l a i n on P a v i l i o n Mountain of approximately 20 square m i l e s . I t i s b e l i e v e d that surfaces of t h i s type are not o l d e r than Miocene. (Thornbury, 1954, p. 26). 2. Sedimentary Rocks Associated 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 miles south of Leon Creek and one m i l e west of the Fraser R i v e r poorly c o n s o l i d a t e d sediments are exposed f o r about one m i l e along the s t e e p l y s l o p i n g margin of a pla t e a u at an e l e v a t i o n of approximately 3500 f e e t . The thi c k n e s s of the exposed s t r a t a i s l e s s than one hundred f e e t , but the u n i t may be much t h i c k e r . The r o c k s , mostly brownish and r e d d i s h , range from sandstone to boulder conglomerate and are i n part w e l l bedded. 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 by c o l o r or g r a i n s i z e . The beds are from one to ten f e e t t h i c k . 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 mainly of chert and a r g i l l i t e , and some g r a n i t i c fragments. Pebbles and sand grains are p o o r l y rounded. The cement c o n s i s t i n g of carbonate and \" i r o n o x i d e \" i s mostly weak. The beds r e s t unconformably on quartz d i o r i t e . A low dip has probably been produced by recent slumping. The sediments seem to have been derived from rocks of the immediate v i c i n i t y . They probably u n d e r l i e o l i v i n e b a s a l t but may only be s l i g h t l y o l d e r than that v o l c a n i c rock. At many l o c a l i t i e s around the margins of the T e r t i a r y b a s a l t the s o i l contains unusually w e l l rounded pebbles and cobbles. These roundstones are probably derived from con-glomerates which u n d e r l i e the b a s a l t s but are hidden by the abundant t a l u s that surrounds t h e i r c l i f f s at the margins. Such conglomerates would be c o r r e l a t i v e w i t h the outcrop de-sc r i b e d above and w i t h the sedimentary rocks 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 to 300 f e e t t h i c k are exposed f o r approximately one m i l e along the upper margin of the p l a t e a u n o r t h of B i g Bar Creek. To the east they 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 to the west t h e i r contact i s covered. The rocks are mostly pebble- or cobble-conglomerate but i n c l u d e boulder-conglomerate, sandstone, and minor amounts of mudstone. The roundstones are made up of c h e r t , a r g i l l i t e , l i mestone, and greenstone, a l l derived from the 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 -u l a r T e r t i a r y b a s a l t s . The fragments are w e l l rounded and f a i r l y w e l l sorted and cemented by carbonate. The s t r e n g t h of the cement v a r i e s i r r e g u l a r l y throughout the rock. The s e d i -ments seem to have been deposited by running water and appar-e n t l y are contemporaneous w i t h the o l i v i n e b a s a l t s . They are probably s l i g h t l y younger than the T e r t i a r y sedimentary rocks near Leon Creek and near P a v i l i o n . 136 3. O l i v i n e B a s a l t A. D i s t r i b u t i o n and Thickness The outcrops 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 s are confined to two narrow zones. One i s s i t u a t e d on the west s i d e of the Fraser R i v e r between McKay Creek and Watson Bar Creek; ( P l a t e X V I I I ) , the other one, l o c a t e d approx-imately 10 miles to the n o r t h , extends along the lower part of B i g Bar Creek. The e l e v a t i o n of the upper surface of the f i r s t zone g r a d u a l l y drops from 4400 f e e t i n the south to 3900 feet i n the n o r t h over a d i s t a n c e of approximately 10 m i l e s ; the upper surface of the second zone drops from 3900 f e e t i n the west to 3600 feet i n the east over a distance of approximately 5 m i l e s . These upper surfaces seem to represent the o r i g i n a l top of the v o l c a n i c flows because they are of great r e g u l a r i t y and marked by coarse v e s i c l e s . They are o v e r l a i n only by a t h i n veneer of s o i l and form plateaus which are w e l l expressed on topo-graphic maps. The e l e v a t i o n s of the lower contacts are known w i t h l e s s accuracy because they are hidden by t a l u s and because the outer margins of the v o l c a n i c plateaus have slumped almost everywhere. Probably the b a s a l t s are nowhere t h i c k e r than 200 f e e t . The sheet south of Leon Creek seems to t h i n out to the west; the flows on B i g Bar Creek appear to be t h i c k e r In the west than i n the 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 flows are from 10 to 50 f e e t t h i c k . Some of them were traced along the margin of the plateaus f o r s e v e r a l hundred f e e t but they may be much more extensive. 137 B. L i t h o l o g y The rocks are red-brown and some of them are r e l a t i v e l y coarse-grained. Dark green c r y s t a l s of o l i v i n e about one to two m i l l i m e t e r s long can be detected w i t h the unaided eye. The upper parts of the flows are h i g h l y v e s i c u l a r . Columnar j o i n t -i n g i s a common f e a t u r e . North of B i g Bar Creek e l l i p s o i d a l s t r u c t u r e s about one foot or a few fe e t t h i c k that resemble p i l l o w s were seen. Seven specimens studied i n t h i n - s e c t i o n c o n s i s t approximately of 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$ \" i r o n o xide\". The balance i s made up dominantly of c l i n o -pyroxene. Orthopyroxene, not i d e n t i f i e d i n a l l of the specimens, forms l e s s than 1$ of the rock. A p a t i t e , z i r c o n ( ? ) , and an unknown mi n e r a l o c c u r r i n g as very 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 the p l a g i o c l a s e are present only i n minute pro-p o r t i o n s . ( P l a t e X IX). The p l a g i o c l a s e forms euhedral to subhedral m i c r o l i t e s that e x h i b i t Carlsbad and a l b i t e twinning. The other twin laws are l e s s commonly represented. The mineral shows zoning, mostly of the normal type, and has an average composition near An^Q' I t i s l i t t l e a l t e r e d . Some c r y s t a l s of o l i v i n e are subhedral, but most of the g r a i n s are anhedral. The composition o f the mineral ranges from F034 to F072 and averages Fo8o» l n s e v e r a l specimens the 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 strongest around the outer margins of the gr a i n s and near f r a c t u r e s but a l s o occurs i n t h e i r i n t e r i o r . 138 The ortho-pyroxene i s subhedral and c o l o r l e s s unless a l t e r e d . In one specimen i t s composition was determined as E n ^ (ny=1.685> - 2v). In some specimens the mineral i s a l t e r e d b y \" i r o n oxide.\" The clinopyroxene forms very f i n e - g r a i n e d subhedral or anhedral grains the composition of which i s d i f f i c u l t to i d e n t i f y . Most of the clinopyroxene seems to be augite but some p i g e o n i t e may be present. In one specimen the augite has an approximate composition of Ca^Mg^Fe-^^ (ny=1.689). Of the \" i r o n ore\" minerals i l m e n i t e i s much more abundant than magnetite. The t e x t u r e of the rocks 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 the 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 of the e s s e n t i a l minerals i n a r e l a t i v e l y coarse-grained specimen ranges approximately from 2mm to .02 mm and i n a f i n e - g r a i n e d rock from 1 mm to .015 mm. Two types of t e x t u r e may be d i s t i n g u i s h e d : e i t h e r o l i v i n e alone forms the l a r g e grains (type I) or the l a r g e grains c o n s i s t of p l a g i o c l a s e and orthopyroxene as w e l l as o l i v i n e (type I I ) . The intermediate range i s dominated by p l a g i o c l a s e but also contains some o l i v i n e and clinopyroxene. The f i n e s t grade i s made up of mostly clinopyroxene and small amounts of p l a g i o c l a s e . TABLE 3 MINERAL COMPOSITION OF 7 SPECIMENS OF OLIVINE BASALT S p e c i - % % % % % nx\" of Compos- n y of Comp. Tex-men p l a g i o - c l i n o - ortho- o l i v - Iron i r o n (001) c l - i t i o n i n o l i v i n e ±n% ture # c l a s e pyr- pyr- ine oxide ore eavage f r a g - % of An oxene oxene a l t e r - ments o f - t 1% p l a g i o -c l a s e l c 51 17 0 16 13 ' 3 1.5587 61 1.6855 84 I I + .001 t .002 l b 59 22 1 14 4 1.5584 60 1.6893 82 I I + .001 t .002 l a 60 20 0 15 5 1.5584 60 1.6900 81 .5 I I i .001 t .002 2c 57 32 t r a c e 8 3 1.5585 60 1.6991 77.5 I I i .001 t .001 2b 50 25 0 15 6 4 1.5586 61 1.7100 72.5 I t .001 t .001 p i l o -t a x i t i c 2a 50 25 0 8 14 3 1.5590 62 1.6900 81 .5 I t .002 i .001 trachy-t i c 3 49 40 0 7 4 1.5581 59 1.6910 81 I t .001 t .002 2 A R.M. Crump and N.B.Kettner, (1953) (3) A. P o l d e r v a a r t , (1950) Specimen l a , b, and c, are taken from three successive flows of the pl a t e a u south o f Leon Creek, and specimen 2a, b, and c, are from three successive flows from the pl a t e a u n o r t h of Leon Creek. The two l o c a l i t i e s are approximately 2 miles apart. Specimen 3 i s from n o r t h of B i g Bar Creek. 140 The present sampling i n d i c a t e s no systematic v a r i a t i o n i n composition. The presence of orthopyroxene i n some flows probably i s not s i g n i f i c a n t because the mineral occurs only i n s m a l l q u a n t i t i e s . The one flow (2b) that contains an o l i v i n e comparatively 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 composition of i t s p l a g i o c l a s e . This l a c k of 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 that the t e x t u r e of the rock i s of type (I) and approaches that of 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 rocks of the P a v i l i o n group and on poorly c o n s o l i d a t e d T e r t i a r y sediments. Their upper surface slopes about 50 f e e t per m i l e to the n o r t h c o r r -esponding to a d i p of l e s s than one degree. They o v e r l i e the Fraser R i v e r f a u l t zone without any signs of disturbance. Being r e l a t i v e l y r e s i s t a n t to weathering 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 underlying rocks which they p r o t e c t . Apparently these weaker rocks are not able to support the load of the b a s a l t s at such slopes and y i e l d by slumping. The margins of the b a s a l t plateaus are also c h a r a c t e r i z e d by numerous f r a c t u r e s along which openings from a few feet to tens of f e e t wide develop. The t e r r a c e - l i k e f a u l t blocks around the b a s a l t p l a t -eaus near Leon Creek are v i s i b l e on air-photographs. ( P l a t e XX) 141 D. Mode of O r i g i n There can be l i t t l e doubt that the four outcrop areas between McKay Creek and Watson Bar Creek are remnants of a continuous sheet of v o l c a n i c flows which o r i g i n a l l y f i l l e d a v a l l e y . Some of the mountain slopes that bounded t h i s v a l l e y on the west are s t i l l preserved. The slopes are u n d e r l a i n by rocks of the Jackass Mountain group and of the Ward Creek assemblage. The v a l l e y i n which the b a s a l t s were l a i d down apparently contained sands and gravels that may have been p a r t l y of f l u v i a t i l e o r i g i n . The d i s t r i b u t i o n of the b a s a l t s on B i g Bar Creek, 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 the presence of p o s s i b l e p i l l o w s t r u c t u r e s suggesting submerged d e p o s i t i o n i n -d i c a t e that these flows l i k e the underlying T e r t i a r y sediments, a l s o occupied a v a l l e y . Because of the u n i f o r m i t y of l i t h o l o g y and e l e v a t i o n and the s i m i l a r i t y of environment i t i s probable that the b a s a l t s along B i g Bar Creek were connected w i t h those south of Watson Bar Creek. As no b a s a l t s are preserved between Watson Bar Creek and B i g Bar Creek such a connection must have u n d e r l a i n areas that have subsequently been eroded down to e l e v a t i o n s lower than 3900 f e e t ; t h e r e f o r e i t must have occupied a narrow zone along the l i n e of the present v a l l e y of the Fraser R i v e r . I t was mentioned that the upper surface of the northern outcrop zone dips at a gradient of approximately 50 f e e t per m i l e to the n o r t h and that the upper surface of the flows on B i g Bar Creek slope w i t h a s i m i l a r gradient to the east. One i s tempted to conclude that the source of the v o l c a n i c flows was l o c a t e d not f a r from the southern extremity of t h e i r present outcrops and that they flowed northward and eastward along v a l l e y s that c o i n c i d e i n part w i t h the present v a l l e y s of Fraser R i v e r and B i g Bar Creek. The f a c t , however, that the upper surfaces of the b a s a l t s south of 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 of 3900 feet t 50 f e e t and that no gradient i s n o t i c e a b l e i n d i c a t e s that some t i l t i n g has occurred since the d e p o s i t i o n of the f l o w s . The d i r e c t i o n o f t i l t and t h e r e f o r e the o r i g i n a l slope of the ancient v a l l e y s are unknown. These b a s a l t s are the o l d e s t v o l c a n i c rocks i n the present map-area that contain o l i v i n e . Their appearance marks the end of the phase dominated by a n d e s i t e . I t i s g e n e r a l l y thought that such flows are derived from a b a s a l t i c l a y e r i n the earth's c r u s t and r i s e through deep reaching f r a c t u r e s . As the flows o v e r l i e one or two major f a u l t s they may w e l l have ascended through f r a c t u r e s associated w i t h the Fraser R i v e r f a u l t zone but a f t e r they ceased to be a c t i v e . This c o n c l u s i o n conforms i n a general way w i t h Dawson's concept that the flows are of l o c a l o r i g i n (Dawson, 1895»p.216B). E. Age Dawson included the b a s a l t s i n h i s \"Upper V o l c a n i c Group\" which he placed i n the Upper Miocene. D u f f e l l and Mc-Taggart c o r r e l a t e d them w i t h the Kamloops group considered as 143 M i o c e n e o r e a r l i e r . H o w e v e r , i n t h e Kamloops a r e a t h e o l i v i n e b a s a l t s r e s t u n e o n f o r m a b l y on t h e Kamloops g r o u p ( W . H . M a t h e w s , p e r s o n a l c o m m u n i c a t i o n ) . As Dawson r e m a r k e d \" t h e i r , p r e s e n t a p p e a r a n c e r e p r e s e n t s a v e r y g r e a t amount o f r i v e r e r o s i o n s i n c e t h e d a t e o f t h e i r f o r m a t i o n . \" (1895, p . 2 1 6 B ) . The d e p t h o f e r o s i o n s i n c e t h e i r d e p o s i t i o n i s more t h a n 3000 f e e t . As t h e F r a s e r R i v e r c o n t a i n s P l e i s t o c e n e d e p o s i t s i t i s i m p r o b a b l e t h a t t h e v o l c a n i c r o c k s a r e y o u n g e r t h a n e a r l y P l e i s t o c e n e . On t h e o t h e r h a n d , t h e y a r e y o u n g e r t h a n t h e F r e n c h B a r c o n g l o m e r a t e because u n l i k e t h a t f o r m a t i o n t h e y have n o t been a f f e c t e d by movements o f t h e F r a s e r R i v e r f a u l t z o n e . T h e i r p o s s i b l e age t h e n r a n g e s f r o m O l i g o c e n e t o e a r l y P l e i s t o c e n e . W i t h i n t h a t s p a n a r e l a t i v e l y young age i s p r o b a b l e because t h e y p r e s e n t an o r i g i n a l s u r f a c e o f f a i r e x t e n t p r e s e r v e d under c o n d i t i o n s o f r a p i d e r o s i o n . F o r t h e s e r e a s o n s a P l i o c e n e o r l a t e M i o c e n e age i s s u g g e s t e d . (Compare T h o r n b u r y , 1954 p . 2 6 ) . W i t h r e s p e c t t o 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 r o c k s c l o s e l y r e s e m b l e b a s a l t s o f t h e Q u e s n e l m a p - a r e a a s s i g n e d by ( T i p p e r 1959) t o t h e M i o c e n e , P l i o c e n e , and p o s s i b l y P l e i s t o c e n e . 2 . INTRUSIVE ROCKS ULTRABASIC INTRUSIONS ULTRABASIC ROCKS NEAR LILLOOET 1 . D i s t r i b u t i o n A b e l t o f u l t r a b a s i c r o c k s l i e s between T r i a s s i c o r 144 o l d e r rocks to the west and the L i l l o o e t group to the east In the v i c i n i t y o f L i l l o o e t . Although outcrops a re sca r c e the s e r -p e n t i n i t e s appear to be one h a l f m i l e wide. The b e l t probably extends beyond the present map area to the nort h e a s t and may be l i n k e d w i t h the u l t r a b a s i c rocks o f the Shulaps Range. 2 . L i t h o l o g y A l l specimens examined are s e r p e n t i n i z e d h a r z b u r g i t e . In most o f them medium-to-coarse-grained l i g h t green e n s t a t i t e or b a s t i t e i s set i n a b l a c k or dark 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 specimen has approximately the f o l l o w i n g composition o f primary m i n e r a l s : o l i v i n e 66$ e n s t a t i t e 30$ c l i n o p y r o x e n e 2fo chromite 1$ The t e x t u r e o f the rock i s a l l o t r i o m o r p h i c -s e r i a t e . The o l i v i n e i s anhedral and r e l a t i v e l y f i n e -g r a i n e d , ranging approximately from .5 to . 2 mm i n s e c t i o n a l diameter. The composition o f the m i n e r a l i s Fa^o ( n 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. The e n s t a t i t e Enc^ ( n y - 1 . 6 7 0 ) i s subhedral or anhedral and ranges i n g r a i n s i z e approximately from one centimeter to 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 clin o p y r o x e n e that are 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 types o f i n c l u s i o n s can be re c o g n i z e d : l a m e l l a e o f uniform width ( . 0 2 5 mm x . 5 mm) and s p i n d l e -shaped or i r r e g u l a r patches (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 the 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 the i n c l u s i o n s Is not the same as that o f the host but i n c e r t a i n s e c t i o n s the e x t i n c t i o n p o s i t i o n o f guest and host 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 decreases from t h e i r c e n t r e toward 145 t h e i r outer margin; as many as ten d i f f e r e n t zones of 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 observed. Clinopyroxene a l s o occurs as i n d i v i d u a l grains that probably have the composition of d i o p s i d e , (ny = 1.678). The grains are subhedral to anhedral and of smaller s i z e than the orthopyroxene. Their s e c t i o n a l diameter l i e s between one and one h a l f m i l l i m e t e r . The chromite i s opaque on brownish t r a n s l u c e n t and anhedral. 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 , ranging from about one quarter to one eighth of a m i l l i m e t e r i n s e c t i o n a l diameter. 3. S e r p e n t i n i z a t i o n Most of the u l t r a b a s i c rocks are s t r o n g l y or completely s e r p e n t i n i z e d ; the l e a s t a l t e r e d specimen seen c o n s i s t s of about 65$ serpentine. The three main s i l i c a t e s are 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 diopside i s l i t t l e a l t e r e d . Some completely s e r p e n t i n i z e d c r y s t a l s of e n s t a t i t e c o n t a i n un-a l t e r e d i n c l u s i o n s of d i o p s i d e . Most of the e n s t a t i t e i s p a r t l y or completely replaced 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 progressed from the margin and from cleavages and the blades of 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 of 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 the s e r p e n t i n i z a t i o n . Replacement from the margin and from f r a c t u r e s has produced two types of mesh s t r u c t u r e s . In the f i r s t type \"serpophite\" i s surrounded by a few blades of a n t i g o r i t e . In some specimens the a n t i g o r i t e shows very roughly a p r e f e r r e d o r i e n t a t i o n which may be the r e s u l t of s t r e s s , (Leech, 1953» p. 32). In others the serpophite i s surrounded by one or s e v e r a l l a y e r s of very 146 f i n e f i b r e s that grow p e r p e n d i c u l a r l y to the w a l l s of the serpophite core. The f i b r e s ( l e n g t h slow, low b i r e f r i n g e n c e ) are p o s s i b l y \" c h r y s o t i l 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 that i s i s o t r o p i c or has low b i r e -f ringence together w i t h grains of an opaque mineral which i s probably secondary magnetite. These grains range from a f r a c t i o n of a micron i n s i z e to l a r g e r , v e i n - l i k e aggregates ranging up to .4 mm i n l e n g t h and .02 mm i n width. The \"serpophite\" and some of the f i b r o u s serpentine 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 which range from .005 to .03 mm i n l e n g t h and are approximately .001 mm t h i c k . The i n c l u s i o n s are also found i n the marginal zones of o l i v i n e g r ains but never i n the core of that m i n e r a l . These outer zones apparently have been a l t e r e d as they show a lower b i r e -f r i n g e n c e than the inner part of the g r a i n s . The r e f r a c t i v e i n d i c e s of the m i n e r a l l i e between 1.51 and 1.53. I t may be s e p i o l i t e , a m i n e r a l which occurs i n serpentine. 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 synthesized by Bowen and T u t t l e at temperatures around 350° C and a pressure of 15,000 l b s . / i n . (Bowen and T u t t l e 1949, p. 443). 4. C a r b o n a t e - S i l i c a - A l t e r a t i o n On the r i d g e northeast of 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 rocks have been replaced by carbonate and quartz. The a l t e r e d rocks form conspicuous, r u s t y weathering c l i f f s . In some specimens from these outcrops remnants of serpentine are preserved but i n others only the presence of chromite i n -d i c a t e s that the rocks o r i g i n a l l y were u l t r a b a s i c . 147 The composition of the carbonate l i e s near the boundary of magnesian dolomite and parankerite (ng-1.699). I t i s present i n a network of v e i n l e t s that encloses quartz and nodules of carbonate some of which i n c l u d e a few f i n e grains of \" i r o n ore\". The centre of the v e i n l e t s c o n tain much secon-dary \" i r o n oxide\". In some specimens the carbonate i s cut by v e i n l e t s of quartz. ( P l a t e X X I ) . 5. Age and O r i g i n Because of i n s u f f i c i e n t exposure the nature of the contacts and the i n t e r n a l s t r u c t u r e of the u l t r a b a s i c rocks are unknown. However, the f o l l o w i n g observations may have some bearing on t h e i r age and o r i g i n . (1) The u l t r a b a s i c rocks occupy a zone between T r i a s s i c or e a r l i e r rocks to the west and the L i l l o o e t group to the east which south of the present map area are i n f a u l t c ontact. ( D u f f e l l and McTaggart, 1953, p. 27). (2) 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 area occur only i n rocks of the P a v i l i o n group. (3) The s e r p e n t i n i t e s are on s t r i k e and p o s s i b l y con-tinuous w i t h the u l t r a m a f i c complex of the Shulaps Range to which they bear a c l o s e l i t h o l o g i c a l resemblance. Leech found that the main mass of the i n t r u s i o n s i n the Shulaps Range cuts Upper T r i a s s i c s t r a t a , and he observed chromite, probably derived from these i n t r u s i o n s , i n Lower J u r a s s i c sediments, (p.39). He i n f e r r e d that the u l t r a b a s i c rocks 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 of s i m i l a r l i t h o l o g y are wide spread i n B r i t i s h Columbia and a t t r i b u t e d by White to the Upper T r i a s s i c C a s s i a r orogeny (White, 1959). Because of the l a s t three p o i n t s i t i s thought that the s e r p e n t i n i t e s west of L i l l o o e t are of an o r i g i n a l Upper T r i a s s i c age. Their 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 can be explained i n two ways. E i t h e r they are i n i n t r u s i v e contact w i t h Cache Creek-type of rocks to the west and i n f a u l t contact w i t h the L i l l o o e t group to the east and antedate the f a u l t i n g , or the 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 T r i a s s i c , were r e m o b i l i z e d i n or a f t e r the Lower Cretaceous and squeezed i n t o the f a u l t . \"Cold i n t r u s i o n s \" have been described by T a l i a f e r r o (1943, p. 205) and Thayer, (1948, p. 64-65), and the concept was r e f e r r e d to the Fraser R i v e r f a u l t zone by D u f f e l l and McTaggart (1953, p. 76), and to the Shulaps Range by Leech, (1953, p. 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 I I of the Cache Creek group. A hand specimen from a dyke exposed on the east bank of the Fraser R i v e r , approximately one m i l e n o r t h of the mouth of Siwash Creek, i s r e d d i s h brown on weathered s u r f a c e s , black 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$ of the primary minerals are c l i n o -pyroxene (endiopside ? ny - 1.675), the balance c o n s i s t s of f o r s t e r i t e (+2v l a r g e r than 87°) and a small amount of a brownish opaque mineral which i s probably chromite. The endiopside i s subhedral and the o l i v i n e and the chromite are anhedral. 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 con-s i s t i n g of o l i v i n e or serpophite cores surrounded by r e l a t i v e -l y broad blades of a n t i g o r i t e that l i e i n s u b p a r a l l e l o r i e n -t a t i o n . The clinopyroxene has been a f f e c t e d by the serpen-t i n i z a t i o n to a much l e s s e r extent than the o l i v i n e . There i s a l s o some carbonate replacement. As these dykes cut rocks that are 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 the adjacent Lower Cretaceous s t r a t a t h e i r age may l i e anywhere between those l i m i t s . L i t h o l o g i c a l l y they are not i d e n t i c a l w i t h the u l t r a -b a s i c rocks west of L i l l o o e t . But as the emplacement of u l t r a -b a s i c rocks i s a rare event i n the h i s t o r y of a small area i t i s l i k e l y that these dykes are contemporaneous w i t h the masses near L i l l o o e t and i n the Shulaps Range. Therefore they are t e n t a t i v e l y r e f e r r e d to the Upper T r i a s s i c . COAST INTRUSIONS 1. EARLY LOWER CRETACEOUS OR OLDER 1. D i s t r i b u t i o n In the present area d i o r i t i c rocks considered to be e a r l y Lower Cretaceous or o l d e r are the most abundant of the igneous rocks assigned to Coast I n t r u s i o n s . A stock u n d e r l i e s Mount Martl e y on the southeastern edge of the map area, (see Figure 6) Another, about 5 miles long and up to 2 miles wide, extends from the mouth of Kelly-Creek to Leon Creek. Parts of a small stock are exposed south o f P a v i l i o n . The present map (Figure 1) suggests that i t i s l e s s extensive than i n d i c a t e d on previous maps, and instead of one l a r g e mass a number of small i n t r u s i o n s are shown. Some of these may be off-s h o o t s of a stock or b a t h o l i t h hidden at depth. A zone of small i n t r u s i o n s extends from P a v i l i o n to K e l l y Creek. A r e l a t i v e l y small plug u n d e r l i e s the slopes at the n o r t h end of P a v i l i o n Lake. In the northern part of the area the Coast I n t r u s i o n s are represented only by a d y k e - l i k e mass on the lowest part of B i g Bar Creek which i s about one m i l e long and a few hundred feet wide. 2. L i t h o l o g y The i n t r u s i o n s are composed of d i o r i t e , quartz d i o r i t e , g r a n o d i o r i t e , and d a c i t e . Quartz d i o r i t e i s the commonest rock type. The p l u t o n i c rocks have a hypidiomorphic equigranular te x t u r e and are mostly medium-grained. Many of the dyke rocks are p o r p h y r i t i c . The e s s e n t i a l minerals present are p l a g i o c l a s e , quartz, hornblende, and b i o t i t e ; augite was n o t i c e d only i n one s p e c i -men. \" I r o n ore\" c o n s t i t u t e s up to 2% of the rock. A p a t i t e i s comparatively common as an accessory m i n e r a l , and z i r c o n and sphene are r a r e . One dyke rock contains muscovite but no mafic s i l i c a t e s . The p l a g i o c l a s e i s mostly subhedral, zoned, and twinned; the zoning i s most commonly of the normal o s c i l l a t o r y type. The m i n e r a l contains i n c l u s i o n s of s e r i c i t e , epidote, and carbonate. P o t a s s i c f e l d s p a r , i f present at a l l , forms l e s s than one per cent of the rocks. The hornblende i s subhedral and some grains are twinned. I t shows pronounced pleochroism being dark green i n the z-d i r e c t i o n and pale brownish green i n the x - d i r e c t i o n . The b i o t i t e i s anhedral or subhedral and brown or green i n c o l o r . Both 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 of \" i r o n o re\" and a p a t i t e and are i n many specimens p a r t l y or completely replaced by c h l o r i t e . The quartz i s anhedral and most grains are f r e e from i n c l u s i o n s . Table 4 shows the range i n the composition of the rocks. I t seems to be tru e i n a general way that the p l a g i o -c l a s e becomes more sodic and that the percentage of mafic minerals decreases as the content of quarta i n c r e a s e s ; but there are exceptions. Near the contacts w i t h rocks of the Pav'llion.group „ the Coast i n t r u s i o n s are l o c a l l y contaminated and c o n t a i n a r e l a t i v e l y high p r o p o r t i o n of hornblende. \"TABLE 4 MINERAL COMPOSITION OF 8 SPECIMENS FROM COAST INTR' L o c a l i t y Composition of p l a g i o c l a s e Dyke on lower B i g Bar Creek South of mouth of K e l l y Creek P l u t o n , southeast of P a v i l i o n , east side C a l c i c andesine, zoned 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 a l t e r e d to a l b i t e Dyke near Moran P l u t o n between Leon Creek and K e l l y Creek Stack., southeast of P a v i l i o n , west side Mount Martley Stock C a l c i c andesine, zoned Intermediate andesine, zoned Zoned from sodic to intermediate andesine Zoned from c a l c i c o l i g o c l a s e to sodic andesine Stack.: at north end of 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 IONS, EARLY LOWER CRETACEOUS OR OLDER % of f0 of C l a s s i f i c a t i o n Quartz mafic o f rock minerals 6 35 d i o r i t e 5 26 d i o r i t e 8 27 d i o r i t e , t r a n s -i t i o n a l to q u a r t z - d i o r i t e 11 25 q u a r t z - d i o r i t e 23 12 q u a r t z - d i o r i t e 33 22 q u a r t z - d i o r i t e 30 19 q u a r t z - d i o r i t e , t r a n s i t i o n a l to g r a n o d i o r i t e 32 13 q u a r t z - d i o r i t e t r a n s i t i o n a l to g r a n o d i o r i t e 153 3. A s s o c i a t e d M i n e r a l i z a t i o n Small s u l f i d e deposits are a s s o c i a t e d w i t h these i n t r u s i o n s i n many l o c a l i t i e s but only the B i g S l i d e Mine (Ml) near the mouth of K e l l y Creek which operated f o r a few months i n 1887 has been of some economic importance. The property was inspected by G.M. Dawson i n 1887 and by A.M. Richmond of the B.C.D epartment of Mines i n 1932. A compil-a t i o n of a l l previous reports was given by D u f f e l l and McTaggart (p. 103 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 of p y r i t e , p y r r h o t i t e , a r s e n o p y r i t e , c h a l c o p y r i t e , marcasite, l i m o n i t e , n a t i v e gold, and carbonate i n two pinching and s w e l l i n g quartz veins that are up to 4 f e e t wide and have an average thickness of eight inches. The host rock i s a small d i o r i t i c mass that intrudes c h e r t , a r g i l l i t e , and minor v o l c a n i c rocks of D i v i s i o n I of the P a v i l i o n group. South of K e l l y Creek, i n the same v i c i n i t y , another small deposit was explored by a shaft and two short l e v e l s . The w r i t e r noted some p y r i t e , b o r n i t e , malachite and a z u r i t e i n an abundant gangue of quartz and carbonate on a surface 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 outcrops on T i f f i n Creek and i n c h e r t , a r g i l l -i t e , and d i o r i t e on the upper part of S a l l u s Creek. A specimen of 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 part of Siwash Creek near the contact between g r a n i t i c dykes and limestone. Small amounts of copper minerals have been found i n the p l u t o n south of Leon Creek. 4. S t r u c t u r e , Mode of O r i g i n Although elongate masses are p a r a l l e l to the s t r i k e o f the host rocks the i n t r u s i o n s l o c a l l y cut across the pre-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 are 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 of shearing and a l t e r a t i o n are present l o c a l l y . That the q u a r t z - d i o r i t e has been emplaced by i n t r u s i o n and not by processes of g r a n i t i z a t i o n i s suggested by the c r o s s c u t t i n g r e l a t i o n of the g r a n i t i c rocks and the very low grade of r e g i o n a l metamorphism i n the country rocks suggesting shallow depth of emplacement. 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 zoning of the p l a g i o -c l a s e . 5. Age The rocks i n t r u d e D i v i s i o n s I and I I of the Cache Creek group and t h e r e f o r e they are 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 contact w i t h the Spences Bridge group or the K i n g s v a l e group of mid-Lower Cretaceous age I t i s a l s o probable that they were emplaced before the e a r l i e s t movement on f a u l t \"e\" of the Fraser R i v e r f a u l t zone, (see F i g -ure 6, p.168) which i s thought to have taken place i n the e a r l y Lower Cretaceous. In the present map-area t h i s group of 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 that 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 present s t r u c t u r a l studies support t h i s c o r r e l a t i o n (see page 176). D u f f e l l and McTaggart suggest that the Mount Ly t t o n b a t h o l i t h i s o l d e r than the i n t r u s i o n s west of the Fraser R i v e r and perhaps contemporaneous w i t h the Guichon Creek b a t h o l i t h , and r e f e r i t to the J u r a s s i c (p. 81). I I . EARLY LOWER CRETACEOUS 1. D i s t r i b u t i o n The Coast I n t r u s i o n s known to be e a r l y Lower Cre-taceous occur as dykes and s i l l s i n the L i l l o o e t group. The l a r g e s t of these i n t r u s i o n s i s a l e n t i c u l a r pluton about 1/2 mile long and s e v e r a l hundred f e e t wide which i s exposed on the east side of the Fraser R i v e r near the r a i l r o a d bridge i n the v i c -i n i t y of L i l l o o e t . 2. L i t h o l o g y A l l specimens examined are q u a r t z - d i o r i t e or d a c i t e . Coarse or medium-grained rocks have a hypidiomorphic 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 of medium- to coarse-grained phenocrysts i n a f i n e - g r a i n e d or a p h a n i t i c groundmass. Some rocks are e n t i r e l y a p h a n i t i c . A specimen from the 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 bridge northeast of L i l l o o e t i s composed of the f o l l o w i n g primary minerals: 156 Feldspar quartz hornblende b i o t i t e \" i r o n o re\", a p a t i t e , sphene 70$ 21$ 8$ 1$ trace The f e l d s p a r c o n s i s t s dominantly of sub-h e d r a l sodic andesine that i s twinned and shows normal or o s c i l l a t o r y normal zoning. Orthoclase which i s subhedral or anhedral makes up only a s m a l l f r a c t i o n of the t o t a l f e l d s p a r . Some of 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 of the hornblende i s subhedral. The mineral 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 subhedral or anhedral and p l e o c h r o i c i n browns. The quartz i s anhedral 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 minerals s e r i c i t e , carbonate, and c h l o r i t e are f a i r l y abundant. The t e x t u r e of the rock i s g r a n i t i c and the s i z e of the e s s e n t i a l minerals ranges from 2.5 mm to 1 mm. The phenocrysts of dyke rocks c o n s i s t of p l a g i o c l a s e which commonly i s zoned andesine. Hornblende and quartz are rare as phenocrysts. The groundmess of the porphyries contains i n a d d i t i o n to these minerals b i o t i t e , and i n some specimens muscovite. Highly a l t e r e d rocks found i n the v i c i n i t y of major f a u l t s are r i c h i n c h l o r i t e , muscovite, carbonate, and p r e h n i t e . G r a n i t i c dykes are abundant i n the lower and middle part of the L i l l o o e t group which are t i g h t l y f o l d e d but l a c k i n g i n the f l a t l y i n g upper p a r t , D i v i s i o n C, and very scarce i n the Jackass Mountain group. I t i s p o s s i b l e that the i n t r u s i o n took place s h o r t l y a f t e r the d e p o s i t i o n of the sediments and was 3 . Age 157 n e a r l y contemporaneous w i t h the main period of f o l d i n g . The age of these q u a r t z - d i o r i t e s probably i s e a r l y Lower Cretaceous. I I I . LATE BARREMIAN 1. D i s t r i b u t i o n The Coast I n t r u s i o n s of t h i s group occur o n l y as dykes or small plugs i n the Jackass Mountain group. In the southern and c e n t r a l parts of the map area they are r a r e . A few dykes are exposed on the n o r t h side of the Fraser R i v e r opposite the mouth of Fountain Creek. Between Fountain and the mouth of Bridge Ri v e r s e v e r a l zones of carbonate a l t e r a t i o n are v i s i b l e on the shores of the Fraser R i v e r some of which are associated w i t h small g r a n i t i c dykes. S i m i l a r zones of a l t e r a t i o n i n the v i c i n -i t y of Lee Creek and B l a c k h i l l Creek that apparently are not r e -l a t e d to major f a u l t s may i n d i c a t e i n t r u s i v e bodies at greater depth. In the northern part of the map-area, i n the v i c i n i t y of Watson Bar Creek, g r a n i t i c rocks are more abundant. The l a r g e s t of these i n t r u s i o n s i s shown on Figure 1. 2. L i t h o l o g y L i t h o l o g i c a l l y these dykes do not d i f f e r from the two other groups of Coast i n t r u s i o n s i n the area; they are por-p h y r i t i c q u a r t z - d i o r i t e s . A t y p i c a l specimen has coarse phenocrysts of zoned andesine and a f i n e - g r a i n e d groundmass con-s i s t i n g of p l a g i o c l a s e , q uartz, hornblende, b i o t i t e , and minor o r t h o c l a s e . \"Iron ore\" and a p a t i t e were noted as a c c e s s o r i e s . 158 Secondary minerals present are s e r i c i t e , epidote, c h l o r i t e , and carbonate. A dyke which probably l i e s i n the immediate v i c i n i t y of f a u l t \"d\" of the Fraser 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 and epidote and the mafic minerals to c h l o r i t e . The rock i s e x t e n s i v e l y replaced by carbonate. 3. Associated M i n e r a l i z a t i o n On the upper part of S t i r r u p Creek four small ( e p i t h e r -mal?) deposits of s t i b n i t e , cinnabar, g o l d , w e h r l i t e , and b a r i t e (Professor H.V.Warren, personal communication) i s assoc-i a t e d w i t h p o r p h y r i t i c quartz d i o r i t e that has intruded l i t h i c sandstone of D i v i s i o n C of the Jackass Mountain group (M2). The minerals occur i n quartz veins that cut bleached porphy-r i t i c q u a r t z - d i o r i t e and s t r o n g l y carbonatized country rock. Occurrences of t h i s type are probably the source of the numerous gold p l a c e r s on S t i r r u p Creek (outside the map a r e a ) . 4. Age As these dykes i n t r u d e D i v i s i o n C of the Jackass Mountain group but have not been found i n the Spences Bridge group or Kingsvale group they probably 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 general area. 159 GABBRO AND DIABASE NEAR LILLOOET 1. D i s t r i b u t i o n , S t r u c t u r e Gabbros and diabases are exposed f o r about 6 miles between a point on the west bank of the Fraser R i v e r about 2 m i l e s southeast of L i l l o o e t and the head of Town Creek on the rid g e northwest of L i l l o o e t . The outcrops are mostly small and separated by expanses of overburden; l a r g e r masses are ex-posed only i n the v i c i n i t y of the power house on Seton Creek. I t i s not known whether the outcrops are connected and thus form one l a r g e i n t r u s i o n or whether they represent numer-ous 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 approximately N 30° W and forms the eastern margin of a zone occupied dominantly by u l t r a b a s i c rocks. To the east the i n t r u s i o n s are p o s s i b l y i n f a u l t contact w i t h the L i l l o o e t group, but t h i s contact i s nowhere exposed. 2 . L i t h o l o g y The rocks on the east shore of the Fraser R i v e r , out-s i d e of the map-area have not been studied during the present i n v e s t i g a t i o n . According to Brock (1956) they are hypersthene gabbros that 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 the west s i d e are g r e y i s h green, med-ium- to 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 . They are hig h -l y a l t e r e d , and t h e i r o r i g i n a l composition i s recognizable only i n a few specimens that range from b r o n z i t e gabbro to augite d i o r i t e . 160 A l l specimens contain augite which shows no systematic v a r i a t i o n i n composition. In one t h i n - s e c t i o n the a u g i t e has \"hour g l a s s \" s t r u c t u r e . In two out of nineteen specimens ortho-pyroxene was recognized. In one specimen i t was b r o n z i t e i n the other one hypersthene, but the two minerals probably do not d i f f e r i n composition by more than 5$ of the e n s t a t i t e molecule. In some of the other rocks orthopyroxene may have been present o r i g i n a l l y but probably has been replaced by minerals of the c h l o r i t e 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 preserved. In the b r o n z i t e gabbro i t s composition l i e s near A n g o In the augite d i o r i t e i t i s zoned from c a l c i c andesine to c a l c i c o l i g o c l a s e . But as the cores of 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 rock are h i g h l y a l t e r e d they may have had a more c a l c i c composition o r i g i n a l l y . Although most of the rocks c o n t a i n hornblende perhaps only i n the augite d i o r i t e i s t h i s m i n e r a l of primary o r i g i n . 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 types i s apparent i n the f o l l o w i n g t a b l e : b ronzite-gabbro p l a g i o c l a s e augite b r o n z i t e c h l o r i t e group, r e p l a c i n g 50% 37% 5% ( b r o n z i t e ?) \" i r o n ore\" 6% 2% augite d i o r i t e hornblende c h l o r i t e group \" i r o n ore\" p l a g i o c l a s e augite 60$ 30$ 8$ 1$ 1$ 161 Table 5 shows the determinations of the main primary-minerals i n 4 c h a r a c t e r i s t i c specimens. I t i s apparent that these gabbros are not uniform i n composition but owing to the l a c k of exposure and the high degree of a l t e r a t i o n the trends and mechanisms of d i f f e r e n -t i a t i o n could not be worked out. The outcrops n o r t h of L i l l o o e t are of medium- to f i n e -grained gabbro and have a hypidiomorphic granular t e x t u r e . Most of them are equigranular, but some are s e r i a t e . In some of the specimens the augite appears s t r a i n e d . The o r i g i n a l t e x t u r e of the rocks has been o b l i t e r a t e d to a l a r g e extent by a l t e r a t i o n . In the outcrops on Seton Creek the degree of a l t e r -a t i o n i s even higher. Some rocks seem to have been f i n e -grained gabbros w i t h a hypidiomorphic granular t e x t u r e . Two specimens resemble o r i g i n a l diabases; one of them shows a v a r i o l i t i c t e x t u r e . TABLE 5 MINERAL COMPOSITION OF 5 SPECIMENS OF ALTERED GABBROIC AND DIORITIC ROCKS Spec. Qrtho-pyro- Measurements xene, comp. x Augite Measurements Hornblende P l a g i o c l a s e Measurement Composition 'Composition + H 14 16 13 12 En 89 t 1% (+) high 2v Ca 4 1Mg 4 4Fe 1 (5 b r o n z i t e ny=1.6721.001 +2% Magnesiam (-)2v close CaoyMgAoFe-j^ h v n e r s - tn Qf)0 ypers-thene absent or completely a l t e r e d absent or a l t e r e d Ca 4 oMg 46Fe 1 4 C a 4 i y g 4 | F e 1 2 ny=1.684t .002 2v=49° nv=1.685t * .002 2v=44° ny=1.6861 y .003 2v=48° ny=1.685l * .002 Absent A n6lt present A n40 but probably probably a l t e r e d secondary absent completely a l t e r e d present Zoned kxi2$-r e p l a c i n g A n ^ augite nx 1 = 1.5591 .001 nx' 1.54721 .001 nx' = 1.554-1.540 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) CN ro 3. Metamorphism and A l t e r a t i o n I n 17 out of 19 specimens 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 and minerals of the epidote group among which p i s t a c i t e seems to be abundant. The orthopyroxene has been replaced p a r t l y or completely by minerals of the c h l o r i t e group. A m i n e r a l of that group showing bladed 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 longation probably 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 preserved than the other minerals but p a r t l y replaced by minerals of the c h l o r i t e group, by horn-blende, or \" i r o n ore\". The rocks are replaced by p r e h n i t e , carbonate, 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 and a l b i t e occur. One specimen i s m y l o n i t i z e d ; i n others the augite appears to be s t r a i n e d and bent. 4. Age The contacts of the gabbros were not seen. An i n d i -c a t i o n of t h e i r age i s given by the f o l l o w i n g o b s e r v a t i o n . East of Fountain Creek, i n the v i c i n i t y of f a u l t \"d\" a specimen was c o l l e c t e d that i s composed of c h l o r i t i z e d c l i n o -pyroxene and hornblende i n a m a t r i x of prehnite and shows a strong s c h i s t o s i t y . I t resembles the h i g h l y a l t e r e d gabbros or d i o r i t e s west of L i l l o o e t . The occurrence of these rocks suggests that they were intruded i n t o major f a u l t zones and 164 t h e r e f o r e are e a r l y Lower Cretaceous or younger. Th e i r a l t e r a t i o n may have been produced by l a t e magmatic s o l u t i o n s . ANDESITIC AND BASIC DYKES A l l rock u n i t s , except f o r the Middle or Late T e r t i a r y o l i v i n e b a s a l t s are intruded by a n d e s i t i c , d i a b a s i c or b a s a l t i c dykes. These dykes may range i n age from e a r l y Mesozoic to Late T e r t i a r y . They are too small to be shown on the accompanying map. 165 CHAPTER I I THE FRASER RIVER FAULT ZONE 1. I n t r o d u c t i o n Although Dawson (1895) considered the s t r u c t u r e of the Fraser R i v e r area as a s e r i e s of t i g h t f o l d s he n o t i c e d the shattered and a l t e r e d nature of the rocks i n many l o c a l -i t i e s and suggested that some of the major contacts are f a u l t s . He d e s c r i b e d , f o r example, the s t r u c t u r e i n the v i c i n i t y of 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 both sides of the r i v e r e n t i r e masses of the rocks have become reddened and decomposed by a c t i o n subsequent to t h e i r d e p o s i t i o n . The beds are a l l much sh a t t e r e d , and l i n e s of f a u l t i n g i n t h i s place undoubtedly run along the v a l l e y one of which apparently bounds the Cretaceous trough on the east side of the v a l l e y . \" (p. 147 B, f.) He sta t e d of the contact of the Jackass Mountain group w i t h the rocks of the Spences Bridge group (which he considered to be T e r t i a r y ) between McKay Creek and Leon Creek: \"The boundary between the Cretaceous rocks on the 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 which i s n e a r l y p a r a l l e l to that of the Fras e r . There i s some reason to suppose that 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 In 1912 N.L.Bowen i n a reconnaissance survey of the Fraser R i v e r v a l l e y from L y t t o n to Vancouver observed that the Cretaceous s t r a t a south of 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 of the Cretaceous beds i s about N 15° W and the beds are commonly at low angles, but c l o s e to 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 or qu i t e v e r t i c a l . The g r a n i t e does not, however, give any evidence of being i n -t r u s i v e . The r e l a t i o n shown i s due to the down f a u l t i n g of the Cretaceous beds. This part of the Fraser V a l l e y i s , i n f a c t , excavated along a b e l t of comparatively s o f t sedimentar-i e s themselves preserved by graben f a u l t i n g . The s t r i p s of P a l e o z o i c r o c ks, too, probably owe t h e i r present p o s i t i o n to t h i s f a u l t i n g , f o r the s t r i k e of t h e i r beds makes a sharp angle w i t h the elongation of the s t r i p s . \" D u f f e l l and McTaggart corroborated Bowen's obser-v a t i o n that i n the southern part of the Ashcroft area the Fraser R i v e r Cretaceous b e l t occupies 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 of f a u l t s i n which the rocks to the west have been elevated r e l a t i v e to those i n the east. They gave evidence of i n t e r m i t t e n t a c t i v -i t y from Lower Cretaceous to post-Eocene time and showed that carbonate, 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 are a s s o c i a t e d w i t h the f a u l t zone. As the probable cause of the f a u l t i n g they suggested u p l i f t and t i l t i n g of the Coast Mountains. Leech (1953) mapped a f a u l t zone i n the Yalakom area 167 that i s probably connected w i t h a major f a u l t discovered by D u f f e l l and McTaggart near L i l l o o e t . McCammon and Wasmith (1956) during a study of p o s s i b l e dam s i t e s on the Fraser R i v e r observed s e v e r a l f a u l t s i n the northern parts of the present map-area which they considered to be p o s s i b l e extensions of the Fraser R i v e r f a u l t zone of the A s h c r o f t area. The present study has added the f o l l o w i n g information: (1) Those f a u l t s of the Ashcroft sheet ( D u f f e l l and McTaggart 1953) that are s i t u a t e d i n the present map area have been mapped i n greater d e t a i l but without major changes. (2) I t i s shown that the western contact of the P a v i l i o n group i s another f a u l t of the Fraser River f a u l t zone. The movement on t h i s f a u l t i s i n the opposite sense to that of the other f a u l t s of the zone, showing a r e l a t i v e downward move-ment of the western block. The s t r u c t u r e of the present map area t h e r e f o r e appears to be a complex graben. I t i s suggested that 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 of D i v i s i o n s B and C of the Jackass Mountain group. (3) Another l o n g i t u d i n a l f a u l t , the nature of i t s movement unknown, has been mapped w i t h i n the P a v i l i o n group. (4) I t i s shown that the l a t e s t movement on one o f the l o n g i t u d i n a l f a u l t s probably took place i n Middle T e r t i a r y time. 2. D e s c r i p t i o n of the Fraser R i v e r F a u l t Zone The main branches of the Fraser River f a u l t zone are shown on Figure 6. The main f a u l t s of the zone trend 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 are r e f e r r e d to as l o n g i t u d i n a l f a u l t s . F a u l t s trending w e s t e r l y , i n part apparently o f f s e t t -i ng 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 recognized i n the map area. At l e a s t two of them are continuous through-out the area and some of them have been shown to extend f a r to the south. I t i s assumed that other f a u l t s e x i s t but have not been recognized because of t h i c k overburden and l a c k of obvious o f f s e t i n the formations t r a n s e c t e d . The l o n g i t u d i n a l f a u l t s s t r i k e northwesterly to n o r t h e r l y , and, judged by t h e i r l a c k of d e f l e c t i o n on the map i n c r o s s i n g ridges or v a l l e y s , dip s t e e p l y . F a u l t \"a\" (see Figure 6) separates the L i l l o o e t group on the east from T r i a s s i c or o l der rocks 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 south ( D u f f e l l and McTaggart, 1953) and i s probably continuous to the n o r t h w i t h a major f a u l t i n the Yalokom area (Leech, 1953). In the present map-area i t has associated 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 diabase which e i t h e r l o c a l i z e d the break or intruded the f a u l t zone. F a u l t 11 b\" brings the L i l l o o e t group i n t o contact w i t h the Jackass Mountain group. I t has s e v e r a l branches near the mouth of Bridge R i v e r that seem to converge to a s i n g l e break to; ,the south and to the north. The f a u l t i s poorly exposed i , V and- has no topographic expression on the western slopes of the Camelsfoot Range and of Fountain Ridge. Where the i n d i v -i d u a l branches cross Fraser R i v e r , the s t r a t a are d i s t u r b e d over widths 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 Jackass Mountain group i n t o two main b l o c k s . A l l three d i v i s i o n s of the group are exposed i n the western block but only D i v i s i o n C i n the eastern block. Near Fountain S t a t i o n three c l o s e l y spaced branches were observed or i n f e r r e d but elsewhere only one could be e s t a b l i s h e d . The eastern branch i s i n d i c a t e d by a narrow b e l t of s t e e p l y dipping and d i s t o r t e d s t r a t a east and northeast of Fountain S t a t i o n along the west shore of the Fraser R i v e r . The west-ern branch i s marked by i n t e n s e l y s t a i n e d and sheared c l i f f s a few hundred f e e t above the road west of Fountain S t a t i o n . The c e n t r a l branch i s exposed only on the shore of the r i v e r but probably continues to the south. I t truncates D i v i s i o n B and brings i t i n t o 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 C. F a u l t \"d\" forms the contact of D i v i s i o n C of the Jackass Mountain group w i t h v o l c a n i c rocks of the Fountain V a l l e y assemblage, the upper D i v i s i o n of the Spences Bridge group, and the Ward Creek assemblage. The f a u l t zone i s exposed east of Fountain Creek at the south shore of the Fraser R i v e r , and again northeast of the mouth of B l a c k h i l l Creek. S e v e r a l 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 the mouth of Fountain Creek. Between the mouths of Gibbs Creek and B l a c k -h i l l Creek, on the west side ' of the Fraser R i v e r , the s t r a t a of D i v i s i o n C, commonly f l a t - l y i n g or gently 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 distances of at l e a s t one-half m i l e west of the f a u l t zone ( P l a t e X X I I ) . Minor branch-es of the zone are exposed at the mouths of S a l l u s and B l a c k h i l l Creeks. In t h i s v i c i n i t y , the main f a u l t seems to have con-t r o l l e d the course of the Fraser R i v e r . Between the upper part of McKay Creek and Leon Creek the f a u l t i s covered f o r about 2-1/2 miles 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 that apparently have not been o f f s e t by the f a u l t . To the n o r t h , on Watson Bar Creek, 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 rocks. F a u l t \"e\" the western boundary f a u l t of the P a v i l i o n group i s w e l l exposed on a c l i f f i n B i g Bar Canyon, where the f a u l t dips about 75° to the southwest. ( P l a t e XXTV) The trace of the f a u l t plane on the c l i f f i s s t r a i g h t , suggesting l i t t l e v a r i a t i o n i n d i p . The f o o t - w a l l here c o n s i s t s of ribbon chert that l i e s approximately p a r a l l e l to the f a u l t plane and con-t a i n s numerous v e i n l e t s of quartz and carbonate. The hanging w a l l i s andesite that has been converted i n t o a l a y e r of gouge about 40 feet t h i c k . Between Watson Bar Creek and French Bar Canyon the existence of a f a u l t contact i s i n d i c a t e d by the steep dips of the otherwise f l a t l y i n g or moderately dipping v o l c a n i c rocks. From Watson Bar Creek to McKay Creek the rocks adjacent to the contact are poorly exposed. Between McKay Creek and a l o c a l i t y about one m i l e northwest of Glen Fraser the f a u l t i s not exposed but i n d i c a t e d by anomalous dips ( P l a t e XXIII) and signs of s h a t t e r i n g and a l t e r a t i o n . Immediately n o r t h of Glen Fraser the l o c a t i o n of the f a u l t i s u n c e r t a i n . From Glen Fraser to the mouth of Gibbs Creek the eastern contact of the P a v i l i o n . : ' group i s covered by overburden. Southwest of the mouth of Gibbs Creek a f a u l t between the lower D i v i s i o n of the Spences Bridge group and the Fountain V a l l e y assemblage was i n -f e r r e d from a cross s e c t i o n (B-B'). This i n f e r r e d f a u l t pro-bably i s continuous w i t h the eastern boundary f a u l t of the P a v i l i o n group traced from northwest of Glen Fraser to north of B i g Bar Creek. F a u l t \"e\" l i e s c l o s e to the western margin of s e v e r a l g r a n i t i c masses. No major plutons i n the present map area are exposed to the east of t h i s f a u l t . F a u l t \" f \" forms the contact between D i v i s i o n I and D i v i s i o n I I of the P a v i l i o n group.. The f a u l t Is exposed on the slope n o r t h of P a v i l i o n Creek and i n d i c a t e d by shearing and a l t e r a t i o n south of Moran. The northwestern c o n t i n u a t i o n of the contact i s obscured by l a c k of outcrop and metamorphism (see p. 5 8 ) . South of P a v i l i o n Creek the contact i s very poorly exposed. On Keatley 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 abrupt l i t h o l o g i c a l change, from the unusual narrowness of D i v i s i o n I and an anomalous s t r a t i g r a p h i c top near the contact. The f a u l t s \"a\", \"b\", \" c \" , and \"d\" appear to be'normal f a u l t s w i t h r e l a t i v e downward movement of the eastern block; 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. 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 complex graben. The sense of movement on f a u l t \" f \" i s un-c e r t a i n . 173 C r o s s - f a u l t s , approximately normal to the l o n g i t u d i n a l f a u l t s , seem to be comparatively short and to show small o f f s e t s . Although h o r i z o n t a l and v e r t i c a l displacements can be e s t a b l i s h e d i n some p l a c e s , i n others o f f s e t s cannot be recognized at a l l and f a u l t i n g i s i n d i c a t e d only 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 of s i n g l e breaks o r , as on Fountain Ridge, of a s e r i e s of c l o s e l y spaced f a u l t s . One o f the cross 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 others appear to stop at 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 the Fraser 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 . The carbonate weathers r u s t y brown. In an a l t e r e d rock from B i g Bar Canyon i t has the composition of magnesiodolomite (n0=1.6795). In con-glomerates, sandstones, and s i l t s t o n e s the carbonate replaces mostly the m a t r i x , but i n the other rocks i t occurs i n v e i n -l e t s and i r r e g u l a r patches. In many l o c a l i t i e s v e i n l e t s of quartz are associated w i t h the carbonate. Igneous rocks and l i t h i c sandstones near major f a u l t s show signs of low grade or r e t r o g r e s s i v e metamorphism. C a l c i c and intermediate p l a g i o c l a s e have been converted to a l b i t e and epidote and the mafic minerals to c h l o r i t e . C h l o r i t e and epidote i n many of these rocks form v e i n l e t s and apparently 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 pointed out that i n many l o c a l i t i e s the 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 prehnite appears i n v e i n l e t s or replaces the p l a g i o c l a s e of the host. In the present map area the mineral was found i n the gabbroic b e l t west of L i l l o o e t , i n a d i o r i t i c dyke near the mouth of Bridge R i v e r , i n a gabbroic or d i o r i t i c dyke and a l i t h i c sandstone east of Fountain Creek and i n the d i o r i t e mass southeast of P a v i l i o n . A l l these l o c a l i t i e s are i n the v i c i n i t y of major f a u l t zones. I t i s p o s s i b l e that the a l t e r i n g s o l u t i o n s and the gabbroic dykes ascended through such f r a c t u r e s and that 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 of L i l l o o e t the gabbros are a l s o veined 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 . 4. H i s t o r y of the Fraser R i v e r F a u l t Zone The h i s t o r y of the Fraser R i v e r f a u l t zone probably i s a long and complex sequence of i n t e r m i t t e n t movements. The evidence f o r the e a r l i e r movements i s incomplete, i n d i r e c t , and l i e s mostly i n the s t r a t i g r a p h i c record. 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 present s t r u c t u r e . Cross s e c t i o n C-C 1 shows that the f a u l t i n g i s younger than the f o l d i n g of the L i l l o o e t group which probably took place i n the Neocomian. The e a r l i e s t i n d i c a t i o n of the existence of the f a u l t zone i s the conglomerate of D i v i s i o n B (Barremian) of the Jackass Mountain group. The great thickness of coarse s e d i -ments i n t h i s u n i t suggests r a p i d u p l i f t of the source area which may have been accomplished by normal f a u l t i n g . 175 There i s also some evidence that the f a u l t zone was a c t i v e during the d e p o s i t i o n of D i v i s i o n C (Barremian) or at the end of that time. About one m i l e n o r t h of the mouth of Gibbs Creek v o l c a n i c rocks of the Spences Bridge group apparently o v e r l i e the P a v i l i o n group w i t h unconformity. About one m i l e to the west s t r a t a of D i v i s i o n C, s e v e r a l thousand feet t h i c k are exposed. The u n i t s are probably separated by two f a u l t s the l a t e s t movement on which took place i n the middle (?) T e r t i a r y . ( C r o s s - s e c t i o n C - C ) . The s i t u a t i o n can be explained i n two ways. E i t h e r the s t r a t a of the Jackass Mountain group never extended to the l o c a l i t y where the Spences Bridge group was l a i d down l a t e r ; or the eastern part of D i v i s i o n C was removed by u p l i f t and e r o s i o n before the d e p o s i t i o n of the Spences Bridge group. In the f i r s t case the sediments of D i v i s i o n C must have been deposited i n a r a p i d l y subsiding trough whose eastern boundary approximately c o i n c i d e d w i t h the present f a u l t . The second explanation i m p l i e s a r a p i d u p l i f t of great magni-tude immediately to the east of the present f a u l t zone. Both explanations suggest movements of the present f a u l t zone; i n the f i r s t case i t would have taken place i n the mid-Lower Cretaceous (Barremian); 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 rocks n o r t h of Gibbs Creek are 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 of the Spences Bridge Group i n the type area, but younger, the f a u l t i n g might be middle or l a t e A p t i a n . Middle 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 be e s t a b l i s h e d , but p e r h a p s t h e v o l c a n i s m o f t h i s t i m e i s r e l a t e d t o t h e F r a s e r R i v e r f a u l t z o n e . (Compare C l o o s , 1939). The y o u n g e s t r o c k s d i s t u r b e d by f a u l t movements a r e t h e v o l c a n i c f l o w s and t u f f s t h a t o v e r l i e t h e F r e n c h B a r f o r m a t i o n ( E o c e n e - O l i g o c e n e ) . The 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 b a s a l t s o v e r l i e f a u l t \" d \" w i t h o u t s i g n s o f d i s t u r b a n c e , 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 o r R e c e n t f a u l t i n g has n o t been f o u n d . 5. 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 t h e movement o n f a u l t s a , b , c , and d , w h i c h show r e l a t i v e d e p r e s s i o n o f the e a s t e r n b l o c k s , t o u p l i f t and t i l t i n g o f t h e C o a s t M o u n t a i n s i n t h e w e s t . B y a n a l o g y f a u l t \" e \" , s h o w i n g r e l a t i v e d e -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 t o u p l i f t o f t h e p l u t o n i c masses s i t u a t e d i m m e d i a t e l y to t h e e a s t . P e r h a p s 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 g r e a t e r d e p t h t h a t i s 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 hand Hans C l o o s (1930) has s u g g e s t e d t h a t t h e g r e a t e s t g r a b e n s o f t h e w o r l d p r o b a b l y were p r o d u c e d by b r o a d domal u p l i f t s and a r e t h e r e s u l t o f t e n s i o n . A n u p l i f t o f t h e F r a s e r R i v e r a r e a i n t h e Lower C r e t a c e o u s i s i n d i c a t e d by t h e g r a d u a l s h i f t f r o m m a r i n e t o c o n t i n e n t a l c o n d i t i o n s . P e r h a p s b o t h p r o c e s s e s a r e r e l a t e d . 177 CHAPTER I I I G e o l o g i c a l H i s t o r y of the Area In the Permian and T r i a s s i c the area was part of a somewhat r e s t r i c t e d marine basin i n which carbonaceous matter was not o x i d i z e d . In the Upper Permian a re e f zone extended through the present Bowman Range and P a v i l i o n Mountains. To the west of the r e e f s a l t e r n a t i n g l a y e r s of mud and r a d i o l -a r i a n debris were l a i d down. The co n d i t i o n s were moderately s t a b l e but some v o l c a n i c eruptions took place. In the T r i a s s i c the area became t e c t o n i c a l l y a c t i v e . Tectonic 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 currents were accompanied by strong volcanism. The deposits of t h i s epoch c o n s i s t e d of l i t h i c sand, t u f f , v o l c a n i c f l o w s , a r g i l l -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 . The t e c t o n i c a c t i v i t y may have culminated i n the Cassia r orogeny (White, 1959). However, i n the present map area the only i n t r u s i o n s marking that event are 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 of L i l l o o e t and east of the Fraser R i v e r . No sedimentary or v o l c a n i c rocks of the time i n t e r v a l between T r i a s s i c and Lower Cretaceous are exposed. The Lower Cretaceous sediments, however, were derived from v o l c a n i c rocks that probably were deposited during t h i s i n t e r v a l . These v o l c a n i c rocks were r i c h i n a l b i t e and probably belong to the 178 s p i l i t e - k e r a t o p h y r e s u i t e . They were p o s s i b l y J u r a s s i c and exposed to the northeast and/or southwest of the Fraser R i v e r f a u l t zone. The source rocks may have been r e l a t e d to the Middle J u r a s s i c keratophyres 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 of g r a n i t i c rocks i n t o the P a v i l i o n group may have taken place i n the J u r a s s i c . In the e a r l i e s t Lower Cretaceous during the d e p o s i t i o n of D i v i s i o n s A and B of the L i l l o o e t group the area was part of a r e s t r i c t e d marine basin which was t e c t o n i c a l l y unstable. The mud of 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 of l i t h i c sand i n D i v i s i o n B were deposited by t u r b i d i t y currents that were accompanied by submarine slumping. During the d e p o s i t i o n of D i v i s i o n B the area g r a d u a l l y rose and then was f o l d e d , i n -truded by d i o r i t i c dykes, elevated above sea l e v e l , and eroded. The uppermost part of the 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 of tuffaceous l i t h i c sandstone, granule conglomerate and a small p r o p o r t i o n of a r g i l l i t e was deposited i n a marine environment perhaps under near-shore c o n d i t i o n s . At the end of that time (Neocomian?) the area again rose above s e a - l e v e l , and the b a s a l conglomerate of the Jackass 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 matter i n d i c a t e s contemporaneous volcanism. During the d e p o s i t i o n of the members A H and A I I I of D i v i s i o n A and of the basal part of D i v i s i o n B of the Jackass Mountain group (Barremian) the area was part of a r e s t r i c t e d 179 marine b a s i n . The sediments of AI consisted dominantly of f i n e sand, those of A l l of mud, s i l t and f i n e sand, and the b a s a l part of D i v i s i o n B was composed of medium-grained sand. This change i n g r a i n s i z e may r e f l e c t a r e l a t i v e depression of the basin followed by a gradual r i s e . The t h i c k conglomerate of D i v i s i o n B i s the e a r l i e s t evidence of a c t i v i t y on the Fraser R i v e r f a u l t zone which con-tinued i n t e r m i t t e n t l y to the Middle T e r t i a r y . The f a u l t i n g may be r e l a t e d to the i s o s t a t i c r i s e of Coast I n t r u s i o n s to the east and to the west or an u p l i f t of the whole area. A complex graben s t r u c t u r e was produced which probably c o n t r o l l e d the sedimentation of D i v i s i o n s B and C of the Jackass Mountain group. D i v i s i o n s B and C c o n s i s t i n g of conglomerate, l i t h i c sandstone, and minor a r g i l l i t e probably were l a i d down i n a narrow elongate trough which subsided r a p i d l y w i t h respect to the bordering mountains but f l u c t u a t e d w i t h respect to sea l e v e l . At times i t may have been connected w i t h the open sea, 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 temp 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 occupied by a l a r g e r i v e r . Graded bedding and slump s t r u c t u r e s are very rare, and i n t h i s respect these \"post t e c t o n i c \" rocks d i f f e r markedly 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 . The sediments were mostly derived from a l b i t e r i c h v o l c a n i c rocks and to a l e s s e r extent from g r a n i t i c i n t r u s i o n s . Rocks younger than the e a r l y Lower Cretaceous are only found to the east of the Lower Cretaceous sedimentary b e l t , and a l l of them are of c o n t i n e n t a l o r i g i n . 180 In the middle and l a t e Lower Cretaceous v o l c a n i c rocks o f great t h i c k n e s s c o n s i s t i n g dominantly of a n d e s i t e were de-p o s i t e d that are l o c a l l y i n t e r c a l a t e d w i t h c o n t i n e n t a l s e d i -ments. Perhaps the v o l c a n i c flows ascended through f r a c t u r e s o f the F r a s e r R i v e r f a u l t zone. Because o f the l a c k o f f o s s i l s the Upper Cretaceous and Paleocene-Eocene h i s t o r y o f the F r a s e r R i v e r v a l l e y i s u n c e r t a i n . Probably the v o l c a n i c a c t i v i t y c o n t i n u e d . In Eocene-Oligocene time g r a v e l and l i t h i c sand o f great t h i c k n e s s d e r i v e d from v o l c a n i c rocks were l a i d down on a f l o o d p l a i n between B i g Bar Creek and the French Bar Canyon. The r i v e r d e p o s i t s were o v e r l a i n by another s e r i e s o f v o l -c a n i c rocks ranging from b a s a l t i c to f e l s i t i c compositions. These v o l c a n i c flows and t u f f s are the youngest rocks found i n the area that have been d i s t u r b e d by movements o f the F r a s e r R i v e r f a u l t zone. Between the Miocene and e a r l i e s t P l e i s t o c e n e l i t h i c sands were d e p o s i t e d on f l o o d p l a i n s near P a v i l i o n , south o f Leon Creek, and on B i g Bar Creek. P o s s i b l y these d e p o s i t s were connected and formed i n a v a l l e y that 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 . These sediments were succeeded by o l i v i n e b a s a l t s which may have r i s e n through 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. T h e i r appearance marks the end o f a long p e r i o d o f v o l c a n i c a c t i v i t y dominated by a n d e s i t i c r o c k s . A l though the area was covered by g l a c i e r s i n the P l e i s t o c e n e a p p a r e n t l y l i t t l e g l a c i a l e r o s i o n took p l a c e . 181 Probably at the end of the last glaciation the valley was occupied by braided streams and glacial 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. The northwestern and central part of the area received thin deposits of volcanic ash. 182 BIBLIOGRAPHY Armstrong, J. E. (1949): Fort St. James map-area, B r i t i s h Columbia; Geol. Surv., Canada, Mem. 252. Bowen, N.L. (1914): Fraser Valley, Lytton to Vancouver; Geol. Survey., Canada, Mem. 252. Bowen, N.L. and Tuttle, O.F. (1949): The system Mg0-Si0 2-H 20: Geol. Soc. America Bull. vol. 60, pp. 439-460. Bramlette, M.N. (1948): The Monterey formation of California and the origin of i t s siliceous rocks. U.S.Geol. Surv., Prof. Paper 212. B r i t i s h Columbia Department of Agriculture (1957): Climate of Br i t i s h Columbia, Report for 1956. Brock, P. (1956): A Study of layered norite near Lillooet, B.C., B.A.Sc. thesis, Univ. B r i t . Col., unpubl. Burley, B.J. (1954): A study of some volcanic rocks from Harrison M i l l s , B r i t i s h Columbia; MSc. thesis, Univ. B r i t . Col., unpubl. Cairnes, C.E. (1923): Geological exploration in the Yale and Similkameen Mining Divisions, Southwestern B r i t i s h Columbia; Geol. Surv., Canada, Sum. Rept. 1922, pt.A, pp. 88-127. (1924 a): Reconnaissance of the Silver Creek, Skagit and Similkameen Rivers, Yale Distr i c t , B r i t i s h Columbia; Geol. Surv., Canada, Sum. Rept. 1923 5 pt. A, pp.46-83. (1924 b): Coquihalla area, B r i t i s h Columbia; Geol. Surv., Canada, Mem. 139. Cloos, H. (1939): Hebung - Spaltung - Vulkanismus: Geol. Rundsch. XXX (4a). Crump, R.M. and Kettner, K.B. (1952): Feldspar optics, in Emmons R.C. et a l . : Selected petrogenic relationships of plagioclase; Geol. Soc. America, Mem. 52, pp. 23-38. Davis, E.F. (1918): The radiolarian cherts of the Franciscan group; Pub. of the Univ. of California, Dept. Geol. Sci. Bull., Vol. II, No. 3 , pp. 235-432. 183 Dawson, G.M. (1879): Report on e x p l o r a t i o n ' i n the southern p o r t i o n of B r i t i s h Columbia; Geol. Surv., Canada, Rept. of Prog. 1877-78, pt. B, pp. 1-173. (1895)* Geol. Surv., Canada, Map 556, Kamloops sheet. (1896): Report on the area of the Kamloops map-sheet; Geol. Surv., Canada, Ann. Rept. f o r 1894, new s e r i e s , v o l . V I I , p t . B pp. 1-427. D u f f e l l , S. and McTaggart, K.C. (1952): Ashcroft map-area; Geol. Surv., Canada, Mem. 262. Drysdale, C.V/. (1914): Geology of the Thompson R i v e r v a l l e y below Kamloops Lake, B.C.; Geol. Surv. of Canada, Sum. Rept. 1912, pp. 115-150. Dunbar, CO. (1932): Neoschwagerina i n the Permian faunas of B r i t i s h Columbia; Trans. Roy. S o c l , Canada, sec. IV, pp. 45-50. F y f e , W.S., Turner, F.J. and Verhoogen, J . (1958): Metamorphic r e a c t i o n s and metamorphic f a c i e s ; Geol. Soc. America, Mem. 73. G e o l o g i c a l A s s o c i a t i o n of Canada (1958) G l a c i a l map of Canada. G o l d s t e i n , A. and Hendricks, Th.A. (1953): S i l i c e o u s sediments of the Ouachita f a c i e s i n Oklahoma; A.A.P.G. v o l . 64, pp. 421-442. Greenman, N.N. (195D: The mechanical a n a l y s i s of sediments from t h i n - s e c t i o n data: Jour. Geol. v o l . 59, pp. 447-462. Hess, H.H. and P h i l l i p s , A.H. (1940): O p t i c a l p r o p e r t i e s and chemical composition of magnesian orthopyroxenes; Am. M i n e r a l , v o l . 25, pp. 271-285. (1949): Chemical composition and o p t i c a l p r o p e r t i e s of common clinopyroxenes. Part I . Am. M i n e r a l . , v o l . 34, pp. 621-666. Hough, J.L. (1942): Sediments of Cape Cod Bay, Massachussets; Jour. Sed. Petrog. v o l . 12, pp. 10-30. I l l i n g , L.V. (1954): Bahaman calcareous sands; A.A.P.G. v o l . 38 pp. 1-95. Jen k i n s , O.P. (1943): Manganese i n C a l i f o r n i a , S t . of C a l i f . Dept. Nat. Resources, Div. Mines, b u l l . 125. 184 van der Kaaden, G e r r i t (1951): O p t i c a l studies on n a t u r a l p l a g i o c l a s e s w i t h high 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 of Utrecht. Krauskopf, 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 of s i l i c a at low temperatures; Geochim. et Cosmochim. Acta. v o l . 10, pp. 1 -26. Krumbein, W.C. and Garrels,. R.M. (1952): O r i g i n and c l a s s i f -i c a t i o n of chemical sediments i n terms of pH and o x i d a t i o n - r e d u c t i o n potentiae; Jour. Geol., 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 of source rocks of sediments: Am. Jour. S c i . v o l . 238, pp. 296-305. Krumbein, W.C. (1953) '• T h i n - s e c t i o n mechanical a n a l y s i s of indurated sediments; Jour. Geol., v o l . 43, pp. 482-496. Lay, Douglas (1940): Fraser River 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 to 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. Mines, B u l l . 3 . Leech, G.B. (1953): Geology and m i n e r a l deposits of the Shulaps Range, southwestern B r i t i s h Columbia, B.C. Dept. Mines, B u l l . 32. Lowenstam, H.A. (1950): Niagaran r e e f s of the Great Lakes area; Jour. Geol., v o l . 58, pp. 430-466. McCammon, J . and Nasmith, H. (1956): Geology of low l e v e l damsites on the Fraser R i v e r ; B.C.Dept. Mines, unpubl. McKenzie, J.P. (1921): A reconnaissance between Taseko Lake and Fraser R i v e r , B r i t i s h Columbia; Geol. Surv., Canada, Sum. Rep., 1920, p t . A, pp. 70A-81A. Mathews, W.H. (1941): Climbs i n the L i l l o o e t Range; Can. Al p i n e Jour., pp. 60-64. (1944): G l a c i a l lakes and i c e r e t r e a t i n south-c e n t r a l B r i t i s h Columbia; Trans. Roy. S o c , Canada, sec. N. pp. 39-57. Paekham, G.H. (1955): Volume, - weight, - and number frequency a n a l y s i s of sediments from t h i n - s e c t i o n data: Jour. Geol. 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 of p h y s i c a l p r o p e r t i e s and chemical composition i n the p l a g i o c l a s e , o l i v i n e , and orthopyroxene s e r i e s ; Am. M i n e r a l . , v o l . 35 , pp. 1067 - 1 0 7 9 . 185 Reinecke, L. (1920): M i n e r a l deposits between L i l l o o e t and P r i n c e George, B r i t i s h Columbia: Geol. Surv. Canada, mem. 118. R e v e l l e , R. ( 1 9 3 4 ) : Physico-chemical 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 of Calcium-carbonate i n sea water; Jour. Sed., Petrog., v o l . 4, pp. 1 0 3 - 1 1 0 . R i c e , H.M. A. (1947): Geology and mineral deposits of the P r i n c e t o n map-area, B r i t i s h Columbia; Geol. Surv., Canada, Mem. 118. Rosenfeld, M.A., Jacobson, L., and Ferm, J.C. ( 1 9 5 3 ) : A comparison of sieve and t h i n - s e c t i o n techniques f o r s i z e - a n a l y s i s ; Jour. Geol., v o l . 6 1 , pp. 114 - 1 3 3 . Selwyn, A.R.C. ( 1 8 7 2 ) : J o u r n a l and report of 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. of Prog. 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 . Thayer, T.P. (1948): R e l a t i o n of serpentine 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 northern Oregon: Geol. Soc. America, 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 , Quesnel, B r i t i s h Columbia, Geol. Surv. 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 Columbia, Washington, and Oregon; Jour. Paleont., v o l . 1 6 , pp. 7 0 0 - 7 1 1 . Thornbury, W.D. ( 1 9 5 4 ) : P r i n c i p l e s of geomorphology. Wiley Trask, P.D., ( 1 9 3 2 ) : O r i g i n and environment of source s e d i -ments of petroleum. Houston, G u l f . P u b l . Co. Warren, H.V., ( 1 9 5 9 ) : The Moran Dam; Canadian Min. Jour. March, 1959 . White, W.H. ( 1 9 5 9 ) : C o r d i l l e r a n tectonism 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., Turner, F.J. and G i l b e r t , Ch.M. ( 1 9 5 5 ) : P e t r o -graphy, W.H.Freeman and Co. 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 of 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 references 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 angles i n zone normal to (010); van der Kaaden, 1 9 5 l 5 Where e x t i n c t i o n angles could not be measured, the Tsuboi-index, n_.' of 001 - cleavage f r a g -ments was used; Crump and K e t t n e r , 1*52. The Tsuboi i n d i c e s have been worked out, so f a r , only f o r low-temperature p l a g i o c l a s e s . But i n the present study i t was found that determinations based on Crump and K e t t n e r 1 s curves do not deviate f a r from those based on van der Kaaden's ex-t i n c t i o n angle curves. 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 Kettner 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 to the u n c e r t a i n t y about the o p t i c a l p r o p e r t i e s of p l a g i o c l a s e the determinations probably have an accuracy only of t 2-5$. However, the 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 . Clinopyroxene: 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 l i v i n e : n y o p t i c a l s i g n ; P o l d e r v a a r t , 1950. Carbonates: no; W i n c h e l l and W i n c h e l l , 1951. The Tsu b o i - i n d i c e s have been determined w i t h an accuracy of approximately t .001, other i n d i c e s w i t h an accuracy of approximately 1 .002. APPENDIX I I PLATES PLATE I PLATE I I The Fraser R i v e r V a l l e y near Moran. View to the northeast. PLATE I I I The Fraser River V a l l e y between Siwash Creek and Leon Creek. View to the northwest. 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 chert and a r g i l l i t e of the P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c . Lower part of K e l l y Creek. View to the north. PLATE V Mount Bowman. View to the south. PLATE VI C a l c a r e n i t e , thin-bedded to lam-in a t e d . At cl o s e i n s p e c t i o n the rock shows graded bedding and i n t r a f o r m a t i o n a l b r e c c i a t i o n . Marble Canyon formation, member I I I , Upper Permian. About two miles northwest of Mount Bowman. PLATE V I I Mount Soues. View to the n o r t h Syncline on Mount Kerr. northwest. V i e w t o t h e PLATE IX Interbedded limestone and c h e r t , showing box-type of f o l d s . Marble Canyon formation, member I l i a , Upper Permian. About one mile west of Mount K e r r . View to the northwest. PLATE X R a d i o l a r i a r i chert nodules i n a r g i l l a c e o u s matrix. A r g i l l -aceous chert from P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c . Crossed n i c o l s x 2 5 . PLATE XI R a d i o l a r i a n chert nodule, showing r a d i a t i n g spines. P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c . L e f t : o r d i n a r y 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 limestone. 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 concen-t r i c s t r u c t u r e and some r e l a t i v e l y -coarse twinned c r y s t a l s of c a l c i t e i n the 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 or T r i a s s i c . Crossed n i c o l s x35. PLATE XIII Migmatite c o n s i s t i n g of hornblende ho 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 of Fraser R i v e r , opposite the mouth of K e l l y Creek. View to the northwest. PLATE XIV 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 . A few c l e a r grains are of q u a r t z , the l i g h t grey grains are mostly of p l a g i o c l a s e . Specimen 2 of f i g u r e 4. Jackass Mountain group, D i v i s i o n C, Barremian. ordi n a r y l i g h t x 3 2 . P L A T S XV P l a g i o c l a s e c r y s t a l , showing twinning and o s c i l l a t o r y normal zoning, 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 French Bar formation. Upper Eocene or Oligocene, near French Bar Canyon. Air-photograph. PLATE XVII Conglomerate of the French Bar f o r -mation, Upper Eocene or Oligocene, near B i g Bar Creek. PLATE XVIII 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 miles n o r t h of McKay Creek. View to the no 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 of clinopyroxene 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 Slide of Middle or Late Tertiary o l i v i n e b a s a l t near Leon Creek. Air-photograph. PLATE XXI A l t e r e d u l t r a b a s i c rock. A g r a i n of chromite, ( d a r k ) , some p a r a n k e r i t e , (medium grey to d a r k ) , p a r t l y pseudo-morphous 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 to l i m o n i t e , and veins of very f i n e - g r a i n e d quartz, (mostly l i g h t grey). U l t r a b a s i c b e l t west of L i l l o o e t , Upper T r i a s s i c (?) Crossed n i c o l s x32. PLATE XXII Steeply dipping s t r a t a of the Jackass Mountain group, D i v i s i o n C, Barremian, near f a u l t \"d\" on the east side of the Fraser R i v e r , between S a l l u s Creek and Gibbs Creek; view to the southwest. PLATE X X I I I Andesite and basalt of the Spences Bridge group, Upper D i v i s i o n , A p t i a n , dipping s t e e p l y to the northeast near f a u l t contact 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 part of McKay Creek. View to the northwest. PLATE XXIV Fau l t \"e\" i n B i g Bar Canyon. View to the southeast. On the northeast side of the f a u l t chert and a r g i l l -i t e of the P a v i l i o n group, D i v i s i o n I , Upper Permian or T r i a s s i c ; on the southwest side b a s a l t and andesite o f the Ward Creek assemblage, Cretaceous or e a r l y T e r t i a r y . The f a u l t plane dips about 75° to the southwest. "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0302669"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Geological Sciences"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Geology of the Fraser River Valley between Lillooet and Big Bar Creek"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/39967"@en .