Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The geology of Hawkesbury Island, Skeena mining division, British Columbia Money, Peter Lawrence 1959

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1959_A6_7 M6 G3.pdf [ 16.59MB ]
Metadata
JSON: 1.0053044.json
JSON-LD: 1.0053044+ld.json
RDF/XML (Pretty): 1.0053044.xml
RDF/JSON: 1.0053044+rdf.json
Turtle: 1.0053044+rdf-turtle.txt
N-Triples: 1.0053044+rdf-ntriples.txt
Original Record: 1.0053044 +original-record.json
Full Text
1.0053044.txt
Citation
1.0053044.ris

Full Text

THE GEOLOGY OF HAWKESBURY ISLAND SKEENA MINING DIVISION, B R I T I S H COLUMBIA by PETER LAWRENCE MONEY B.Sc, M c G i l l U n i v e r s i t y , 1956 A t h e s i s s u b m i t t e d i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r t h e d e g r e e o f MASTER OF SCIENCE i n t h e De p a r t m e n t o f GEOLOGY We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BR I T I S H COLUMBIA A p r i l , 1959 ABSTRACT Hawkesbury I s l a n d i s i n t h e S k e e n a M i n i n g D i v i s i o n o f B r i t i s h C o l u m b i a . I t i s u n d e r l a i n by C o a s t I n t r u s i o n s , y o u n g e r l a m p r o p h y r e dykes and o l d e r m e t a m o r p h i c r o c k s . The l a t t e r f o r m p a r t o f t h e E c s t a l l septum o r r o o f p e n d a n t . The m e t a m o r p h i c r o c k s a r e m a i n l y a m p h i b o l i t e s and q u a r t z - f e l d s p a r g n e i s s e s . A few bands o f q u a r t z i t e , c r y s t a l l  i n e l i m e s t o n e , k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t and o t h e r r o c k t y p e s a r e p r e s e n t . T h e s e r o c k s have been formed by d y n a m o t h e r m a l metamorphism o f t h e r e g i o n a l t y p e . T h e y g e n e r  a l l y have a s s e m b l a g e s i n d i c a t i v e o f t h e s t a u r o l i t e - q u a r t z and k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s o f t h e a l m a n d i n e a m p h i b o l i t e f a c i e s . S h e a r z o n e s a r e s t r o n g l y s e r i c i t i z e d . S m a l l p e r c e n t a g e s o f s e r i c i t e and c h l o r i t e a r e common t h r o u g h o u t t h e m e t a m o r p h i c r o c k s . T h e s e m i n e r a l s have been f o r m e d d u r i n g r e t r o g r e s s i v e metamorphism. A p a r t f r o m a few s m a l l metamorphosed i g n e o u s b o d i e s , t h e s e r o c k s were o r i g i n a l l y a t h i c k e u g e o s y n c l i n a l s e q u e n c e c o n s i s t i n g m a i n l y o f t u f f a c e o u s s e d i m e n t s and s e m i - p e l i t i c o r a r k o s i c s e d i m e n t s . The m e t a m o r p h i c r o c k s have p r o b a b l y u ndergone a t l e a s t two p e r i o d s o f d e f o r m a t i o n , so t h a t t h e i r s t r u c t u r e i s complex. However, t h e f o l i a t i o n has a g e n e r a l t r e n d o f n o r t h 50° west t o n o r t h 70° west i n t h e n o r t h e r n p a r t o f t h e septum and o f n o r t h 2 0 ° e a s t t o n o r t h 55° e a s t i n t h e s o u t h e r n p a r t . The C o a s t I n t r u s i o n s have r e a c h e d t h e i r p r e s e n t p o s i t i o n s by i n t r u s i o n . T h e y have n o t been f o r m e d by g r a n i t i - z a t i o n i n s i t u . Some a s s i m i l a t i o n o f t h e c o u n t r y r o c k has o c c u r r e d b u t t h i s i s a m a r g i n a l f e a t u r e . The C o a s t I n t r u s i o n s have had l i t t l e a f f e c t on t h e g r a d e o f metamorphism o f t h e m e t a m o r p h i c r o c k s . I n p r e s e n t i n g 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 t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D epartment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . The U n i v e r s i t y o f B r i t i s i V a n c o u v e r Canada. Department o f D ate CL^iJ . tig? TABLE OF CONTENTS C h a p t e r Page I . I n t r o d u c t i o n 1 P r e l i m i n a r y S t a t e m e n t 1 F i e l d Methods 1 L o c a t i o n and A c c e s s . 2 T o p o g r a p h y and G l a c i a t i o n 4 D r a i n a g e 7 C l i m a t e 8 F l o r a 9 F a u n a 10 I I . G e n e r a l G e o l o g y 12 P r e v i o u s G e o l o g i c a l Work 12 G e n e r a l G e o l o g y 13 I I I . The M e t a m o r p h i c R o c k s 20 I n t r o d u c t i o n 20 P e t r o l o g y o f t h e P l a g i o c l a s e A m p h i b o l i t e s . . . . 20 (1) P l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s . . . 22 (2) P l a g i o c l a s e - h o r n b l e n d e - b i o t i t e - e p i d o t e r o c k s 32 (3) P l a g i o c l a s e - h o r n b l e n d e - d i o p s i d e amphi b o l i t e s 34 (4) P l a g i o c l a s e - s t a u r o l i t e a m p h i b o l i t e s . . . . 37 P e t r o l o g y o f t h e M e t a s e d i m e n t s 44 (1) P l a g i o c l a s e - q u a r t z - b i o t i t e - h o r n b l e n d e g n e i s s 44 (2) P l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s . . . 47 (3) K y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t . 57 (4) S i l l i m a n i t e - q u a r t z - p l a g i o c l a s e g n e i s s . . . 68 (5) G r a p h i t i c q u a r t z - p l a g i o c l a s e s c h i s t . . . . 70 (6) Q u a r t z i t e 75 (7) Q u a r t z - t r e m o l i t e - z o i s i t e r o c k s 75 (8) C r y s t a l l i n e l i m e s t o n e 79 (9) S e r i c i t e - e p i d o t e s c h i s t 81 (10) A l b i t i z e d and p o t a s h - e n r i c h e d r o c k s . . . . 83 P e t r o l o g y o f t h e M e t a - i g n e o u s R o c k s 87 (1) M e t a - i e g n e o u s a m p h i b o l i t e s 87 (2) A c i d p e g m a t i t e s 92 O r i g i n o f t h e M e t a m o r p h i c Rocks 92 The Grade o f Metamorphism 104 (1) M e t a m o r p h i c F a c i e s 104 (2) T e m p e r a t u r e - P r e s s u r e C o n d i t i o n s I l l The C a u s e s o f Metamorphism 114 IV. The Ign e o u s Rocks 118 P e t r o l o g y o f t h e C o a s t I n t r u s i o n s 118 O r i g i n and N a t u r e o f t h e C o a s t I n t r u s i o n s . . . . 128 O t h e r I n t r u s i o n s 129 (1) C a r b o n a t i z e d A n d e s i t i c ( ? ) Rocks 129 (2) Lamprophyre Dykes 133 Chapter Pa%e V. Structural Geology 137 General Structure of the Northern Part of the Coast Mountains 137 Major Structural Features of the Map Area . . . 138 Small-scale Structures 149 (1) In the metamorphic rocks 149 (2) In the igneous rocks 151 VI. Conclusions 153 Bibliography 156 LIST OF ILLUSTRATIONS Figure Page 1. Index map of Western Bri t i s h Columbia 3 2. ACF diagram showing the range in composition of the plagioclase-hornblende-biotite rocks . . 23 3. Photomicrograph of plagioclase-hornblende amphibolite 40 4. Photomicrograph of plagioclase-hornblende- epidote rock 40 5. Photomicrograph of plagioclase-hornblende- epidote rock 41 6. Photomicrograph of plagioclase-biotite-epidote rock 41 7. Photomicrograph of plagioclase-biotite-epidote- rock 42 8. Photomicrograph of plagioclase-diopside-horn- blende amphibolite 42 9. - 1 0 . Photomicrographs of plagioclase-staurolite amphibolite 43 11.-12. Photomicrographs of plagioclase-K feldspar- quartz gneiss . . . 55 13.-14. Photomicrographs of plagioclase-K feldspar- quartz gneiss 56 15. ACF diagram showing the range in composition of the kyanite-staurolite-almandine mica schists 59 16. -17. Photomicrographs of kyanite-staurolite- almandine mica schist 64 18.-19. Photomicrographs of kyanite-staurolite- almandine mica schist 65 20v-21. Photomicrographs of kyanite-staurolite- almandine mica schist 66 2 2 . - 2 3 . Photomicrographs of kyanite-staurolite- almandine mica schist . 67 24 . -25. Photomicrographs of sillimanite-quartz- pla&ioclase gneiss 69 2 6 . - 2 7 . Photomicrographs of graphitic--quart z-: . - plagioclase schist . 73 28 . -29. Photomicrographs of graphitic quartz- plagioclase schist 74 30. Photomicrograph of quartz i t e 78 31. Photomicrograph of quartz-tremolite-zoisite rock 78 32. Photomicrograph of crystalline limestone . . . 80 33. Photomicrograph of sericite-epidote schist . . 83 34. Photomicrograph of albitized rock 86 35. - 3 6 . Photomicrographs of meta-igneous amphibolite . 91 37. ACF diagram showing the compositional ranges of three: rock units 93 F i g u r e Page 38.-39. P h o t o m i c r o g r a p h s o f q u a r t z d i o r i t e 126 40. P h o t o m i c r o g r a p h o f m o n z o n i t e 127 41. P h o t o m i c r o g r a p h o f g r a n o d i o r i t e 127 42. -43. P h o t o m i c r o g r a p h o f ( ? ) a n d e s i t i c r o c k 132 44.-45. P h o t o m i c r o g r a p h o f l a m p r o p h y r e . 135 46. P o l e s o f F o l i a t i o n o f t h e M e t a m o r p h i c Rocks o f Hawkesbury I s l a n d 141 47. I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c Rocks i n A r e a I 142 48. I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c Rocks i n A r e a I I 143 49. I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c Rocks i n A r e a I I I 144 50. I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c Rocks i n A r e a IV 145 51. I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c Rocks i n A r e a V 146 52. The A z i m u t h and P l u n g e o f D r a g F o l d s i n t h e M e t a m o r p h i c Rocks 147 53. Map o f t h e G e o l o g y o f Hawkesbury I s l a n d , 1 i n c h = 1 m i l e adft- pookejfc~7{Ym? 54. Map o f t h e S t r u c t u r e o f Hawkesbury I s l a n d , f >^ 1 i n c h = 1 m i l e i n poeteefr ^ ACKNOWLEDGMENT The w r i t e r w o u l d l i k e t o t h a n k t h e E c s t a l l M i n i n g Company and i t s o f f i c e r s f o r t h e i r k i n d p e r m i s s i o n t o u s e f i e l d work c a r r i e d o ut f o r t h e company as a b a s i s f o r t h i s t h e s i s and f o r t h e u s e o f company maps, a e r i a l p h o t o g r a p h s and t h i n s e c t i o n s . A s s i s t a n c e d u r i n g t h e p r e p a r a t i o n o f t h e t h e s i s by D r . W. H. W h i t e , D r . K.C . M c T a g g a r t and D r . G.V. R o s s i s g r a t e f u l l y a c k n o w l e d g e d . The w r i t e r i s a l s o i n d e b t e d t o Mr. W.A. Padgham and Mr. C.C. S h e n g , who c a r r i e d o u t p a r t o f t h e f i e l d m a p p i n g , Mr. K. Roy and Mr. W. P h i l i p s , who a b l y s e r v e d as f i e l d a s s i s t a n t s , and t o Mr. R. Greggs f o r i d e n  t i f i c a t i o n o f f o s s i l s c o l l e c t e d d u r i n g t h e f i e l d work. CHAPTER I INTRODUCTION PRELIMINARY STATEMENT T h i s t h e s i s i s b a s e d on f i e l d work u n d e r t a k e n d u r i n g t h e summer o f 1958 w h i l e t h e w r i t e r was employed by t h e E c s t a l l M i n i n g Company, and s u b s e q u e n t l a b o r a t o r y work c a r r i e d out d u r i n g t h e w i n t e r o f 1958-59. I t s o b j e c t i s t o p r e s e n t a n a c c o u n t o f t h e g e o l o g y o f Hawkesbury I s l a n d , w i t h p a r t i c u l a r emphasis on t h e p e t r o l o g y o f t h e m e t a m o r p h i c r o c k s o f t h e i s l a n d and t h e r e l a t i o n s h i p o f t h e C o a s t I n t r u s i o n s t o t h e s e r o c k s and t o t h e metamorphism. F I E L D METHODS Compass and a l t i m e t e r t r a v e r s e s were r u n a t i n t e r v a l s o f 2000 t o 6000 f e e t o v e r most o f Hawkesbury I s l a n d . T h e s e t r a v e r s e s were s u p p l e m e n t e d by l i m i t e d work w i t h a h e l i c o p t e r , c o n s i s t i n g o f m a k i n g c o n f i r m a t o r y c h e c k s on g e o l o g i c a l f e a t u r e s a t a number o f p o i n t s . T r a v e r s e r o u t e s were c h o s e n w i t h t h e a i d o f v e r t i c a l a e r i a l p h o t o g r a p h s and a t o p o g r a p h i c map. Owing t o t h e s t e e p g r a d i e n t o f t h e v a l l e y s i d e s t r a v e r s e s were g e n e r a l l y r u n a l o n g r i d g e t o p s a n d , t o a l e s s e r e x t e n t , on v a l l e y f l o o r s . P o i n t s were l o c a t e d on s t e e p s l o p e s by u s e o f an a l t i m e t e r , w h i c h was c o r r e c t e d a t p o i n t s o f known e l e v a t i o n . 2 T h e s e p o i n t s a r e b e l i e v e d t o be a c c u r a t e t o w i t h i n one h u n d r e d v e r t i c a l f e e t . R e f e r e n c e p o i n t s on r i d g e t o p s 5 a n d i n v a l l e y s , were l o c a t e d by use o f a e r i a l p h o t o g r a p h s , a l t i m e t e r r e a d i n g s , and s i g h t i n g s on l a n d m a r k s w h e r e v e r p o s s i b l e . The l o c a t i o n o f p o i n t s on t h e r i d g e s i s b e l i e v e d t o be a c c u r a t e . However, owing t o t h e h e a v y t i m b e r c o v e r i n t h e v a l l e y s , p o i n t s i n t h e s e may be l o c a t e d v e r y i n a c c u r a t e l y . The p o s s i b l e e r r o r i n one c a s e i s i n t h e o r d e r o f one t h o u s a n d f e e t . The f i e l d work was c a r r i e d o u t f r o m e i g h t b a s e camps. A B e l l m o d e l G-2 h e l i c o p t e r was u s e d f o r m o v i n g camp, c a r r y i n g s u p p l i e s , and sometimes c a r r y i n g men t o s t a r t i n g p o i n t s o f t r a v e r s e s . The o n l y a l t e r n a t i v e method o f mapping t h e i s l a n d w o u l d be a c o m b i n a t i o n o f work f r o m t h e s h o r e , u s i n g a . b o a t , and b a c k - p a c k i n g . I t i s d o u b t f u l , i n v i e w o f t h e e x t r e m e l y r u g g e d t o p o g r a p h y and v e r y h e a v y u n d e r g r o w t h , and h e a v y r a i n  f a l l , i f m a pping c o u l d have been c o m p l e t e d d u r i n g one f i e l d s e a s o n by t h i s method. LOCATION AND ACCESS Hawkesbury I s l a n d i s l o c a t e d i n t h e S k e e n a M i n i n g D i v i s i o n o f B r i t i s h C o l u m b i a . I t i s t h e l a r g e s t o f s e v e r a l i s l a n d s i n a f i o r d a t t h e head o f w h i c h K i t i m a t i s l o c a t e d . I t has an a r e a o f a p p r o x i m a t e l y 95 s q u a r e m i l e s . The n o r t h e r n t i p o f Hawkesbury I s l a n d i s a b o u t 21 m i l e s s o u t h e a s t o f K i t i m a t . The i s l a n d i s a b o u t 80 m i l e s s o u t h - e a s t o f P r i n c e R u p e r t by a i r , and i t s s o u t h e r n t i p i s 85 m i l e s by t h e s h o r t e s t 3 Figure 1 w a t e r r o u t e . The g e o g r a p h i c a l c e n t r e o f t h e i s l a n d i s a t a p p r o x i m a t e l y 53° 06' n o r t h and l o n g i t u d e 129° 07' West. Hawkesbury I s l a n d may be r e a c h e d by b o a t f r o m e i t h e r K i t i m a t o r P r i n c e R u p e r t . T h e r e i s a s h e l t e r e d n a t u r a l h a r b o u r between K i t s a w a y I s l a n d and Hawkesbury I s l a n d , but most p a r t s o f t h e i s l a n d a r e d i f f i c u l t t o l a n d on, p a r t i c u l a r l y w i t h an o n s h o r e w i n d . I t was f o u n d t h a t a h e l i c o p t e r i s i d e a l f o r w o r k i n g i n t h i s a r e a and f o r e a s y a c c e s s t o any p a r t o f t h e i s l a n d . I t c o u l d be l a n d e d a l m o s t anywhere on t h e r i d g e t o p s and u s u a l l y i n a t l e a s t one p l a c e i n e a c h m a j o r v a l l e y . A s m a l l f l o a t p l a n e c o u l d p r o b a b l y l a n d on t h e t h r e e o r f o u r l a r g e s t l a k e s o f t h e i s l a n d , b u t i t w o u l d be i m p o s s i b l e t o map t h e i s l a n d a d e q u a t e l y u s i n g a f l o a t p l a n e a l o n e . TOPOGRAPHY AND GLACIATION Hawkesbury I s l a n d i s i n t h e C o a s t M o u n t a i n s s u b  d i v i s i o n o f t h e W e s t e r n S y s t e m o f t h e C o r d i l l e r a n R e g i o n . The t o p o g r a p h i c f e a t u r e s o f t h e i s l a n d have b e e n d e v e l o p e d m a i n l y by an o v e r r i d i n g i c e s h e e t and l a t e r v a l l e y g l a c i e r s . The a r e a c o n s i s t s o f numerous U - s h a p e d , s t e e p - w a l l e d g l a c i a l v a l l e y s s e p a r a t e d by n a r r o w r o u n d - t o p p e d r i d g e s . V a l l e y t r e n d s seem l a r g e l y u n a f f e c t e d by a s t r u c t u r a l c o n t r o l , w i t h t h e p o s s i b l e e x c e p t i o n o f A n g l e V a l l e y , and i t seems l i k e l y t h a t t h e o r i g i n a l c o n t r o l was l a r g e l y t o p o g r a p h i c , snow and i c e a c c u m u l a t i n g on t h e h i g h e r p a r t s o f t h e i s l a n d and g l a c i e r s d e s c e n d i n g a l o n g f o r m e r s t r e a m c h a n n e l s . 5 The r o u n d e d r i d g e t o p s , a b s e n c e o f m a t t e r h o r n p e a k s and t h e p r e s e n c e o f g l a c i a l s t r i a e , c h a t t e r marks and e r r a t i c s on t h e h i g h e s t p a r t s o f t h e s e r i d g e s s u g g e s t t h a t a t one s t a g e g l a c i e r s had c o m p l e t e l y o v e r r i d d e n t h e i s l a n d . G l a c i a l s t r i a e and c h a t t e r marks on t h e r i d g e t o p s i n d i c a t e a d i r e c t i o n o f i c e movement o f 225° t o 245° f o r t h i s o v e r r i d i n g s h e e t . O n l y t h r e e o r f o u r s e t s o f s t r i a e were s e e n i n v a l l e y s . T h e s e , as i s t o be e x p e c t e d , i n d i c a t e a movement p a r a l l e l t o t h e v a l l e y w a l l . I n a d d i t i o n t o t h e m a i n g l a c i a l v a l l e y s numerous s m a l l t r i b u t a r y h a n g i n g v a l l e y s a r e p r e s e n t . T h e s e have t h e t y p i c a l U -shaped p r o f i l e and were o b v i o u s l y o c c u p i e d by s m a l l t r i b u t a r y g l a c i e r s . T h e s e v a l l e y s have f l o o r s 500' t o 1700' above t h e m a i n v a l l e y f l o o r s . The s e q u e n c e o f d e v e l o p m e n t o f t h e g l a c i e r s p r o b a b l y i n c l u d e d an e a r l y s t a g e o f v a l l e y g l a c i e r s , a s e c o n d s t a g e d u r i n g w h i c h a l a r g e g l a c i e r was f o r m e d w h i c h a p p a r e n t l y moved down V e r n e y P a s s a g e t o t h e e a s t and Sue C h a n n e l and D o u g l a s C h a n n e l t o t h e w est t o t h e o c e a n , a n d a t one s t a g e c o m p l e t e l y c o v e r e d t h e i s l a n d ; and a tfhird s t a g e d u r i n g w h i c h v a l l e y g l a c i e r s were f o r m e d , p o s s i b l y f r o m r e m n a n t s o f t h e l a r g e o v e r  r i d i n g g l a c i e r . D u r i n g t h e s e c o n d s t a g e t h e g l a c i e r i m m e d i a t e l y a d j a c e n t t o t h e i s l a n d may have been 4000' o r more i n t h i c k n e s s . The minimum f i g u r e i s 3300 f e e t . T h i s f i g u r e makes an a l l o w  a nce f o r l a t e r i s o s t a t i c r e c o v e r y and u p l i f t o f 500 f e e t , w h i c h i s b a s e d on t h e p r e s e n c e o f m a r i n e p o s t - g l a c i a l c l a y s a t 6 300+ f e e t a bove s e a l e v e l . I t makes no a l l o w a n c e f o r t h e t h i c k n e s s o f t h e g l a c i e r b e l o w s e a l e v e l o r i t s t h i c k n e s s above t h e h i g h e s t p o i n t on Hawkesbury I s l a n d . The G l a c i a l Map o f  Canada, p u b l i s h e d i n 1958 by t h e G e o l o g i c a l A s s o c i a t i o n o f Canada, shows t h e 4000 f o o t c o n t o u r o f i c e t h i c k n e s s as c r o s s  i n g Hawkesbury I s l a n d i n t h e v i c i n i t y o f G a l e M o u n t a i n , w h i c h has an e l e v a t i o n o f 3900+ f e e t and i s t h e h i g h e s t p o i n t on t h e i s l a n d . The t o p o g r a p h y o f a r e a s u n d e r l a i n by m e t a m o r p h i c and g r a n i t i c r o c k s has s i g n i f i c a n t d i f f e r e n c e s , a p p a r e n t l y due t o t h e f a r more homogeneous c h a r a c t e r o f t h e i g n e o u s r o c k s . The v a l l e y s i n g r a n i t i c a r e a s have a much more s y m m e t r i c a l c r o s s - s e c t i o n and g e n e r a l l y a more r e g u l a r a p p e a r a n c e t h a n t h o s e i n a r e a s o f m e t a m o r p h i c r o c k s . C i r q u e s a r e p r a c t i c a l l y h e m i s p h e r i c a l i n t h e f o r m e r r o c k s and g e n e r a l l y v e r y i r r e g u l a r i n t h e l a t t e r r o c k s . On t h e m a i n l a n d t h e g r a n i t i c r o c k s f o r m c o n s i d e r a b l y h i g h e r p e a k s t h a n t h e a d j a c e n t m e t a m o r p h i c s b u t on t h e i s l a n d t h e l o c a l r e l i e f i s a b o u t t h e same f o r b o t h t y p e s . T h i s i s p r o b a b l y due t o t h e h a r d and r e s i s t a n t n a t u r e o f t h e m e t a m o r p h i c r o c k s o f Hawkesbury I s l a n d as compared w i t h t h o s e o f t h e m a i n l a n d . S e v e r a l t r u n c a t e d s p u r s were n o t e d i n v a l l e y s i n t h e g r a n i t i c r o c k s b u t none seem t o be p r e s e r v e d i n a r e a s o f m e t a m o r p h i c r o c k s . T o t a l r e l i e f on Hawkesbury I s l a n d i s 3950 f e e t ± 40 f e e t . The h i g h e s t p o i n t i s t h e peak o f G a l e M o u n t a i n . Over most o f t h e map a r e a t h e t o p s o f r i d g e s have e l e v a t i o n s r a n g i n g 7 f r o m 3000 f e e t t o 3200 f e e t . The o n l y m a j o r e x c e p t i o n i s t h e G a l e M o u n t a i n - S i d e b a c o n L a k e - B a c k b a c o n Lake a r e a , where r i d g e t o p s a v e r a g e 3600 f e e t . T h e s e r i d g e t o p s may r e p r e s e n t an o l d , f a i r l y l e v e l s u r f a c e , a s maximum e l e v a t i o n s a r e so r e m a r k a b l y c o n s i s t e n t o v e r most o f t h e i s l a n d t h a t i t seems u n l i k e l y t h e g l a c i e r s c o u l d be w h o l l y r e s p o n s i b l e . V a l l e y f l o o r s g e n e r a l l y have e l e v a t i o n s o f 100-500 f e e t above s e a l e v e l , b u t r e a c h up t o 1000 f e e t a t t h e i r h e a d s . A v e r a g e l o c a l r e l i e f , b e tween v a l l e y f l o o r and r i d g e t o p , i s o f t h e o r d e r o f 2000 f e e t t o 2500 f e e t . DRAINAGE D r a i n a g e on Hawkesbury I s l a n d i s by i n n u m e r a b l e t i n y r i v u l e t s w h i c h f a l l o v e r v a l l e y w a l l s and c o a l e s c e t o f o r m s t r e a m s d r a i n i n g o ut t h r o u g h t h e g l a c i a l v a l l e y s t o t h e o c e a n . The l a r g e r t r i b u t a r y s t r e a m s , and t h e m a i n s t r e a m s n e a r t h e i r h e a d s , h a ve b u i l t up v e r y l a r g e f a n s and g e n e r a l l y f l o w b e  n e a t h t h e s e , a p p e a r i n g o n l y where r i d g e s o f b e d r o c k c r o s s t h e i r b e d s . I n t h e u p p e r p a r t s o f s t r e a m s and n e a r t h e c o a s t where most o f t h e v a l l e y f l o o r s d r o p o f f s h a r p l y t o s e a l e v e l w a t e r f a l l s and r a p i d s a r e u s u a l l y p r e s e n t . T h r o u g h o u t most o f t h e i r c o u r s e t h e m a i n s t r e a m s f l o w o v e r a c o m b i n a t i o n o f a l l u v i a l m a t e r i a l and p o s t - g l a c i a l m a r i n e c l a y s . T h e y a r e c h a r a c t e r i z e d by numerous abandoned c h a n n e l s and t h e p r e s e n c e o f n a t u r a l l e v e e s . The l a t t e r a r e p a r t i c u l a r l y w e l l d e v e l o p e d i n r e g i o n s o f m a r i n e c l a y s . F o r t h e most p a r t t h e o l d c h a n n e l s 8 l i e only a few feet from the new ones and have rarely been abandoned for more than a few tens of feet. It is probable that the channel used varies from year to year, controlled by where the bulk of the material carried by spring floods is deposited. The main streams have an average width of ten to twenty-five feet and a maximum depth of one to five feet, except for plunge pools which may be up to twenty feet deep. A most interesting example of channel control by a l l u v i a l material is South Beaver Creek, near the west coast of the island. This stream drains into Beaver Creek through two separate channels which reach the latter creek some 2000 feet apart. During the summer of 1958, due to most of the material from the spring freshets being deposited in the middle of the channel, this stream divided and flowed through both channels, which may be termed distributaries. It seems lik e l y that during some years a l l the water flows through one of the alter nate channels instead of forming this distributary system. Most of the lakes on the island are of the tarn type. The principal exceptions are Sidebacon and Backbacon Lakes, which are finger lakes; and possibly Evelyn Lake, Roy Lake and Beaver Lake, which are in low overburden-filled valleys and appear to be held back by marine clays, a l l u v i a l material and possibly some morainal deposits. CLIMATE Hawkesbury Island, like most of the Coast Mountains of 9 B r i t i s h C o l u m b i a , has a v e r y humid and f a i r l y m i l d c l i m a t e . The a v e r a g e a n n u a l p r e c i p i t a t i o n a t m e t e o r o l o g i c a l s t a t i o n s i n Kemano, K i t i m a t and P r i n c e R u p e r t , t h e t h r e e n e a r e s t s t a t i o n s t o Hawkesbury I s l a n d i s a p p r o x i m a t e l y 74 i n c h e s , 94 i n c h e s and 95 i n c h e s r e s p e c t i v e l y . A v e r a g e p r e c i p i t a t i o n d u r i n g t h e summer months (May-September) v a r i e s f r o m a p p r o x i m a t e l y 15 i n c h e s i n Kemano t o 29 i n c h e s i n P r i n c e R u p e r t . A v e r a g e m o n t h l y t e m p e r  a t u r e f o r t h e t o t a l p e r i o d o f r e c o r d f o r t h e s e s t a t i o n s i s 49° - 50° i n May, 53° - 55° i n J u n e , 56° - 61° i n J u l y , 57° - 6 1 ° i n A u g u s t and 54° - 55° i n Se p t e m b e r . The a v e r a g e number o f h o u r s o f s u n s h i n e f o r P r i n c e R u p e r t v a r i e s f r o m 136 h o u r s i n May t o 95 h o u r s i n S e p t e m b e r , i . e f r o m a b o u t 4.3 t o a b o u t 3.1 h o u r s p e r day. The summer o f 1958 was e x c e p t i o n a l l y m i l d and d r y . Most o f t h e mapping on Hawkesbury I s l a n d was c a r r i e d o u t between May 20 and J u l y 23. D u r i n g t h i s p e r i o d o n l y 3 d a y s were l o s t due t o r a i n , and t o t a l r a i n f a l l was p r o b a b l y l e s s t h a n an i n c h . A b o u t o n e - t h i r d o f t h e d a y s were c l o u d y b u t t o t a l h o u r s o f s u n s h i n e was p r o b a b l y f a r above t h e a v e r a g e f i g u r e . The snow w h i c h u s u a l l y m a n t l e s t h e h i g h e r p e a k s a l l summer, o r u n t i l e a r l y S e p t e m b e r , had c o m p l e t e l y d i s a p p e a r e d , a p a r t f r o m s h e l t e r e d p a t c h e s i n some o f t h e h i g h e r v a l l e y s , by t h e end o f J u l y . FLORA The v a l l e y s s u p p o r t h e a v y s t a n d s o f hem l o c k , y e l l o w c e d a r and b a l s a m f i r t o a n e l e v a t i o n o f ab o u t 2000 f e e t . Hem-10 l o c k i s t h e most abundant s p e c i e s . S i t k a s p r u c e , j a c k p i n e , j u n i p e r and r e d c e d a r a r e a b u n d a n t l o c a l l y and a few t a m a r a c k were s e e n i n p a r t i c u l a r l y wet a r e a s . B e c a u s e o f m i l d w i n t e r s a n d h e a v y r a i n f a l l some o f t h e t r e e s r e a c h a v e r y l a r g e s i z e and t h e u n d e r g r o w t h , m a i n l y a l d e r , D e v i l ' s C l u b , h u c k l e b e r r y , and s i m i l a r s h r u b s , i s l u x u r i a n t . S e v e r a l h e m l o c k s were f o u n d t o have a d i a m e t e r o f a b o u t f o u r f e e t . L u m b e r i n g has b e e n c a r r i e d o u t n e a r t h e mouth o f E v e l y n C r e e k and a l o n g t h e s h o r e l i n e between Danube Bay and E v a P o i n t , b u t no work has be e n done e l s e w h e r e . FAUNA W i l d l i f e i s n o t p l e n t i f u l on Hawkesbury I s l a n d . Of t h e l a r g e r a n i m a l s , o n l y b l a c k b e a r s seem common. M o u n t a i n g o a t s a r e b e l i e v e d t o be p r e s e n t b u t v e r y s c a r c e . T h e y were n e v e r s e e n , b u t t h e i r t r a i l s r u n a l o n g t h e t o p s o f a l l t h e r i d g e s and t r a c k s were s e e n on s e v e r a l o c c a s i o n s . A l t h o u g h t h e g r i z z l y b e a r i s common on t h e m a i n l a n d , no e v i d e n c e o f i t s p r e s e n c e on t h e i s l a n d was f o u n d . O l d b e a v e r dams and c u t t i n g s were f o u n d i n t h e v i c i n i t y o f E v e l y n Lake and Roy Lake and i n A n g l e and B e a v e r V a l l e y s . No f r e s h c u t t i n g s were s e e n and t h e dams a r e i n a s t a t e o f d i s r e p a i r , s o t h a t i t seems l i k e l y t h e b e a v e r s have d i e d o u t . B i r d s a r e numerous. A l l t h e l a r g e r ponds and s t r e a m s seem t o have one o r two f a m i l i e s o f b l a c k d u c k s l i v i n g on them. Geese were s e e n s e v e r a l t i m e s d u r i n g t h e summer. P a r t r i d g e a r e p r e s e n t b u t r a r e . The o n l y 11 f r e s h - w a t e r f i s h s e e n were b r o o k t r o u t , n e v e r o v e r s i x i n c h e s l o n g . T h e s e a r e n o t common. 0 CHAPTER I I GENERAL GEOLOGY PREVIOUS GEOLOGICAL WORK L i t t l e g e o l o g i c a l mapping has b e e n done i n t h e C o a s t M o u n t a i n s , p r i m a r i l y b e c a u s e o f t h e few known d e p o s i t s o f e c onomic i n t e r e s t and c l i m a t i c and t o p o g r a p h i c f e a t u r e s s u c h as h e a v y r a i n f a l l , r u g g e d n e s s , s c a r c i t y o f o u t c r o p and h e a v y t i m b e r c o v e r w h i c h make t r a n s p o r t a t i o n e x t r e m e l y d i f f i c u l t and mapping s l o w and e x p e n s i v e . The o n l y p r e v i o u s work on Hawkesbury I s l a n d a b o u t w h i c h a n y t h i n g i s p u b l i s h e d i s t h e m a p p i n g o f t h e s h o r e l i n e d u r i n g 1921 and 1922 by D r . V. D o l m a g e , 1 * 2 ' f o r t h e G e o l o g i c a l S u r v e y o f C a nada. T h i s mapping was o f a v e r y g e n e r a l i z e d r e c o n n a i s s a n c e n a t u r e , t h e c o a s t l i n e b e i n g mapped a t an a v e r a g e r a t e o f some 20 m i l e s a d a y , and d i f f e r e n t i a t e d i n t o o n l y two d i v i s i o n s , C o a s t I n t r u s i o n s and m e t a m o r p h i c r o c k s . P r e v i o u s work i n t h e v i c i n i t y o f Hawkesbury I s l a n d c o n s i s t s o f (1) mapping o f some 30 s q u a r e m i l e s a r o u n d t h e E c s t a l l M i n e i n 1951» w h i c h was c a r r i e d o u t i n c o n j u n c t i o n w i t h 1 V. Dolmage, " C o a s t and I s l a n d s o f B r i t i s h C o l u m b i a Between B u r k e I n l e t and D o u g l a s C h a n n e l " , G.S.C.Summary R e p o r t 1921, P a r t A, pp. 22-49. 2 V. Dolmage, " C o a s t and I s l a n d s o f B r i t i s h C o l u m b i a B etween D o u g l a s C h a n n e l and t h e A l a s k a n B o u n d a r y " , G.S.C.  Summary R e p o r t . 1922, P a r t A, pp. 9-34. 13 extensive development work on this property, (2) the mapping of a large part of the Ec s t a l l septum between the Skeena River 3 and Douglas Channel during the summer of 1958 by W.A. Padgham and (3) the mapping of the mouth of the Skeena river along the Grand Trunk Pacific Railway in 1912 by R.G.McConnell.4 Of the reports on this work the f i r s t is not available to the public and McConnell's contains l i t t l e about the metamorphic rocks of the Ecstall septum, so that the only work of any value in dis cussing the geology of Hawkesbury Island is Padgham's. Un fortunately this work was carried out on so large a scale that the numerous rock types present could only be subdivided into groups rather than separate petrologic units, as w i l l be attempted in this thesis. Other reports have appeared on mines and mineral occurr ences in the Coast Mountains, but none of these has any direct connection with the geology of Hawkesbury Island, so they w i l l not be discussed here. A l l of these reports which the writer has been able to find are listed in the bibliography. GENERAL GEOLOGY The rocks of Hawkesbury Island consist of metamorphic rocks o f the Ecstall series, both igneous and sedimentary in 3 W.A. Padgham, Geology of the Ecstall-Quaal River  Area, Bri t i s h Columbia. 1958, Unpublished M.A.Sc Thesis, University of Br i t i s h Columbia. 4 R.G.McConnell "Geological Section Along the Grand Trunk Pacific Railway from Prince Rupert to Aldermere, B.C.," G.S.C. Summary Report, 1912, pp. 55-62. 14 origin, which are intruded by plutons of granitic rocks of the Coast Intrusions and of at least one ahdesitic(?) s i l l . The Ecstall Series rocks and Coast Intrusions are intruded by a few late hornblende lamprophyre dykes. The youngest deposits are unconsolidated a l l u v i a l material, marine blue-grey clays and scarce glacial and g l a c i a l - f l u v i a l deposits. A table of rock units, showing the nature of the contact, the age of the units and their major subdivisions is on., the following page. The rocks of the Ecstall Series form a mass which is surrounded by granitic rocks of the Coast Intrusions. It is not known whether this mass is a roof pendant or a septum. The presence of small stocklike bodies of granitic rocks surrounded by extensive swarms of granitic dykes in the central parts of the Ecstall series in the map area suggests a gran i t i c floor at no great depth, i.e. that this mass is a roof pendant. The rocks of the Ecstall Series, on the other hand, might actually not be floored by the Coast Intrusions but : form a "screen" between several of the numerous intrusions i.e. be a septum. The Ecstall septum, or roof pendant, is known to extend from north of the Skeena River south through the Ecstall River area, across Hawkesbury Island and up Gardner Canal. Its minimum length is 80 miles. Probably i t continues south of Gardiner Canal to Graham Reach or Sheep Passage and north of the Skeena River to Portland Canal, which would give i t a total length of some 180 miles. Its width ranges from less than 3 15 TABLE OF ROCK UNITS Age P l e i s t o c e n e and R e c e n t U n c o n s o l i d a t e d s e d i m e n t s C l a y , s a n d , g r a v e l , e t c . , ( i n c l u d i n g m a r i n e b l u e - g r e y c l a y s ) U n c o n f o r m i t y Age Unknown H o r n b l e n d e L a m p r o p h y r e d y k e s and s i l l s I n t r u s i v e C o n t a c t J u r a s s i c - C r e t a c e o u s ( p r o b a b l y Upper C o a s t I n t r u s i o n s : J u r a s s i c ) P e g m a t i t e G r a n i t i c d y k e s G r a n o d i o r i t e , q u a r t z m o n z o n i t e , M o n z o n i t e , q u a r t z d i o r i t e and d i o r i t e Age Unknown A n d e s i t i c ( ? ) s i l l s and d y k e s I n t r u s i v e C o n t a c t P r e - J u r a s s i e A ( p o s s i b l y O r d o v i c i a n - E c s t a l l S e r i e s R o c k s : D e v o n i a n ) " M e t a - i g n e o u s a m p h i b o l i t e s " I n t r u s i v e C o n t a c t " P l a g i o c l a s e a m p h i b o l i t e s , " q u a r t z - K - f e l d s p a r - p l a g i o c l a s e g n e i s s e s , k y a n i t e - s t a u r o  l i t e - a l m a n d i n e m i c a s c h i s t s , q u a r t z i t e s , l i m e s t o n e s , g r a p h i t i c q u a r t z - p l a g i o c l a s e s c h i s t s , e t c . & The w r i t e r w i l l r e f e r t o t h e m e t a m o r p h i c r o c k s f o r m i n g t h e E c s t a l l r o o f p e n d a n t o r septum as t h e " E c s t a l l S e r i e s " t h r o u g h o u t t h i s t h e s i s . T h i s i s m a i n l y a m a t t e r o f c o n  v e n i e n c e b u t a l s o r e f l e c t s t h e w r i t e r ' s b e l i e v e t h a t t h e s e r o c k s p o s s i b l y do f o r m a t i m e u n i t . m i l e s a t t h e E c s t a l l m ine t o more t h a n 11 m i l e s i n t h e Amoeba L a k e - F o c h L a k e a r e a j u s t t o t h e n o r t h o f D o u g l a s C h a n n e l . The w i d t h on Hawkesbury I s l a n d a v e r a g e s 10 m i l e s . The m e t a m o r p h i c r o c k s o f t h e Hawkesbury I s l a n d a r e a may be s u b d i v i d e d i n t o t h r e e b r o a d g r o u p s . T h e s e a r e t h e metamorphosed i g n e o u s r o c k s , t h e " p l a g i o c l a s e a m p h i b o l i t e s " and t h e metamorphosed s e d i m e n t s . The metamorphosed i g n e o u s r o c k s , t h e " i g n e o u s a m p h i b o l i t e s " , a r e o f v e r y m i n o r e x t e n t . The " p l a g i o c l a s e a m p h i b o l i t e s " , r a t h e r b a s i c r o c k s w h i c h seem t o be c o n f o r m a b l e w i t h t h e metamorphosed s e d i m e n t s , f o r m some 55 p e r c e n t o f t h e E c s t a l l s e r i e s . The metamorphosed s e d i m e n t s c o n s i s t o f numerous r o c k t y p e s , t h e m a j o r d i v i s i o n s o f w h i c h a r e l i s t e d i n t h e t a b l e o f r o c k u n i t s . Of a l l t h e s e t y p e s , t h e p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s e s a r e t h e most a b u n d a n t . They make up a b o u t 40 p e r c e n t o f t h e r o c k s o f t h e septum. Of t h e o t h e r t y p e s t h e q u a r t z i t e s and k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s a r e t h e most i m p o r t a n t . E a c h o f t h e s e makes up a b o u t one p e r c e n t o f t h e r o c k s o f t h e septum. The metamorphosed i g n e o u s r o c k s a r e f o u n d t h r o u g h o u t t h e E c s t a l l s e r i e s c u t t i n g t h e o t h e r r o c k t y p e s ; b u t - a r e p a r  t i c u l a r l y common i n t h e s o u t h e r n p a r t o f t h e septum. The " p l a g i o c l a s e a m p h i b o l i t e s " a r e a l s o p a r t i c u l a r l y common i n t h e s o u t h e r n h a l f o f t h e map a r e a and t h e p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s e s i n t h e n o r t h e r n h a l f . C o n s i d e r a b l e 17 i n t e r b e d d i n g between t h e s e u n i t s o c c u r s . The q u a r t z i t e s , k y a n i t e - s t a u r o l i t e - k y a n i t e m i c a s c h i s t s and l i m e s t o n e s o c c u r i n t e r b e d d e d w i t h t h e " p l a g i o c l a s e a m p h i b o l i t e s " i n t h e s o u t h e r n p a r t o f t h e septum o n l y . The g r a p h i t i c q u a r t z - p l a g i o c l a s e s c h i s t s o c c u r i n t e r b e d d e d w i t h t h e " p l a g i o c l a s e a m p h i b o l i t e s " i n b o t h t h e s o u t h e r n and n o r t h e r n p a r t s o f t h e septum. The one known o c c u r r e n c e o f t h e a n d e s i t i c ( ? ) r o c k s i s i n t h e T r e n c h B r o o k s a r e a where t h e y f o r m a 10 f o o t by 3 f o o t b o u d i n . T h i s r o c k t y p e i s b e l i e v e d t o h a v e b e e n i n t r u d e d l a t e r t h a n t h e m a i n p e r i o d o f d e f o r m a t i o n . I t s r e l a t i o n s h i p t o t h e o t h e r i n t r u s i v e r o c k s i s unknown. The C o a s t I n t r u s i o n s examined on Hawkesbury I s l a n d c o n s i s t o f t h e N o r t h H i l l i n t r u s i o n , w h i c h i s a m a r g i n a l f a c i e s o f one o f t h e m a i n b a t h o l i t h i c masses t o t h e n o r t h o f t h e septum, and s e v e r a l s m a l l s t o c k - l i k e p l u t o n s and i n n u m e r a b l e p e g m a t i t e v e i n s and dykes and s i l l s o f g r a n i t i c r o c k s w i t h i n t h e septum. The s t o c k - l i k e p l u t o n s a r e t h e S i d e b a c o n L a k e p l u t o n , u n d e r l y i n g a t l e a s t 13 s q u a r e s m i l e s , t h e B e a v e r L a k e p l u t o n , u n d e r l y i n g a t l e a s t 4 s q u a r e m i l e s and t h e Danva p l u t o n u n d e r l y i n g a t l e a s t one s q u a r e m i l e . E a c h p l u t o n has a swarm o f g r a n i t i c d ykes a s s o c i a t e d w i t h i t . The w i d t h o f t h e z o n e s i n w h i c h t h e dyke swarms a r e f o u n d i s r o u g h l y p r o p o r t i o n a l i n w i d t h t o t h e s i z e o f t h e p l u t o n . The dyke swarm a r o u n d t h e S i d e b a c o n L a k e p l u t o n i s a b o u t 4 m i l e s w i d e , t h a t a r o u n d t h e B e a v e r L a k e p l u t o n i s one m i l e w i d e and t h a t a r o u n d t h e Danva p l u t o n 2000 t o 3000 f e e t w i d e . W i t h i n t h e s e a r e a s g r a n i t i c 18 r o c k s may l o c a l l y make up as much as 75 p e r c e n t o f t h e t o t a l o u t c r o p and a v e r a g e p e r h a p s 10 t o 15 p e r c e n t . O u t s i d e t h e s e a r e a s d y k e s a r e q u i t e s c a r c e . T h e r e a r e v e r y few dy k e s i n t h e v i c i n i t y o f t h e b a t h o l i t h e x p o s e d t o t h e n o r t h o f t h e septum on Hawkesbury I s l a n d . R e c e n t d e p o s i t s a r e c o n f i n e d m a i n l y t o t h e v a l l e y s . They c o n s i s t o f t a l u s , a l l u v i a l f a n s and o t h e r a l l u v i a l d e  p o s i t s and p o s t - g l a c i a l b l u e - g r e y m a r i n e c l a y s . I t i s p r o b a b l e some m o r a i n a l m a t e r i a l i s a l s o p r e s e n t , b u t none d e f i n i t e l y was i d e n t i f i e d . G l a c i a l e r r a t i c s a r e f o u n d s c a t t e r e d o v e r t h e r i d g e s t o a n a l t i t u d e o f 3300 f e e t . The a l l u v i a l d e p o s i t s a r e u n s t r a t i f i e d o r w e a k l y s t r a t i f i e d o u twash and c o n s i s t o f w e l l - r o u n d e d t o s u b - a n g u l a r r o c k f r a g m e n t s r a n g i n g f r o m b o u l d e r s f i v e f e e t o r more i n d i a m e t e r t o s i l t s i z e p a r t i c l e s . T h e y g e n e r a l l y c a r p e t t h e v a l l e y f l o o r s i n a t h i n v e n e e r t h r o u g h w h i c h t h e b e d r o c k common l y o u t c r o p s . T h e i r t h i c k n e s s i s b e l i e v e d t o be f i v e t o f i f t y f e e t t h r o u g h o u t most o f t h e v a l l e y s , a l t h o u g h t h e f a n s a t t h e heads o f some v a l l e y s a r e a p p a r e n t l y much t h i c k e r . The b l u e - g r e y m a r i n e c l a y s a r e f o u n d p r i n c i p a l l y i n A n g l e V a l l e y and i n t h e v i c i n i t y o f E v e l y n L a k e . T h e i r maximum r e c o r d e d e l e v a t i o n ( i n A n g l e V a l l e y ) i s 330 f e e t above . s e a l e v e l , p r o b a b l y i n d i c a t i n g a n i s o s t a t i c r e a d j u s t m e n t o f a t l e a s t 330 f e e t s i n c e t h e r e t r e a t o f t h e v a l l e y g l a c i e r i n t h i s v a l l e y . A t an e l e v a t i o n o f 250 f e e t i n A n g l e V a l l e y s e v e r a l 19 s p e c i m e n s o f S a x i c a v a a r c t i c a were c o l l e c t e d f r o m s i m i l a r c l a y s , e s t a b l i s h i n g t h e i r m a r i n e o r i g i n . U n f o r t u n a t e l y t h i s p e l e c y p o d has a s t r a t i g r a p h i c r a n g e o f M i o c e n e t o R e c e n t and a g e o g r a p h i c r a n g e f r o m Panama t o G r e e n l a n d , m a k i n g i t u s e l e s s f o r age d e t e r m i n a t i o n s o r d e t e r m i n a t i o n s o f c l i m a t i c c o n d i t i o n s . The b l u e - g r e y c l a y i s b edded and i n most p l a c e s i s h o r i z o n t a l . However, a t t h e l o c a l i t y i n A n g l e V a l l e y where t h e s p e c i m e n s o r > S a x i c a v a a r c t i c a were c o l l e c t e d , i t s t r i k e s n o r t h 4 0 ° e a s t and d i p s 2 0 ° S.E. I t i s p o s s i b l e t h i s a t t i t u d e may be due t o s l u m p i n g as t h i s e x p o s u r e i s i n a s t r e a m bank. CHAPTER I I I THE METAMORPHIC ROCKS INTRODUCTION The m e t a m o r p h i c r o c k s a r e s u b - d i v i d e d i n t o t h e u n i t s l i s t e d i n t h e T a b l e o f Rock U n i t s and i n t o s m a l l e r u n i t s on t h e b a s i s o f m i n e r a l o g i c a l c o m p o s i t i o n , f i e l d r e l a t i o n s h i p s and t e x t u r a l f e a t u r e s . The r o c k s i n c l u d e d i n t h e m e t a - s e d i - m e n t a r y c a t e g o r y have a l a c k o f c r o s s c u t t i n g r e l a t i o n s h i p s and a l l have c o m p o s i t i o n s c o m p a t i b l e w i t h p o s s i b l e s e d i m e n t a r y o r i g i n . R e c r y s t a l l i z a t i o n has d e s t r o y e d any s e d i m e n t a r y f e a t u r e s w h i c h may have b e e n p r e s e n t i n t h e s e r o c k s . The " p l a g i o c l a s e a m p h i b o l i t e s " a r e r a t h e r a n o m a l o u s . T h e i r mode o f o c c u r r e n c e s u g g e s t s a s e d i m e n t a r y o r i g i n b u t t h e i r compos i t i o n i s f a r t o o b a s i c f o r a n o r m a l s e d i m e n t . The " i g n e o u s a m p h i b o l i t e s " have c o m p o s i t i o n s and i n most o c c u r r e n c e s t e x  t u r e s w h i c h i n d i c a t e t h e y a r e n o t o f s e d i m e n t a r y o r i g i n . PETROLOGY OF THE PLAGIOCLASE AMPHIBOLITES The p l a g i o c l a s e a m p h i b o l i t e s a r e r o c k s c o n t a i n i n g more t h a n 25 p e r c e n t and l e s s t h a n 50 p e r c e n t o f combined h o r n  b l e n d e , b i o t i t e and d i o p s i d e . Rocks w i t h l e s s t h a n 25 p e r c e n t o f t h e s e m i n e r a l s a r e i n c l u d e d i n t h e m e t a - s e d i m e n t a r y d i v i s i o n and those w i t h more t h a n 50 p e r c e n t i n t h e m e t a - i g n e o u s d i v i s i o n . The plagioclase amphibolites are subdivided into (1) plagioclase-hornblende-biotite rocks, lacking diopside and containing 5 per cent or less of epidote group minerals (2) plagioclase-hornblende-biotite-epidote rocks, similar to the above but with more than 5 per cent epidote; (3) plagioclase-hornblende-biotite-diopside amphibolites; (4) plagioclase-staurolite amphibolites, containing both staurolite and hornblende. These divisions are further subdivided on the basis of the relative proportions of these minerals. A l l the plagioclase amphibolites havec.a similar appear ance in hand specimen and may be described together. They are dark grey, generally fine-grained ( 1 mm.) but occasionally medium-grained ( 1 mm to 5 mm) rocks most of which are grano- blastic in texture. A few specimens are porphyroblastic. The plagioclase amphibolites weather to various shades of brown or reddish brown. The weathered layer is normally quite thin, 1/4 inch or less, but in sulphide rich rocks i t may be several inches thick, making i t d i f f i c u l t to take a fresh sample. Turner defines schistosity or foli a t i o n (which he considers to be synonymous) as "any parallel structure, of metamorphic origin, that induces a more or less planar f i s s i - b i l i t y in a rock.""'' In these rocks the degree of f o l i a t i o n is determined mainly by the percentage of biotite, chlorite and, to a lesser extent, muscovite, in the rock. Those rocks 1 H. Williams, F.J. Turner, CM. Gilbert, Petrography (W.H.Freeman and Co., 1955)) p. 169. l a c k i n g b i o t i t e h a v e , i n hand s p e c i m e n , a t b e s t an extremely- weak s c h i s t o s i t y w h i c h i s m a i n l y due t o a p l a n a r a l i g n m e n t o f u n u s u a l l y f l a t and t a b u l a r h o r n b l e n d e c r y s t a l s , as w e l l as some s l i g h t t e n d e n c y f o r t h e q u a r t z and f e l d s p a r t o be f l a t t e n e d p a r a l l e l t o t h e h o r n b l e n d e . The l a t t e r t e n d e n c y i s n o t i c e a b l e o n l y i n medium g r a i n e d v a r i e t i e s and o n l y t h e n a f t e r e t c h i n g w i t h h y d r o f l u o r i c a c i d . L i n e a t i o n g e n e r a l l y i s weak o r l a c k i n g . S e g r e g a t i o n i n t o m a f i c - r i c h and m a f i c - p o o r bands i s p r e s e n t i n one o r more s p e c i m e n s o f a l l t h e s u b - t y p e s e x c e p t t h e p l a g i o c l a s e - h o r n b l e n d e - s t a u r o l i t e a m p h i b o l i t e . I t i s q u i t e common b u t i n most o c c u r r e n c e s i s n o t w e l l d e v e l o p  ed, s e p a r a t i o n o f t h e l i g h t c o l o r e d and d a r k c o l o r e d m i n e r a l s b e i n g f a r f r o m c o m p l e t e . The a v e r a g e w i d t h o f t h e bands i s g e n e r a l l y 1 mm (1/25 i n c h ) o r l e s s . N e a r t h e e a s t e r n t i p o f E v e l y n L a k e , however, an a r e a o f a m p h i b o l i t e s e v e r a l h u n d r e d f e e t w i d e has bands up t o 15 cm (6 i n c h e s ) a c r o s s , a l t h o u g h a v e r a g i n g o n l y 5 t o 7.5 cm. (2 t o 3 i n c h e s ) . (1) The p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s The p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s f o r m t h e l a r g e s t s u b d i v i s i o n o f t h e p l a g i o c l a s e a m p h i b o l i t e s . Of 24 t h i n s e c t i o n s o f t h e a m p h i b o l i t e g r o u p r o c k s , 17 b e l o n g t o t h i s s u b d i v i s i o n . T h e s e r o c k s may be f u r t h e r d i v i d e d i n t o p l a g i o c l a s e - h o r n b l e n d e a m p h i b o l i t e s c o n t a i n i n g 5 p e r c e n t o r l e s s o f b i o t i t e ; p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e a m p h i b o l i t e s , c o n t a i n i n g g r e a t e r t h a n 5 p e r c e n t e a c h o f h o r n b l e n d e and o f b i o t i t e , and p l a g i o c l a s e - b i o t i t e g n e i s s e s , c o n t a i n i n g 5 p e r 23 c e n t o r l e s s o f h o r n b l e n d e . T h e s e d i v i s i o n s a r e so s m a l l t h a t t h e y a r e n o t mappable f i e l d u n i t s , on t h e p r e s e n t s c a l e o f m apping. The p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s a r e t h e m a i n r o c k t y p e s i n t h e m a j o r s o u t h e r n band o f p l a g i o c l a s e a m p h i b o l i t e s . F i g u r e 2 shows t h e a p p r o x i m a t e r a n g e o f c o m p o s i t i o n o f F i g u r e 2. ACF d i a g r a m f o r t h e a l m a n d i n e a t a m p h i b o l i t e f a c i e s , s t a u r o l i t e - q u a r t z s u b f a c i e s , s h o w i n g t h e r a n g e o f c o m p o s i t i o n o f t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s c o n s i d e r e d t o be made up o f s t a b l e m i n e r a l a s s e m b l a g e s . F o r e a s e o f p l o t t i n g , a r b i t r a r y c o m p o s i t i o n s o f b i o t i t e and h o r n b l e n d e , i n d i c a t e d by c r o s s e s , were assumed. The c o m p o s i t i o n c h o s e n f o r t h e h o r n b l e n d e , w h i c h w i l l be shown p r o b a b l y t o be a r a t h e r a l u m  i n o u s v a r i e t y , c o n t a i n s t h e maximum amount o f aluminum p o s s i b l e w i t h o u t m a k i n g any o f t h e s e r o c k s f a l l i n t h e s t a u r o l i t e - e p i d o t e - a l m a n d i n e f i e l d o f t h e ACF d i a g r a m . A h i g h a l u m i n a , l o w m a g n e s i a c o m p o s i t i o n was c h o s e n f o r t h e b i o t i t e a s a t r i a l and e r r o r p l o t t i n g o f c e r t a i n s p e c i m e n s showed t h i s was t h e most s a t i s f a c t o r y . P l a g i o c l a s e - h o r n b l e n d e a m p h i b o l i t e and p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e a m p h i b o l i t e a r e t h e commonest s u b - t y p e s o f t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s . The p l a g i o c l a s e - b i o t i t e g n e i s s e s a r e c o m p a r a t i v e l y r a r e . The c o m p o s i t i o n a l r a n g e o f t h e s e t y p e s a r e as f o l l o w s : 1. P l a g i o c l a s e - H o r n b l e n d e A m p h i b o l i t e ( b a s e d on 8 t h i n s e c t i o n s ) M i n e r a l T o t a l V a r i a t i o n i n P e r c e n t a g e Mean P e r c e n t a g e H o r n b l e n d e 30 - 35% W° B i o t i t e 1 - 3% 1% P l a g i o c l a s e 24 - 61% 59% (An2Qto A n 4 0 ) a Q u a r t z - w 3 - 22# 5% E p i d o t e none - 5% JO A p a t i t e S phene <1% C h l o r i t e none - 2$ S e r i c i t e none - 1% " I r o n O r e " <1% & A l l d e t e r m i n a t i o n s o f An c o n t e n t were made by m e a s u r i n g X'A010 f o r s e c t i o n s l a o r by m e a s u r i n g N x ' o n c l e a v a g e f r a g  ments u s i n g s p e c i a l i n d e x o i l s and a m o n o c h r o m a t i c l i g h t s o u r c e . 25 2. P l a g i o c l a s e - H o r n b l e n d e - B i o t i t e A m p h i b o l i t e ( b a s e d on 7 t h i n s e c t i o n s ) M i n e r a l T o t a l V a r i a t i o n i n P e r c e n t a g e s H o r n b l e n d e B i o t i t e P l a g i o c l a s e (An^o t o A n 4 3 ) Q u a r t z E p i d o t e A l m a n d i n e A p a t i t e Sphene S e r i c i t e " I r o n O r e " 15 - 35% 10 - 20$ 40 - 5 - 15% none - 5% none - 2% < 1% < 1 - 2% < 1% none - 1% Mean P e r c e n t a g e 25$ 12% 48% 8% 2% 3. P l a g i o c l a s e - B i o t i t e G n e i s s ( b a s e d on 2 t h i n s e c t i o n s ) M i n e r a l T o t a l V a r i a t i o n i n P e r c e n t a g e s H o r n b l e n d e B i o t i t e P l a g i o c l a s e (An3i t o Anog) Q u a r t z E p i d o t e A l m a n d i n e C h l o r i t e M u s c o v i t e S e r i c i t e A p a t i t e " I r o n O r e " none 20 54 27$ 63% io - 15% none < 1 none 1% < 1% <1% < 1% Mean P e r c e n t a g e T h e s e s u b - t y p e s a r e q u i t e s i m i l a r i n t e x t u r e i n t h i n - s e c t i o n . Most s p e c i m e n s o f f i n e - g r a i n e d p l a g i o c l a s e - h o r n - b l e n d e a m p h i b o l i t e s have a w e l l d e v e l o p e d g r a n o b l a s t i c t e x t u r e . I n a l l m e d i u m - g r a i n e d p l a g i o c l a s e - h o r n b l e n d e a m p h i b o l i t e s , and i n a l l t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e a m p h i b o l i t e s , most o f t h e h o r n b l e n d e g r a i n s and some o f t h e p l a g i o c l a s e g r a i n s , commonly e n c l o s e s m a l l g r a i n s o f o t h e r m i n e r a l s , so t h a t a s i e v e o r p o i k i l o b l a s t i c t e x t u r e i s d e v e l o p e d . H o r n b l e n d e i n 26 t h e p l a g i o c l a s e - b i o t i t e g n e i s s e s a l s o has . t h i s s i e v e t e x t u r e . H o r n b l e n d e i s g e n e r a l l y e u h e d r a l b u t i n some s p e c i m e n s s u b h e d r a l . I t i s r a r e l y t w i n n e d on (100) and i s b i a x i a l n e g a t i v e w i t h a l a r g e 2V. T h e r e i s a s y s t e m a t i c v a r i a t i o n i n p l e o c h r o i c f o r m u l a and Z A c as shown i n t h e f o l l o w i n g t a b l e . Rock Type P l a g i o c l a s e - b i o t i t e g n e i s s P l a g i o c l a s e - h o r n b l e n d e - b i o t i t e a m p h i b o l e P l a g i o c l a s e - h o r n b l e n d e a m p h i b o l i t e P l a g i o c l a s e - h o r n b l e n d e a m p h i b o l i t e P l e o c h r o i c f o r m u l a X p a l e y e l l o w Y p a l e b l u e g r e e n Z b l u e g r e e n X p a l e y e l l o w Y b l u e g r e e n Z d a r k g r e e n 2 1 ° - 2 2 c 22°-23c X p a l e y e l l o w 23°-24° Y b r o w n i s h g r e e n i s h Z d a r k b r o w n i s h g r e e n X p a l e brown Y brown Z d a r k brown I n c r e a s i n g l y deep p l e o c h r o i c c o l o r s and h i g h e r ZAc w i t h i n c r e a s i n g g r a d e o f metamorphism have been n o t e d by T u r n e r 2 and Compton^. The f o r m e r f o u n d t h a t most o f t h e h o r n b l e n d e s o f t h e a m p h i b o l i t e f a c i e s have Z = deep b l u e g r e e n b u t a t h i g h e r g r a d e s o f metamorphism ( w i t h i n t h e f a c i e s ) Z = b r o w n i s h g r e e n . 2 H . W i l l i a m s , F . J . T u r n e r , C M . G i l b e r t , P e t r o g r a p h y (W.H. F reeman and Co., 1955)> p. 242 3 R.R.Compton, " S i g n i f i c a n c e o f A m p h i b o l e P a r a g e n e s i s i n t h e B i d w e l l B a r R e g i o n , C a l i f o r n i a , " A m e r i c a n M i n e r a l o g i s t S e p t . 1958, pp. 890-907. 27 Both Compton4" and Eskola^ analysed a number of horn blendes and found an increase in A120^, MgO and CaO and decrease in FeO and F e , ^ with a higher grade of metamorphism. They suggest that the color of hornblende is controlled mainly by the amount of alumina, a deeply colored hornblende being a highly aluminous one. Biotite occurs as tabular plates, euhedral apart from ragged terminations. In thin sections containing horn blende most of the biotite is marginal to the hornblende or cuts through i t , and is obviously a later mineral, than the horn blende which i t replaces. Most of the biotite grains are parallel or sub-parallel to the f o l i a t i o n , but in one section of biotite gneiss, in which the biotite lies along the grain boundaries of the plagioclase and quartz, many biotite plates have developed along these boundaries at large angles to the general foliation. These are noticeably smaller than the biotite plates parallel to the fol i a t i o n . Most of the biotite is a strongly colored variety which is pleochroic from deep reddish brown (Z) to pale brown or straw yellow (X) but in some sections of plagioclase-hornblende-biotite amphi- bolite, Z is a very dark brown and in a section of plagio- clase-biotite gneiss, i t is brown with a greenish cast. In one 4 Compton, loc. c i t . 5 P. Eskola, "On the petrology of the Orijarvd region in southwestern Finland, "Comm. Geol. Finlande B u l l . No. 40 (1914), p. 113. t h i n s e c t i o n o f p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e a m p h i b o l i t e t h e b i o t i t e , i n t h e v i c i n i t y o f an opaque m i n e r a l , p r o b a b l y p y r i t e , i s b l e a c h e d and i s p l e o c h r o i c f r o m g o l d e n y e l l o w t o p a l e s t r a w y e l l o w . The b l e a c h e d p o r t i o n has low b i r e f r i n g e n c e , p e r h a p s i n d i c a t i n g a l t e r a t i o n t o w a r d s a c h l o r i t e . B i o t i t e i s b e n t and f r a c t u r e d i n one t h i n s e c t i o n b u t i n most s e c t i o n s shows no e v i d e n c e o f s t r a i n . P l a g i o c l a s e g e n e r a l l y o c c u r s i n l a r g e s u b h e d r a l t o ( r a r e l y ) a n h e d r a l g r a i n s , but a l s o o c c u r s i n s m a l l r o u n d e d i n c l u s i o n s i n p o i M l o b l a s t i c h o r n b l e n d e . The p l a g i o c l a s e i n a l l o f t h e s e r o c k t y p e s i s , as shown i n t h e t a b l e on page 25» g e n e r a l l y medium o r s l i g h t l y s o d i c a n d e s i n e , b u t i s o c c a s  i o n a l l y h i g h l y s o d i c a n d e s i n e o r h i g h l y c a l c i c o l i g o c l a s e . The f e l d s p a r i s e x c e p t i o n a l l y f r e s h and s e r i c i t e i s v e r y s c a r c e . A few p l a g i o c l a s e g r a i n s a r e w e a k l y z o n e d . The o n l y s a t i s f a c t o r y d e t e r m i n a t i o n i n d i c a t e d a c o r e o f A n ^ i and a r i m o f An-jg, i . e . r e v e r s e d z o n i n g . Most o f t h e t w i n n e d g r a i n s have o n l y a l b i t e t w i n n i n g . Many o f t h e a l b i t e t w i n s , p r o b a b l y 60 p e r c e n t o r more, c o n s i s t o f as few as t h r e e t o e i g h t s u b - i n d i v i d u a l s . I n most g r a i n s i n d i v i d u a l t w i n l a m e l l a e a r e v e r y b r o a d , a l t h o u g h n a r r o w l a m e l l a e a r e n o t r a r e . P e r h a p s 1 o r 2 p e r c e n t o f t h e t w i n n e d g r a i n s have complex t w i n n i n g o f a t y p e i n w h i c h two s e t s o f p o l y s y n t h e t i c t w i n s d e v e l o p a t , o r n e a r l y a t , r i g h t a n g l e s t o one a n o t h e r . Where t h i s t y p e o f t w i n n i n g i s p r e s e n t one s e t o f l a m e l l a e a r e u s u a l l y q u i t e i n d i s t i n c t . I t i s n o t d e f i n i t e what t y p e s o f t w i n s a r e 29 represented here, but albite-pericline is probably the common est combination which would have this appearance. No Carlsbad- albite twins were noted. Quartz occurs as large anhedral grains and also as small inclusions in poikiloblastic hornblende, and more rarely in plagioclase. In one thin section of plagioclase-horn- blende amphibolite vein quartz is also present. It is not a major mineral, generally forming between 5 per cent and 15 per cent of the rock. As i t is d i f f i c u l t to distinguish from untwinned plagioclase, particularly as this is unaltered or nearly so in most thin-sections, percentage estimates were checked by making optical determinations on ten grains per section, and by hydrofluoric acid etching on several specimens. Quartz only rarely shows evidence of strain. The common epidote group mineral, present, pistacite, is colorless, has a large negative 2V, anomalous "berlin blue" interference colors and a birefringence of approximately 0.03, which corresponds to a composition of about 18 per cent BX^Fe-^SI^O^ a n d $2 per cent HCa^l^Si^O^' T t i e c l i n o " zoisite-pistacite boundary is drawn at about 10 per cent IK^Fe^S 130^ 2• T n e maximum known percentage of IK^Fe^Si^O-^ in pistacite is about 40 per cent, so i t would seem this is a moderately iron-poor pistacite. Turner'7 notes that the epidote 6 A.N. Winchell, Elements of Optical Mineralogy Part II (John Wiley and Sons, 1948), p. 313 7 H.Williams, F.J. Turner, C.M.Gilbert, Petrography (W.H.Freeman and Co., 1955)» p. 242. 30 ( p i s t a c i t e ) o f a m p h i b o l i t e s i s e i t h e r c o l o r l e s s o r v e r y p a l e y e l l o w i s h . I n one t h i n s e c t i o n a p l e o c h r o i c , y e l l o w t o c o l o r  l e s s p i s t a c i t e o c c u r s as a r i m s u r r o u n d i n g a g r a i n o f " i r o n o r e " , p r o b a b l y p y r i t e . The " i r o n o r e " i s l a t e r t h a n any o f t h e o t h e r m i n e r a l s , and m i g h t p o s s i b l y be h y d r o t h e r m a l , as t h i s i s a r a t h e r a l t e r e d t h i n s e c t i o n w i t h b l e a c h e d b i o t i t e and a h i g h p e r c e n t a g e o f o p a q u e s . I t seems p r o b a b l e t h i s e p i d o t e i s t h e r e s u l t o f h y d r o t h e r m a l a l t e r a t i o n o f p l a g i o c l a s e . An e p i d o t e o f u n d o u b t e d h y d r o t h e r m a l o r i g i n o c c u r s i n a t h i n s e c t i o n o f p l a g i o c l a s e - h o r n b l e n d e a m p h i b o l i t e . T h i s i s a n o n - p l e o c h r o i c , c o l o r l e s s p i s t a c i t e w i t h p r o p e r t i e s v e r y much l i k e t h o s e o f t h e u s u a l p i s t a c i t e i n t h e s e r o c k s , b u t i t o c c u r s a l o n g t h e m a r g i n s o f p y r i t e - q u a r t z v e i n s and i r r e g u l a r masses o f p y r i t e , and i s a l w a y s a n h e d r a l and c l e a r l y r e p l a c e s p l a g i o c l a s e . A l l a n i t e o c c u r s i n a t h i n s e c t i o n o f p l a g i o c l a s e - b i o t i t e g n e i s s . I t i s p l e o c h r o i c d a r k brown t o p a l e brown, and o c c u r s as c o r e s s u r r o u n d e d by r i m s o f c o l o r l e s s p i s t a c i t e o f s i m i l a r c r y s t a l o r i e n t a t i o n but d i f f e r e n t e x t i n c t i o n p o s i t i o n . Most g r a i n s o f e p i d o t e g r o u p m i n e r a l s a r e e u h e d r a l o r s u b h e d r a l , and o c c u r on g r a i n b o u n d a r i e s between h o r n b l e n d e o r 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 f o r m i s p a r t i c u l a r l y w e l l d e v e l o p e d when t h e e p i d o t e i s p a r t i a l l y e n c l o s e d i n b i o t i t e , w h i c h a p p a r e n t l y o f f e r e d l e s s r e s i s t a n c e t o i t s c r y s t a l l i z a t i o n t h a n h o r n b l e n d e o r p l a g i o c l a s e . A l m a n d i n e g a r n e t i s a r a r e a c c e s s o r y m i n e r a l . I t i s f o u n d i n o n l y t h r e e t h i n s e c t i o n s , two o f p l a g i o c l a s e -31 h o r n b l e n d e - b l o t i t e a m p h i b o l i t e and one o f p l a g i o c l a s e - b i o t i t e g n e i s s . I t o c c u r s i n c o l o r l e s s t o p a l e p i n k , i s o t r o p i c , r a g g e d a n h e d r a l g r o u p s o f g r a i n s , t o e u h e d r a l , p o r p h y r o b l a s t s w h i c h have s i e v e t e x t u r e . I n c l u s i o n s a r e m a i n l y o f p l a g i o c l a s e , b u t some a r e o f s p h e n e , a p a t i t e , q u a r t z , b i o t i t e and " i r o n o r e s " . The i n c l u s i o n s do n o t show any p r e f e r r e d o r i e n t a t i o n and t h e r e i s no e v i d e n c e o f any " s n o w b a l l " o r s i m i l a r e f f e c t s . B i o t i t e - and h o r n b l e n d e - r i c h bands a p p e a r t o f l o w a r o u n d t h e g a r n e t s . A p a t i t e and sphene a r e t h e o n l y common a c c e s s o r y m i n e r a l s . A p a t i t e , i n s m a l l , r o u n d e d g r a i n s t o e u h e d r a l , s h o r t s t u b b y , p r i s m a t i c c r y s t a l s , o c c u r s s c a t t e r e d t h r o u g h o u t c r y s t a l s o f t h e m a j o r m i n e r a l s and a l s o i s f o u n d a t g r a i n b o u n d a r i e s . Sphene i s f o u n d i n a l l t h i n - s e c t i o n s o f t h e p l a g i o  c l a s e - h o r n b l e n d e and p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e amphi b o l i t e , b u t i s a b s e n t i n t h e p l a g i o c l a s e - b i o t i t e g n e i s s . I t i s a f a i n t l y p l e o c h r o i c brown v a r i e t y w h i c h o c c u r s as r o u n d e d g r a n u l e s and wedge-shaped c r y s t a l s s c a t t e r e d t h r o u g h o u t t h e r o c k , b u t p a r t i c u l a r l y a t t h e b o u n d a r i e s between l a r g e r c r y s t a l s . C h l o r i t e o c c u r s as r o s e t t e s and f i b r o u s a g g r e g a t e s r e p l a c i n g h o r n b l e n d e and b i o t i t e i n t h e v i c i n i t y o f h y d r o - t h e r m a l p y r i t e i n one s p e c i m e n o f p l a g i o c l a s e - b i o t i t e g n e i s s . I t i s a l s o f o u n d r e p l a c i n g b i o t i t e and a l m a n d i n e I n t h e o t h e r t h i n s e c t i o n o f t h i s r o c k u n i t . The c h l o r i t e i s p l e o c h r o i c f r o m g r e e n t o c o l o r l e s s , l e n g t h f a s t , has p a r a l l e l o r n e a r l y p a r a l l e l e x t i n c t i o n , and anomalous p a l e y e l l o w g r e y i n t e r  f e r e n c e c o l o r s . 32 " I r o n o r e s " c o n s i s t c h i e f l y o f p y r i t e and m a g n e t i t e . The p y r i t e i s p r o b a b l y p a r t i a l l y h y d r o t h e r m a l i n o r i g i n as . i t .forms v e i n s i n one s e c t i o n and i s s u r r o u n d e d by a z o n e o f p i s t a c i t e i n a n o t h e r s e c t i o n . I n some t h i n s e c t i o n s t h e n o r m a l l y opaque " i r o n o r e s " a r e p a r t i a l l y o r w h o l l y a l t e r e d t o a r e d d i s h t r a n s l u c e n t m a t e r i a l w h i c h i s p r o b a b l y h e m a t i t e o r l i m o n i t e . (2) The p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e - e p i d o t e r o c k s T h i s u n i t f orms a r a t h e r s m a l l s u b d i v i s i o n o f t h e s e d i m e n t a r y a m p h i b o l i t e s . On t h e b a s i s o f t h i n s e c t i o n s t h i s r o c k t y p e i s b e l i e v e d t o be p a r t i c u l a r l y abundant i n t h a t p a r t o f t h e mai n p l a g i o c l a s e a m p h i b o l i t e band w h i c h e x t e n d s f r o m t h e west s i d e o f A n g l e V a l l e y n o r t h - w e s t t o t h e s e a , and f r o m t h e s o u t h s i d e o f I c e - C a k e Lake s o u t h - w e s t t o t h e c o n t a c t w i t h t h e S i d e b a c o n L a k e s t o c k . T h e s e r o c k s a l s o o c c u r e l s e w h e r e t h r o u g h o u t t h e m a i n p l a g i o c l a s e a m p h i b o l i t e band, b u t t h e y a r e o f v e r y m i n o r e x t e n t . O u t s i d e o f t h i s band t h e o n l y a r e a t h e s e r o c k s a r e known t o o c c u r i n i s Wye V a l l e y where t h e y a r e f o u n d i n t e r b e d d e d w i t h p l a g i o c l a s e - q u a r t z - K f e l d s p a r augen g n e i s s . The m a j o r m i n e r a l s i n t h e f o u r t h i n s e c t i o n s made o f t h e s e r o c k s a r e as f o l l o w s : T h i n S e c t i o n Number E p i d o t e 6% 30% 15% H o r n b l e n d e 30% 28$ 3% — B i o t i t e 25% 25% P l a g i o c l a s e ^ (Anon t o An Q ) Q u a r t s & — 27% A-2% 4-3% Wo 10% 16% ft D e t e r m i n e d by m e a s u r i n g X'A010 f o r s e c t i o n s l a T h i n s e c t i o n #17-5 has v e r y w e l l d e v e l o p e d b a n d i n g . The bands v a r y i n c o m p o s i t i o n f r o m 95 p e r c e n t e p i d o t e , 5 p e r c e n t h o r n b l e n d e t o 45 p e r c e n t e p i d o t e , 55 p e r c e n t h o r n b l e n d e . T e x t u r e i s g e n e r a l l y g r a n o b l a s t i c . I n some s e c t i o n s h o r n b l e n d e may be p o r p h y r o b l a s t i c and have s i e v e t e x t u r e ( s e e f i g u r e s 4 and 5) E p i d o t e i n some s e c t i o n s o c c u r s as a m o s a i c o f s m a l l , r o u n d e d t o s u b h e d r a l g r a i n s and i n o t h e r s e c t i o n s as i n d i v i d u a l s u b h e d r a l t o e u h e d r a l c r y s t a l s most o f w h i c h o c c u r on t h e b o r d e r o f b i o t i t e f l a k e s o r c o m p l e t e l y e n c l o s e d by b i o t i t e . The e p i d o t e i s p i s t a c i t e w h i c h has t h e same p r o p e r  t i e s as t h e p i s t a c i t e i n t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s e x c e p t i n one t h i n s e c t i o n where t h e b i r e f r i n g e n c e i s 0.021 t o 0.023, c o r r e s p o n d i n g t o 13 m o l e c u l a r p e r c e n t o f HCa^Fe^Si^O-j^. H o r n b l e n d e i s v e r y s i m i l a r t o t h e h o r n b l e n d e i n t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s i n o c c u r r e n c e and p r o p  e r t i e s . Z A c i s 21° - 22° and t h e p l e o c h r o i c f o r m u l a i s X = p a l e y e l l o w , Y = b l u e g r e e n and Z = d a r k g r e e n . 34 B i o t i t e i n most s e c t i o n s i s p l e o c h r o i c f r o m r e d d i s h brown o r g o l d e n brown (Z) t o s t r a w y e l l o w (X) b u t i n a few s e c t i o n s i s p l e o c h r o i c f r o m a v e r y d a r k brown t o s t r a w . P l a g i o c l a s e i s v e r y s i m i l a r i n o c c u r r e n c e and p r o p  e r t i e s t o t h a t i n t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s . A few g r a i n s a r e w e a k l y z o n e d . Q u a r t z o c c u r s as l a r g e a n h e d r a l g r a i n s and as s m a l l i n c l u s i o n s i n s i e v e t e x t u r e h o r n b l e n d e . I t shows no e v i d e n c e o f s t r a i n . A p a t i t e and sphene a r e t h e o n l y a c c e s s o r y m i n e r a l s . T h e y have s i m i l a r p r o p e r t i e s and o c c u r s i m i l a r l y t o t h e a p a t i t e and sphene i n t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s . S e r i c i t e r e p l a c e s f e l d s p a r s i n a l l s e c t i o n s , b u t i n m i n u t e q u a n t i t i e s . C h l o r i t e , o f t h e t y p e f o u n d i n t h e p l a g i o  c l a s e - h o r n b l e n d e - b i o t i t e r o c k s , i s f o u n d r e p l a c i n g b i o t i t e a r o u n d p y r i t e i n one s e c t i o n . The p y r i t e i s i n i r r e g u l a r masses o f no p a r t i c u l a r o r i e n t a t i o n and may be h y d r o t h e r m a l . A p a r t f r o m t h i s p y r i t e opaques a r e v e r y r a r e i n t h e s e s e c t i o n s . (3) The P l a g i o - c l a s e - h o r n b l e n d e - b i o t i t e - d i o p s i d e a m p h i b o l i t e s The p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e - d i o p s i d e amphi b o l i t e s a r e r e p r e s e n t e d by o n l y t h r e e t h i n s e c t i o n s . T h e y a r e a v e r y m i n o r d i v i s i o n o f t h e p l a g i o c l a s e a m p h i b o l i t e s . 35 The c o m p o s i t i o n o f t h e s e c t i o n s i s as f o l l o w s : T h i n S e c t i o n Numbers 8-6A 13-6 26-7 H o r n b l e n d e 30$ 20$ 6$ D i o p s i d e 3$ 25$ 7$ B i o t i t e 5$ — 22$ P l a g i o c l a s e 53$ 37$ 25$ (An -DQ t o A n A P ) Q u a r t z ^ 5$ 6$ 9$ E p i d o t e 3$ 10$ 13$ C h l o r i t e — — 2$ S e r i c i t e < 1$ <1$ 11$ Sphene < 1$ ^ 1$ < 1$ A p a t i t e < 1$ <1$ <1$ " I r o n O r e " < 1$ <1$ <1$ C a l c i t e — — 5$ I n t h i n - s e c t i o n t h e s e r o c k s have e s s e n t i a l l y t h e same t e x t u r e as t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e a m p h i b o l i t e s and p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e - e p i d o t e a m p h i b o l i t e s . One s e c t i o n has p o r p h y r o b l a s t i c h o r n b l e n d e and d i o p s i d e . Some o f t h e p o r p h y r o b l a s t s l i e a c r o s s t h e s c h i s t o s i t y . The o t h e r s e c t i o n s a r e e s s e n t i a l l y g r a n o b l a s t i c . H o r n b l e n d e o c c u r s as s u b h e d r a l g r a i n s r e p l a c i n g o r b e i n g r e p l a c e d by d i o p s i d e and as e u h e d r a l t o s u b h e d r a l g r a i n s e l s e w h e r e . T w i n n i n g on (100) was n o t e d b u t i s r a r e . V a r i a t i o n s i n Z A c a n d , t h e p l e o c h r o i c f o r m u l a f o l l o w : T h i n S e c t i o n s #8-6A, #26-7 X = p a l e y e l l o w Y = b l u e g r e e n Z = d a r k g r e e n Z A c = 22° - 23° 36 T h i n S e c t i o n #13-6 X = p a l e y e l l o w Y = g r e e n Z = b r o w n i s h g r e e n Z A c = 2 4 ° T h i s h o r n b l e n d e i s v e r y s i m i l a r t o t h e h o r n b l e n d e o f t h e o t h e r p l a g i o c l a s e a m p h i b o l i t e r o c k s . B i o t i t e r e p l a c e s b o t h h o r n b l e n d e and d i o p s i d e . I t i s p l e o c h r o i c f r o m g o l d e n brown o r r e d d i s h brown (Z) t o c o l o r  l e s s o r s t r a w y e l l o w (X). I n one t h i n s e c t i o n t h e b i o t i t e i s p a r t i a l l y a l t e r e d t o c h l o r i t e and s e r i c i t e . D i o p s i d e o c c u r s as e u h e d r a l t o s u b h e d r a l g r a i n s . I t i s c o l o r l e s s o r has a v e r y f a i n t p a l e g r e e n t i n t and i s n o t n o t i c e a b l y p l e o c h r o i c . The maximum i n t e r f e r e n c e c o l o r i s s e c o n d o r d e r y e l l o w . Z A c i s - 3 9 ° t o - 4 1 ° and t h e d i o p s i d e i s b i a x i a l p o s i t i v e w i t h a m o d e r a t e l y l a r g e 2V. The p l a g i o c l a s e , q u a r t z , e p i d o t e ( p i s t a c i t e ) , a p a t i t e and sphene p r e s e n t have t h e same p r o p e r t i e s and o c c u r r e n c e as i n t h e p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e r o c k s . " I r o n o r e " c o n s i s t s o f s m a l l e u h e d r a l and r a g g e d g r a i n s a n d , i n #26-7, a few l a r g e a n h e d r a l g r a i n s . T h e s e opaques a r e p r o b a b l y m a i n l y p y r i t e and m a g n e t i t e . The abundant s e r i c i t e i n #26-7 (11 p e r c e n t ) i n c l u d e s 3 p e r c e n t o f a l t e r e d b i o t i t e , and 8 p e r c e n t o f f i n e f e l t y mass f o r m e d by t h e a l t e r a t i o n o f f e l d s p a r . T h i s i s a h e a v i l y a l t e r e d r o c k , as th e c h l o r i t e and c a l c i t e w h i c h a r e p r e s e n t i n i t a r e a l s o p r o b a b l y a l t e r a t i o n p r o d u c t s , a l t h o u g h t h e c a l  c i t e may be i n t r o d u c e d v e i n m a t e r i a l . The c h l o r i t e has 37 p a r a l l e l e x t i n c t i o n , anomalous y e l l o w g r e y i n t e r f e r e n c e c o l o r s and a m o d e r a t e r e l i e f . I t o c c u r s r e p l a c i n g b i o t i t e . The c a l c i t e o c c u r s i n e l o n g a t e a r e a s composed o f m o s a i c s o f l a r g e g r a i n s . (4) The p l a g i o c l a s e - s t a u r o l i t e a m p h i b o l i t e s T h i s u n i t i s r e p r e s e n t e d by o n l y one t h i n s e c t i o n f r o m t h e head o f S o u t h B e a v e r V a l l e y , where t h i s r o c k t y p e f o r m s a band some 20 f e e t w i de on e i t h e r s i d e o f a 5 - f o o t w i d e band o f k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t . I t i s p r o b a b l e t h a t s i m i l a r r o c k s may o c c u r e l s e w h e r e i n t h e v i c i n i t y o f k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s , as t h i s u n u s u a l r o c k t y p e was n o t s u s p e c t e d t o e x i s t i n t h e f i e l d and t h i s i s t h e o n l y t h i n s e c t i o n made o f an a m p h i b o l i t e f r o m h e a r t h e c o n t a c t w i t h t h e s e r o c k s . The c o m p o s i t i o n o f t h i s s p e c i m e n i s s t a u r o l i t e 5 p e r c e n t , h o r n b l e n d e 20 p e r c e n t , b i o t i t e 15 p e r c e n t , c h l o r i t e 5 p e r c e n t , p l a g i o c l a s e 44 p e r c e n t , q u a r t z 4 p e r c e n t , a l m a n d i n e 5 p e r c e n t and l e s s t h a n 1 p e r c e n t o f a p a t i t e s p h e n e , " i r o n o r e s " and s e r i c i t e . A l m a n d i n e and s t a u r o l i t e o c c u r a s p o r p h y r o b l a s t s w i t h a p o o r l y - d e v e l o p e d s i e v e t e x t u r e . A l m a n d i n e p o r p h y r o b l a s t s r e a c h 1/2 i n c h (1 .2 cm) i n d i a m e t e r . The s t a u r o l i t e g r a i n s a r e much s m a l l e r and h i g h l y a l t e r e d . The o t h e r m i n e r a l s a r e m e d i u m - g r a i n e d . D e s p i t e t h e h i g h c o n t e n t o f b i o t i t e f o l i a t  i o n i s o n l y m o d e r a t e l y w e l l d e v e l o p e d . 38 H o r n b l e n d e o c c u r s i n e u h e d r a l t o s u b h e d r a l g r a i n s . Z^e i s 2 2 ° and t h e p l e o c h r o i c f o r m u l a i s X = p a l e y e l l o w , Y = b l u e g r e e n and Z = d a r k g r e e n . T h i s i s t h e common a l u m i n  ous h o r n b l e n d e o f t h e a m p h i b o l i t e s o f t h i s a r e a . S t a u r o l i t e o c c u r s i n i r r e g u l a r g r a i n s b e i n g r e p l a c e d by c h l o r i t e . I t c o n t a i n s a few n o n - o r i e n t a t e d i n c l u s i o n s o f q u a r t z and p l a g i o c l a s e . I t i s b i a x i a l p o s i t i v e w i t h a l a r g e 2V, has weak b i r e f r i n g e n c e , h i g h r e l i e f and s t r o n g p l e o - c h r o i s m f r o m deep g o l d e n y e l l o w t o p a l e y e l l o w . B i o t i t e i s f o u n d as s u b h e d r a l p l a t e s r e p l a c i n g h o r n  b l e n d e and p o s s i b l y s t a u r o l i t e . I t i s p l e o c h r o i c f r o m d a r k brown (Z) t o s t r a w y e l l o w ( X ) . C h l o r i t e o c c u r s as r a g g e d f l a k e s and a g g r e g a t e s o f f l a k e s r e p l a c i n g b i o t i t e , a l m a n d i n e , and s t a u r o l i t e . The c h l o r i t e r e p l a c i n g s t a u r o l i t e i s p a r t l y s t r u n g out p a r a l l e l t o t h e f o l i a t i o n b u t i n p a r t p r e s e r v e s t h e shape o f t h e o r i g i n a l s t a u r o l i t e g r a i n s . A l l t h e c h l o r i t e has p a r a l l e l o r n e a r l y p a r a l l e l e x t i n c t i o n , i s p l e o c h r o i c f r o m medium g r e e n t o p a l e g r e e n and has anomalous g r e y i s h y e l l o w i n t e r f e r e n c e c o l o r s . I t i s l e n g t h - f a s t . Most g r a i n s o f p l a g i o c l a s e a r e s u b h e d r a l . I t s com p o s i t i o n ( unzoned g r a i n s ) was d e t e r m i n e d as A n ^ by f i n d i n g N x ' f o r c l e a v a g e f l a k e s w i t h i n d e x o i l s and a sodium l i g h t s o u r c e , and as An44 by m e a s u r i n g X' A 010 f o r s e c t i o n s i - t o a , i . e . t h i s i s a s l i g h t l y c a l c i c a n d e s i n e . Many o f t h e p l a g i o  c l a s e g r a i n s a r e z o n e d . G e n e r a l l y z o n e b o u n d a r i e s a r e v e r y 39 vague and i r r e g u l a r . Some o f t h e z o n i n g a p p e a r s t o be c y c l i c b u t commonly i t i s o f t h e r e v e r s e t y p e . One d e t e r m i n a t i o n i n d i c a t e d a r i m o f A n ^ £ and a c o r e o f An.^. T w i n n i n g i s s i m p l e a l b i t e i n about t w o - t h i r d s o f t h e p l a g i o c l a s e and compl e x i n t h e r e s t . Q u a r t z o c c u r s as a n h e d r a l g r a i n s w h i c h o c c a s i o n a l l y h ave u n d u l a t o r y e x t i n c t i o n . I t a l s o i s f o u n d as i n c l u s i o n s i n s t a u r o l i t e and a l m a n d i n e . The o n l y a l m a n d i n e p o r p h y r o b l a s t f o u n d i n t h i s t h i n s e c t i o n i s a l m o s t e u h e d r a l , b u t m a r g i n a l a l t e r a t i o n t o c h l o r i t e has r o u n d e d i t . The g a r n e t has a few n o n - o r i e n t e d i n c l u s i o n s o f p l a g i o c l a s e and q u a r t z . I t i s p a l e p i n k and i s o t r o p i c . A p a t i t e o c c u r s i n u n u s u a l l y l a r g e g r a i n s i n t h i s t h i n s e c t i o n . The l a r g e s t a r e as b i g as t h e a v e r a g e p l a g i o  c l a s e g r a i n . I t forms e x t r e m e l y s h o r t , s t u b b y h e x a g o n a l p r i s m s w h i c h may be e u h e d r a l o r s u b h e d r a l . Sphene i s n o t v e r y common. I t has t h e same p r o p e r t i e s and o c c u r r e n c e as t h e s p h e n e i n t h e o t h e r t y p e s o f p l a g i o c l a s e a m p h i b o l i t e . " I r o n o r e " f o r m s l a r g e , a n h e d r a l g r a i n s r e p l a c i n g c h l o r i t e and t h e o t h e r m i n e r a l s . S e r i c i t e i s f o u n d i n s m a l l amounts as a f e l t y mass r e p l a c i n g p l a g i o c l a s e and a l s o p s e u d o - morphous a f t e r b i o t i t e and c h l o r i t e . F i g u r e 3. P h o t o m i c r o g r a p h o f p l a g i o c l a s e - h o r n b l e n d e a m p h i b o l i t e . P l a i n l i g h t X64. C o n t a i n s h o r n b l e n d e , p l a g i o c l a s e and q u a r t z and m i n o r sphene and a p a t i t e . F i g u r e 4. P h o t o m i c r o g r a p h o f p l a g i o c l a s e - h o r n b l e n d e - e p i d o t e r o c k . P l a i n l i g h t X24. C o a r s e p o r p h y r o b l a s t i c h o r n b l e n d e , f i n e g r a n u l a r e p i  d o t e , q u a r t z and p l a g i o c l a s e . Figure 5. Photomicrograph of plagioclase- hornblende- epidote rock. Polarized light. X64. Same thin section as Figure 4. Figure 6. Photomicrograph of plagioclase- biotite-epidote rock. Plain light. X24 Elongate biotite laths, euhedral to subhedral epidote, plagioclase and quartz. 42 F i g u r e 7. P h o t o m i c r o g r a p h o f p l a g i o c l a s e - b i o t i t e - e p i d o t e r o c k . P o l a r  i z e d l i g h t . X24. As F i g u r e 6. F i g u r e 8. P h o t o m i c r o g r a p h o f p l a g i o c l a s e - B i o p s i d e - h o r n b l e n d e a m p h i b o l i t e . P l a i n l i g h t . X64. D a r k h o r n b l e n d e , l i g h t e r d i o p s i d e , p l a g i o c l a s e , q u a r t z , and m i n o r a p a t i t e and s p hene. 43 F i g u r e 9. P h o t o m i c r o g r a p h o f p l a g i o c l a s e - s t a u r o l i t e a m p h i b o l i t e . P l a i n l i g h t . X24. S t a u r o l i t e , h o r n  b l e n d e , b i o t i t e , c h l o r i t e , a p a  t i t e , p l a g i o c l a s e and q u a r t z . F i g u r e 10. P h o t o m i c r o g r a p h o f p l a g i o c l a s e - s t a u r o l i t e a m p h i b o l i t e . P l a i n l i g h t . X24, s i m i l a r to F i g u r e 9. 44 PETROLOGY OF THE METASEDIMENTS M a j o r s u b d i v i s i o n s o f t h e m e t a s e d i m e n t s a r e as f o l l o w s : (1 (2 (3 (4 (5 (6 (7 (8 (9 (10 P l a g i o c l a s e - q u a r t z - b i o t i t e - h o r n b l e n d e g n e i s s P l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s K y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t S i l l i m a n i t e - q u a r t z - p l a g i o c l a s e g n e i s s G r a p h i t i c q u a r t z - p l a g i o c l a s e s c h i s t Q u a r t z i t e Q u a r t z - t r e m o l i t e - z o i s i t e r o c k s C r y s t a l l i n e l i m e s t o n e S e r i c i t e - e p i d o t e s c h i s t A l b i t i z e d and p o t a s h - e n r i c h e d r o c k s I t i s r e a l i z e d t h a t t h e d i v i s i o n s i n t h i s c l a s s i f i c  a t i o n a r e a r b i t r a r y , b u t i t i s f e l t t h a t e a c h d i v i s i o n r e  p r e s e n t s some r e a l d i f f e r e n c e i n c o m p o s i t i o n o r g r a d e o f metamorphism o f t h e r o c k and hence i s j u s t i f i e d . A d e t a i l e d p e t r o l o g i c a l d e s c r i p t i o n o f e a c h r o c k t y p e f o l l o w s : (1) P l a g i o c l a s e - q u a r t z - b i o t i t e - h o r n b l e n d e g n e i s s T h i s d i v i s i o n was c r e a t e d t o i n c l u d e r o c k s w h i c h do n o t c o n t a i n K f e l d s p a r b u t c o n t a i n l e s s t h a n 25 p e r c e n t o f combined b i o t i t e and h o r n b l e n d e . I t i s r e p r e s e n t e d by t h r e e t h i n s e c t i o n s , f r o m w i d e l y s c a t t e r e d a r e a s , and does n o t f o r m any mappable u n i t s a t t h e p r e s e n t s c a l e o f map p i n g . I t a p p a r e n t l y r e p r e s e n t s t h e e x t r e m e s o f c o m p o s i t i o n o f t h e two m a j o r m e t a m o r p h i c r o c k t y p e s , i . e . t h e K f e l d s p a r - b e a r i n g g n e i s s e s and p l a g i o c l a s e a m p h i b o l i t e s , and may be i m p o r t a n t i n a c o n s i d e r a t i o n o f t h e o r i g i n and c o n d i t i o n s o f f o r m a t i o n o f t h e l a t t e r . (See t h e s e c t i o n on t h e o r i g i n o f t h e m e t a  m o r p h i c r o c k s i n t h i s c h a p t e r ) . 45 In hand specimen these rocks have a close resemblance to the plagioclase amphibolites. They are fine-grained to medium grained dark grey rocks which appear to almost completely lack schistosity. Lineation is weak or lacking. Hornblende may be porphyroblastic. The composition of the three thin sections is as follows: Thin Section Number 15-3A 18-9 24T4 Plagioclase 57% 65% 55% (An,« - A n . , ) * Quartg *L 20% 15% 7% Hornblende 13% 15% 3% Biotite 8% 5% 15% Epidote <1% — 10% Sericite < 1% <1% Sphene <1% <1% < 1% Apatite <1% <1% < 1% "Iron Ore" <1% <1% < 1% & Determined by measuring N x' or x'A010 for sections -L a It is apparent in thin section that a l l these rocks actually have a f a i r l y strong foliation. Texturally they have l i t t l e else in common. One section has an essentially grano- blastic texture, modified by later dynamic metamorphism which has resulted in undulatory extinction In the quartz, granu lation of quartz and plagioclase and a series of parallel fractures in the section at a large angle to the original foliation. The other sections have porphyroblastic textures. Plagioclase is usually anhedral to subhedral. Twins are of the albite type (60%-Q5%) or are complex twins. No Carlsbad or Carlsbad-albite twins are definitely identified. 46 A l l q u a r t z g r a i n s a r e a n h e d r a l . U n d u l a t o r y e x t i n c t i o n i s w e l l d e v e l o p e d i n #15-3A and i s f o u n d i n two o r t h r e e g r a i n s i n #24-4. H o r n b l e n d e i s e u h e d r a l t o s u b h e d r a l e x c e p t when i t o c c u r s as r a g g e d a n h e d r a l p o r p h y r o b l a s t s . I t i s t h e same t y p e as t h e common h o r n b l e n d e i n t h e p l a g i o c l a s e a m p h i b o l i t e s . B i o t i t e o c c u r s i n s u b h e d r a l p l a t e s , commonly w i t h r a g g e d t e r m i n a t i o n s . I n one t h i n s e c t i o n a few s e c t i o n s o f b i o t i t e c u t s u b p a r a l l e l t o t h e c l e a v a g e show t h a t i t i s i n t e r - grown w i t h v e r m i c u l a r q u a r t z . The b i o t i t e i s p l e o c h r o i c f r o m d a r k brown t o s t r a w y e l l o w . E p i d o t e i s g e n e r a l l y e u h e d r a l b u t o c c a s i o n a l l y s u b  h e d r a l . I t i s a l m o s t a l w a y s a s s o c i a t e d w i t h b i o t i t e . The e p i d o t e i s c o l o r l e s s p i s t a c i t e , b i a x i a l n e g a t i v e w i t h a l a r g e 2V, and has a b i r e f r i n g e n c e o f a b o u t 0.03> i n d i c a t i n g i t c o n t a i n s a p p r o x i m a t e l y 18 p e r c e n t o f t h e HC^Fe-^S 13013 m o l e c u l e . S e r i c i t e i s common i n t h e s e c t i o n w h i c h has u n d e r g o n e g r a n u l a t i o n . H e r e i t o c c u r s as a f i n e f e l t y mass r e p l a c i n g t h e p l a g i o c l a s e and a l s o i n a s e t o f n a r r o w f r a c t u r e s whenever t h e s e c r o s s a f e l d s p a r g r a i n . I t i s r a r e i n t h e o t h e r s e c t i o n s . Sphene i s f o u n d as wedge-shaped c r y s t a l s and r o u n d e d g r a n u l e s i n a l l t h i n s e c t i o n s . I t i s a v e r y f a i n t l y p l e o  c h r o i c ( p a l e brown t o c o l o r l e s s ) t y p e . A p a t i t e o c c u r s i n s m a l l h e x a g o n a l g r a i n s w h i c h a r e 47 e u h e d r a l o r s u b h e d r a l . " I r o n o r e " , f o u n d o n l y i n #18-9, o c c u r s as l a r g e a n h e d r a l g r a i n s . I t i s p r o b a b l y p y r i t e . (2) P l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s e s T h i s , d i v i s i o n c o n t a i n s some 40 p e r c e n t o f t h e m e t a  m o r p h i c r o c k s o f Hawkesbury I s l a n d and f o r m s , e x c l u d i n g t h e p l a g i o c l a s e a m p h i b o l i t e s , t h e l a r g e s t u n i t o f p r o b a b l y m e t a - s e d i m e n t a r y r o c k s t h e r e . T h e r e seems t o be d i s t i n c t d i f f e r  ences i n c o m p o s i t i o n and i n t e x t u r e i n t h e r o c k s o f t h i s d i v i s i o n i n d i f f e r e n t p a r t s o f t h e i s l a n d , so t h a t t h r e e s u b  d i v i s i o n s have been e r e c t e d . T h e s e a r e ( a ) t h e " N o r m a l " t y p e , (b) t h e Augen M o u n t a i n t y p e and ( c ) t h e S i d e b a c o n L a k e t y p e . The " N o r m a l " t y p e i s t h e common p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s o f t h e i s l a n d . I t forms t h e K f e l d s p a r g n e i s s e s w h i c h o c c u r i n t e r b e d d e d w i t h p l a g i o c l a s e a m p h i b o l i t e s i n t h e a r e a between Augen m o u n t a i n and N o r t h m o u n t a i n . I t i s a l s o f o u n d i n t h e u p p e r p a r t o f Wye v a l l e y and i n t e r b e d d e d w i t h t h e m a i n p l a g i o c l a s e a m p h i b o l i t e band i n t h e s o u t h p a r t o f t h e i s l a n d . The Augen M o u n t a i n t y p e forms a band some 7000* w i d e w h i c h e x t e n d s a c r o s s Hawkesbury I s l a n d . I t f o r m s a l l o f Augen M o u n t a i n e x c e p t t h e n o r t h s l o p e , and a l s o u n d e r l i e s t h e n o r t h  ernmost b r a n c h o f Wye v a l l e y and a s m a l l p a r t o f t h e r i d g e t o t h e s o u t h o f t h i s v a l l e y . The S i d e b a c o n Lake t y p e i s c o n f i n e d t o t h e a r e a i m m e d i a t e l y t o t h e n o r t h o f t h i s l a k e , where i t f orms two s e p a r a t e bands; one a b o u t 3000 f e e t w i d e and t h e o t h e r o f unknown w i d t h . The "Normal" t y p e and S i d e b a c o n L a k e t y p e a r e v e r y 48 s i m i l a r and w i l l be d e s c r i b e d t o g e t h e r , b u t t h e Augen M o u n t a i n t y p e i s so d i f f e r e n t i n t e x t u r e , a p p e a r a n c e and c o m p o s i t i o n i t w i l l be d e s c r i b e d s e p a r a t e l y . (a) The "Normal" and S i d e b a c o n Lake T y p e s o f G n e i s s I n hand s p e c i m e n t h e s e r o c k s a r e u s u a l l y medium o r f i n e - g r a i n e d , and w h i t i s h t o p i n k i n c o l o r , b u t t h e v a r i e t i e s w i t h a h i g h p e r c e n t a g e o f m a f i c s may be g r e y . The w e a t h e r e d s u r f a c e has much t h e same c o l o r as t h e f r e s h r o c k . A g i v e n s p e c i m e n may show a c o m p l e t e l a c k o f f o l i a t i o n , but t h i s i s u s u a l l y p r e s e n t a l t h o u g h e x t r e m e l y weak. I n t h e f i e l d , f o l  i a t i o n i s much more e v i d e n t due t o d i f f e r e n c e s i n w e a t h e r i n g and g r a i n s i z e f r o m band t o band and t h e p r e s e n c e o f o c c a s  i o n a l m a f i c - r i c h b a n d s . S u c h f o l i a t i o n as i s v i s i b l e seems t o be m a i n l y due t o t h e p a r a l l e l a l i g n m e n t o f b i o t i t e and o t h e r p l a t y m i n e r a l s . C o m p o s i t i o n a l b a n d i n g i s l a c k i n g o r weak. Where i t i s d e v e l o p e d , t h r e e s e t s o f bands a r e p r e s e n t - m a f i c - r i c h , f e l d s p a r - r i c h , and q u a r t z - r i c h . A l l t h r e e s e t s t e n d t o f o r m e l o n g a t e l e n s e s r a t h e r t h a n c o n t i n u o u s b a n d s , w i t h a maximum l e n g t h o f an i n c h o r so and w i d t h o f a b o u t 1/10 o f an i n c h . Rocks o f t h i s t e x t u r e h a v e been r e f e r r e d t o as " l e p t y n i t e " , " g r a n u l i t e " , " l e p t i t e " , " q u a r t z s c h i s t " and " g n e i s s " i n the p a s t . The t e r m g r a n u l i t e i s now r e s e r v e d f o r r o c k s o f t h e h i g h t e m p e r a t u r e g r a n u l i t e f a c i e s . T h e s e c h a r a - t e r i s t i c a l l y l a c k m i c a and h o r n b l e n d e . The t e r m l e p t i t e , and i t s v a r i a n t l e p t y n i t e , i m p l y t e x t u r a l f e a t u r e s l a c k i n g i n t h e Hawkesbury I s l a n d K - f e l d s p a r r o c k s . The w r i t e r p r e f e r s t o 49 c a l l t h e s e r o c k s g n e i s s e s r a t h e r t h a n s c h i s t s as he w o u l d r e s e r v e t h e t e r m s c h i s t f o r r o c k s w i t h a w e l l d e v e l o p e d f o l i a t i o n . The c o m p o s i t i o n o f t h e " N o r m a l " t y p e o f p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s i s p l a g i o c l a s e 35 t o 54 p e r c e n t , mean v a l u e 48 p e r c e n t ; K f e l d s p a r 2 t o 20 p e r c e n t , mean v a l u e 5 p e r c e n t ; q u a r t z 10 t o 36 p e r c e n t , mean v a l u e 28 p e r c e n t ; and b i o t i t e l e s s t h a n 1 t o 20 p e r c e n t , mean v a l u e 8 p e r c e n t . S e r i c i t e , c h l o r i t e , e p i d o t e , a l l a n i t e , s p h e n e , a p a t i t e and g a r n e t may be p r e s e n t , b u t g e n e r a l l y o c c u r i n amounts o f l e s s t h a n 1 p e r c e n t . The S i d e b a c o n L a k e t y p e g n e i s s e s have p l a g i o c l a s e 35 t o 41 p e r c e n t , K f e l d s p a r 35 t o 42 p e r c e n t , q u a r t z 18 t o 20 p e r c e n t , and b i o t i t e l e s s t h a n 1 t o 2 p e r c e n t . H o r n b l e n d e , e p i d o t e , c h l o r i t e , s e r i c i t e , s p h e ne, a p a t i t e and opaques a r e m i n o r c o n s t i t u e n t s . The d i f f e r e n c e s between t h e two t y p e s a r e m a i n l y i n K f e l d s p a r and b i o t i t e c o n t e n t . The t e x t u r e , i n t h i n s e c t i o n , i s s e e n t o be complex. A p o o r f o l i a t i o n has d e v e l o p e d due t o a r a t h e r i n c o m p l e t e s u b - p a r a l l e l o r i e n t a t i o n o f b i o t i t e and h o r n b l e n d e , and a t e n d e n c y f o r f e l d s p a r and q u a r t z t o o c c u r i n e l o n g a t e l e a v e s s u b - p a r a l l e l t o t h e s e m i n e r a l s . S u p e r i m p o s e d upon t h i s , however, i s a w e l l d e v e l o p e d p s e u d o c a t a c l a s t i c t e x t u r e w h i c h i s f o r m e d by a r e p l a c e m e n t o f p o t a s s i u m i n K f e l d s p a r s by sodium and c a l c i u m t o f o r m p l a g i o c l a s e , w i t h a c o n s e q u e n t l i b e r a t i o n o f s i l i c a w h i c h a p p e a r s as f r e e q u a r t z . T h i s 50 r e s u l t s i n a t e x t u r e i n w h i c h l a r g e x e n o m o r p h i c g r a i n s o f q u a r t z and f e l d s p a r a r e s e t i n a f i n e - g r a i n e d m a t r i x o f t h e same m i n e r a l s . I t d i f f e r s f r o m c a t a c l a s t i c t e x t u r e i n t h a t f i n e r g r a i n s o f groundmass a r e n o t f r a g m e n t s o f t h e l a r g e r g r a i n s and a l s o i n t h a t t h e r e i s a s t r o n g s u g g e s t i o n o f c o r r o s i o n o f t h e l a r g e r g r a i n s by t h e groundmass. C a t a c l a s t i c t e x t u r e f e a t u r e s g r a n u l a t i o n o f q u a r t z and b e n t t w i n l a m e l l a e i n f e l d s p a r s . The d i f f i c u l t y i n d e c i d i n g w h i c h t e x t u r e i s p r e s e n t i n t h a t r o c k s w i t h a s u i t a b l e c h e m i c a l c o m p o s i t i o n t o d e v e l o p p s e u d o c a t a c l a s t i c t e x t u r e u s u a l l y have s u i t a b l e p h y s i c a l p r o p e r t i e s t o d e v e l o p c a t a c l a s t i c t e x t u r e . I n t h e t h i n s e c t i o n s examined, however, o n l y one f e l d s p a r g r a i n was s e e n w h i c h i s f r a c t u r e d , g r a n u l a t e d q u a r t z was n o t o b s e r v e d and t h e l a r g e r g r a i n s g e n e r a l l y a p p e a r t o have c o r r o d e d mar g i n s . T h i s s u g g e s t s t h a t , a l t h o u g h m i n o r c a t a c l a s t i c e f f e c t s may be p r e s e n t , t h i s t e x t u r e i s m a i n l y p s e u d o c a t a c l a s t i c . P l a g i o c l a s e ' has a c o m p o s i t i o n o f A n ^ t o A ^ Q * M E D : I ' U M a n d e s i n e , i n b o t h t y p e s o f g n e i s s . T h e s e d e t e r m i n a t i o n s a r e b a s e d on m e a s u r i n g X'^ 010 f o r s e c t i o n s J~ a. Most o f t h e i: - t w i n n e d g r a i n s have s i m p l e a l b i t e t w i n n i n g b u t complex t w i n s a r e a l s o p r e s e n t . Zoned f e l d s p a r s a r e p r e s e n t but r a r e . The p o t a s s i u m f e l d s p a r p r e s e n t i s u s u a l l y u n t w i n n e d i n t h e " N o r m a l " t y p e g n e i s s . S u c h t w i n n i n g as i s p r e s e n t i s o f t h e q u a d r i l l e t y p e , s h owing t h a t t h e t w i n n e d f e l d s p a r i s m i c r o c l i n e r a t h e r t h a n o r t h o c l a s e . T w i n n i n g i s u s u a l l y p r e s e n t a t t h e edges o f g r a i n s o n l y . Whether t h e u n t w i n n e d K f e l d s p a r 51 i s m i c r o c l i n e o r o r t h o c l a s e i s n o t known. I t has b e e n s u g g  e s t e d t h a t o r t h o c l a s e may i n v e r t t o m i c r o c l i n e u n d e r s t r e s s . I f t h i s i s t h e c a s e t h i s u n t w i n n e d K f e l d s p a r i s p r o b a b l y o r t h o c l a s e . I n t h e S i d e b a c o n Lake t y p e g n e i s s e s t h e K f e l d  s p a r i s p r a c t i c a l l y a l l t w i n n e d m i c r o c l i n e . K f e l d s p a r , where i n c o n t a c t w i t h p l a g i o c l a s e , i s o f t e n f r i n g e d by-Mlwart- 8 l i k e " by m y r m e k i t e . The p l a g i o c l a s e o f t h e m y r m e k i t e i s o p t i c a l l y c o n t i n u o u s w i t h t h e p r i m a r y p l a g i o c l a s e , e v e n t o t h e e x t e n t t h a t t w i n l a m e l l a e may e x t e n d w i t h o u t change i n t o t h e m y r m e k i t e . L a r g e g r a i n s o f q u a r t z commonly have u n d u l a t o r y e x t i n c t i o n . T h i s m i n e r a l has no o t h e r u n u s u a l p r o p e r t i e s . B i o t i t e o c c u r s i n s m a l l p l a t e s w i t h r a g g e d t e r m i n  a t i o n s . I t i s p l e o c h r o i c f r o m d a r k brown t o s t r a w y e l l o w , u n l i k e t h e common r e d - b r o w n b i o t i t e o f t h e p l a g i o c l a s e a m p h i b o l i t e . The m i n o r m i n e r a l s a r e h o r n b l e n d e , e p i d o t e , a l l a n i t e , c h l o r i t e , s e r i c i t e , s p h e ne, a p a t i t e , g a r n e t and o p a q u e s . H o r n b l e n d e o c c u r s as l a r g e s u b h e d r a l g r a i n s i n one t h i n s e c t i o n o f t h e S i d e b a c o n L a k e t y p e g n e i s s e s . I t i s a p l e o c h r o i c d a r k brown t y p e . The e p i d o t e g r o u p m i n e r a l p r e s e n t i s p r o b a b l y p i s t a c i t e , as i t s b i r e f r i n g e n c e v a r i e s f r o m a b o u t 0.026 t o 0.031 i n d i c a t i n g 16 t o 19 m o l e c u l a r p e r c e n t o f HCa 2Fe3Si^0]_3. I t o c c u r s as s m a l l a n h e d r a l t o s u b h e d r a l g r a i n s s c a t t e r e d t h r o u g h  o u t t h e r o c k . I n one t h i n s e c t i o n o f t h e S i d e b a c o n L a k e t y p e 8 G . H . A n d e r s o n , " G r a n i t i z a t i o n , A l b i t i z a t i o n and R e l a t e d Phenomena i n t h e N o r t h e r n I n y o Range o f C a l i f o r n i a - N e v a d a , G . S.A. B u l l e t i n , v o l . 48, 1937, pp 37-39. 52 g n e i s s a few c o r e s o f a l l a n i t e a r e p r e s e n t s u r r o u n d e d by a p i s t a c i t e r i m . C h l o r i t e and s e r i c i t e a r e a l t e r a t i o n p r o d u c t s o f b i o t i t e and f e l d s p a r . T h e y o c c u r i n r a g g e d g r a i n s , a n d , i n t h e c a s e o f t h e c h l o r i t e , as f e l t y m a s s e s . B o t h a r e v e r y m i n o r c o n s t i t u e n t s . The c h l o r i t e has " b e r l i n b l u e " i n t e r  f e r e n c e c o l o r s , p a r a l l e l e x t i n c t i o n , and i s p l e o c h r o i c f r o m g r e e n t o r e d d i s h brown. I t i s p r o b a b l y p e n n i n e , w h i c h i s t h e o n l y common c h l o r i t e w i t h t h e s e p r o p e r t i e s . Sphene i s p r e s e n t i n a l m o s t e v e r y t h i n s e c t i o n , b u t i s r a r e r t h a n i n t h e p l a g i o  c l a s e a m p h i b o l i t e s . I t i s w e a k l y p l e o c h r o i c f r o m p a l e brown t o c o l o r l e s s and o c c u r s as s m a l l wedge-shaped e u h e d r a l and s u b h e d r a l c r y s t a l s . A p a t i t e o c c u r s i n t i n y h e x a g o n a l p r i s m s . I t i s f o u n d i n most t h i n s e c t i o n s . G a r n e t i s f o u n d i n a b o u t h a l f o f t h e t h i n s e c t i o n s o f " N o r m a l " t y p e g n e i s s . I t i s i s o t r o p i c and i s f o u n d i n s m a l l e u h e d r a l t o s u b h e d r a l c r y s t a l s . I t i s a p a l e p i n k shade e v e n i n t h i n s e c t i o n . " I r o n o r e s " a r e v e r y s c a r c e i n a l l t h i n s e c t i o n s and c o n s i s t o f s m a l l a n h e d r a l g r a i n s , p r o b a b l y o f m a g n e t i t e . (b) The Augen M o u n t a i n Type o f G n e i s s I n hand s p e c i m e n t h e s e r o c k s a r e g r e y on b o t h f r e s h and w e a t h e r e d s u r f a c e s . T h ey a l w a y s have a p o r p h y r o b l a s t i c t e x t u r e . The p o r p h y r o b l a s t s a r e o v a l f e l d s p a r augens w h i c h have a maximum d i a m e t e r o f a b o u t one i n c h (2.5 cm). A s t r o n g f o l i a t i o n and w e l l d e f i n e d b a n d i n g i s p r e s e n t i n t h e v a r i e t i e s w i t h w e l l d e v e l o p e d a u g e n s . V a r i e t i e s w i t h s m a l l augens l a c k 53 b a n d i n g and have c o m p a r a t i v e l y weak f o l i a t i o n , a l t h o u g h s t r o n g e r t h a n t h a t o f most s p e c i m e n s o f t h e " N o r m a l " and S i d e - b a c o n L a k e t y p e g n e i s s e s . The c o m p o s i t i o n o f t h e Augen M o u n t a i n t y p e o f p l a g i o  c l a s e - K f e l d s p a r - q u a r t z g n e i s s i s p l a g i o c l a s e 30 t o 50 p e r c e n t , K f e l d s p a r 15 t o 20 p e r c e n t , q u a r t z 20 t o 25 p e r c e n t , b i o t i t e 5 t o 15 p e r c e n t , e p i d o t e 4 t o 15 p e r c e n t , h o r n b l e n d e 2 t o 3 p e r c e n t . C h l o r i t e and s e r i c i t e , may be p r e s e n t . Sphene, a p a t i t e and " i r o n o r e s " a r e a l w a y s p r e s e n t as a c c e s s o r y m i n e r a l s . I n t h i n s e c t i o n , t h e t e x t u r e o f t h e s e r o c k s i s s e e n t o be e s s e n t i a l l y p o r p h y r o b l a s t i c , m o d i f i e d t o a m i n o r ex t e n t by p s e u d o c a t a c l a s t i c and c a t a c l a s t i c e f f e c t s . A good example o f c a t a c l a s t i c t e x t u r e i s p r e s e n t i n one t h i n s e c t i o n ( s e e f i g u r e s 13s 14) i n w h i c h a l a r g e g r a i n f o r m i n g most o f a p l a g i o c l a s e augen i s s t r o n g l y f r a c t u r e d . P l a g i o c l a s e has a c o m p o s i t i o n o f An-^g t o An-^g, medium a n d e s i n e , as d e t e r m i n e d by m e a s u r i n g X*A010 f o r s e c t i o n s l a . Twinned g r a i n s u s u a l l y have a l b i t e t w i n n i n g , a l t h o u g h c o m p l e x t w i n s a r e p r e s e n t . No z o n e d g r a i n s were n o t e d . P l a g i o c l a s e o c c u r s i n t h e groundmass as s u b h e d r a l t o a n h e d r a l g r a i n s and a l s o as l a r g e r g r a i n s f o r m i n g a u g e n s . The o n l y l a r g e p l a g i o  c l a s e augen s e e n i n t h i n s e c t i o n i s c o m p o s i t e , b e i n g composed o f one v e r y l a r g e and s e v e r a l s m a l l e r s u b h e d r a l p l a g i o c l a s e g r a i n s . K f e l d s p a r i s a l l o f an u n t w i n n e d t y p e , e i t h e r o r t h o -54 c l a s e o r m i c r o c l i n e . I t forms t h e l a r g e s t augens i n t h e s e r o c k s and a l s o o c c u r s as s m a l l a n h e d r a l g r a i n s . I t i s n o t known w h e t h e r t h e augens a r e c o m p o s i t e o r n o t as none a r e f o u n d i n t h i n s e c t i o n . T h ey were i d e n t i f i e d i n hand s p e c i m e n by e t c h i n g w i t h h y d r o f l u o r i c a c i d and s t a i n i n g i n a s o d i u m c o b a l t i - n i t r i t e s o l u t i o n . The K f e l d s p a r s a r e f r i n g e d by " w a r t - l i k e " m y r m e k i t e s o f t h e t y p e p r e s e n t i n t h e o t h e r p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s e s . Q u a r t z , i n a n h e d r a l l e a v e s and g r a i n s , commonly has u n d u l a t o r y e x t i n c t i o n . B i o t i t e i s f o u n d i n l a r g e s u b h e d r a l p l a t e s . I t i s p l e o c h r o i c f r o m d a r k brown t o s t r a w . H o r n b l e n d e f o r m s s u b h e d r a l t o e u h e d r a l g r a i n s f r i n g e d by b i o t i t e . I t i s b i a x i a l n e g a t i v e w i t h Z A c = 2 2 ° , and a p l e o c h r o i c f o r m u l a o f X = p a l e y e l l o w Y = b l u e g r e e n , and Z = d a r k g r e e n , i . e . i s t h e common a l u m i n o u s h o r n b l e n d e o f t h i s a r e a . C h l o r i t e and s e r i c i t e o c c u r i n i r r e g u l a r s h r e d s as m i n o r a l t e r a t i o n p r o d u c t s . The c h l o r i t e i s p l e o c h r o i c g r e e n t o brown, and has p a r a l l e l e x t i n c t i o n and " b e r l i n b l u e " i n t e r f e r e n c e c o l o r s . I t i s p r o b a b l y p e n n i n e . Sphene and a p a t i t e o c c u r as s m a l l e u h e d r a l t o s u b  h e d r a l c r y s t a l s . Sphene i s t h e common w e a k l y p l e o c h r o i c ( p a l e brown t o c o l o r l e s s ) v a r i e t y . " I r o n o r e s " a r e s c a r c e i n most s e c t i o n s and c o n s i s t o f a few a n h e d r a l t o c u b i c e u h e d r a l ( p y r i t e ? m a g n e t i t e ? ) g r a i n s . 55 Figure 11. Photomicrograph of "Normal" type of plagioclase-K feldspar-quartz gneiss. Plain light. X24. Rounded garnets, plagioclase, K feldspar and quartz. Figure 12. Photomicrograph of "Normal" type of plagioclase K feldspar-quartz gneiss. Polarized light X24. As Figure 11. 56 Figure 1 3 . Photomicrograph of Augen Mountain type of plagioclase-K feldspar- quartz gneiss. Plain light X24. Large plagioclase augen containing small epidote grains. Some bio tite outside of the augen. Figure 14. Photomicrograph of Augen Mountain type of plagioclase-K feldspar- quartz gneiss. Polarized light X24. As Figure 1 3 . Fracturing is evid ent i n the augen. 57 (3) The K y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s T h e s e r o c k s , a l t h o u g h q u i t e l i m i t e d i n e x t e n t , a r e among t h e most i m p o r t a n t o f t h e septum f r o m t h e p o i n t o f v i e w o f d e t e r m i n a t i o n o f m e t a m o r p h i c f a c i e s a n d , t o a l e s s e r d e g r e e , o f t h e h i s t o r y o f t h e m e t a m o r p h i c r o c k s . T h i s u n i t i s b e t t e r known t h a n t h e o t h e r u n i t s o f t h e E c s t a l l s e r i e s as d e  t a i l e d f i e l d mapping o f i t was c a r r i e d o u t . T h i s r o c k t y p e o c c u r s as a s e r i e s o f bands i n t e r b e d d e d w i t h p l a g i o c l a s e a m p h i b o l i t e s e x t e n d i n g e a s t f r o m t h e head o f S o u t h B e a v e r v a l l e y , t h r o u g h t h e I c e Cake L a k e - K y a n i t e . P o n d a r e a , a l m o s t t o E l l e n L a k e on t h e e a s t s i d e o f t h e i s l a n d . The maximum w i d t h o f t h e i n t e r b e d d e d z o n e i s 6000 f e e t . Most o f t h e k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t a r e f o u n d i n t h e s o u t h e r n h a l f o f t h i s band. I n d i v i d u a l bands v a r y c o n s i d e r a b l y i n shape and e x t e n t . Some bands v a r y f r o m a few f e e t t o o v e r 100 f e e t i n w i d t h i n a v e r y s h o r t d i s t a n c e . The l o n g e s t band o f t h i s r o c k i s 7000 f e e t l o n g and has an a v e r a g e w i d t h o f 40 f e e t and a maximum w i d t h o f 89 f e e t . The t h r e e o t h e r m a j o r bands have l e n g t h s o f 2000 f e e t t o 5000 f e e t and s i m i l a r w i d t h s . T h e s e r o c k s , when s e e n f r o m a d i s t a n c e , a r e w h i t e , p i n k , o r g r e y , d e p e n d i n g on t h e r e l a t i v e p r o p o r t i o n s o f t h e i r c o n s t i t u e n t m i n e r a l s . The w e a t h e r e d s u r f a c e i s much l i k e t h e f r e s h s u r f a c e , b u t k y a n i t e , a l m a n d i n e and s t a u r o l i t e p o r  p h y r o b l a s t s become p r o m i n e n t as t h e m u s c o v i t e w e a t h e r s o u t f r o m a r o u n d them. The m a t r i x i s n o r m a l l y medium g r a i n e d t o 58 c o a r s e g r a i n e d . A s t r o n g s c h i s t o s i t y i s n o r m a l l y p r e s e n t due t o a p a r a l l e l o r i e n t a t i o n o f m u s c o v i t e f l a k e s and t h e f o r  m a t i o n o f e l o n g a t e l e a v e s o f q u a r t z and f e l d s p a r , b u t t h i s b e  comes much weaker when t h e p o r p h y r o b l a s t s a r e l a r g e enough and common enough t o d i s t o r t t h i s o r i e n t a t i o n . B a n d i n g i n t o musco- v i t e - r i c h and p l a g i o c l a s e - q u a r t z - r i c h bands i s o c c a s i o n a l l y w e a k l y d e v e l o p e d . A l m a n d i n e o c c u r s as deep r e d s u b h e d r a l t o e u h e d r a l p o r p h y r o b l a s t s w h i c h may r e a c h 2 i n c h e s i n d i a m e t e r . The l a r g e r c r y s t a l s a r e u s u a l l y e u h e d r a l d o d e c a h e d r o n s w h i c h a r e somewhat f l a t t e n e d p a r a l l e l t o t h e s c h i s t o s i t y . S m a l l c r y s t a l s a r e commonly r o u n d e d and show no s i g n s o f t h i s f l a t t e n  i n g . T h e r e a r e e x c e p t i o n s t o t h i s g e n e r a l r u l e , o f w h i c h t h e most s t r i k i n g a r e l a r g e a n h e d r a l r o u n d e d a g g r e g a t e s o f g a r n e t up t o 3 i n c h e s i n d i a m e t e r , w h i c h c o n t a i n i n c l u s i o n s o f q u a r t z , f e l d s p a r , s t a u r o l i t e , and m u s c o v i t e up t o 1/4 i n c h i n d i a m e t e r . S t a u r o l i t e o c c u r s as s t u b b y b l a c k p r i s m a t i c c r y s t a l s , t h e l a r g e s t 1^ - i n c h e s l o n g , w h i c h l i e p a r a l l e l t o t h e s c h i s t o s i t y . K y a n i t e , w h i c h i s v a r y i n g s h a d e s o f b l u e , o c c u r s as a c i c u l a r c r y s t a l s a few m i l l i m e t e r s l o n g t o l a r g e f l a t b l a d e s w h i c h may be 8 i n c h e s l o n g , 1 i n c h w i d e , and 1/2 i n c h t h i c k . N e a r l y a l l o f t h e s e c r y s t a l s a r e o r i e n t a t e d w i t h t h e i r l e n g t h p a r a l l e l t o t h e s c h i s t o s i t y and a r e s u b - p a r a l l e l t o e a c h o t h e r , p r o  d u c i n g a l i n e a t i o n . The c o m p o s i t i o n o f t h i s r o c k u n i t i s e x t r e m e l y v a r i a b l e , as may be s e e n f r o m f i g u r e l5» an ACF d i a g r a m f o r t h e s t a u r o - l i t e - q u a r t z s u b f a c i e s o f t h e a l m a n d i n e a m p h i b o l i t e f a c i e s t o 59 Figure 15. ACF diagram for the almandine amphibolite facies, staurolite quartz subfacies, showing the range of composition of the Kyanite-staurolite-almandine mica schists. 60 w h i c h t h e r o c k s i n t h i s u n i t w i t h e q u i l i b r i u m a s s e m b l a g e s b e l o n g . Sample Number K - l 11-6A 24-7B PX-3 17-6. 11-4 K-2 P l a g i o c l a s e — 15% 31% 14% 51% 18% 50% Q u a r t z 55% 46% 23% 51% 3% 20% 4% M u s c o v i t e 14% 3% 10% 15% 15% 35% 25% K y a n i t e —— — 15% <i% 10% — 20% S t a u r o l i t e 25% 30$ 15% 10% 10% 5% <1% A l m a n d i n e 5% 5% 5% < i% 10% 20% C h l o r i t e <i% <1% <1% 8% <1% <1% -— L e s s t h a n 1 p e r c e n t o f a p a t i t e and opaques a r e p r e s e n t i n a l l t h i n s e c t i o n s , m i n o r b i o t i t e and sphene a r e p r e s e n t i n a few and s i l l i m a n i t e ( ? ) i s p r e s e n t i n one s e c t i o n . I n t h i n s e c t i o n t h e s t r o n g s c h i s t o s i t y i s t h e most n o t i c e a b l e f e a t u r e . B a n d i n g i s more n o t i c e a b l e t h a n i n hand s p e c i m e n . An a l m o s t c o m p l e t e s e g r e g a t i o n i n t o q u a r t z - f e l d s p a r and m u s c o v i t e bands i s p r e s e n t i n some s p e c i m e n s . The a l m a n  d i n e and s t a u r o l i t e p o r p h y r o b l a s t s a r e s e e n t o h a v e w e l l de v e l o p e d s i e v e t e x t u r e s . I n some t h i n s e c t i o n s t h e i n c l u s i o n s i n t h e g a r n e t a r e s u b p a r a l l e l but a r e a t v a r y i n g a n g l e s t o t h e s c h i s t o s i t y , i n d i c a t i n g r o t a t i o n o f t h e g a r n e t a f t e r g r o w t h . I n o t h e r s t h e r e i s no e v i d e n c e o f r o t a t i o n . S t a u r o l i t e u s u a l l y shows l i t t l e o r no r o t a t i o n a l e f f e c t s , b u t i n one t h i n s e c t i o n one l a r g e g r a i n seems t o have grown u n d i s t u r b e d f o r most o f i t s f o r m a t i o n , r o t a t e d a b o u t 8 0 ° , and t h e n grown u n d i s t u r b e d a g a i n u n t i l t h e end o f i t s p e r i o d o f f o r m a t i o n ( s e e F i g u r e 18) O t h e r g r a i n s i n t h i s s e c t i o n show o t h e r r o t a t i o n a l e f f e c t s . K y a n i t e p o r p h y r o b l a s t s have few i n c l u s i o n s , whose o r i e n t a t i o n i s e v i d e n t l y c r y s t a l l o g r a p h i c a l l y c o n t r o l l e d , and show no r o t a t i o n a l a f f e c t s . A n o t h e r t e x t u r e or m i c r o s t r u c t u r e i s f o u n d i n t h i n s e c t i o n PX -3 . T h i s i s a n a l t e r a t i o n r i m ( s e e f i g u r e s 20 and 21) s u r r o u n d i n g a l l t h e s t a u r o l i t e p o r p h y r o - b l a s t s i n t h e s e c t i o n . I t c o n s i s t s o f a b r o a d r i m o f f a i r l y f i n e - g r a i n e d f e l t y s e r i c i t e o u t s i d e o f w h i c h I s an i n c o m p l e t e r i m o f f a i r l y c o a r s e - g r a i n e d c h l o r i t e . T h i s I s e x p l a i n e d by 9 H a r k e r as b e i n g due t o t h e i n c r e a s e i n volume w h i c h o c c u r s when s t a u r o l i t e i s a l t e r e d t o s e r i c i t e - c h l o r i t e . The c h l o r i t e i s more s o l u b l e and, b e c a u s e o f t h i s volume change, i t i s d i s s o l v e d and r e d e p o s i t e d away f r o m t h e s t a u r o l i t e g r a i n . P l a g i o c l a s e i s a n h e d r a l t o s u b h e d r a l and o c c u r s i n g r a i n s and a g g r e g a t e s r a n g i n g f r o m s l i g h t l y e l o n g a t e p a r a l l e l t o t h e f o l i a t i o n t o l e n s - s h a p e d e l o n g a t e " l e a v e s " . I t a l s o o c c u r s i n p o i k i l o b l a s t i c a l m a n d i n e . The c o m p o s i t i o n o f t h e p l a g i o c l a s e i s q u i t e v a r i a b l e . I n t h e s e c t i o n s i n w h i c h i t was measured i t was A ^ t j , ^26 ' ^30 ' ^ n ^ , a n d A n 4 0 * ^ n e f i r s t two d e t e r m i n a t i o n s a r e b a s e d on m e a s u r i n g N x ' u s i n g i n d e x o i l s and m o n o c h r o m a t i c (s o d i u m ) l i g h t s o u r c e and t h e o t h e r s a r e ba s e d on m e a s u r i n g X'A010 f o r s e c t i o n s X a. Z o n i n g i s p r e s e n t b u t q u i t e uncommon. Q u a r t z o c c u r s as e l o n g a t e a n h e d r a l l e a v e s o r as m o s a i c s o f a n h e d r a l g r a i n s w i t h s u t u r e d b o u n d a r i e s . I t u s u a l l y has u n d u l a t o r y e x t i n c t i o n . 9 A. H a r k e r , Metamorphism, (Methuen and C o . L t d . 1950) P. 350 62 M u s c o v i t e i s c o a r s e - g r a i n e d and g e n e r a l l y o c c u r s as bands o r o c c a s i o n a l i s o l a t e d s u b h e d r a l t a b u l a r c r y s t a l s . I n some p l a c e s i t has r e p l a c e d k y a n i t e , s t a u r o l i t e o r p l a g i o c l a s e as t a b u l a r c r y s t a l s and as f i n e - g r a i n e d f e l t y masses o f s e r i c i t e . K y a n i t e i s e u h e d r a l o r s u b h e d r a l . I t c o n t a i n s i n  c l u s i o n s o f p l a g i o c l a s e , q u a r t z and o p a q u e s . I t i s c o l o r l e s s , b i a x i a l n e g a t i v e v / i t h a l a r g e 2V, has h i g h r e l i e f , m o d e r a t e b i r e f r i n g e n c e , and two p r o m i n e n t c l e a v a g e s . S t a u r o l i t e i s e u h e d r a l t o a n h e d r a l . I t c o n t a i n s i n  c l u s i o n s o f q u a r t z , o p a q u e s , and p l a g i o c l a s e . I t i s commonly p l e o c h r o i c f r o m p a l e g o l d e n y e l l o w t o a l m o s t c o l o r l e s s , b u t i n one t h i n s e c t i o n i s p l e o c h r o i c f r o m deep y e l l o w i s h o r a n g e t o p a l e o r a n g e . I t has a d i s t i n c t c l e a v a g e and a l s o a p a r t i n g and i s u n t w i n n e d . Most o f t h e a l m a n d i n e i s s u b h e d r a l t o r o u n d e d a n h e d r a l . I t c o n t a i n s i n c l u s i o n s o f q u a r t z , opaques and p l a g i o c l a s e . I t i s i s o t r o p i c and a p a l e r e d c o l o r i n t h i n s e c t i o n . I t a l w a y s i s m a r g i n a l l y a l t e r e d t o c h l o r i t e . S i l l i m a n i t e ( ? ) o c c u r s o n l y i n s e c t i o n #11-4. The m i n e r a l t h o u g h t t o be s i l l i m a n i t e i s v i s i b l e o n l y under h i g h power. I t o c c u r s as a few a c i c u l a r n e e d l e s r e p l a c i n g b i o t i t e and m u s c o v i t e . I t i s l e n g t h - s l o w , c o l o r l e s s , has h i g h r e l i e f , r a t h e r s t r o n g b i r e f r i n g e n c e , and p a r a l l e l e x t i n c t i o n . The o n l y m i n e r a l s w i t h t h i s d e s c r i p t i o n a r e s i l l i m a n i t e , a n t h o - p h y l l i t e and m u l l i t e , and i t i s e x t r e m e l y u n l i k e l y t h a t a n t h o -63 p h y l l i t e o r m u l l i t e w o u l d o c c u r i n t h i s f a s h i o n o r i n a r o c k o f t h i s c o m p o s i t i o n . B i o t i t e o c c u r s as s m a l l s u b h e d r a l p l a t e s . I t i s an uncommon m i n e r a l i n t h e s e r o c k s , a n d , where s e e n , i s u s u a l l y a l t e r i n g t o m u s c o v i t e o r c h l o r i t e . I t s p l e o c h r o i c f o r m u l a i s g e n e r a l l y d a r k brown t o s t r a w . C h l o r i t e i s f o u n d a s i r r e g u l a r s h r e d s and f l a k e s . I t r e p l a c e s g a r n e t ( a l m a n d i n e ) i n a l l s e c t i o n s i n w h i c h t h i s m i n e r a l o c c u r s , and i s a l s o f o u n d as an a l t e r a t i o n p r o d u c t o f s t a u r o l i t e and b i o t i t e . T h e r e does n o t seem t o be any d i f f e r  ence i n t h e c h l o r i t e s f ormed f r o m t h e s e m i n e r a l s . T h e y a l l have p a r a l l e l o r n e a r l y p a r a l l e l e x t i n c t i o n , a r e p l e o c h r o i c f r o m medium g r e e n t o n e a r l y c o l o r l e s s , and have anomalous •, " b e r l i n b l u e " i n t e r f e r e n c e c o l o r s , i n d i c a t i n g t h e y may be p e n n i n e . A p a t i t e and sphene a r e t h e common a c c e s s o r y m i n e r a l s i n t h e k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s . T h e y have t h e same p r o p e r t i e s as i n a l l t h e p r e v i o u s l y d e s c r i b e d r o c k s . Opaques a r e common i n t h e s e r o c k s . They o c c u r as f i n e f i l m s i n t e r l a m i n a t e d w i t h m u s c o v i t e and as l a r g e a n h e d r a l t o e u h e d r a l c u b i c g r a i n s . I n r e f l e c t e d l i g h t t h e y a r e a l w a y s b l a c k . The f i l m s and p o s s i b l y some o f t h e a n h e d r a l g r a i n s a r e p r o b a b l y g r a p h i t e whereas t h e r e s t o f t h i s m a t e r i a l " i s p r o b a b l y m a g n e t i t e . F i g u r e 16 . Photomicrograph of k y a n i t e - s t a u r o l i t e almandine mica s c h i s t . P l a i n l i g h t X24. P o r p h y r o b l a s t i c almandine (on the r i g h t ) and s t a u r o l i t e (on the l e f t ) w i t h muscovite l a t h s , q u a r t z , p l a g i o c l a s e and minor opaques and c h l o r i t e (rimming the almandine) I n c l u s i o n s i n d i c a t e r o t a t i o n of the garnet. F i g u r e 17 . Photomicrograph of k y a n i t e - s t a u r o l i t e - almandine mica s c h i s t . P l a i n l i g h t X24. Kyanite p o r p h y r o b l a s t s ( r e c t a n g u l a r cleavage) muscovite l a t h s , q u a r t z , p l a g i o c l a s e , opaques. A sma l l k y a n i t e g r a i n i n the lower l e f t corner i s veined by opaques. 65 Figure 18. Photomicrograph of kyanite- staurolite-almandine mica schist. Plain light. X24. Part of a large rotated staucolite porphyroblast. Figure 19. Photomicrograph of kyanite- staurolite-almandine mica schist. Plain light. X24, Twinned (?) rotated(?) staurolite porphyro blast. 66 L 9 I- * * wm 0 Figure 20. Photomicrograph of Kyanite- staurolite-almandine mica schist. Plain light X24. An alteration rim of sericite and chlorite surrounding staurolite. Figure 21. Photomicrograph of Kyanite- staurolite-almandine mica schist. Plain light X64. Similar to Figure 20. 67 F i g u r e 22. P h o t o m i c r o g r a p h o f K y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t . P l a i n l i g h t X24. K y a n i t e , s t a u r o  l i t e , a l m a n d i n e , m u s c o v i t e , q u a r t z , p l a g i o c l a s e and opaques. 68 (4) S i l l i m a n i t e - q u a r t z - p l a g i o c l a s e g n e i s s T h i s r o c k t y p e has b een f o u n d i n one l o c a l i t y on t h e r i d g e b etween u p p e r A n g l e V a l l e y and F i s h t r a p B a y , where i t o c c u r s as a 25 f o o t w i d e band o f unknown l e n g t h i n t e r b e d d e d w i t h p l a g i o c l a s e a m p h i b o l i t e . I n o u t c r o p t h i s i s a p a l e g r e y , f i n e - g r a i n e d r o c k w i t h c o n s p i c u o u s r o u n d e d k n o t s o f w h i t e s i l l i m a n i t e up t o 1/5 i n c h a c r o s s and 3/10 o f an i n c h l o n g . The s i l l i m a n i t e i s r e s i s t a n t and s t a n d s o u t on t h e w e a t h e r e d s u r f a c e . T h i s r o c k i s r e p r e s e n t e d by one t h i n s e c t i o n w h i c h has t h e f o l l o w i n g c o m p o s i t i o n : q u a r t z 36 p e r c e n t , p l a g i o c l a s e 38 p e r c e n t , b i o t i t e 12 p e r c e n t , s i l l i m a n i t e 15 p e r c e n t , m u s c o v i t e 8 p e r c e n t and l e s s t h a n 1 p e r c e n t o f s p h e n e , c h l o r i t e , a p a t i t e and o p a q u e s . Under t h e m i c r o s c o p e a s t r o n g f o l i a t i o n i s s e e n w h i c h i s due t o a s u b p a r a l l e l o r i e n t a t i o n o f b i o t i t e , m u s c o v i t e and bands o f s m a l l s i l l i m a n i t e g r a i n s . The s i l l i m a n i t e bands a r e formed o f numerous s m a l l a c i c u l a r e u h e d r a l g r a i n s w h i c h a r e g e n e r a l l y s u b p a r a l l e l . T h e s e bands have g r e a t v a r i a t i o n i n w i d t h , o c c a s i o n a l l y s w e l l i n g out i n t o t h e " k n o t s " n o t e d i n t h e o u t c r o p . B i o t i t e and m u s c o v i t e o c c u r i n l a r g e e l o n g a t e s u b h e d r a l t o a n h e d r a l g r a i n s a p p a r e n t l y b e i n g r e p l a c e d by t h e s i l l i m a n i t e . C h l o r i t e i s f o u n d i n i r  r e g u l a r s h r e d s r e p l a c i n g b i o t i t e . The b i o t i t e l a m e l l a e a r e commonly b e n t and t h e s i l l i m a n i t e bands a r e g e n t l y f o l d e d . Q u a r t z and f e l d s p a r a r e f o u n d i n l a r g e a n h e d r a l g r a i n s w i t h a Figure 24. Photomicrograph of sillimanite- quartz-plagioclase gneiss. Plain light X24. Fine-grained acicular sillimanite in "knots" and swirling aggregates with biotite laths, elongate grains of opaques, plagio clase and quartz. Figure 25. Photomicrograph of sillimanite- quartz-plagioclase gneiss. Polarized light X24. As Figure 24. weak e l o n g a t i o n s u b - p a r a l l e l t o t h e f o l i a t i o n . Q u a r t z o c c a s  i o n a l l y has u n d u l a t o r y e x t i n c t i o n . The s i l l i m a n i t e i s so f i n e - g r a i n e d p o s i t i v e i d e n t i f i  c a t i o n was made by powder X - r a y methods. P l a g i o c l a s e was d e t e r m i n e d as A n ^ by f i n d i n g N x ' f o r c l e a v a g e f l a k e s . Most t w i n s a r e o f t h e a l b i t e t y p e b u t complex t w i n s a r e a l s o p r e s e n t . B i o t i t e i s p l e o c h r o i c f r o m medium brown t o s t r a w y e l l o w . Sphene i s t h e common w e a k l y p l e o c h r o i c v a r i e t y . The opaques c o n s i s t o f r a g g e d l a r g e a n h e d r a l p y r i t e g r a i n s . (5) G r a p h i t i c q u a r t z - p l a g i o c l a s e s c h i s t s T h e s e r o c k s a r e q u i t e l i m i t e d i n e x t e n t . They o c c u r i n t e r b e d d e d w i t h p l a g i o c l a s e a m p h i b o l i t e i n t h e T r e n c h B r o o k a r e a and on t h e e a s t s i d e o f F i s h t r a p B a y . I n t h e f o r m e r l o c a l i t y , a l t h o u g h a t most some 20 t o 30 f e e t w i d e , t h e y a p p e a r t o e x t e n d a c r o s s t h e i s l a n d , a d i s t a n c e o f a l i t t l e u n d e r 3 m i l e s . I n hand s p e c i m e n t h e s e a r e f i n e - g r a i n e d , b l a c k o r d a r k g r e y l a y e r e d r o c k s w i t h o r w i t h o u t a s t r o n g s c h i s t o s i t y . The l a y e r s a r e s h a r p l y d i s t i n c t , o f w i d e l y v a r y i n g c o m p o s i t i o n , have g r e a t v a r i a t i o n s i n t h i c k n e s s ( p a p e r t h i n t o 1/4 i n c h ) and a r e v e r y p e r s i s t e n t s o t h a t i t seems l i k e l y t h e y r e p r e s e n t r e l i c t b e d d i n g . T h ey do n o t r e s e m b l e l a y e r s f o r m e d by m e t a m o r p h i c d i f f e r e n t i a t i o n . 71 The c o m p o s i t i o n , b a s e d on s e v e r a l t h i n s e c t i o n s , i s q u a r t z 42 t o 62 p e r c e n t , p l a g i o c l a s e 16 t o 30 p e r c e n t , t r e m o l i t e none t o 1 p e r c e n t , b i o t i t e none t o 3 p e r c e n t , z o i s i t e none t o l e s s t h a n 1 p e r c e n t , s phene l e s s t h a n 1 p e r c e n t , m u s c o v i t e - s e r i c i t e l e s s t h a n 1 t o 5 p e r c e n t , c a l c i t e none t o 4 p e r c e n t , a p a t i t e l e s s t h a n 1 p e r c e n t , d i o p s i d e none t o 1 p e r c e n t and opaques 7 p e r c e n t t o 20 p e r c e n t . The amount o f g r a p h i t e i s e s t i m a t e d t o be 6 t o 15 p e r c e n t . One hand s p e c i m e n c o n t a i n s a b o u t 80 p e r c e n t g r a p h i t e . T h i s i s f r o m a p i n c h i n g and s w e l l i n g l e n s o f g r a p h i t e - r i c h r o c k a bout 100 f e e t l o n g and a t t h e most 10 f e e t w i d e i n t h e T r e n c h B r o o k s a r e a . I n t h i n s e c t i o n t h e r o c k i s s e e n t o c o n  s i s t o f a m o s a i c o f a n h e d r a l q u a r t z and p l a g i o c l a s e g r a i n s w i t h s u t u r e d c o n t a c t s and w i t h a s l i g h t t e n d e n c y t o s u b - p a r a l l e l e l o n g a t i o n , c o n t a i n i n g o c c a s i o n a l s m a l l g r a i n s o f e u h e d r a l t o s u b h e d r a l d i o p s i d e and t r e m o l i t e , t h e l a t t e r f r e q u e n t l y rimming t h e f o r m e r , s u b h e d r a l z o i s i t e , e u h e d r a l t o s u b h e d r a l sphene and r a g g e d s h r e d s o f b i o t i t e and m u s c o v i t e . The t r e m o l i t e and m i c a c e o u s m i n e r a l s a r e o r i e n t a t e d s u b - p a r a l l e l t o t h e e l o n g a t e q u a r t z and f e l d s p a r g r a i n s , w i t h " t h e e x c e p t i o n o f f e l t y s e r i c i t e i n t h e p l a g i o c l a s e . G r a p h i t e i s f o u n d i n e l o n g a t e l a t h - l i k e g r a i n s w i t h a s t r o n g p r e f e r r e d o r i e n t a t i o n p a r a l l e l t o t h a t o f t h e q u a r t z , b i o t i t e , e t c . I t o c c u r s a l o n g t h e m a r g i n s o f t h e q u a r t z g r a i n s o r w i t h i n one g r a i n or c u t t i n g a c r o s s s e v e r a l . C o m p o s i t i o n a l b a n d i n g i n t o graphite-rich and graphite poor bands is well developed in the rocks from the Trench Brooks area but is lacking in most specimens from Fishtrap Bay. Quartz occasionally has undulat- ory extinction but rarely shows other evidence of strain. Only two reliable determinations could be made on the feldspars. These are A n ^ a n d -k^^' t l i e f o r m e r determined by measuring N x ' for cleavage flakes and the latter by measuring X* A 010 for a section l a . Tremolite is the type found in the quartzites and calcareous quartzites. It has Z Ac = 18° - 19°. Diopside is a colorless variety. Its maximum interference color is second order yellow. Z Ac is at least -38°. Zoisite is the non-ferrian variety. It is biaxial positive with a small 2V and deep blue interference colors. Biotite is a variety which is pleochroic from reddish brown to straw. Sphene as an extremely pleochroic variety, from deep red brown to a l  most colorless. Calcite and muscovite-sericite are second ary minerals, the former probably replacing plagioclase and the latter plagioclase and biotite. The calcite is found in large enhedral grains. The opaques, in addition to graphite, consist of euhedral to subhedral cubes of pyrite. 73 quartz and plagioclase Figure 27. Photomicrograph of graphitic quartz-plagioclase s c h i s t . Polarized l i g h t X24. As Figure 26. Figure 28. Photomicrograph of graphitic quartz plagioclase schist. Plain light X24. Calc i te , pyrite, epidote, graphite, plagioclase and quartz. The calc i te , pyrite and epidote are probably secondary Figure 2 9 . Photomicrograph of graphitic quartz- plagioclase schist. Plain light X64 Diopside, graphite, quartz and plagioclase. 75 (6) and (7) Q u a r t z i t e s and q u a r t z - t r e m o l i t e - z o i s i t e r o c k s ( C a l c a r e o u s q u a r t z i t e s ) T h e s e r o c k s a r e o f l i m i t e d e x t e n t i n t h e septum. They o c c u r i n t e r b e d d e d w i t h t h e p l a g i o c l a s e a m p h i b o l i t e s i n t h r e e known l o c a l i t i e s , a t one o f w h i c h t h e y a r e a l s o i n t e r  bedded w i t h p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s e s . The t h i c k e s t s e q u e n c e o f q u a r t z i t e s , t o t h e n o r t h o f S i d e b a c o n l a k e , has a t o t a l t r u e t h i c k n e s s o f a b o u t 500 f e e t . The l o n g e s t band, between t h e two s o u t h e r n m o s t b r a n c h e s o f Exe V a l l e y , h as a minimum l e n g t h o f a b o u t 5000 f e e t . The c a l c a r  eous q u a r t z i t e s a r e i n c l u d e d w i t h t h e q u a r t z i t e s as t h e y o c c u r w i t h them and p r o b a b l y r e p r e s e n t p a r t i c u l a r l y i m p ure bands i n t h e o r i g i n a l s e d i m e n t s . B o t h t y p e s a r e f i n e - g r a i n e d w h i t e r o c k s w h i c h commonly have a banded a p p e a r a n c e . I n t h e c a l c a r  eous q u a r t z i t e s t h i s b a n d i n g i s marked by a l t e r n a t e w h i t i s h and v e r y p a l e g r e e n i s h l a y e r s . I n t h e q u a r t z i t e s , q u a r t z - r i c h bands 1/8 t o 1/4 i n c h t h i c k a r e p r o m i n e n t on t h e w e a t h e r e d s u r f a c e , due t o t h e s e g r e g a t i o n o f a m i n e r a l o r m i n e r a l s w h i c h w e a t h e r e a s i l y i n p a p e r t h i n bands between t h e q u a r t z - r i c h b a n d s . I t i s n o t known wh e t h e r t h i s i s b e d d i n g o r a r e s u l t o f m e t a m o r p h i c d i f f e r e n t i a t i o n , b u t t h e w r i t e r i s i n  c l i n e d t o f a v o r t h e f o r m e r e x p l a n a t i o n on t h e b a s i s o f t h e s h a r p n e s s o f t h e c o n t a c t s between t h e bands and t h e i r g r e a t e x t e n t and r e g u l a r i t y . The w e a t h e r e d s u r f a c e i s n o r m a l l y w h i t e i n t h e q u a r t z i t e s , b u t i n a s p e c i m e n o f c a l c a r e o u s q u a r t z i t e a 1/4 i n c h t h i c k l a y e r o f r u s t y w e a t h e r i n g i s 76 p r e s e n t due t o a h i g h p y r i t e c o n t e n t . The c o m p o s i t i o n o f t h e two t h i n s e c t i o n s o f q u a r t z i t e and one o f c a l c a r e o u s q u a r t z i t e w h i c h were made f o l l o w s : T h i n S e c t i o n Number 14-4 25-4 11-1 Q u a r t z 91% 96% 62% P l a g i o c l a s e 3% 1% 8% T r e m o l i t e 2% - 15% Z o i s i t e <1% - 13% B i o t i t e 2% 3% 1% M u s c o v i t e — < 1% < 1% Sphene < 1% <1% <1% A p a t i t e < 1% <1% <1% I n t h i n s e c t i o n t h e q u a r t z i t e i s s e e n t o c o n s i s t o f b r o a d a l t e r n a t e bands o f a n h e d r a l e l o n g a t e g r a i n s o r l e a v e s o f q u a r t z o f d i f f e r e n t g r a i n s i z e s . Most g r a i n s have s u t u r e d c o n  t a c t s and u n d u l a t o r y e x t i n c t i o n . The n a r r o w b a n d s , e a s i l y w e a t h e r e d , a r e m a r k e d by a r e l a t i v e abundance o f s m a l l g e n e r a l l y s u b h e d r a l g r a i n s o f b i o t i t e , t B e m o l i t e , p l a g i o c l a s e , z o i s i t e and e u h e d r a l g r a i n s o f s p h e n e . The b i o t i t e and t r e m o l i t e a r e o r i e n t a t e d s u b - p a r a l l e l t o t h e q u a r t z b a n d s . A l l o f t h e s e m i n e r a l s a l s o o c c u r as s m a l l g r a i n s between, and i n c l u d e d i n , q u a r t z g r a i n s t h r o u g h o u t t h e r o c k . I n t h e c a l c a r e o u s q u a r t  z i t e s i m i l a r bands o f q u a r t s o f v a r y i n g g r a i n s i z e a r e p r e s e n t . S u b h e d r a l z o i s i t e and s u b h e d r a l t o a n h e d r a l t r e m o l i t e , w i t h m i n o r b i o t i t e s h r e d s , e u h e d r a l wedge-shaped sphene and s m a l l h e a v i l y s e r i c i t i z e d p l a g i o c l a s e g r a i n s a r e p a r t i a l l y s e g r e g a t e d i n bands o r o c c u r as s i n g l e g r a i n s sub p a r a l l e l t o t h e e l o n  g a t i o n o f t h e q u a r t z g r a i n s t o g i v e a w e l l d e v e l o p e d f o l i a t i o n . 77 The q u a r t z commonly i s f r a c t u r e d . The c o m p o s i t i o n o f t h e p l a g i o c l a s e i s n o t known, as no s u i t a b l e s e c t i o n s a r e p r e s e n t f o r d e t e r m i n a t i o n s , but i t i s a t l e a s t Ano,o on t h e b a s i s o f t h e M i c h e l - L e v y method. I t s r e  f r a c t i v e i n d i c e s a r e e q u a l t o o r g r e a t e r t h a n t h o s e o f q u a r t z , p u t t i n g i t i n t h e r a n g e An^Q - ^ n ^ , w i t h i n t h e r a n g e f o r a n d e s i n e . T w i n n i n g i s a l l o f t h e a l b i t e t y p e . T r e m o l i t e i s c o l o r l e s s i n t h i n s e c t i o n and i s b i a x i a l w i t h s u c h a l a r g e 2V t h e s i g n c o u l d n o t be d e f i n i t e l y d e t e r  m i n e d . A l l known t r e m o l i t e i s n e g a t i v e . Z A c e q u a l s 19°) w h i c h c o r r e s p o n d s t o a maximum o f 2 o r 3 m o l e c u l a r p e r c e n t o f H 2 C a 2 F e ^ S i g 0 2 4 and 97 t o 98 m o l e c u l a r p e r c e n t o f R^CagMgj-SigO^ B i r e f r i n g e n c e i s m o d e r a t e . Z o i s i t e i s b i a x i a l p o s i t i v e w i t h a s m a l l 2V ( a b o u t 30°), t h e o p t i c p l a n e p a r a l l e l t o 010,and f i r s t o r d e r w h i t e t o deep b l u e i n t e r f e r e n c e c o l o r s . I t i s c o l o r l e s s . I t i s a p p a r  ent t h i s i s t h e n o n - f e r r i a n v a r i e t y o f z o i s i t e , i . e . T e r m i e r ' s cc- z o i s i t e . A few g r a i n s have a p a r t i n g p a r a l l e l , o r n e a r l y s o , t o 001. B i o t i t e i s p l e o c h r o i c f r o m g o l d e n brown t o s t r a w y e l l o w . M u s c o v i t e i s f o u n d as an a l t e r a t i o n p r o d u c t o f b i o  t i t e as w e l l as r e p l a c i n g p l a g i o c l a s e as s e r i c i t e . S phene i s h i g h l y p l e o c h r o i c f r o m deep r e d d i s h brown t o p a l e brown. I n v i e w o f t h e a p p a r e n t low i r o n c o n t e n t o f t h e s e r o c k s i t seems l i k e l y t h a t sphene does n o t owe i t s p l e o c h r o i s m t o i r o n . F i g u r e 30. Photomicrograph of q u a r t z i t e . P o l a r i z e d l i g h t . X24. S t r o n g l y developed undulatory e x t i n c t i o n i n q u artz. A few t r e m o l i t e and z o i s i t e g r a i n s are present. F i g u r e 31. Photomicrograph of quartz-tremo l i t e - z o i s i t e rock. P l a i n l i g h t X24. Z o i s i t e , t r e m o l i t e (on the r i g h t ) quartz and minor sphene 79 (8) C r y s t a l l i n e l i m e s t o n e C r y s t a l l i n e l i m e s t o n e o c c u r s i n t e r b e d d e d w i t h p l a g i o  c l a s e a m p h i b o l i t e a t t h e head o f A n g l e V a l l e y and on t h e e a s t s i d e o f E v e l y n C r e e k . I t s t h i c k n e s s i s unknown i n b o t h l o c a l i t i e s , as i n t h e f o r m e r i t i s much f o l d e d and c r u m p l e d , and i n t h e l a t t e r i t i s e x p o s e d i n a c r e e k bed t h a t p a r a l l e l s i t s s t r i k e . I n b o t h l o c a l i t i e s i t i s a w h i t i s h t o g r e y i s h , c o a r s e t o m e d i u m - g r a i n e d , a l m o s t m a s s i v e r o c k . A weak b a n d i n g i s v i s i b l e due t o d a r k , n a r r o w p a r a l l e l bands o f i m p u r i t i e s . T h i s i s p r o b a b l y an o r i g i n a l b e d d i n g f e a t u r e . The one t h i n s e c t i o n made f r o m t h e A n g l e V a l l e y o c c u r r e n c e , i s m a i n l y c a l c i t e . M i n o r m i n e r a l s a r e q u a r t z , f e l d s p a r , s p h e n e , m u s c o v i t e , a p a t i t e , t r e m o l i t e , and o p a q u e s , a l l o f w h i c h a r e p r e s e n t i n amounts o f l e s s t h a n 1 p e r c e n t . C a l c i t e f o r m s a m o s a i c o f l a r g e a n h e d r a l g r a i n s t h r o u g h w h i c h t h e o t h e r m i n e r a l s o c c u r i n s m a l l i s o l a t e d g r a i n s . One o f t h e bands o f i m p u r  i t i e s i s p r e s e n t and i s f o u n d t o c o n s i s t m a i n l y o f r a g g e d a n h e d r a l g r a i n s o f opaques (? g r a p h i t e ) s c a t t e r e d t h r o u g h o u t t h e c a l c i t e . M u s c o v i t e i s f o u n d i n l a r g e s u b h e d r a l g r a i n s and t r e m o l i t e as m i n u t e e u h e d r a l g r a i n s . Q u a r t z and f e l d s p a r a r e f o u n d as v e r y s m a l l r o u n d e d g r a i n s w h i c h may be o f d e t r i t a l o r i g i n . The c o m p o s i t i o n o f t h e f e l d s p a r i s unknown as i t i s u n t w i n n e d , t o o s m a l l t o i s o l a t e and o c c u r s i n c o n t a c t w i t h c a l c i t e o n l y . The t r e m o l i t e i s c o l o r l e s s . Z A c c o u l d n o t be measured b u t t h i s r o c k a p p a r e n t l y has a v e r y low i r o n c o n t e n t and this mineral has the same properties, as far as can be ascertained, as the nearly pure tremolite of the calcareous quartzites. Figure 32. Photomicrograph of crystalline lime stone. Plain light X24. A mosaic of large calcite grains containing a few small grains of opaques (?graphite), quartz and feldspar. (9) S e r i c i t e - e p i d o t e s c h i s t s and r e l a t e d r o c k s The s e r i c i t e - e p i d o t e s c h i s t s a r e g e n e r a l l y s i l v e r y w h i t e t o p a l e g r e e n i n c o l o r , d e p e n d i n g on t h e abundance o f e p i d o t e . T h ey a l w a y s have a h i g h p y r i t e c o n t e n t and w e a t h e r t o a r u s t y r e d c o l o r . T h e y a r e c o n f i n e d t o s h e a r z o n e s and i n t e n s e l y d r a g f o l d e d a r e a s . Most s p e c i m e n s , i n a d d i t i o n t o a s t r o n g s c h i s t o s i t y , have a s t r o n g s e c o n d a r y f o l i a t i o n due t o d r a g f o l d i n g . T h i s p e r s i s t s down t o m i c r o s c o p i c d i m e n s i o n s O n l y one l a r g e s h e a r zone was f o u n d on Hawkesbury I s l a n d . T h i s s h e a r z o n e , a t l e a s t 5 0 0 0 f e e t l o n g and up t o 3 0 0 f e e t w i d e , i s i n A n g l e V a l l e y a b o u t 1 0 , 0 0 0 f e e t f r o m i t s mouth. The c o m p o s i t i o n o f t h i s u n i t i s q u i t e v a r i a b l e as i n d i c a t e d by t h e f o l l o w i n g t a b l e . T h i n S e c t i o n Numbers 2-1 6-1B 6-1X P l a g i o c l a s e 27% 15% 15% E p i d o t e 3 0 $ 5% 25% B i o t i t e 10% 1% 15% M u s c o v i t e ( S e r i c i t e ) 10% 50% 15% Q u a r t z 20% 22% 25% P y r i t e 2% 5% 3% M u s c o v i t e ( s e r i c i t e ) o c c u r s as l a r g e s u b - p a r a l l e l p l a t e s w h i c h a r e g e n e r a l l y s u b h e d r a l . B i o t i t e and c h l o r i t e a r e f o u n d as s m a l l a n h e d r a l c o r e s l a r g e l y a l t e r e d t o m u s c o v i t e The b i o t i t e i s p l e o c h r o i c f r o m g o l d e n brown t o c o l o r l e s s . B i o t i t e a l s o o c c u r s as s m a l l s u b h e d r a l p l a t e s w h i c h a p p e a r t o 82 be r e p l a c i n g t h e m u s c o v i t e . T h e s e a r e a l w a y s a s s o c i a t e d w i t h c o n c e n t r a t i o n s o f p y r i t e . P l a g i o c l a s e o c c u r s as s m a l l a n h e d r a l g r a i n s . I t i s u s u a l l y c l o u d e d due t o a l t e r a t i o n . No s e c t i o n s s u i t a b l e f o r d e t e r m i n a t i o n o f An c o n t e n t a r e p r e s e n t , b u t t h e r e l i e f , f o r a l l g r a i n s examined, was h i g h e r t h a n t h a t f o r N 0 o f q u a r t z but l o w e r o r e q u a l t o t h a t o f q u a r t z i n o t h e r o r i e n t a t i o n s , s u g g e s t i n g a n a n o r t h i t e c o n t e n t between An^Q and An^g i . e . a n d e s i n e . Q u a r t z i s f o u n d as e l o n g a t e a n h e d r a l l e a v e s between m u s c o v i t e g r a i n s and as m o s a i c s o f s m a l l g r a n u l a t e d g r a i n s . The f o r m e r i n v a r i a b l y have u n d u l a t o r y e x t i n c t i o n . E p i d o t e i s a l w a y s t h e v a r i e t y p i s t a c i t e . I t i s c o l o r l e s s , b i a x i a l n e g a t i v e w i t h a l a r g e 2V, and has a b i r e  f r i n g e n c e o f 0.030 t o 0.032 w h i c h c o r r e s p o n d s t o a b o u t 18 t o 20 m o l e c u l a r p e r c e n t o f HCagFe^Si^O^* I n most s e c t i o n s t h e e p i d o t e i s f o u n d as s m a l l a n h e d r a , but i n one t h i n s e c t i o n i t o c c u r s as l a r g e r a g g e d a n h e d r a l g r a i n s w i t h s i e v e t e x t u r e w h i c h a r e e l o n g a t e p a r a l l e l t o t h e s c h i s t o s i t y and c o n t a i n i n c l u s i o n s o f b i o t i t e , m u s c o v i t e , q u a r t z and a p a t i t e . P y r i t e i s f o u n d as l a r g e e u h e d r a l cubes and s u b h e d r a l and a n h e d r a l g r a i n s . I n p a r t i t i s o r i e n t a t e d p a r a l l e l t o t h e s c h i s t o s i t y and i n p a r t t r a n s e c t s i t , so t h a t i t must have been f o r m e d b o t h d u r i n g and a f t e r a c t i v e s h e a r i n g . A p a t i t e i s f o u n d as s m a l l c o l o r l e s s h e x a g o n a l p r i s m s . Sphene o c c u r s as s m a l l a n h e d r a l o r s u b h e d r a l g r a i n s . I t i s w e a k l y p l e o c h r o i c f r o m p a l e brown t o c o l o r l e s s . 8 3 Figure 33. Photomicrograph of sericite- epidote schist, Plain light X 2 4 . Folding outlined by muscovite (sericite) laths. Minor biotite, epidote, pyrite, plagioclase and quartz. (10) Albitized and potash-enriched Rocks Strong albitization and potash enrichment is very rare on Hawkesbury although myrmekites and augens indicate some metasomatic exchange in most of the plagioclase-quartz-K f e l d s p a r g n e i s s e s . The o n l y known example was f o u n d i n t e r  bedded w i t h q u a r t z i t e on t h e e a s t s i d e o f t h e s o u t h e r n m o s t b r a n c h o f Exe V a l l e y , f a i r l y c l o s e t o t h e c o n t a c t w i t h t h e B e a v e r Lake p l u t o n . I t forms a band a b o u t e i g h t i n c h e s t h i c k o f unknown l e n g t h . The hand s p e c i m e n i s a f i n e - g r a i n e d w h i t e r o c k w i t h a d e c i d e d p u r p l i s h t i n t . E x a m i n a t i o n w i t h t h e b i n o c u l a r m i c r o  s c o p e f a i l e d t o show any r e a s o n f o r t h i s t i n t . I t has a weak, s c a r c e l y v i s i b l e f o l i a t i o n due t o a s u b - p a r a l l e l o r i e n  t a t i o n o f b i o t i t e f l a k e s and a t e n d e n c y f o r t h e b i o t i t e t o be s e g r e g a t e d i n t o n a r r o w b a n d s . The n o r m a l p u r p l i s h r o c k has a few i r r e g u l a r v e i n l i k e p a t c h e s o f w h i t e m a t e r i a l i n i t , some o f w h i c h a r e a t l a r g e a n g l e s t o t h e f o l i a t i o n . I n t h i n s e c t i o n t h e c o m p o s i t i o n o f t h e r o c k i s s e e n t o be p l a g i o c l a s e 50 p e r c e n t , q u a r t z 30 p e r c e n t K f e l d s p a r 15 p e r c e n t , b i o t i t e 2 p e r c e n t and l e s s t h a n 1 p e r c e n t o f e p i d o t e , c h l o r i t e , s e r i c i t e , sphene and a p a t i t e . The t h i n s e c t i o n does n o t c o n t a i n a ny o f t h e v e i n - l i k e m a t e r i a l . The t e x t u r e i s e s s e n t i a l l y g r a n o b l a s t i c and t h e f o l i a t i o n a p p e a r s t o be e v e n weaker t h a n i t does i n t h e hand s p e c i m e n . The m a i n m i n e r a l s f o r m a m o s a i c l a c k i n g any d i r e c t  i o n a l t e x t u r e e x c e p t f o r a few o f t h e l a r g e r g r a i n s w h i c h have a weak s u b - p a r a l l e l e l o n g a t i o n . The f e l d s p a r s p r e s e n t a r e (1) p l a g i o c l a s e An^Q, (2) p l a g i o c l a s e AnQ4 (3) m i c r o c l i n e and (4) u n t w i n n e d K f e l d  s p a r . The a n d e s i n e (An4o) o c c u r s as numerous s m a l l , g e n e r a l l y 85 a n h e d r a l g r a i n s w i t h w e l l d e v e l o p e d a l b i t e t w i n n i n g , i n m y r m e k i t e s and i n l a r g e g r a i n s o f r e p l a c e m e n t t y p e p e r t h i t e s i n w h i c h i t i s b e i n g r e p l a c e d by an u n t w i n n e d f e l d s p a r o f much l o w e r r e l i e f . I t was i d e n t i f i e d by m e a s u r i n g x'AOTO f o r s e c t i o n s _La and by i t s h i g h r e l i e f . The a l b i t e f orms p a r t o f t h e w h i t e v e i n - l i k e p a t c h e s . I t was i d e n t i f i e d by m e a s u r i n g N x ' f o r c l e a v a g e f r a g m e n t s f r o m t h e s e p a t c h e s . As i t was n o t s e e n i n t h i n s e c t i o n i t s r e l a t i o n s h i p t o t h e o t h e r m i n e r a l s i s n o t w e l l known. M i c r o c l i n e o c c u r s as a few s m a l l a n h e d r a l g r a i n s s c a t t e r e d t h r o u g h o u t t h e t h i n s e c t i o n . I t i s u s u a l l y f r i n g e d by m y r m e k i t e . K f e l d s p a r , e i t h e r m i c r o c l i n e o r o r t h o c l a s e , i s f o u n d as s m a l l a n h e d r a l g r a i n s s c a t t e r e d t h r o u g h o u t t h e t h i n s e c t i o n , p r o b a b l y r e p l a c e s p l a g i o c l a s e i n t h e p e r t h i t e s n o t e d a b o v e , and forms p a r t o f t h e w h i t e v e i n l i k e p a t c h e s . I t was i d e n t i f i e d i n t h e l a t t e r by e t c h i n g w i t h h y d r o f l u o r i c a c i d and s t a i n i n g w i t h s o d i u m c o b a l t i n i t r i t e . A n d e s i n e , m i c r o c l i n e , u n t w i n n e d K f e l d s p a r ( i n s m a l l g r a i n s ) and myrme k i t e s a r e common f e a t u r e s o f t h e n o r m a l p l a g i o c l a s e - q u a r t z - K f e l d s p a r g n e i s s e s so t h a t i t i s f e l t t h e s e a r e p r o b a b l y e a r l y . The v e i n l i k e a l b i t e and K f e l d s p a r and p o s s i b l y t h e K f e l d s p a r o f t h e r e p l a c e m e n t p e r t h i t e s a r e p r o b a b l y t h e r e s u l t s o f a l o c a l a d d i t i o n o f s o d a and p o t a s h t o t h i s r o c k , l a t e r t h a n t h e w i d e s p r e a d a d d i t i o n o f p o t a s h and s o d a w h i c h r e s u l t e d i n t h e m y r m e k i t e s and augens o f most o f t h e p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s e s . Q u a r t z o c c u r s as a n h e d r a l g r a i n s . L a r g e g r a i n s may 86 have undulatory e x t i n c t i o n . E p i d o t e i s found as s m a l l anhedral to subhedral g r a i n s . I t i s e i t h e r p i s t a c i t e or c l i n o z o i s i t e but could not be de f i n i t e l y i d e n t i f i e d . I t commonly has " b e r l i n b l u e " i n t e r  ference c o l o r s . B i o t i t e i s found as s m a l l subhedral p l a t e s . I t i s p l e o c h r o i c from golden brown to straw. I t i s commonly a l t e r e d to a c h l o r i t e (? pennine) which i s v e r y weakly p l e o c h r o i c from green to c o l o r l e s s and has deep blue anomalous i n t e r f e r e n c e c o l o r s . S t r i n g s of g r a n u l a r , weakly p l e o c h r o i c sphene between f o l i a of c h l o r i t e are a l s o secondary a f t e r the b i o t i t e , being formed from the excess t i t a n i u m present a f t e r the a l t e r a t i o n of b i o t i t e to c h l o r i t e . F i g u r e 34. Photomicrograph of a l b i t i z e d rock. P o l a r i z e d l i g h t X64. A l a r g e g r a i n of replacement p e r - t h i t e . A n d e s i t e i s being r e p l a c e d by a lower r e l i e f f e l d s p a r . Twinning p e r s i s t s i n the ande s i n e i n the p e r t h i t e ( r e c o g n i z a b l e to the l e f t ) 87 A l i t t l e s e r i c i t e i s p r e s e n t as an a l t e r a t i o n p r o  d u c t o f t h e f e l d s p a r s and o f b i o t i t e and c h l o r i t e . A p a t i t e i s f o u n d as v e r y s m a l l c o l o r l e s s p r i s m a t i c g r a i n s s c a t t e r e d t h r o u g h o u t t h e t h i n s e c t i o n . PETROLOGY OF THE META-IGNEOUS ROCKS (1) T h e " m e t a - i g n e o u s a m p h i b o l i t e s " The m e t a - i g n e o u s a m p h i b o l i t e s a r e o f v e r y l i m i t e d ex t e n t . T h e y o c c u r as s m a l l b o d i e s , most o f w h i c h a r e p r o b a b l y s i l l s o r f l o w s , i n t e r b e d d e d w i t h o r i n t r u s i v e i n t o t h e o t h e r r o c k t y p e s o f t h e E c s t a l l s e r i e s . T h e y a r e e s p e c i a l l y common i n t h e m a i n p l a g i o c l a s e a m p h i b o l i t e band. The l a r g e s t body, a p p a r e n t l y c o n f o r m a b l e t o t h e a d j a c e n t p l a g i o c l a s e a m phi b o l i t e , i s f o u n d j u s t n o r t h o f S i d e b a c o n L a k e . I t i s o v e r 2000 f e e t w i d e . The a v e r a g e w i d t h o f t h e s e b o d i e s i s p r o b a b l y o n l y 50 t o 100 f e e t . I n o u t c r o p , hand s p e c i m e n and t h i n s e c t i o n t h e r e i s a g r e a t d e a l o f v a r i a t i o n i n t e x t u r e o f t h e s e r o c k s , and a l s o c o n s i d e r a b l e v a r i a t i o n i n c o m p o s i t i o n . Most o f them a r e p o r p h y r o b l a s t i c . F o l i a t i o n and l i n e a t i o n a r e e i t h e r v e r y p o o r l y , d e v e l o p e d , o r a b s e n t . S u c h f o l i a t i o n and l i n e a t i o n as i s p r e s e n t i s due t o a s u b p a r a l l e l o r i e n t a t i o n o f e l o n g a t e p l a t e y h o r n b l e n d e l a t h s . The h o r n b l e n d e commonly o c c u r s i n e l o n g a t e c r y s t a l s f r o m 1/8 o f an i n c h l o n g t o one i n c h l o n g and 1/2 i n c h w i d e , but i n one s p e c i m e n f r o m a s m a l l p l u t o n n e a r t h e e a s t c o a s t o f t h e i s l a n d and j u s t t o t h e n o r t h o f t h e n o r t h e a s t b r a n c h o f Wye v a l l e y , i t o c c u r s i n s h o r t s t u b b y c r y s t a l s a b o u t one q u a r t e r i n c h a c r o s s . The l a t t e r r o c k c o m p l e t e l y l a c k s f o l i a t i o n and l i n e a t i o n . A r a r e r t y p e o f m e t a i g n e o u s a m p h i b o l i t e i s e s s e n t i a l l y g r a n o b l a s t i c and f i n e  g r a i n e d . I t has a s t r o n g f o l i a t i o n due t o a s u b - p a r a l l e l o r i e n t a t i o n o f b r o a d p l a t e y h o r n b l e n d e g r a i n s , and a weaker l i n e a t i o n due t o a t e n d e n c y o f t h e h o r n b l e n d e g r a i n s t o have t h e i r l o n g axes s i m i l a r l y o r i e n t a t e d i n t h e p l a n e o f t h e f o l i a t i o n . T h e s e r o c k s v a r y f r o m d a r k g r e e n t o b l a c k i n c o l o r , d e p e n d i n g on t h e c o l o r o f t h e h o r n b l e n d e , and have a brown o r b l a c k w e a t h e r e d s u r f a c e . The c o m p o s i t i o n o f a number o f s e l e c t e d s p e c i m e n s f o l l o w s : S p e c i m e n Number 6-9B 10-4 14-6 16-9 PA-2 H o r n b l e n d e 65$ 55% 96% 55% 70$ B i o t i t e 4% 2% P l a g i o c l a s e 30$ 41$ — 26$ 29$ Q u a r t z 1$ — — 4$ E p i d o t e <1$ <1$ 3$ 12$ O t h e r m i n e r a l s p r e s e n t i n c l u d e a c c e s s o r y a p a t i t e , s p h e n e , and opaques i n a l l t h i n s e c t i o n s , r u t i l e i n #6-9B, m i n o r s e r i c i t e , and 2$ d i o p s i d e i n #16-9. H o r n b l e n d e i s commonly e u h e d r a l t o s u b h e d r a l . Where p o r p h y r o b l a s t i c i t o c c a s i o n a l l y has a s i e v e t e x t u r e . I n one s e c t i o n a few g r a i n s have t w i n n i n g on (100). The p l e o  c h r o i c f o r m u l a and ZAc show c o n s i d e r a b l e v a r i a t i o n . T h e i r r a n g e i s as f o l l o w s : 89 Sample No. Z Ae Pleochroic formula X Y Z PA-2 24° Pale brown brown dark brown 16-9 23° very pale pale green green yellow 10-4 23° 14-6 21° pale yellow blue green dark green 6-9B 20° This relationship corresponds quite closely with the results obtained for the plagioclase amphibolites and other rocks, ex cept for the hornblende in #16-9, which has very pale colors for a Z Ac of 23°. This hornblende occurs in stubby euhedral crystals and may be an original igneous hornblende, l i t t l e affected by metamorphism, which would explain why i t s pro perties do not f i t into the metamorphic hornblende series. Biotite occurs in subhedral flakes. It is pleochroic from golden brown to straw. It is commonly found rimming hornblende or in small flakes cutting through the hornblende. Plagioclase is usually found in small subhedral to anhedral grains. In most specimens i t has a composition of approximately An^ to An^ 0, but in #6-9B the composition i s An^. Zoned feldspars are present but not very common. A single determination in #6-9B indicated normal zoning with a core of A n ^ and a rim of An^. Complex twins are quite common. A l l seem to be combinations of polysynthetic twins. Quartz occurs in anhedral grains. Most grains have undulatory extinction. The epidote present is pistacite. It occurs as small e u h e d r a l t o s u b h e d r a l g r a i n s and as l a r g e masses composed o f s u b h e d r a l t o a n h e d r a l g r a i n s . I t may be p l e o c h r o i c f r o m c o l o r  l e s s t o p a l e y e l l o w , o r c o l o r l e s s . I t has a b i r e f r i n g e n c e o f a p p r o x i m a t e l y 0.03 t o 0.035 i n d i c a t i n g a c o m p o s i t i o n o f 18 p e r c e n t t o 24 p e r c e n t EC^^Q^^^Pl^ a n d ®2 *° ^  p e r cen* D i o p s i d e o c c u r s as s m a l l s u b h e d r a l t o a n h e d r a l g r a i n s rimmed by h o r n b l e n d e . I t i s c o l o r l e s s . The maximum i n t e r  f e r e n c e c o l o r i s s e c o n d o r d e r y e l l o w . The d i o p s i d e i s b i a x i a l p o s i t i v e w i t h a m o d e r a t e l y l a r g e 2V and a Z A c o f - 4 2 ° . S e r i c i t e i s f o u n d i n most s e c t i o n s as a few m i n u t e s h r e d s f o r m e d by t h e a l t e r a t i o n o f f e l d s p a r . The a c c e s s o r y m i n e r a l s p r e s e n t i n c l u d e a p a t i t e , s p h e n e , r u t i l e and o p a q u e s . A p a t i t e i s f o u n d i n s m a l l r o u n d e d g r a i n s t o e u h e d r a l p r i s m a t i c c r y s t a l s . Sphene may o c c u r as l a r g e s u b h e d r a l t o e u h e d r a l g r a i n s w i t h s i e v e t e x t u r e , e n c l o s i n g p l a g i o c l a s e , o r as s t r i n g s and c l u s t e r s o f s m a l l a n h e d r a , u s u a l l y w i t h opaque c o r e s . I t i s a w e a k l y p l e o c h r o i c t y p e . R u t i l e , o c c u r s as s m a l l h i g h l y b i r e f r i n g e n t p a l e y e l l o w a c i c - u l a r c r y s t a l s . G e n i c u l a t e d ("elbow") t w i n s , t w i n n e d on 101, a r e p r e s e n t b u t r a r e . Opaques a r e p r e s e n t as r o u n d e d t o c u b i c e u h e d r a l g r a i n s . The opaque c o r e s rimmed by s p h e n e a r e p r o b a b l y i l m e n i t e . The opaques i n o t h e r s e c t i o n s a r e p r o b a b l y m a i n l y i l m e n i t e a n d / o r m a g n e t i t e . Figure 35. Photomicrograph of a meta-igneous amphibolite. Plain light. X24 Minerals are hornblende and plagioclase. Figure 36. Photomicrograph of meta-igneous amphibolite. Plain light X24. Minerals are hornblende and plagioclase. 92 (2) A c i d P e g m a t i t e s P e g m a t i t e s w h i c h a p p a r e n t l y h a v e b e e n i n v o l v e d i n t h e metamorphism a r e n o t common b u t have b e e n n o t e d i n t h e E v e l y n L a k e - F i s h t r a p Bay a r e a . On t h e s h o r e o f F i s h t r a p Bay a two- f o o t w i d e band o f p e g m a t i t e forms b o u d i n s and n a r r o w e r bands o f p e g m a t i t e h a ve p t y g m a t i c f o l d i n g . O t h e r s m a l l s t r i n g e r s o f p e g m a t i t e have been n o t e d f o l d e d w i t h t h e m e t a m o r p h i c r o c k s i n m i n o r f o l d s and e r e n u l a t i o n s . T h ey c o n s i s t o f l a r g e w h i t e s u b h e d r a l K f e l d s p a r g r a i n s w i t h i n t e r s t i t i a l a n h e d r a l c o l o r  l e s s q u a r t z and o c c a s i o n a l b i o t i t e f l a k e s o r s h r e d s . T h e y l a c k t h e g r e e n i s h m u s c o v i t e f o u n d i n t h e l a t e r p e g m a t i t e s . ORIGIN OF THE METAMORPHIC ROCKS The c o m p o s i t i o n o f t h e p l a g i o c l a s e a m p h i b o l i t e s p l a c e s o most o f t h i s g r o u p i n t h e b a s i c c l a s s o f T u r n e r . P a r t o f i t f a l l s i n t h e q u a r t z o - f e l d s p a t h i c c l a s s n e a r i t s b o u n d a r y w i t h t h e b a s i c c l a s s ( s e e f i g u r e 37). The " q u a r t z o - f e l d s p a t h i c " members o f t h i s g r o u p a c t u a l l y c o n t a i n l i t t l e q u a r t z , a l t h o u g h t h e y do have a r a t h e r h i g h f e l d s p a r c o n t e n t . T h e y a r e b e s t c o n s i d e r e d as r e p r e s e n t i n g a h i g h a l u m i n a v a r i e t y o f t h i s r o c k u n i t . T u r n e r ' s b a s i c c l a s s i n c l u d e s d e r i v a t i v e s o f b a s i c and s e m i - b a s i c i g n e o u s r o c k s , t u f f s and some t u f f a c e o u s 9 W.S. F y f e , F . J . T u r n e r , J . V e r h o o g e n , M e t a m o r p h i c R e a c t i o n s and M e t a m o r p h i c F a c i e s , G.S.A. Mem. 73 ( W a v e r l y P r e s s , 1958), p. 200. 93 F i g u r e 37. ACF d i a g r a m showing t h e c o m p o s i t  i o n a l r a n g e s o f I. K y a n i t e - s t a u r o l i t e - a l m a n d i n e M i c a S c h i s t ; II. P l a g i o c l a s e A m p h i b o l i t e ; III. M e t a - i g n e o u s A m p h i b o l i t e . s e d i m e n t s . T u r n e r s t a t e s t h a t i n t h e a m p h i b o l i t e s d e r i v e d f r o m b a s i c i g n e o u s r o c k s , . . . " h o r n b l e n d e and p l a g i o c l a s e t e n d t o be e q u a l l y a b u n d a n t . ... Q u a r t z and b i o t i t e a r e g e n e r a l l y m i n o r m i n e r a l s , t h o u g h t h e y may be c o n s p i c u o u s i n r o c k s d e r i v e d f r o m t u f f s . " 10 10 H; W i l l i a m s , F . J . T u r n e r , C M . G i l b e r t , P e t r o g r a p h y pp. 241-242. The p l a g i o c l a s e a m p h i b o l i t e s o f t h e map a r e a g e n e r a l l y have a b o u t 55 t o 60 p e r c e n t p l a g i o c l a s e and 35 p e r c e n t o r l e s s o f h o r n b l e n d e . The p e r c e n t a g e o f b i o t i t e i s 12 p e r c e n t o r l e s s i n t h e commoner p l a g i o c l a s e a m p h i b o l i t e s . Q u a r t z a v e r  ages a b o u t 8 p e r c e n t . On Hawkesbury I s l a n d t h e p l a g i o c l a s e a m p h i b o l i t e s o c c u r , i n a t l e a s t one l o c a l i t y , i n t e r b e d d e d w i t h q u a r t z - K f e l d s p a r - p l a g i o c l a s e g n e i s s e s i n beds a few i n c h e s t h i c k o v e r s e v e r a l h u n d r e d f e e t . T h e y show no e v i d e n c e o f i n t r u s i v e r e l a t i o n s h i p s . The t h i c k e s t band o f p l a g i o c l a s e a m p h i b o l i t e has w i t h i n i t a number o f s m a l l s u b - p a r a l l e l bands o f c r y s t a l l i n e l i m e s t o n e , c a l c a r e o u s q u a r t z i t e and q u a r t z i t e , k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t , g r a p h i t i c q u a r t z o - f e l d s p a t h i c g n e i s s and q u a r t z - K f e l d s p a r - p l a g i o c l a s e g n e i s s . T h i s i n d i c a t e s t h e p l a g i o c l a s e a m p h i b o l i t e s a r e s e d i m e n t s . On t h e b a s i s o f c o m p o s i t i o n t h e y must be t u f f s o r t u f f a c e o u s s e d i m e n t s . T u f f a c e o u s s e d i m e n t s a r e r o c k s com p o s e d o f v o l c a n i c m a t e r i a l and n o r m a l s e d i m e n t a t i o n p r o d u c t s . T h e y may be formed when showers o f p y r o c l a s t i c e j e c t a f a l l i n t o b a s i n s where n o r m a l s e d i m e n t a t i o n i s g o i n g on, o r by p r o c e s s e s o f e r o s i o n and r e d e p o s i t i o n . I t i s i n t e r e s t i n g t o n o t e t h a t i n t h e P a n h a n d l e o f A l a s k a t u f f a c e o u s greywacke forms a l a r g e p a r t o f t h e D e v o n i a n r o c k s , and g reywackes f o r m most o f t h e P a l e o z o i c r o c k s and a r e f o u n d i n e v e r y s y s t e m o f M e s o z o i c r o c k s . T u f f s a r e a l s o common. The E c s t a l l m e t a m o r p h i c s e r i e s p r o b a b l y e x t e n d s t o P o r t l a n d C a n a l and f r o m P o r t l a n d C a n a l i n t o A l a s k a , and may be t h e metamorphosed e q u i v a l e n t o f p a r t o f t h e A l a s k a n s e d i  m e n t a r y r o c k s . However, i t i s i m p o s s i b l e t o make any d e f i n i t e c o r r e l a t i o n a t p r e s e n t between t h e E c s t a l l r o c k s and any s y s t e m or s y s t e m s i n A l a s k a . The above d i s c u s s i o n has n o t t a k e n i n t o a c c o u n t t h e p o s s i b i l i t y o f m e t a s o m a t i c e f f e c t s c a u s e d by t h e C o a s t I n  t r u s i o n s . I t i s f e l t t h a t t h e s e e f f e c t s , i f p r e s e n t , h a v e n o t c a u s e d any l a r g e changes i n c o m p o s i t i o n . T h e r e does n o t seem t o be any s i g n i f i c a n t d i f f e r e n c e i n c o m p o s i t i o n b e t w e e n t h e p l a g i o c l a s e a m p h i b o l i t e , n e a r t h e C o a s t I n t r u s i o n s : : and a c o n s i d e r a b l e d i s t a n c e f r o m them. Any a d d i t i o n s t o m e t a m o r p h i c r o c k s f r o m g r a n i t i c r o c k s d u r i n g m e t a s o m a t i s m a r e u s u a l l y m a i n l y o f p o t a s s i u m , s o d i um and s i l i c a . The p l a g i o c l a s e a m p h i b o l i t e i s v e r y low i n p o t a s s i u m and s o d i u m . No K f e l d  s p a r s a r e p r e s e n t and t h e r e i s no e v i d e n c e o f a l t e r a t i o n o f t h e p l a g i o c l a s e t o more s o d i c v a r i e t i e s . The p l a g i o c l a s e - q u a r t z - b i o t i t e - h o r n b l e n d e g n e i s s e s a r e v e r y s i m i l a r i n c o m p o s i t i o n t o t h e p l a g i o c l a s e amphibo l i t e s , t h e o n l y d i f f e r e n c e b e i n g a l o w e r h o r n b l e n d e and b i o t i t e c o n t e n t . I t seems most l i k e l y t h a t t h e y were fo r m e d by t h e c o n t a m i n a t i o n o f t u f f s by n o r m a l s e d i m e n t a r y m a t e r i a l s or by t h e c o n t a m i n a t i o n o f s e d i m e n t s by p y r o c l a s t i c m a t e r i a l . I n e i t h e r c a s e t h e r e s u l t w o u l d be a t u f f a c e o u s s e d i m e n t i . e . a t u f f a c e o u s greywacke o r some s i m i l a r r o c k . The o c c u r  r e n c e o f t h e s e r o c k s i n t e r b e d d e d w i t h p l a g i o c l a s e a m p h i b o l i t e 96 and plagioclase-K feldspar-quartz gneiss, which probably were tuffs or tuffaceous sediments and arkosic or p e l i t i c sed iments respectively, supports this view. The mean composition of the various types of plagio clase-K feldspar-quartz gneiss is as follows: (1) "Normal" type; plagioclase 48 per cent, K-feldspar 5 per cent, quartz 28 per cent and biotite 8 per cent (2) Sidebacon Lake type: plagioclase 38 per cent, K feldspar 39 per cent, quartz 19 per cent and biotite 1 per cent (3) Augen Mountain type: plagioclase 40 per cent, K feldspar 18 per cent, quartz 23 per cent biotite 9 per cent, epidote 8 per cent and hornblende 2 per cent. A l l of these rocks belong to the quartzo-feldspathic group and, i f metasomatism has not been important, are deri vatives of sandstones and/or of acid igneous rocks. Inter- bedding with other rock types and a lack of intrusive relation ships suggests these rocks are probably metamorphosed sediments. The "Normal" and Sidebacon Lake types have abundant myrmekites and the Augen Mountain type abundant K feldspar and plagioclase augens. These features are commonly inter preted as being caused by metasomation, in the former case involving introduction of soda and in the latter of potash and soda. It seems probable therefore that metasomatism has, to some extent, changed the composition of these rocks. However they have at present such an extremely high s i l i c a and alumina 97 c o n t e n t , and v e r y low i r o n and m a g n e s i a c o n t e n t t h a t i t seems u n l i k e l y t h e i r p r e s e n t c o m p o s i t i o n i s due s o l e l y t o m e t a  s o m a t i s m . The o r i g i n a l s e d i m e n t a r y r o c k was t h e r e f o r e p r o  b a b l y a ' h i g h s i l i c a , h i g h a l u m i n a t y p e , i . e . s e m i - p e l i t i c ( q u a r t z - f e l d s p a r - c l a y m i n e r a l ) r o c k o r an a r k o s i c ( q u a r t z - f e l d s p a r ) r o c k . The k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s a l l f a l l i n t o T u r n e r ' s p e l i t i c c l a s s o r t h e q u a r t z o - f e l d s p a t h i c c l a s s n e a r i t s b o u n d a r y w i t h t h e p e l i t i c c l a s s (See f i g u r e 37). The l a t t e r r o c k s may b e s t be c o n s i d e r e d t o be s e m i - p e l i t i c . The p e l i t i c c l a s s r o c k s a r e d e r i v a t i o n s o f a l u m i n o u s s e d i m e n t s i . e . o f s i l t s t o n e s , s h a l e s , e t c . The s e m i - p e l i t i c r o c k s o f t h i s a r e a p r o b a b l y r e p r e s e n t metamorphosed s a n d y s h a l e s o r s i l t s t o n e s r a t h e r low i n c a l c i u m c o n t e n t . The e r r a t i c c h a n g e s o f c o m p o s i t i o n o f t h e s e r o c k s , b o t h a l o n g and a c r o s s s t r i k e , i n d i c a t e s p o o r s o r t i n g o f t h e o r i g i n a l m a t e r i a l s f o r m  i n g t h e r o c k and, p o s s i b l y , r a p i d d e p o s i t i o n . The s i l l i m a n i t e b e a r i n g r o c k s a r e e q u i v a l e n t t o t h e k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s c h e m i c a l l y . T h e y a l s o a r e metamorphosed p e l i t i c r o c k s . The q u a r t z i t e s a r e o b v i o u s l y metamorphosed q u a r t z s a n d s t o n e s . The two t h i n s e c t i o n s e x a m i n e d o f t h e s e r o c k s b o t h c o n t a i n o v e r 90 p e r c e n t q u a r t z and a r e t h e metamorphosed e q u i v a l e n t o f G i l b e r t ' s 1 1 q u a r t z a r e n i t e . The i n t e r b e d d e d and 11 H . W i l l i a m s , F . J . T u r n e r , C . M . G i l b e r t , P e t r o g r a p h y (W.H.Freeman and Co. 1955), p. 291. 98 much rarer quartz-tremolite-zoisite rocks represent calcar eous sandstones. The crystalline limestones of the area, on the basis of their accessory minerals such as tremolite, muscovite, ?graphite, quartz and feldspar, and of textural features, must be sedimentary rather than hydrothermal. These accessory minerals represent siliceous and argillaceous impurities. The limestone, one occurrence of which is on a granodiorite contact, is composed of calcite rather than of dolomite, indicating a complete lack here of magnesium metasomatism, due to the Coast Intrusions. This limestone was probably deposited in a marine environment as i t contains 97 per cent calcite. Fresh-water deposition of limestone does take place, but fresh water lime stone is usually marly or contains other impurities. The graphitic quartz-plagioclase schists have a general compositional range of quartz 42 to 62 per cent, plagioclase 16 to 30 per cent, graphite 7 to 15 per cent with minor trem o l i t e , biotite, zoisite, pyrite, se r i c i t e , calcite, epidote, etc. One exceptional lens-like bed contains 80 per cent or more of graphite. This composition indicates a calcareous and aluminous quartoze rock. As the graphite is probably of organic origin i t would seem these schists are metamorphosed sediments. It is possible the graphite-rich bed represents metamorphosed coal, which would indicate swampy or shallow water conditions of formation, but this is very problematical, particularly in view of the fact that none of the association 99 r o c k s h a v e c o m p o s i t i o n s r e s e m b l i n g t h a t o f t h e u n d e r c l a y s u s u a l l y f o u n d w i t h c o a l b e d s . The m e t a - i g n e o u s a m p h i b o l i t e s a r e so c l a s s i f i e d on t h e b a s i s o f t e x t u r e , c o m p o s i t i o n , and f i e l d r e l a t i o n s h i p s . Most o f t h e s e r o c k s a r e c o a r s e - g r a i n e d and l a c k o r have w e a k l y d e v e l o p e d d i r e c t i o n a l t e x t u r e s . T h ey a p p e a r t o be m e t a  morphosed c o a r s e - g r a i n e d r o c k s o f o r i g i n a l l y g a b b r o i c compos i t i o n and commonly f o r m s m a l l s t o c k - l i k e m a s s e s . The f i n e  g r a i n e d more s c h i s t o s e m e t a - i g n e o u s a m p h i b o l i t e s seem t o be c o n f o r m a b l e . T h e y i n c l u d e p r o b a b l y u l t r a b a s i c and b a s i c r o c k s w h i c h may be s i l l s o r p y r o c l a s t i c s o r f l o w s . The o r i g i n o f t h e p e g m a t i t e s w h i c h have been i n v o l v e d i n t h e metamorphism i s unknown. I f as t h e w r i t e r b e l i e v e s t h e C o a s t I n t r u s i o n s o f t h e a r e a a r e l a t e r t h a n t h e m a i n p e r i o d o f metamorphism, t h e n t h e p o s s i b i l i t i e s a r e (1) t h a t t h e s e a r e a c t u a l l y v e n i t e s " s weated o u t " o f t h e c o u n t r y r o c k d u r i n g metamorphism (2) t h a t t h e s e a r e t r u e i n j e c t i o n p e g m a t i t e s a s s o c i a t e d w i t h a n o l d e r i n t r u s i o n o r (3) t h a t t h e s e r o c k s a c t u a l l y b e l o n g t o t h e C o a s t I n t r u s i o n s e r i e s and have been i n v o l v e d i n some l a t e r p e r i o d o f m i n o r d e f o r m a t i o n . T h e r e does n o t seem t o be any e v i d e n c e o f o l d e r a c i d i n t r u s i o n s i n t h e a r e a so t h a t t h e s e c o n d p o s s i b i l i t y c a n p r o b a b l y be d i s c o u n t e d . L a t e r m i n o r d e f o r m a t i o n , s u c h as i s p o s t u l a t e d i n t h e t h i r d e x p l a n a t i o n , w o u l d p r o b a b l y c a u s e some c a t a c l a s t i c e f f e c t s i n t h e m e t a m o r p h i c r o c k s , u n l e s s i t t o o k p l a c e a t a v e r y h i g h t e m p e r a t u r e . A t h i n s e c t i o n c u t f r o m a p l a g i o c l a s e a m p h i b o l i t e sample t a k e n r i g h t b e s i d e one o f t h e b o u d i n s i n t h e F i s h t r a p B a y o c c u r r e n c e shows no e v i d e n c e o f t h i s . A l t h o u g h t h i s i s n o t c o n c l u s i v e , i t l e a d s t h e w r i t e r t o t h i n k t h a t t h e s e r o c k s a r e v e n i t e s . The p t y g m a t i c : ' f o l d i n g , n o t n o t e d e l s e w h e r e on t h e i s l a n d , a s s o c i a t e d w i t h t h e F i s h t r a p B a y o c c u r r e n c e s u g g e s t p l a s t i c f l o w and p o s s i b l y p a r t i a l f u s i o n o f t h e amphi b o l i t e s t h e r e . I t i s i n t e r e s t i n g t o n o t e t h a t t h e s e o c c u r r e n  c e s o f p o s s i b l e v e n i t e s a r e a l l a t a l t i t u d e s o f l e s s t h a n 300 f e e t a bove s e a l e v e l , and t h a t most o f t h e w e l l e x p o s e d o u t  c r o p s , i . e . t h e r i d g e t o p s , a r e 1000 f e e t above s e a l e v e l o r more. No p o s s i b l e " v e n i t e s " were n o t e d on t h e s e r i d g e t o p s , s u g g e s t i n g t h a t , i f t h e s e r o c k s a r e v e n i t e s , t h e m e t a m o r p h i c r o c k s c u r r e n t l y e x p o s e d on Hawkesbury I s l a n d a r e t h o s e f o r m e d i n t h e 700 t o 4000 f e e t i m m e d i a t e l y a b o v e t h e z o n e o f p a r t i a l f u s i o n . T h i s i s p r o b a b l y b e s t c o n s i d e r e d as w i l d s u r m i s e . I f t h e a n a l y s i s o f t h e e v i d e n c e p r o v i d e d by f i e l d r e l a t i o n s h i p s and c o m p o s i t i o n i s c o r r e c t , t h e E c s t a l l s e r i e s i s composed m a i n l y o f metamorphosed s e d i m e n t s and p o s s i b l y t u f f s w i t h , p e r h a p s , m i n o r i n t e r b e d d e d v o l c a n i c s , i n t r u d e d by a few s m a l l i g n e o u s b o d i e s . A t p r e s e n t t h e E c s t a l l s e r i e s r o c k s h a v e a t h i c k n e s s o f some 4300 f e e t b etween t h e c o n t a c t w i t h t h e N o r t h M o u n t a i n p l u t o n and t h e bend i n A n g l e V a l l e y . A l t h o u g h t h e r e i s no o b v i o u s d u p l i c a t i o n o f f o l d i n g t h e map a r e a p r o b a b l y has b e e n i n v o l v e d i n a t l e a s t two p e r i o d s o f d e f o r m a t i o n so t h a t t h e t h i c k n e s s i n d i c a t e d may be g r e a t l y i n e r r o r . A minimum 101 t h i c k n e s s o f somewhere between 10,000 f e e t and 20,000 f e e t seems r e a s o n a b l e . Most o f t h e s e q u e n c e i s composed o f t u f f s o r t u f f a e - eous s e d i m e n t s and a r k o s i c o r s e m i - p e l i t i c r o c k s . The t h i c k  n e s s o f t h e s e r i e s and t h e p r e s e n c e o f l i m e s t o n e s s u g g e s t s m a r i n e d e p o s i t i o n . The p r e s e n c e o f abu n d a n t a r k o s i c r o c k s ( i f t h e s e r o c k s a r e t r u l y a r k o s i c ) , t h e g r e a t v a r i a t i o n s o f c o m p o s i t i o n i n t h e a r g i l l i c r o c k s , t h e l e n s - s h a p e d and l o c a l c h a r a c t e r o f t h e q u a r t z i t e s , a r g i l l i c r o c k s , e t c . , s u g g e s t l a c k o f s o r t i n g and r a p i d d e p o s i t i o n , p r e s u m a b l y i n s h a l l o w w a t e r . The t h i c k n e s s o f t h e s e d i m e n t a r y s e q u e n c e and p r o  b a b l e s h a l l o w w a t e r c o n d i t i o n s o f d e p o s i t i o n w o u l d seem t o i n d i c a t e d e p o s i t i o n i n a g e o s y n c l i n a l b a s i n . T h i s i s s u p p o r t  ed by t h e p r e s e n c e o f l a r g e amounts o f m a t e r i a l o f v o l c a n i c o r i g i n a s s o c i a t e d w i t h t h e s e d i m e n t a t i o n , w h i c h i s n o t f o u n d i n n o r m a l m a r i n e d e p o s i t s . The v o l c a n i c m a t e r i a l i n d i c a t e s a e u g e o s y n c l i n e , i . e . an a c t i v e l y s u b s i d i n g g e o s y n c l i n e w i t h 12 a s s o c i a t e d v o l c a n i c s . Padgham came t o t h e c o n c l u s i o n t h a t t h e s e d i m e n t a r y r o c k s o f t h e E c s t a l l s e r i e s i n t h e E c s t a l l - Q u a a l R i v e r s a r e a t o t h e n o r t h o f Hawkesbury I s l a n d r e p r e s e n t a s h a l l o w w a t e r m a r i n e s h e l f f a c i e s , l a i d down i n p a r t i n a s t a b l e s h e l f e n v i r o n m e n t b u t m a i n l y i n an u n s t a b l e s h e l f e n v i r o n m e n t . The c o n c e p t o f a s t a b l e s h e l f e n v i r o n m e n t i s b a s e d m a i n l y on t h e p r e s e n c e o f a t h i c k s e q u e n c e o f q u a r t z i t e s and m i n o r i n t e r b e d d e d l i m e y and ? t u f f a c e o u s m a t e r i a l ( t h e Mine S e r i e s and Agnes La k e Q u a r t z i t e s ) . T h e s e have a maximum 12 W. Padgham, G e o l o g y o f t h e E c s t a l l - Q u a a l R i v e r s A r e a , B r i t i s h C o l u m b i a , ( u n p u b l i s h e d M.A.Sc. T h e s i s , U n i v e r s i t y of* B r i t i s h C o l u m b i a ,1958) pp.189-192 102 t h i c k n e s s o f o v e r 20,000 f e e t , a s s u m i n g no r e p e t i t i o n . T h e s e q u a r t z i t e s , on t h e w e s t e r n edge o f t h e septum, t h i n o u t t o  wards D o u g l a s C h a n n e l and do n o t a p p e a r on Hawkesbury I s l a n d . The r e s t o f t h e s e q u e n c e i n t h e E c s t a l l - Q u a a l R i v e r s a r e a a r e v e r y s i m i l a r t o t h e Hawkesbury I s l a n d r o c k s , a l t h o u g h t h e p l a g i o c l a s e a m p h i b o l i t e s , i . e . p r o b a b l y metamorphosed t u f f s o r t u f f a c e o u s g r e y w a c k e s , a r e much l e s s a b u n d a n t i n t h e E c s t a l l - Q u a a l a r e a . The w r i t e r f e e l s t h e most l i k e l y e x p l a n a t i o n i s t h a t t h i s r e g i o n was o r i g i n a l l y s t a b l e and became an u n s t a b l e r a p i d l y s u b s i d i n g b a s i n . The q u a r t z i t e s e r i e s w o u l d r e p r e s e n t d e p o s i t s o f t h e f i r s t s t a g e and t h e s e r i e s o f t u f f s o r t u f f a c e o u s s e d i m e n t s and a r k o s e s o r s e m i - p e l i t i c r o c k s d e  p o s i t s o f t h e s e c o n d s t a g e . Whether t h e r e i s an u n c o n f o r  m i t y between t h e q u a r t z i t e s e r i e s and t h e l a t e r r o c k s i s unknown. I t i s c o n s i d e r e d most u n l i k e l y t h a t t h e q u a r t z i t e s a r e y o u n g e r t h a n t h e g e o s y n c l i n a l t y p e s e d i m e n t s , as t h e r e i s l i t t l e o r no e v i d e n c e o f g e o s y n c l i n e s c e a s i n g r a p i d s u b  s i d e n c e and b ecoming s t a b l e a r e a s , p a r t i c u l a r l y i m m e d i a t e l y p r i o r t o o r o g e n y . Hawkesbury I s l a n d i s i n t h e a r e a b e l i e v e d t o h a v e b e e n o c c u p i e d by t h e P a c i f i c o r w e s t e r n t r o u g h o f t h e C o r d i l l e r a n g e o s y n c l i n e d u r i n g P a l e o z o i c and p o s s i b l y e a r l y M e s o z o i c t i m e . A c c o r d i n g t o E a r d l e y "The s e d i m e n t s o f t h e w e s t e r n t r o u g h f r o m C a l i f  o r n i a t o A l a s k a a r e c h a r a c t e r i z e d by a l a r g e amount o f v o l c a n i c m a t e r i a l and g r e y w a c k e i n e v e r y s y s t e m . P h y l l i t e s , s l a t e s , a r g i l l i t e s 103 s c h i s t s , g n e i s s e s , r e c r y s t a l l i z e d c h e r t , marble;?, m e t a c o n g l o m e r a t e , m e t a - a n d e s i t e and v a r i o u s metamorphosed p y r o c l a s t i c s make up t h e t h i c k sequence. "13 He s u g g e s t s t h a t t h e v o l c a n i c m a t e r i a l s came f r o m a v o l c a n i c a r c h i p e l a g o t o t h e west w h i c h was v e r y s i m i l a r t o t h e i s l a n d a r c o f t h e p r e s e n t J a p a n e s e a r c h i p e l a g o . T h i s v i e w s t r o n g l y s u p p o r t s t h e i d e a o f t h e Hawkesbury I s l a n d r o c k s b e i n g a e u g e o s y n c l i n a l s e q u e n c e . T h e y were p r o  b a b l y d e p o s i t e d i n t h e A l e x a n d e r d i v i s i o n o f t h e P a c i f i c 14 t r o u g h , w h i c h i s b e l i e v e d by E a r d l e y t o have e x t e n d e d f r o m s o u t h e r n A l a s k a i n t o t h e r e g i o n i n w h i c h t h e s e r o c k s a r e now f o u n d . T h e i r age may be P a l e o z o i c o r e a r l y M e s o z o i c . D o l - 15 mage y b e l i e v e s t h e s e r o c k s may be Upper T r i a s s i c i n age on t h e b a s i s o f s t r o n g l i t h o l o g i c a l s i m i l a r i t i e s t o r o c k s o f known Upper T r i a s s i c age w h i c h a r e w i d e l y d i s t r i b u t e d a l o n g 16 t h e c o a s t t o t h e s o u t h ( V a n c o u v e r f o r m a t i o n ) . W h i t e , however, i n a much more r e c e n t work, i n d i c a t e s t h a t t h e map a r e a was a s i t e o f d e p o s i t i o n d u r i n g t h e O r d o v i c i a n t o D e v o n i a n b u t n o t d u r i n g l a t e r p e r i o d s , as f a r as i s known. He i n d i c a t e s t h a t t h e s e r o c k s a r e p r o b a b l y t h e s o u t h e r n metamorphosed e x t e n s i o n o f t h e r o c k s o f t h e P a n h a n d l e o f A l a s k a , where t h e O r d o v i c i a n 13 A . J . E a r d l e y , " P a l e o z o i c C o r d i l l e r a n G e o s y n c l i n e and r e l a t e d o r o g e n y " , J o u r . G e o l . , v o l . 55 (1947), p . 309. !4 I b i d . . p. 309-310 15 V. Dolmage, " C o a s t and I s l a n d s o f B r i t i s h C o l u m b i a between B u r k e and D o u g l a s C h a n n e l s , " G.S.C. Summary R e p o r t s (1921), p. 25A 16 VJ.H.White, " C o r d i l l e r a n T e c t o n i c s i n B r i t i s h C o l u m b i a " , AAPG B u l l . , J a n , 1959, p. 63. 104 t o Lower D e v o n i a n have a combined s t r a t i g r a p h i c t h i c k n e s s o f ab o u t 21,000 f e e t , m a i n l y greywacke b u t w i t h much i n t e r b e d d e d c h e r t y b l a c k s l a t e , l i m e s t o n e , c o n g l o m e r a t e , a n d e s i t i c l a v a and p y r o c l a s t i c s . THE GRADE OF METAMORPHISM (1) M e t a m o r p h i c F a c i e s I n d i s c u s s i n g g r a d e o f metamorphism t h e w r i t e r w i l l u s e t h e c o n c e p t o f m e t a m o r p h i c f a c i e s as d e f i n e d by E s k o l a and q u o t e d by T u r n e r , i . e . " I n a d e f i n i t e f a c i e s a r e u n i t e d r o c k s w h i c h f o r i d e n t i c a l b u l k c o m p o s i t i o n e x h i b i t an i d e n t i c a l m i n e r a l c o m p o s i t i o n , b u t whose m i n e r a l com p o s i t i o n f o r v a r y i n g b u l k c o m p o s i t i o n v a r i e s a c c o r d i n g t o d e f i n i t e laws. " 1 7 The c l a s s i f i c a t i o n o f f a c i e s u s e d i s t h a t g i v e n by F y f e , T u r n e r and V e r h o o g e n i n M e t a m o r p h i c R e a c t i o n s and M e t a  m o r p h i c F a c i e s ( G e o l . S o c . o f A m e r i c a Mem. 73). T h i s c l a s s i  f i c a t i o n d i f f e r s c o n s i d e r a b l y f r o m t h e o l d e r c l a s s i f i c a t i o n g i v e n i n I g n e o u s and M e t a m o r p h i c P e t r o l o g y by T u r n e r and V e r h o o g e n . I n most c a s e s some r e f e r e n c e t o t h e l a t t e r c l a s s i  f i c a t i o n w i l l a l s o be made. Among t h e p l a g i o c l a s e a m p h i b o l i t e s t h e f o l l o w i n g a s s e m b l a g e s may be r e g a r d e d as s t a b l e : (1) H o r n b l e n d e - p l a g i o - c l a s e - e p i d o t e - a l m a n d i n e - ( q u a r t z - b i o t i t e ) (2) H o r n b l e n d e - p l a g i o c l a s e - e p i d o t e - ( q u a r t z - b i o t i t e ) (3) H o r n b l e n d e - p l a g i o - 17 W.S. F y f e , F . J . T u r n e r , I . V e r h o o g e n , M e t a   m o r p h i c R e a c t i o n s and M e t a m o r p h i c F a c i e s , G.S.A. Mem. 73> p . 9. 105 c l a s e - d i o p s i d e - q u a r t z . A l l t h e s e a s s e m b l a g e s b e l o n g t o t h e a l m a n d i n e a m p h i b o l i t e f a c i e s ( f o r m e r l y p a r t o f t h e a m p h i b o l i t e f a c i e s ) . The f i r s t two a r e s t a b l e i n t h e s t a u r o l i t e - q u a r t z and k y a n i t e - m u s c o v i t e - q u a r t z s u b - f a c i e s ( w h i c h were f o r m e r l y combined i n t o t h e s t a u r o l i t e - k y a n i t e s u b - f a c i e s ) , and t h e l a t t e r a s s e m b l a g e i s s t a b l e i n t h e s i l l i m a n i t e - a l m a n d i n e s u b - f a c i e s . I f s m a l l amounts o f s e r i c i t e and c h l o r i t e a r e d i s  r e g a r d e d , two t h i n s e c t i o n s o f p l a g i o c l a s e a m p h i b o l i t e b e l o n g t o t h e f i r s t a s s e m b l a g e , s i x t e e n b e l o n g t o t h e s e c o n d a s s e m  b l a g e , one b e l o n g s t o t h e t h i r d a s s e m b l a g e and f i v e do n o t b e l o n g t o any o f t h e s e a s s e m b l a g e s . S e r i c i t e and c h l o r i t e , w h i c h a r e g e n e r a l l y v e r y s c a r c e , a r e t h e r e s u l t s o f s l i g h t r e t r o g r e s s i v e metamorphism as f r o m t h e i r o c c u r r e n c e i t i s o b v i o u s t h e y a r e l a t e m i n e r a l s . The s o l e t h i n s e c t i o n i n d i c a t i n g t h e s i l l i m a n i t e - a l m a n d i n e s u b - f a c i e s i s f r o m t h e head o f A n g l e V a l l e y n e a r t h e c o n t a c t o f t h e S i d e b a c o n L a k e s t o c k . A l l t h e r e s t o f t h e a r e a u n d e r l a i n by t h e s e r o c k s has a p p a r e n t l y r e a c h e d t h e s t a u r o  l i t e - q u a r t z a n d / o r o r k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s , w i t h t h e e x c e p t i o n o f t h e p a r t t h a t t h e f i v e n o n - s t a b l e assem b l a g e s a r e f r o m . Of t h e s e f i v e , two a r e p l a g i o c l a s e - b i o t i t e g n e i s s e s w h i c h l a c k h o r n b l e n d e , two have a s s e m b l a g e s c o n  t a i n i n g h o r n b l e n d e , b i o t i t e and d i o p s i d e and one i s a p l a g i o  c l a s e - h o r n b l e n d e s t a u r o l i t e a m p h i b o l i t e . The two p l a g i o c l a s e - b i o t i t e g n e i s s e s p r o b a b l y i n d i c a t e a l o w e r g r a d e o f metamorphism. The p r e s e n c e o f b i o t i t e and 106 a n d e s i n e and l a c k o f h o r n b l e n d e i n d i c a t e s n o n - e q u i l i b r i u m c o n d i t i o n s . I t i s n o t known w h e t h e r t h e s e r o c k s r e a c h e d t h e i r p r e s e n t s t a t e by r e t r o g r e s s i v e metamorphism, o r i f t h i s , i s t h e h i g h e s t d e g r e e o f metamorphism t h e y e v e r a t t a i n e d . O t h e r t h i n s e c t i o n s i n d i c a t e t h a t most o f t h e r o c k i n t h e a r e a s t h e s e s p e c i m e n s a r e f r o m b e l o n g t o t h e s t a u r o l i t e - q u a r t z a n d / o r k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s o f t h e a l m a n d i n e amphi b o l i t e f a c i e s . The h o r n b l e n d e - d i o p s i d e - b i o t i t e b e a r i n g r o c k s , p r o b a b l y r e p r e s e n t a t r a n s i t i o n f r o m t h e k y a n i t e - m u s c o v I t e - q u a r t z s u b  f a c i e s t o t h e s i l l i m a n i t e - a l m a n d i n e s u b f a c i e s o r v i c e - v e r s a . One s p e c i m e n i s f r o m u p p e r A n g l e V a l l e y n e a r a l a r g e g r a n i t i c d yke swarm and t h e o t h e r comes f r o m t h e edge o f t h e D a n v a p l u t o n . The specimen; o f p l a g i o c l a s e - h o r n b l e n d e - s t a u r o l i t e a m p h i b o l i t e , f r o m S o u t h B e a v e r V a l l e y , i s a r e p r e s e n t a t i v e o f a v e r y i n t e r e s t i n g r o c k t y p e . A l t h o u g h u n s t a b l e on t h e b a s i s o f m i n e r a l a s s e m b l a g e i t p r o b a b l y i n d i c a t e s a p p r o x i m a t e l y t h e same g r a d e o f metamorphism as t h e o t h e r a m p h i b o l i t e s . T u r n e r 18 and V e r h o o g e n n o t e t h a t a s s o c i a t i o n s o f k y a n i t e o r s t a u r o l i t e and a m p h i b o l e s , a l t h o u g h c o m p a r a t i v e l y r a r e , have b e e n r e c o r d e d f r o m w i d e l y s e p a r a t e d l o c a l i t i e s . T h e y s u g g e s t t h i s p a r a - g e n e s i s may be c o n n e c t e d w i t h t h e l i m i t e d c a p a c i t y f o r Mg t o r e p l a c e Fe i n a l m a n d i n e g a r n e t s , w h i c h , i n an MgO r i c h r o c k , 18 F . J . T u r n e r , J . V e r h o o g e n , I g n e o u s and M e t a m o r p h i c  P e t r o l o g y , ( M c G r a w - H i l l Book Co. I n c . , 195D, p. 4-55. 107 w o u l d r e s u l t i n t o o much Mg b e i n g p r e s e n t t o be acc o m o d a t e d i n t h e h o r n b l e n d e a f t e r c r y s t a l l i z a t i o n o f t h e a l m a n d i n e , i f a l l t h e A l i s t o be a c c o m o d a t e d . C r y s t a l l i z a t i o n o f k y a n i t e w o u l d r e s u l t i n t h e r e m o v a l o f much o f t h e A l m a k i n g i t p o s s  i b l e f o r t h e h o r n b l e n d e t o accomodate a l l t h e e x c e s s Mg. However, i t i s d i f f i c u l t t o sse how t h i s e x p l a n a t i o n c o u l d a p p l y t o t h e f o r m a t i o n o f s t a u r o l i t e i n one o f t h e s e r o c k s , as i t does n o t seem l i k e l y a n i r o n r i c h m i n e r a l s u c h as s t a u r o l i t e w o u l d f o r m i n a Mg r i c h (and F e p o o r ) e n v i r o n m e n t . The p l a g i o c l a s e - q u a r t z - b i o t i t e - h o r n b l e n d e g n e i s s e s a l l h ave t h e a s s e m b l a g e h o r n b l e n d e - p l a g i o c l a s e - e p i d o t e - ( q u a r t z - b l o t i t e,)' and i n d i c a t e t h e a l m a n d i n e a m p h i b o l i t e f a c i e s , s t a u r o l i t e - q u a r t z a n d / o r k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s . S m a l l amounts o f s e r i c i t e a r e a r e s u l t o f r e t r o g r e s s i v e metamorphism. The p l a g i o c l a s e - K f e l d s p a r - q u a r t z g n e i s s e s commonly have t h e a s s e m b l a g e q u a r t z - m i c r o c l i n e - p l a g i o c l a s e - b i o t i t e - m u s c o v i t e - e p i d o t e , w h i c h i s s t a b l e i n t h e s t a u r o l i t e - q u a r t z and k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s o f t h e a l m a n d i n e amphi b o l i t e f a c i e s . The c o r r e s p o n d i n g r o c k s o f t h e s i l l i m a n i t e - a l m a n d i n e s u b f a c i e s w o u l d p r o b a b l y c o n t a i n s m a l l amounts o f s i l l i m a n i t e and a l m a n d i n e . No o t h e r s t a b l e a s s e m b l a g e s a r e r e p r e s e n t e d by t h e s e r o c k s . S m a l l amounts o f s e r i c i t e and c h l o r i t e , p r e s e n t i n some s e c t i o n s , a r e t h e r e s u l t s o f s l i g h t r e t r o g r e s s i v e metamorphism. The k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s a l w a y s c o n t a i n q u a r t z , s t a u r o l i t e and m u s c o v i t e and u s u a l l y c o n t a i n p l a g i o c l a s e , k y a n i t e and a l m a n d i n e . When a l m a n d i n e i s p r e s e n t i t i s a l w a y s a c c o m p a n i e d by s m a l l amounts o f c h l o r i t e . T h i s c h l o r i t e i s c o n s i d e r e d t o be a r e s u l t o f r e t r o g r e s s i v e m e t a  morphism. D i s r e g a r d i n g t h e c h l o r i t e , however, o n l y two s p e c i m e n s , w i t h a s s e m b l a g e s q u a r t z - s t a u r o l i t e - a l m a n d i n e - m u s c o v i t e - b i o t i t e and p l a g i o c l a s e - q u a r t z - s t a u r o l i t e - k y a n i t e - m u s c o v i t e r e s p e c t i v e l y , have e q u i l i b r i u m a s s e m b l a g e s . B o t h o f t h e s e a r e s t a b l e i n t h e s t a u r o l i t e - q u a r t z s u b f a c i e s . A l l t h e o t h e r t h i n s e c t i o n s a n d / o r hand s p e c i m e n s c o n t a i n k y a n i t e , s t a u r o l i t e and a l m a n d i n e . A c c o r d i n g t o T u r n e r and V e r h o o g e n " S t a u r o l i t e a p p e a r s t o be s t a b l e o v e r a n a r r o w l y l i m i t e d r a n g e o f t e m p e r a t u r e . A t t h e b o u n d a r y between t h e z o n e s o f s t a u r o l i t e and k y a n i t e , a l m a n d i n e - k y a n i t e becomes a s t a b l e a s s o c i a t i o n a t t h e e xpense o f s t a u r o l i t e . " 1 9 3 F e A l 4 S i 2 0 l 0 ( O H ) 2 + S i 0 2 ^ F e ^ A l g ( S i O ^ + S A l g S i O ^ + S H ^ O S t a u r o l i t e Q u a r t z A l m a n d i n e K y a n i t e Water K y a n i t e - a l m a n d i n e i s s t a b l e a t a h i g h e r t e m p e r a t u r e t h a n s t a u r o l i t e . Any a s s e m b l a g e c o n t a i n i n g a l l t h r e e o f t h e s e m i n e r a l s i s p r e s u m a b l y u n s t a b l e , a l t h o u g h g e n e r a l l y i n d i c a t i v e o f a t r a n s i t i o n f r o m t h e s t a u r o l i t e - q u a r t z s u b f a c i e s t o t h e k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s . I t i s i n t e r e s t i n g t o n o t e t h a t one s p e c i m e n a l s o c o n t a i n s a few n e e d l e s o f a m i n e r a l t e n t a t i v e l y i d e n t i f i e d as s i l l i m a n i t e . I f t h i s m i n e r a l i s a c t u a l l y s i l l i m a n i t e , i t s u g g e s t s t h e r e a c t i o n s t a u r o l i t e + q u a r t z ^ a l m a n d i n e + k y a n i t e + w a t e r i s so s l o w t h a t i t . may 19 F . J . T u r n e r , J . V e r h o o g e n , Igneous and M e t a m o r p h i c  P e t r o l o g y , ( M c G r a w - H i l l Book C o . I n c . , ) 1951, p. 454. be i n c o m p l e t e when s i l l i m a n i t e b e g i n s t o f o r m . T h e r e a r e two o t h e r p o s s i b i l i t i e s c o n c e r n i n g t h e s t a u r o l i t e - k y a n i t e - a l m a n - d i n e a s s e m b l a g e s . One o f t h e s e i s t h a t t h e s e t h r e e m i n e r a l s a c t u a l l y do f o rm a s t a b l e a s s e m b l a g e . T h i s , however, i s a p p a r e n t l y n o t s u p p o r t e d by any e v i d e n c e f r o m o t h e r d i s t r i c t s . The o t h e r p o s s i b i l i t y i s t h a t t h e c o m p o s i t i o n o f t h e s e r o c k s i s so v a r i a b l e t h e y may be r e g a r d e d as b e i n g composed o f two s e p a r a t e s y s t e m s , one o f w h i c h has a c o m p o s i t i o n w h i c h r e s u l t s i n t h e f o r m a t i o n o f k y a n i t e and s t a u r o l i t e and t h e o t h e r a c o m p o s i t i o n w h i c h r e s u l t s i n t h e f o r m a t i o n o f s t a u r o l i t e and a l m a n d i n e . I f t h i s were t h e c a s e t h e s e r o c k s w o u l d a c t u a l l y be s t a b l e i n t h e s t a u r o l i t e - q u a r t z s u b f a c i e s . The c o m p o s i t i o n o f t h e k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s i s e x t r e m e l y v a r i a b l e , as may be s e e n by r e f e r r i n g t o f i g u r e 15. However, i n a t l e a s t one p l a c e ( s e e f i g u r e s 22 and 23) t h e s e t h r e e m i  n e r a l s a r e s e e n a l m o s t i n c o n t a c t w i t h one a n o t h e r , w h i c h i s h a r d l y s u g g e s t i v e o f two s e p a r a t e c o m p o s i t i o n a l s y s t e m s . The q u a r t z i t e s and c a l c a r e o u s q u a r t z i t e s h a v e t h e a s s e m b l a g e q u a r t z - p l a g i o c l a s e - t r e m o l i t e - b i o t i t e - z o i s i t e - s e r i - c i t e . T h i s i s n o t an e q u i l i b r i u m a s s e m b l a g e b u t does c l o s e l y a p p r o a c h t h e a s s e m b l a g e q u a r t z - p l a g i o c l a s e - t r e m o l i t e - e p i d o t e ( z o i s i t e ) , p a r t i c u l a r l y s i n c e b o t h b i o t i t e and s e r i c i t e a r e v e r y s c a r c e c o n s t i t u e n t s . The l a t t e r a s s e m b l a g e i s s t a b l e i n t h e s t a u r o l i t e - q u a r t z and k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s o f t h e a l m a n d i n e a m p h i b o l i t e f a c i e s . The a s s e m b l a g e o f t h e g r a p h i t i c q u a r t z o - f e l d s p a t h i c 110 s c h i s t s i s commonly q u a r t z - p l a g i o c l a s e - g r a p h i t e - s e r i c i t e - p y r i t e . T r e m o l i t e , b i o t i t e , e p i d o t e , c a l c i t e and d i o p s i d e may be p r e s e n t . None o f t h e t h i n s e c t i o n s h a v e a s t a b l e a s s e m b l a g e , a l t h o u g h t h e i r a s s e m b l a g e s a r e c l o s e t o t h o s e s t a b l e i n t h e a l m a n d i n e a m p h i b o l i t e f a c i e s . The s i l l i m a n i t e - q u a r t z - p l a g i o c l a s e g n e i s s has t h e a s s e m b l a g e p l a g i o c l a s e - q u a r t z - b i o t i t e - s i l l i m a n i t e - m u s c o v i t e . The s t a b l e a s s e m b l a g e i n t h e s i l l i m a n i t e a l m a n d i n e s u b - f a c i e s i s q u a r t z - m i c r o c l i n e - s i l l i m a n i t e - a l m a n d i n e - ( p l a g i o c l a s e - b i o t i t e ) The p r e s e n c e o f abundant m u s c o v i t e i n p l a c e o f m i c r o c l i n e i n d i c a t e s t h a t e i t h e r t h i s r o c k was n o t s u f f i c i e n t l y h e a t e d t o r e a c h t h i s g r a d e o f metamorphism, o r t h a t l a t e r r e t r o g r e s s  i v e metamorphism has t a k e n p l a c e . The m u s c o v i t e and b i o t i t e a r e a p p a r e n t l y b e i n g r e p l a c e d by t h e s i l l i m a n i t e , s u g g e s t i n g t h e f o r m e r i s t h e c a s e . The a s s e m b l a g e o f t h e c r y s t a l l i n e l i m e s t o n e , c a l c i t e - q u a r t z - f e l d s p a r - m u s c o v i t e - t r e m o l i t e i s a n o n - e q u i l i b r i u m one w h i c h i s , however, a l s o s u g g e s t i v e o f t h e a l m a n d i n e amphi b o l i t e f a c i e s . The s e r i c i t i c s c h i s t s and r e l a t e d r o c k s , w i t h q u a r t z - p l a g i o c l a s e ( a n d e s i n e ) - e p i d o t e - b i o t i t e - m u s c o v i t e ( s e r i c i t e - c h l o r i t e and s i m i l a r a s s e m b l a g e s , a r e p l a i n l y u n s t a b l e , as t h e p r e s e n c e o f a n d e s i n e i n d i c a t e s t h e a l m a n d i n e a m p h i b o l i t e f a c i e s o r a h i g h e r g r a d e o f metamorphism, and t h e abundant s e r i c i t e and b i o t i t e t h e g r e e n s c h i s t f a c i e s . T h e i r o c c u r r e n c e i n s h e a r z o n e s and i n t e n s e l y d r a g f o l d e d a r e a s s u g g e s t t h e s e r o c k s I l l were formed by retrogressive metamorphism, probably largely dynamic in nature. The presence of relatively abundant pyrite suggests the presence of sulphur and possibly iron bearing solutions, although there was probably sufficient iron in the original rock to account for i t s forming pyrite. The meta-igneous amphibolites a l l have assemblages similar to those of the majority of the "plagioclase amphi bolites" and also indicate the staurolite-quartz or kyanite- muscovite-quartz sub-facies. To summarize, the rocks of the Ecstall series under lying Hawkesbury Island have,on the whole, reached the alman dine amphibolite facies, staurolite-quartz and/or kyanite- muscovite-quartz sub-facies. Locally rocks of slightly higher or lower grade exist, but only one specimen belongs to the sillimanite-almandine sub-facies. Widespread minor retro gressive metamorphism has taken place, which may be intense locally in shear zones and strongly drag folded areas. (2) Temperature-Pressure Conditions 20 Bowen has given a series of curves for the st a b i l i t y relationships of the various minerals which form during the metamorphism of silicous limestone and dolomite. The assem blage calcite, tremolite and quartz, found in thin section #13-4, is stable between 100° C and 200° C at 1 atmosphere, 20 N.L.Bowen, "Progressive Metamorphism of Siliceous Limestone and Dolomite," Jour. Geol. 48 (1940), p. 256. 112 between 475° C and 525° C at 500 atmospheres and between 540° C and 560° C at 1800 atmospheres, estimated from these curves. Increase in pressure above 1800 atmospheres has l i t t l e effect on the temperature boundaries of the st a b i l i t y f i e l d . ?1 F.G. Smith determined the decrepitation temper atures of 23 specimens of almandine garnets and found that their temperature of crystallization averaged 607° C and had a total range of 463° C to 707° C. A pressure correction must be made but Smith feels this is small. 22 Barth gives a figure showing the temperature of formation of equilibrium assemblages containing epidote and plagioclase of various anorthite contents. On the basis of his figures the temperature of formation of the rocks is equil ibrium on Hawkesbury Island ranges from 395° C to 420° C. However, this figure is based on the assumption that epidote group minerals are unstable above 450° C. Clinozoisite has been observed forming at 600° C and 12,000 atmospheres and epidote has recently been synthesized at 900° C so that i t is obvious his figures must be considerably revised. Turner, Verhoogen and Fyfe place the upper limit of o 24 the greenschist facies at about 400 C and suggest that i f 21 F.G.Smith, "Decrepitation Characteristics of Garnet" American Mineralogist, Vol. 37 (1952), pp. 470-491. 22 T.F.W.Barth, Theoretical Petrology, (John Wiley and Sons, Inc., 1952), p. 285. 23 W.S.Fyfe, F.J.Turner, J. Verhoogen, Metamorphic red actions and Metamorphic Facies, G.S.A. Mem. 73, 1958, pp 165-166 24 Ibid., p. 173 113 t h i s i s due t o d e p t h o f b u r i a l a l o n e l o a d p r e s s u r e s o f 3000 t o 4000 b a r s s h o u l d p r e v a i l . The a l m a n d i n e a m p h i b o l i t e f a c i e s p r e s u m a b l y forms a t h i g h e r t e m p e r a t u r e s . Due t o a l a c k o f knowledge o f t h e s t a b i l i t y f i e l d s o f h o r n b l e n d e , k y a n i t e and s i l l i m a n i t e i t i s i m p o s s i b l e t o g i v e any d e f i n i t e f i g u r e s b a s e d on t h e s e m i n e r a l s . I t i s s t a t e d by T u r n e r , V e r h o o g e n and F y f e t h a t f o r t h e a m p h i b o l i t e f a c i e s " i t w o u l d seem t h a t t h e p r e s s u r e - t e m p e r a t u r e f i e l d i s e x t e n s i v e . The c o m p o s i t i o n o f g a r n e t s , t h e o c c u r r e n c e o f s i l l i m a n i t e and a n d a l u s i t e , and t h e marked p r e v a l e n c e o f h y d r o u s m i n e r a l s .... c o n  s t i t u t e s t r o n g e v i d e n c e p o i n t t o p r e s s u r e s and t e m p e r a t u r e s l o w e r t h a n t h o s e o f t h e g r a n u l i t e f a c i e s . Water p r e s s u r e s a r e h i g h enough t o a l l o w h y d r a t e d s i l i c a t e s t o c r y s t a l l i z e . A t c o n s t a n t p r e s s u r e o f w a t e r , i n c r e a s i n g t e m p e r a t u r e a l o n e w i l l l e a d t o a t r a n s i t i o n f r o m a m p h i b o l i t e t o h o r n b l e n d e - b i o t i t e g r a n u l i t e and e v e n t u a l l y t o p y r o x e n e g r a n u l i t e . A t c o n s t a n t t e m p e r a t u r e , i n t h e h i g h p r e s s u r e r a n g e , a f a l l i n t h e w a t e r p r e s s u r e m i g h t i n d u c e t r a n s i t i o n o f a m p h i b o l i t e t o g r a n u l i t e , and i n l o w e r p r e s s u r e r e g i o n s t o p y r o x e n e h o r n s f e l s . " 2 5 I n c o n n e c t i o n w i t h t h e v a r i o u s s u b - f a c i e s t h e y s t a t e 'From t h e meager p h y s i c a l d a t a a v a i l a b l e i t i s t e n t a t i v e l y c o n j e c t u r e d t h a t t h e s i l l i m a n i t e - a l m a n  d i n e s u b - f a c i e s c o r r e s p o n d s t o m a x i m a l t e m p e r a t u r e s i n t h e a m p h i b o l i t e f a c i e s . From i t s f i e l d r e  l a t i o n s h i p s t o t h e s t a u r o l i t e - k y a n i t e s u b - f a c i e s , i t m i g h t r e a s o n a b l y be i n f e r r e d t h a t l o a d p r e s s u r e s o f t h e two a r e a p p r o x i m a t e l y t h e same'.'20 To sum up, t h e p o s s i b l e t e m p e r a t u r e r a n g e f o r t h e a l m a n d i n e a m p h i b o l i t e s i s p r o b a b l y 400° C t o 700+°C and p r e s s u r e c o n d i t i o n s a r e unknown. The a s s e m b l a g e i n t h i n 25 T u r n e r , V e r h o o g e n and F y f e , op. c i t . , p. 170 26 I b i d . , p. 166 114 s e c t i o n #13-4 ( l i m e s t o n e ) s u g g e s t s t h i s r o c k was metamor p h o s e d a t under 600° C. The above d i s c u s s i o n l a r g e l y i g n o r e s Y o d e r 1 s work, i n w h i c h he c l a i m e d t o have p r o d u c e d a s s e m b l a g e s s u p p o s e d l y b e l o n g i n g t o a number o f f a c i e s a t 600° C and 15000 p s i w a t e r 27 p r e s s u r e ( a b o u t 1000 b a r s ) . T u r n e r , V e r h o o g e n and F y f e f i n d most o f Y o d e r ' s s t a t e m e n t s u n a c c e p t a b l e , and g i v e d e t a i l e d r e a s o n s f o r t h i s , b u t t h e y s t a t e he has s u c c e s s f u l l y shown t h a t t h e b o u n d a r y between t h e a m p h i b o l i t e f a c i e s and p y r o x e n e h o r n f e l s f a c i e s a t 600° C i s d e t e r m i n e d by t h e w a t e r p r e s s u r e , a f a c t o f g r e a t s i g n i f i c a n c e t o m e t a m o r p h i c p e t r o l o g y . THE CAUSES OF METAMORPHISM The p r e c e e d i n g d i s c u s s i o n has shown t h a t t h e r o c k s o f Hawkesbury I s l a n d were metamorphosed u n d e r c o n d i t i o n s o f r a i s e d t e m p e r a t u r e and p r o b a b l y o f s t r o n g c o m p r e s s i v e f o r c e s . I t a l s o seems p r o b a b l e t h a t t h e s e r o c k s , w h i c h seem t o be e u g e o s y n c l i n a l s e q u e n c e , have been c a r r i e d t o a g r e a t d e p t h a t some t i m e d u r i n g t h e o r o g e n y o r o r o g e n i e s w h i c h r e s u l t e d i n t h e d i s a p p e a r a n c e o f t h e P a c i f i c g e o s y n c l i n e and t h e f o r m a t i o n o f t h e C o a s t I n t r u s i o n s . I t wou l d seem t h e r e a r e two p o s s i b l e c a u s e s o f metamorphism. One o f t h e s e i s t h e a b o v e - m e n t i o n e d deep b u r i a l , w h i c h was p r e s u m a b l y a c c o m p a n i e d by r a i s e d tempera- 27 I b i d . , p 19-20 115 t u r e s and p r e s s u r e s . The o t h e r p o s s i b i l i t y i s e s s e n t i a l l y t h e r m a l metamorphism due t o t h e C o a s t I n t r u s i o n s , a c c o m p a n i e d by s t r o n g c o m p r e s s i o n due t o some o t h e r c a u s e -. The p o s s i b i l i t y t h a t t h e C o a s t I n t r u s i o n s were p r o d u c e d by g r a n i - t i z a t i o n i n s i t u o f t h e m e t a m o r p h i c r o c k s a t d e p t h i s d i s  r e g a r d e d b e c a u s e t h e f o r m e r r o c k s have a n o b v i o u s l y i n t r u s i v e c h a r a c t e r . T h i s i s d i s c u s s e d more f u l l y i n c h a p t e r TV w h i c h d e a l s w i t h t h e i g n e o u s r o c k s . I f t h e metamorphism i s due t o t h e C o a s t I n t r u s i o n s t h e s e must have been i n t r u d e d d u r i n g a p e r i o d o f s t r o n g c o m p r e s s i o n . The w r i t e r does n o t f e e l t h i s has o c c u r r e d as (1) t h e C o a s t I n t r u s i o n s o f t h e map a r e a l a c k any s t r o n g f o l i a t i o n o r g r a n u l a t i o n w h i c h i s a t t r i b u t a b l e t o c o m p r e s s i o n d u r i n g emplacement (2) t h e r e does n o t seem t o be any marked t e n d e n c y f o r e l o n g a t i o n o f t h e p l u t o n s p a r a l l e l t o t h e f o l  i a t i o n o f t h e m e t a m o r p h i c r o c k s i . e . p e r p e n d i c u l a r t o t h e d i r e c t i o n o f maximum c o m p r e s s i o n d u r i n g t h e i r p e r i o d o f f o r m a t i o n (3) dykes o f t h e C o a s t I n t r u s i o n s s e r i e s a p p e a r t o have e s s e n t i a l l y random o r i e n t a t i o n (4) t h e r e i s l i t t l e e v i d e n c e o f a d i f f e r e n c e i n m e t a m o r p h i c g r a d e n e a r t h e C o a s t I n t r u s i o n s , and s u c h e v i d e n c e as i s p r e s e n t i s c o m p a t a b l e w i t h t h e r m a l metamorphism o f p r e v i o u s l y d y n a m o t h e r m a l l y metamorphosed r o c k s . S u c h g r a n u l a t i o n and f r a c t u r i n g o f q u a r t z and f e l d  s p a r as i s p r e s e n t i n t h e s e r o c k s i s much more i n t e n s e n e a r t h e c o n t a c t s o f t h e i n t r u s i o n s and becomes v e r y weak away f r o m t h e c o n t a c t s . I t i s most l i k e l y t h i s f e a t u r e was d e v e l o p e d 116 d u r i n g i n t r u s i o n o f a p a r t i a l l y s o l i d i f i e d magma i . e . i s n o t a t t r i b u t a b l e t o c o m p r e s s i o n d u r i n g emplacement. The o n l y e v i d e n c e o f a d i f f e r e n c e i n m e t a m o r p h i c g r a d e n e a r t h e C o a s t I n t r u s i o n s a r e (1) t h e o c c u r r e n c e o f d i o p s i d e - b e a r i n g a m p h i b o l i t e s w i t h i n 200 t o 300 f e e t o f t h e Denva and S i d e b a c o n Lake p l u t o n s and (2) t h e o c c u r r e n c e o f a s i l l i m a n i t e - b e a r i n g r o c k some 13,000 f e e t f r o m t h e S i d e b a c o n Lake p l u t o n . O t h e r samples o f a m p h i b o l i t e f r o m a l m o s t as c l o s e t o t h e p l u t o n s , i . e . a b o u t 500 f e e t , a r e n o r m a l h o r n - b l e n d e - b i o t i t e a m p h i b o l i t e s , s o t h a t t h e h i g h e r g r a d e amphi b o l i t e s , e v e n i f t h e y f o r m a zone a r o u n d t h e p l u t o n , a r e m i n o r i n e x t e n t . U n f o r t u n a t e l y t h e age r e l a t i o n s h i p between t h e h o r n b l e n d e and d i o p s i d e i n t h e d i o p s i d e - b e a r i n g a m phi b o l i t e s i s n o t c l e a r , so t h a t i t i s n o t known w h e t h e r t h i s l o c a l i z e d h i g h e r g r a d e o f metamorphism was p r o d u c e d d u r i n g t h e m a j o r p e r i o d o f metamorphism o r i s l a t e r s u p e r i m p o s e d t h e r m a l metamorphism. The k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s , t h e l o w e r g r a d e e q u i v a l e n t s o f t h e s i l l i m a n i t e - b e a r i n g r o c k s , o u t c r o p w i t h i n a b o u t 4,000 f e e t o f t h e B e a v e r V a l l e y p l u t o n and w i t h i n some 15,000 f e e t o f t h e S i d e b a c o n Lake p l u t o n , so t h a t t h e one known o u t c r o p o f s i l l i m a n i t e b e a r i n g r o c k s c a n h a r d l y be r e g a r d e d as p r o o f o f h i g h e r g r a d e metamorphism n e a r p l u t o n s . To summarize, t h e r e does n o t seem t o be -any s t r o n g p o s i t i v e e v i d e n c e t h a t t h e C o a s t I n t r u s i o n s , a c c o m p a n i e d by c o m p r e s s i o n due t o some o t h e r c a u s e , were r e s p o n s i b l e f o r t h e metamorphism o f t h e E c s t a l l s e r i e s r o c k s . The w r i t e r f e e l s i t i s u n l i k e l y t h a t t h e y were r e s p o n s i b l e f o r most o f t h e metamorphism, a l t h o u g h t h e d i o p s i d e - b e a r i n g a m p h i b o l i t e s (and s i l l i m a n i t e - b e a r i n g r o c k s ? ) may be t h e r e s u l t s o f l a t e r s u p e r i m p o s e d t h e r m a l metamorphism. I t w o u l d seem t h a t t h e metamorphism o f t h e r o c k s o f t h e E c s t a l l s e r i e s i s p r o b a b l y due t o deep b u r i a l o f t h e s e r o c k s i n a h i g h p r e s s u r e h i g h t e m p e r a t u r e e n v i r o n m e n t d u r i n g o r o g e n y . T h i s must have o c c u r r e d p r i o r t o t h e i n t r u s i o n o f t h e C o a s t I n t r u s i o n s , as i f t h e s e were o l d e r t h e y s h o u l d show much e v i d e n c e o f c o m p r e s s i o n . The C o a s t I n t r u s i o n s may be r e l a t e d t o a l a t e r p h a s e o f t h i s o r o g e n y o r p o s s i b l y t o a s e p a r a t e o r o g e n y . CHAPTER IV THE IGNEOUS ROCKS PETROLOGY OF THE COAST INTRUSIONS The r o c k s o f t h e C o a s t I n t r u s i o n s on Hawkesbury I s l a n d have c o n s i d e r a b l e v a r i a t i o n i n c o m p o s i t i o n . 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 , m o n z o n i t e and q u a r t z m o n z o n i t e (adam- e l l i t e ) a r e a l l p r e s e n t i n t h e m a j o r i n t r u s i v e b o d i e s . The dykes and s i l l s examined a r e m a i n l y q u a r t z m o n z o n i t e o r g r a n o d i o r i t e . I n a d d i t i o n q u a r t z - K f e l d s p a r p e g m a t i t e s a r e common. The dykes and p e g m a t i t e s i n t r u d e t h e p l u t o n s and a r e i n p a r t a t l e a s t , d e f i n i t e l y y o u n g e r t h a n them. The N o r t h M o u n t a i n i n t r u s i o n p r e s u m a b l y p a r t o f t h e m a r g i n o f one o f t h e m a j o r b a t h o l i t h i c masses o f t h e C o a s t I n t r u s i o n s i s p a r t i c u l a r l y i n t e r e s t i n g . I t c o n s i s t s o f a 4 0 0 0 - f o o t w i d e band o f d i o r i t e and q u a r t z d i o r i t e t o t h e s o u t h w h i c h grade i n t o q u a r t z m o n z o n i t e t o t h e n o r t h . The d i o r i t e - q u a r t z d i o r i t e r o c k s a r e c o a r s e t o m e d i u m - g r a i n e d d a r k g r e y r o c k s w i t h a p r o n o u n c e d f o l i a t i o n a n d / o r l i n e a t i o n i n o u t c r o p . T h i s f o l i a t i o n o r l i n e a t i o n i s due t o a s u b - p a r a l l e l a l i g n m e n t o f i n d i v i d u a l h o r n b l e n d e c r y s t a l s , b i o t i t e f l a k e s , c l o t s o f m a f i c s and i n c l u s i o n s o f m a f i c - r i c h r o c k . The l a t t e r r e s e m b l e p l a g i o c l a s e amphi b o l i t e . T h i s i s a c o n t a m i n a t e d b o r d e r f a c i e s o f t h e b a t h o l i t h . The f o l i a t i o n i s p a r a l l e l t o b o t h t h e m a r g i n o f t h e b a t h o l i t h and t h e s t r i k e o f E c s t a l l s e r i e s r o c k s i m m e d i a t e l y t o t h e s o u t h , so t h a t i t i s n o t known w h e t h e r i t i s a r e s u l t o f f l o w b a n d i n g f o r m e d d u r i n g i n j e c t i o n o f a p a r t i a l l y c r y s t a l l i z e d magma o r o f g r a n i t i z a t i o n and p a r t i a l a s s i m i l a t i o n o f t h e r o c k s o f t h e E c s t a l l s e r i e s . S i m i l a r c l o t s and i n c l u s i o n s o f p l a g i o c l a s e a m p h i b o l i t e i n t h e Danva p l u t o n a r e s u b - p a r a l l e l t o t h e s t r i k e o f t h e p l a g i o c l a s e a m p h i b o l i t e n e a r t h e p l u t o n and, i n some p l a c e s , n e a r l y p e r p e n d i c u l a r t o t h e m a r g i n o f t h e p l u t o n . T h e s e must have formed by p a r t i a l a s s i m i l a t i o n o f t h e p l a g i o c l a s e a m p h i b o l i t e o f t h i s a r e a . However, t h e g r a n u l a t i o n o f t h e s e r o c k s s u b - p a r a l l e l t o t h e i r c o n t a c t s and a weak l i n e a t i o n i n t h e q u a r t z m o n z o n i t e seem t o be r e s u l t s o f f l o w . The c o m p o s i t i o n o f t h e d i o r i t e - q u a r t z d i o r i t e g r o u p i s a p p r o x i m a t e l y 50 p e r c e n t t o 70 p e r c e n t p l a g i o c l a s e , 8 t o 15 p e r c e n t q u a r t z , 8 t o 20 p e r c e n t h o r n b l e n d e , 5 t o 17 p e r c e n t b i o t i t e w i t h m i n o r a p a t i t e , s p h e n e , z i r c o n , o p a q u e s , c h l o r i t e , e p i d o t e , a l l a n i t e and s e r i c i t e . No K f e l d s p a r was n o t e d i n t h i n s e c t i o n o r by u s i n g s t a i n i n g t e s t s . I t may be p r e s e n t i n v e r y s m a l l p e r c e n t a g e s however. The m a f i c p e r  c e n t a g e may be much h i g h e r l o c a l l y t h a n t h a t r e c o r d e d a b o v e . I n t h i n s e c t i o n p l a g i o c l a s e i s s e e n commonly t o be a n h e d r a l o r s u b h e d r a l , a l t h o u g h o c c a s i o n a l l y e u h e d r a l , and t o v a r y g r e a t l y i n g r a i n s i z e . Q u a r t z i s f o u n d as s m a l l a n h e d r a l g r a i n s i n t e r s t i t i a l t o t h e p l a g i o c l a s e . H o r n b l e n d e o c c u r s i n 120 l a r g e g e n e r a l l y s u b h e d r a l c r y s t a l s some o f w h i c h have s i e v e t e x t u r e . B i o t i t e i s f o u n d as s m a l l s u b h e d r a l p l a t e y g r a i n s . T h e r e i s u s u a l l y e x t e n s i v e g r a n u l a t i o n o f t h e q u a r t z and f e l d s p a r . P l a g i o c l a s e has a c o m p o s i t i o n o f A n ^ £ t o An^g (medium a n d e s i n e ) . T h i s was d e t e r m i n e d by m e a s u r i n g X A 010 f o r s e c t i o n s _La a n d , i n one c a s e , by measurements on a C a r l s b a d - a l b i t e t w i n . Complex t w i n n i n g i s common a l t h o u g h C a r l s b a d - a l b i t e c o m b i n  a t i o n s a r e r a r e . Zoned f e l d s p a r s a r e v e r y r a r e , w h i c h i s u n u s u a l i n r o c k s o f t h i s n a t u r e . The z o n i n g i s o f t h e r e v e r s e t y p e i n one g r a i n t h e c o r e b e i n g a b o u t A n ^ and t h e r i m An^Q. H o r n b l e n d e i s b i a x i a l n e g a t i v e . Z A c e q u a l s 22° - 23° and t h e p l e o c h r o i c f o r m u l a i s X - p a l e y e l l o w , Y - g r e e n , and Z - deep g r e e n t o b r o w n i s h g r e e n . S i m p l e t w i n s on 100 a r e v e r y common. B i o t i t e i s p l e o c h r o i c f r o m d a r k brown t o s t r a w . I t i s o c c a s i o n a l l y a l t e r e d t o a c h l o r i t e w i t h anomalous deep b l u e i n t e r f e r e n c e c o l o r s , p o s s i b l y p e n n i n e . The commonest v a r i e t y o f e p i d o t e p r e s e n t i s p i s t a c i t e . I t i s s t r o n g l y p l e o c h r o i c f r o m y e l l o w t o c o l o r l e s s , h i g h l y b i r e f r i n g e n t , and b i a x i a l n e g a t i v e w i t h a l a r g e 2V. The p i s t a c i t e o c c a s i o n a l l y e n c l o s e d c o r e s o f a l l a n i t e w i t h t h e same c r y s t a l l o g r a p h i c o r i e n t a t i o n b u t d i f f e r e n t e x t i n c t i o n p o s i t i o n . The a l l a n i t e i s p l e o c h r o i c f r o m^deep brown t o c o l o r l e s s . T h e s e m i n e r a l s o c c u r as s m a l l s u b h e d r a l o r a n h e d r a l g r a i n s . 121 S e r i c i t e , n e v e r i n amounts o f g r e a t e r t h a n 1 p e r c e n t , i s p r e s e n t as s m a l l f l a k e s and f e l t y masses i n most p l a g i o  c l a s e g r a i n s . A c c e s s o r y m i n e r a l s p r e s e n t i n c l u d e a p a t i t e , s p h e n e , z i r c o n and o p a ques. A p a t i t e i s f o u n d as v e r y s m a l l s u b h e d r a l o r e u h e d r a l p r i s m s o f low b i r e f r i n g e n c e and l e n g t h f a s t c h a r  a c t e r . Sphene and z i r c o n o c c u r as somewhat l a r g e r g r a i n s , t h e f o r m e r as a n h e d r a l g r a n u l e s and s u b h e d r a l t o e u h e d r a l wedge shaped c r y s t a l s w h i c h a r e w e a k l y p l e o c h r o i c f r o m p a l e brown t o c o l o r l e s s , and t h e l a t t e r as s u b h e d r a l s q u a r i s h c r y s t a l s o f u n i a x i a l p o s i t i v e c h a r a c t e r . Opaques a r e f o u n d as a n  h e d r a l g r a i n s and s u b h e d r a l c r y s t a l s o f c u b i c s h a p e , and a r e p r o b a b l y m a i n l y m a g n e t i t e o r p y r i t e . T h e y a r e v e r y uncommon i n t h e s e r o c k s . The q u a r t z m o n z o n i t e o f t h e N o r t h M o u n t a i n i n t r u s i o n i s medium t o c o a r s e - g r a i n e d and i s p i n k i n c o l o r . I t commonly has a v e r y weak f o l i a t i o n . I t s c o m p o s i t i o n a v e r a g e s 39 p e r c e n t p l a g i o c l a s e , 27 p e r c e n t K f e l d s p a r , 27 p e r c e n t q u a r t z , 1 t o 2 p e r c e n t h o r n b l e n d e , 2 p e r c e n t b i o t i t e , 1 t o 2 p e r c e n t c h l o r i t e and l e s s t h a n 1 p e r c e n t o f e p i d o t e , a l l a n i t e , s e r i c i t e , a p a t i t e z i r c o n , sphene and o p a q u e s . I n t h i n s e c t i o n p l a g i o c l a s e i s commonly e u h e d r a l o r s u b h e d r a l b u t may o c c u r i n m y r m e k i t e s as a n h e d r a l g r a i n s c o n  t a i n i n g v e r m i c u l a r q u a r t z . I t i s commonly i n l a r g e r g r a i n s t h a n t h e o t h e r m i n e r a l s . Q u a r t z i s a n h e d r a l and i n t e r s t i t i a l . 122 K f e l d s p a r i s f o u n d i n l a r g e s u b h e d r a l o r a n h e d r a l g r a i n s w i t h f r i n g e s o f m y r m e k i t e . B i o t i t e and h o r n b l e n d e a r e f o u n d a s s m a l l s u b h e d r a l g r a i n s . A n e x t r e m e l y weak l i n e a t i o n i s p r e s e n t due t o a weak s u b - p a r a l l e l o r i e n t a t i o n o f b i o t i t e and h o r n  b l e n d e . Q u a r t z commonly has u n d u l a t o r y e x t i n c t i o n and t h e f e l d s p a r s may be f r a c t u r e d , b u t t h e e x t e n s i v e g r a n u l a t i o n common i n t h e q u a r t z d i o r i t e - d i o r i t e i s l a c k i n g . D e s p i t e t h e weak f o l i a t i o n and some d e f o r m a t i o n t h e t e x t u r e i s e s s e n t i a l l y h y p i d i o m o r p h i c g r a n u l a r . P l a g i o c l a s e has a c o m p o s i t i o n o f An^Q t o An^g* Complex t w i n s a r e common, i n c l u d i n g a few o f t h e C a r l s b a d - a l b i t e t y p e . Z o n i n g i s a p p a r e n t l y a b s e n t . The K f e l d s p a r p r e s e n t u s u a l l y h as w e a k l y d e v e l o p e d g r i d t w i n n i n g and so i s m i c r o c l i n e i n p a r t a t l e a s t . No C a r l s b a d t w i n s were n o t e d . H o r n b l e n d e and b i o t i t e a r e t h e same t y p e s as t h o s e f o u n d i n t h e d i o r i t e - q u a r t z d i o r i t e . T h e y a r e b o t h rimmed and r e p l a c e d by a c h l o r i t e w i t h d a r k p u r p l i s h anomalous i n t e r f e r e n c e c o l o r s . A p a t i t e , s p h e n e , z i r c o n and t h e opaques p r e s e n t a r e a l s o t h e same t y p e s as t h o s e f o u n d i n t h e d i o r i t e - q u a r t z d i o r i t e r o c k s . The s p h e n e , however, i s u s u a l l y e u h e d r a l and may be i n e x t r e m e l y l a r g e g r a i n s . I t commonly e n c l o s e s ' opaque c o r e s w h i c h may be i l m e n i t e . The e p i d o t e g r o u p m i n e r a l s a r e p a r t i c u l a r l y i n t e r e s t  i n g i n t h e s e r o c k s . T hey c o n s i s t o f p i s t a c i t e and a l l a n i t e . 123 The a l l a n i t e may f o r m t h e c e n t r e o f t h e g r a i n and have a m a r g i n o f p i s t a c i t e , o r o c c u r a s i r r e g u l a r p a t c h e s i n t h e p i s t a c i t e o r as s e p a r a t e g r a i n s . P i s t a c i t e i s b i a x i a l n e g a t i v e , s t r o n g l y b i r e f r i n g e n t , and may be i n t e n s e l y p l e o c h r o i c f r o m b r i g h t y e l l o w t o c o l o r l e s s , o r w e a k l y p l e o c h r o i c . A l l a n i t e i s a l w a y s s t r o n g l y p l e o c h r o i c f r o m d a r k brown t o l i g h t brown. E p i d o t e may o c c u r i n a n h e d r a l , s u b h e d r a l , o r e u h e d r a l g r a i n s . S e r i c i t e i s much more common i n t h e s e r o c k s t h a n i n t h e d i o r i t e - q u a r t z d i o r i t e . I t o c c u r s n o t o n l y as f e l t y masses t h r o u g h o u t t h e f e l d s p a r g r a i n s b u t a l s o o c c a s i o n a l l y i n f r a c t u r e s i n t h e s e g r a i n s . The Danva p l u t o n has a w i d e v a r i a t i o n i n c o m p o s i t i o n . Of t h e f o u r t h i n s e c t i o n s s t u d i e d two a r e m o n z o n i t e , one i s q u a r t z m o n z o n i t e and one i s g r a n o d i o r i t e . I n a d d i t i o n a v e r y n a r r o w b o r d e r p h a s e , s i m i l a r t o t h e q u a r t z d i o r i t e - d i o r i t e o f t h e N o r t h M o u n t a i n i n t r u s i o n , i s p r e s e n t . I n b o t h hand s p e c i m e n and t h i n s e c t i o n t h e s e r o c k s a r e t e x t u r a l l y and m i n e r a l o g i c a l l y , e x c e p t f o r a d i f f e r e n c e i n p r o p o r t i o n s , a l m o s t i d e n t i c a l t o t h e N o r t h M o u n t a i n q u a r t m o n z o n i t e . The m o n z o n i t e has t h e f o l l o w i n g a v e r a g e c o m p o s i t i o n : p l a g i o c l a s e 55 p e r c e n t , K f e l d s p a r 35 p e r c e n t , q u a r t z 5 p e r c e n t and l e s s t h a n 1 p e r c e n t e a c h o f c h l o r i t e , s e r i c i t e , b i o t i t e , h o r n b l e n d e , e p i d o t e , a l l a n i t e , s p h e ne, a p a t i t e , z i r c o n and opaques. The p l a g i o c l a s e i s A n ^ 2 t o A n ^ , d e t e r  mined by m e a s u r i n g X '/vOlO f o r s e c t i o n s i . a. Complex t w i n s a r e r a t h e r uncommon and no z o n i n g i s p r e s e n t . The q u a r t z monzon-124 i t e has 50 p e r c e n t p l a g i o c l a s e , 30 p e r c e n t m i c r o c l i n e , 15 p e r c e n t q u a r t z , and t h e same m i n o r m i n e r a l s as t h e monzon- i t e . I t s p l a g i o c l a s e has a c o m p o s i t i o n o f A n ^ d e t e r m i n e d by m e a s u r i n g X ^ O I O f o r s e c t i o n s X a. A p a r t f r o m t h e s e f e a t u r e s t h i s r o c k i s i d e n t i c a l w i t h t h e m o n z o n i t e . The g r a n o d i o r i t e h a s 55 p e r c e n t p l a g i o c l a s e , 15 p e r c e n t m i c r o c l i n e and 25 p e r c e n t q u a r t z and t h e same m i n o r m i n e r a l s as t h e above r o c k s . The p l a g i o c l a s e p r e s e n t i s An^Q, d e t e r m i n e d f o r a C a r l s b a d - a l b i t e t w i n . The B e a v e r Lake p l u t o n has n o t b e e n s t u d i e d i n d e t a i l . I n o u t c r o p , i n hand s p e c i m e n , and i n t h i n s e c t i o n , t h i s r o c k i s v e r y s i m i l a r t o t h e r o c k s o f t h e Danva p l u t o n and t o t h e N o r t h M o u n t a i n i n t r u s i o n q u a r t z m o n z o n i t e . The o n l y t h i n s e c t i o n s t u d i e d i s q u a r t z m o n z o n i t e w i t h 40 p e r c e n t p l a g i o  c l a s e , 38 p e r c e n t m i c r o c l i n e , 20 p e r c e n t q u a r t z and l e s s t h a n 1 p e r c e n t o f e a c h o f b i o t i t e , a p a t i t e , c h l o r i t e , and s e r i c i t e . No sphene, z i r c o n , o p a q u e s , o r e p i d o t e g r o u p m i n e r  a l s a r e p r e s e n t . The t e x t u r e i s h y p i d i o m o r p h i c g r a n u l a r w i t h l i t t l e e v i d e n c e o f d e f o r m a t i o n . The m i n e r a l s p r e s e n t a l l have t h e same p r o p e r t i e s as t h o s e i n t h e q u a r t z m o n z o n i t e o f t h e N o r t h M o u n t a i n i n t r u s i o n . C o m p o s i t i o n o f t h e p l a g i o c l a s e i s An^o? b a s e d on m e a s u r i n g N x ' f o r c l e a v a g e f r a g m e n t s . The S i d e b a c o n L a k e p l u t o n i s a l s o i n a d e q u a t e l y s t u d i e d . I t seems t o be composed o f r o c k s i m i l a r t o t h e g r a n o d i o r i t e - q u a r t z m o n z o n i t e - m o n z o n i t e o f t h e o t h e r l a r g e m a s s e s . The o n l y t h i n s e c t i o n examined c o n t a i n s 45 p e r c e n t p l a g i o c l a s e , 125 20 p e r c e n t m i c r o c l i n e , 25 p e r c e n t q u a r t z , 5 p e r c e n t b i o t i t e , 2 p e r c e n t e p i d o t e and l e s s t h a n 1 p e r c e n t o f e a c h o f h o r n  b l e n d e , a p a t i t e , z i r c o n , s p h e n e , o p a q u e s , c h l o r i t e and s e r i  c i t e . T h i s i s a q u a r t z m o n z o n i t e b u t i s v e r y c l o s e t o t h e c o m p o s i t i o n b o u n d a r y between g r a n o d i o r i t e and q u a r t z m o n z o n i t e . The r o c k i s e s s e n t i a l l y h y p i d i o r m o r p h i c g r a n u l a r w i t h o u t any d i r e c t i o n a l t e x t u r e s . Q u a r t z commonly has u n d u l a t o r y ex t i n c t i o n and t h e f e l d s p a r s may be f r a c t u r e d and b i o t i t e b e n t , b u t d e f o r m a t i o n i s q u i t e m i n o r . The p l a g i o c l a s e o f t h i s r o c k has a c o m p o s i t i o n o f A n ^ b a s e d on d e t e r m i n a t i o n s o f N x> f o r c l e a v a g e f r a g m e n t s . I t i s n o t z o n e d . B i o t i t e i s p l e o c h r o i c f r o m g r e e n i s h brown t o c o l o r l e s s . The e p i d o t e i s n o t q u i t e as s t r o n g l y p l e o c h r o i c as t h a t o f t h e N o r t h M o u n t a i n q u a r t z m o n z o n i t e b u t does show d i s t i n c t y e l l o w t o c o l o r l e s s p l e o c h r o i s m . The o t h e r m i n e r a l s p r e s e n t a l l have t h e same p r o p e r t i e s as t h o s e i n t h e N o r t h M o u n t a i n q u a r t z m o n z o n i t e . The dykes b e l o n g i n g t o t h e C o a s t I n t r u s i o n s a r e v e r y s i m i l a r t o t h e l a r g e r b o d i e s , a l t h o u g h t h e y t e n d t o be f i n e r g r a i n e d . Many a r e a p l i t e s . T h e i r t e x t u r e i s commonly h y p i d i o m o r p h i c g r a n u l a r . T h ey commonly l a c k f o l i a t i o n b u t may be s t r o n g l y g r a n u l a t e d , p r o b a b l y i n d i c a t i n g i n t r u s i o n i n p a r t l y c r y s t a l l i n e f o r m . T h e i r c o m p o s i t i o n r a n g e s f r o m g r a n o  d i o r i t e t o q u a r t z m o n z o n i t e . The same m a j o r and m i n o r m i n e r a l s a r e p r e s e n t as t h o s e i n t h e p l u t o n s . An i n t e r e s t i n g f e a t u r e o f t h e s e dykes i s t h a t most o f them c o n t a i n numerous i n c l u s -F i g u r e 38. P h o t o m i c r o g r a p h o f q u a r t z d i o r i t e f r o m t h e N o r t h M o u n t a i n i n t r u s i o n . P l a i n l i g h t X24. The r a g g e d b i o t i t e , h o r n b l e n d e and m i n o r e p i d o t e a r e p r o b a b l y due t o a s s i m i  l a t i o n o f c o u n t r y r o c k . F i g u r e 39. P h o t o m i c r o g r a p h o f q u a r t z d i o r i t e f r o m t h e N o r t h M o u n t a i n i n t r u s i o n . P o l a r i z e d l i g h t X24. As F i g u r e 29. 1 2 7 Figure 40. Photomicrograph of monzonite from the Danva pluton. Polarized light X24. Microcline, plagio clase, quartz and myrmekite are present. Figure 41. Photomicrograph of granodiorite. Plain light X24. A contaminated dyke containing biotite, horn blende, epidote and sphene. 128 i o n s o f c o u n t r y r o c k i n v a r i o u s s t a g e s o f d i g e s t i o n , and i n c o n s e q u e n c e t h i n s e c t i o n s may be crowded w i t h s u c h m i n e r a l s as h o r n b l e n d e , b i o t i t e and e p i d o t e , and c o n t a i n some a l m a n  d i n e , a l l o f w h i c h have r e s i s t e d d i g e s t i o n . The p e g m a t i t e s c o n s i s t o f q u a r t z , K f e l d s p a r and i n some c a s e s b i o t i t e o r p a l e g r e e n i s h m u s c o v i t e . S m a l l e u h e d r a l i g a r n e t s ' were f o u n d i n one p e g m a t i t e . The q u a r t z and K f e l d  s p a r a r e commonly f o u n d i n g r a p h i c i n t e r g r o w t h s . The K f e l d s p a r i s u s u a l l y w h i t e and t h e q u a r t z g l a s s y and c o l o r l e s s . B i o t i t e and m u s c o v i t e a r e f o u n d as s m a l l s c a t t e r e d f l a k e s * O c c a s i o n a l l y m u s c o v i t e o c c u r s as " b o o k s " o f m i c a up t o 2 i n c h e s t h i c k and 4 i n c h e s a c r o s s . The g a r n e t i s a deep r e d t y p e s i m i l a r i n a p p e a r a n c e t o t h e g a r n e t s o f t h e meta  m o r p h i c r o c k s . I t may have b e e n f o r m e d f r o m m a t e r i a l a s s i m i l  a t e d f r o m t h e w a l l r o c k . ORIGIN AND NATURE OF THE COAST INTRUSIONS The g r a n i t i c r o c k s o f Hawkesbury I s l a n d o c c u r i n m a i n  l y d i s c o r d a n t b o d i e s . The b o u n d a r i e s o f t h e p l u t o n s a r e i n some p l a c e s n e a r l y p e r p e n d i c u l a r t o t h e f o l i a t i o n o f t h e m e t a m o r p h i c r o c k s . The dykes and p e g m a t i t e s a r e g e n e r a l l y o f random o r i e n t a t i o n and i n t r u d e t h e p l u t o n s , so t h a t t h e y c a n n o t be r e g a r d e d as e v i d e n c e o f p a r t i a l g r a n i t i z a t i o n o f t h e c o u n t r y r o c k . The b o u n d a r i e s o f t h e p l u t o n s and d y k e s a r e q u i t e s h a r p and n o t d i f f u s e i n n a t u r e . T h e r e a r e many x e n o l i t h s i n t h e m a r g i n a l p a r t s o f t h e p l u t o n s and i n t h e d y k e s . 129 T h e s e x e n o l i t h s a p p e a r t o have t h e same o r i e n t a t i o n as t h e same r o c k t y p e o u t s i d e t h e p l u t o n s and d y k e s . T h e s e f e a t u r e s a p a r t f r o m t h e x e n o l i t h s , i n d i c a t e t h a t t h e C o a s t I n t r u s i o n s o f t h i s a r e a a r e t r u l y i n t r u s i v e i n c h a r a c t e r and a r e n o t p r o d u c t s o f g r a n i t i z a t i o n i n s i t u . However, t h e x e n o l i t h s show t h e y have a s s i m i l a t e d a good d e a l o f c o u n t r y r o c k w i t h  out d i s p l a c i n g i t t o any g r e a t e x t e n t . T h i s a s s i m i l a t i o n i s m a r g i n a l i n t h e c a s e o f t h e p l u t o n s and may be c o n s i d e r e d t o be a c o n t a c t e f f e c t . The two m a i n modes o f o r i g i n c u r r e n t l y f a v o r e d f o r g r a n i t i c r o c k s o f d e f i n i t e l y i n t r u s i v e c h a r a c t e r a r e (1) s e l e c t i v e f u s i o n o f p r e v i o u s l y s o l i d i f i e d r o c k s c a r r i e d t o d e p t h and i n t r u s i o n o f t h e f u s e d f r a c t i o n and (2) t h e f o r  m a t i o n o f a g r a n i t i c magma by d i f f e r e n t i a t i o n o f a b a s a l t i c magma. The p r o d u c t s o f e i t h e r o f t h e s e p r o c e s s e s w o u l d p r o b a b l y be i n d i s t i n g u i s h a b l e . A t any r a t e , t h e w r i t e r has f o u n d no e v i d e n c e i n t h e map a r e a s u p p o r t i n g one o f t h e s e v i e w s a g a i n s t t h e o t h e r and w i l l n o t d i s c u s s t h i s p o i n t any f u r t h e r . OTHER INTRUSIONS (1) C a r b o n a t i z e d A n d e s i t i c ( ? ) Roc k s T h i s r o c k t y p e was n o t e d o n l y i n West T r e n c h b r o o k , a t e l e v a t i o n 390 f e e t . H e r e i t o c c u r s as a b o u d i n and has a t o t a l known e x t e n t o f some llO f e e t by 3 f e e t . A l t h o u g h t h e b r o o k f l o w s a l o n g s t r i k e no o t h e r b o u d i n s were n o t e d . i I n hand s p e c i m e n t h i s i s a p a l e b r o w n i s h g r e y a p h a n - I 130 i t i c r o c k v e i n e d by numerous c a l c i t e - f i l l e d f r a c t u r e s . I t w e a t h e r s t o a p a l e b r o w n i s h c o l o r . I n t h i n s e c t i o n i t i s f o u n d t o c o n s i s t o f a v e r y f i n e - g r a i n e d groundmass composed m a i n l y o f p l a g i o c l a s e w i t h m i n o r opaques, i s o t r o p i c m a t e r i a l ( g l a s s ? ) and a l t e r a t i o n p r o d u c t s . No q u a r t z o r K f e l d s p a r was n o t e d . A few l a r g e p h e n o c r y s t s c o m p l e t e l y r e p l a c e d by c a l c i t e a n d / o r a f i n e a g g r e g a t e o f u n i d e n t i f i e d m a t e r i a l a l s o o c c u r . Numerous v e i n s o f c a l c i t e and m i n o r q u a r t z a r e p r e s e n t . One a p a t i t e c r y s t a l was s e e n i n a c a l c i t e v e i n . The p l a g i o c l a s e o f t h e groundmass o c c u r s as l a t h  l i k e g r a i n s i n t e r w o v e n i n t o a f e l t y , n o n - d i r e c t i o n a l a g g r e g a t e . Two o r t h r e e ( a l b i t e ? ) t w i n l a m e l l a e c a n be s e e n u n d e r h i g h power i n some l a t h s . The c o m p o s i t i o n o f t h e p l a g i o c l a s e i s An]_3, ( o l i g o c l a s e ) d e t e r m i n e d by m e a s u r i n g N x ' f o r c l e a v a g e f r a g m e n t s . I t p r o b a b l y forms a t l e a s t 9 0 p e r c e n t o f t h e groundmass. The opaque m a t e r i a l i s f o u n d as v e r y s m a l l a n h e d r a l and a z b h e d r a l g r a i n s and o c c a s i o n a l l y as e u h e d r a l g r a i n s w i t h c u b i c o r o c t a h e d r a l o u t l i n e s . I t i s p r o b a b l y m a g n e t i t e . I t a p p e a r s t o be s c a t t e r e d a t random t h r o u g h o u t t h e r o c k , o f w h i c h i t f o r m s p e r h a p s 1 p e r c e n t . The m a t e r i a l between t h e f e l d s p a r l a t h s i s m a i n l y i s o t r o p i c and has t h e same r e l i e f as b a l s a m . I t i s p r o b a b l y g l a s s . I t may f o r m 5 p e r c e n t o f t h e groundmass. The commonest a l t e r a t i o n p r o d u c t i s a b r o w n i s h s u b  s t a n c e w h i c h l o o k s opaque under medium power b u t i s s e e n t o be 131 t r a n s p a r e n t u nder h i g h power. I t o c c u r s i n e x t r e m e l y s m a l l r o u n d e d g r a i n s and i s so f i n e t h a t b i r e f r i n g e n c e and o t h e r p r o p e r t i e s c o u l d n o t be d e t e r m i n e d . T h i s m a t e r i a l i s s c a t t e r e d t h r o u g h o u t t h e s e c t i o n b u t i s p a r t i c u l a r l y common i n , and a l o n g t h e m a r g i n s o f , t h e a l t e r e d p h e n o c r y s t s . I t s p r e s e n c e a l o n g t h e i r m a r g i n s makes t h e p h e n o c r y s t s q u i t e c o n s p i c u o u s i n o r d i n a r y l i g h t . A n o t h e r a l t e r a t i o n p r o d u c t , c o n f i n e d t o t h e p h e n o c r y s t s , i s a f i n e - g r a i n e d , c o l o r l e s s , a n i s o t r o p i c a g g  r e g a t e w i t h low r e l i e f and maximum i n t e r f e r e n c e c o l o r s o f f i r s t o r d e r w h i t e . I t may be composed o f s e c o n d a r y f e l d s p a r s . The shape o f t h e p h e n o c r y s t s s u g g e s t s t h e y may have been p y r o x e n e s , a m p h i b o l e s , and f e l d s p a r s . Most o f them have a s h o r t r h o m b i c o u t l i n e ( p y r o x e n e o r a m p h i b o l e s ? ) b u t a few a r e s q u a r e o r n e a r l y s o ( f e l d s p a r ? ) . The v e i n m a t e r i a l i s m a i n l y s u b h e d r a l c a l c i t e . Q u a r t z o c c u r s as a few l a r g e l e n s - s h a p e d masses i n , and a s s o c i a t e d w i t h , c a l c i t e . The s i n g l e a p a t i t e c r y s t a l n o t e d i s an e l o n g a t e p r i s m a t i c g r a i n w i t h s e v e r a l c r o s s f r a c t u r e s . On a compos i t iona-^ b a s i s i t seems l i k e l y t h i s r o c k was an a n d e s i t e o r a s i m i l a r r o c k . I t seems e s s e n t i a l l y c o n c o r d e n t and may be a n i n t r u s i v e ( s i l l ) o r e x t r u s i v e ( f l o w ) . The age o f t h i s r o c k t y p e i s i n d o u b t . I t may be o l d e r t h a n , y o u n g e r t h a n o r i n t r o d u c e d d u r i n g t h e m a i n p e r i o d o f metamorphism. The t h i r d p o s s i b i l i t y may be d i s m i s s e d , as t h e g r a d e o f metamorphism i s s u c h t h a t i t i m p l i e s deep b u r i a l and h i g h t e m p e r a t u r e d u r i n g metamorphism. Any r ock i n t r u d e d under t h e s e c o n d i t i o n s w o u l d n o t have t h e g l a s s y m a t r i x and 132 Figure 42. Photomicrograph of (?) andesitic rock. P l a i n l i g h t X64. A phenocryst replaced by c a l c i t e and rimmed by extremely f i n e  grained brownish material i n a ground- mass of feldspar l a t h s , glass (?), opaques, etc. A vein of c a l c i t e i s also present. Figure 43. Photomicrograph of (?) andesitic rock. Polarized l i g h t X64. Similar to figure 42. A small phenocryst i s present i n the upper centre replaced by a f i n e  grained aggregate of secondary feldspar(?) 133 t e x t u r e t h i s r o c k h a s . I t i s d i f f i c u l t t o s e e how t h i s r o c k w o u l d r e t a i n i t s t e x t u r e i f i n t r u d e d p r i o r t o metamorphism. The t e m p e r a t u r e w o u l d p r o b a b l y n o t be h i g h enough t o s e r i o u s l y a f f e c t t h e m a i n m i n e r a l s i n t h i s r o c k b u t t h e g l a s s s h o u l d r e c r y s t a l l i z e . I f t h e a n d e s i t e ( ? ) i s l a t e r t h a n t h e m a i n p e r i o d o f metamorphism, i t must have b e e n i n v o l v e d i n some l a t e r d e f o r m a t i o n . The p r e s e n c e i n t h i s a r e a o f s l i c k e n s i d e s i n a g r a p h i t i c bed and o f m i n o r s e r i c i t e s c h i s t s , common i n s h e a r z o n e s e l s e w h e r e , s u g g e s t s t h i s may have been t h e c a s e . Due t o s e r i o u s d o u b t s as t o w h e t h e r t h i s r o c k c o u l d have s u r v i v e d , w i t h i t s p r e s e n t a s s e m b l a g e , t h r o u g h t h e p e r i o d o f r e g i o n a l metamorphism, t h e w r i t e r b e l i e v e s i t i s most l i k e l y t h i s i s an i n t r u s i o n w h i c h i s y o u n g e r t h a n t h i s metamorphism. I n t h i s c a s e i t w o u l d o f n e c e s s i t y be a s i l l o r d y k e . (2) Lamprophyre D y k e s : Lamprophyre d y k e s a r e n o t a b u n d a n t on Hawkesbury I s l a n d , b u t a r e f o u n d h e r e and t h e r e c u t t i n g t h r o u g h t h e E c s t a l l s e r i e s . I n one l o c a l i t y t h e y were o b s e r v e d c u t t i n g t h r o u g h g r a n i t i c d ykes b e l o n g i n g t o t h e C o a s t I n t r u s i o n s . I n d i v i d u a l dykes a r e g e n e r a l l y o n l y a b o u t 1 t o 20 f e e t w i d e , b u t one dyke was s e e n t h a t i s a b o u t 150 f e e t w i d e . Most dykes a r e q u i t e s t r a i g h t and o f f a i r l y c o n s t a n t w i d t h , b u t s e v e r a l were n o t e d w h i c h p i n c h e d and s w e l l e d and t h e o c c a s i o n a l dyke s p l i t s i n t o two o r more b r a n c h e s w h i c h may o r may n o t r e j o i n . The l a m p r o p h y r e i s d a r k g r e e n t o g r e y - b l a c k i n c o l o r . It commonly weathers to a rusty brown shade. It consists of numerous black hornblende phenocrysts up to 1/3 of an inch in length set in an aphanitic groundmass. The hornblende pheno crysts are commonly long, prismatic, rod-like crystals, but may be in part short and stubby. They commonly make up some 15 per cent to 20 per cent of the rock but may reach 40 per cent. In thin section the hornblende phenocrysts are seen to be embedded in a groundmass composed of plagioclase laths, smaller hornblende crystals^" and generally subhedral grains of magnetite. A few elongate apatite laths are also present. The magnetite grains may make up as much as 5 per cent of the rock and the plagioclase and alteration products up to 75 per cent. Secondary minerals, comprising calcite, chlorite, epidote and sericite, are always presents The hornblende is commonly in euhedral crystals. These are occasionally fractured and cemented by plagioclase or various alteration products. The hornblende is a deep brown variety which has well developed rhythmic zoning in some thin sections. It commonly has simple twins on (100). The plagioclase, generally in euhedral elongate laths, has a composition of An^Q to An^ 4 in various thin sections, determined by measuring N x'for cleavage flakes. Of the secondary minerals; calcite, epidote and se r i  cite are found replacing plagioclase and chlorite and calcite occurs replacing hornblende. These minerals vary greatly in 135 Figure 44. Photomicrograph of lamprophyre. P l a i n l i g h t X64. Elongate horn blende phenocrysts i n a groundmass of feldspar, epidote, c h l o r i t e , apatite and opaques. Figure 45. Photomicrograph of lamprophyre P l a i n l i g h t X24. Stubby zoned hornblende phenocrysts of various sizes i n a groundmass of feldspar, epidote, apatite, c h l o r i t e , c a l c i t e and opaques. 136 amount, a t a maximum c o m p r i s i n g some 40 p e r c e n t o f t h e t h i n s e c t i o n . They a r e a l l g e n e r a l l y a n h e d r a l , e x c e p t t h a t i n c a s e s o f c o m p l e t e r e p l a c e m e n t t h e y may f o r m e u h e d r a l o r s u b  h e d r a l pseudomorphs. E p i d o t e i s a f a i n t l y p l e o c h r o i c p i s t a c i t e . C h l o r i t e has anomalous g r e y i s h y e l l o w t o g r e y i s h g r e e n i n t e r f e r e n c e c o l o r s , p a r a l l e l o r n e a r l y p a r a l l e l ex t i n c t i o n , and i s w e a k l y p l e o c h r o i c f r o m p a l e g r e e n t o c o l o r  l e s s . C a l c i t e and s e r i c i t e have t h e u s u a l p r o p e r t i e s o f t h e s e m i n e r a l s . CHAPTER V STRUCTURAL GEOLOGY GENERAL STRUCTURE OF THE NORTHERN PART OF THE COAST MOUNTAINS The n o r t h e r n p a r t o f t h e C o a s t I n t r u s i o n s o f B r i t i s h C o l u m b i a have a g e n e r a l t r e n d o f a l i t t l e west o f n o r t h . T h i s t r e n d i s p a r a l l e l e d by numerous r o o f p e n d a n t s , s e p t a , e t c . , w h i c h g e n e r a l l y s t r i k e between n o r t h and n o r t h 15° w e s t . The E c s t a l l septum o r r o o f p e n d a n t has a g e n e r a l s t r i k e o f n o r t h 15° west i n t h e D o u g l a s C h a n n e l - S k e e n a R i v e r a r e a and p r o b a b l y a s i m i l a r s t r i k e n o r t h o f t h e S k e e n a and s o u t h o f G a r d n e r C a n a l . However, a c r o s s Hawkesbury I s l a n d t h e g e n e r a l s t r i k e o f t h e septum i s n o r t h 6 0 ° w e s t . The t r e n d o f t h e C o a s t M o u n t a i n s g e o l o g i c a l p r o v i n c e and o f t h e s t r u c t u r e s w i t h i n i t a r e r e f l e c t i o n s o f t h e f o r c e s and c o n d i t i o n s w h i c h have a f f e c t e d and a r e p r o b a b l y s t i l l a f f e c t i n g t h i s r e g i o n . The g e n e r a l n o r t h t o n o r t h - w e s t t r e n d o f t h e C o a s t M o u n t a i n s p r o b a b l y r e f l e c t s t h e e f f e c t s o f s t r o n g c o m p r e s s i v e f o r c e s w h i c h have a c t e d i n a d i r e c t i o n a p p r o x i m a t e l y a t r i g h t a n g l e s t o t h i s t r e n d . The bend o r warp o f t h e E c s t a l l septum a c r o s s Hawkesbury I s l a n d f i n d s p a r a l l e l s i n t h e K o o t - enay A r c h c o m p o s i t e f o l d s y s t e m , i n a s i m i l a r s y s t e m i n t h e Skeen a M o u n t a i n s between l a t i t u d e 55° and 57° N, and i n warps i n o t h e r s e p t a a n d / o r r o o f p e n d a n t s o f t h e C o a s t Range, as p o i n t e d o u t by White." 1' T h e s e f e a t u r e s a r e a l l c o n v e x e a s t w a r d , 1 W.H.White, " C o r d i l l e r a n T e c t o n i c s i n B r i t i s h C o l u m b i a " A.A.P.G. B u l l . , J a n , 1959 5 p. 60, et s e q . 138 and, according to White "resemble drag folds orientated to conform with a counter-clockwise rotation of the entire con- 0 tinental margin around the North Pacific basin." MAJOR STRUCTURAL FEATURES OF THE MAP AREA The general trend of the foliation of the Ecstall series rocks on Hawkesbury Island is north 60° west to north 70° west north of a line running approximately from Backbacon Lake to Evelyn Lake. South of this line there is considerable variation in strike and dip but strikes of about north 45° east are predominant. There is a change in strike from north 60° to 70° west to north 45° east over a narrow transitional zone. The variation in strike probably is due to folding as there is no evidence of major faulting and the rocks which have the different trends are very similar in lithology. In order to determine what deformation or deformations have affected the metamorphic rocks of this area figures 46 to 52 have been constructed. If these rocks have been affected by one period of deformation, the intersections of the planes of foliation, shown in figures 47 to 51» should have one strong maxima. The position of this maxima should indicate the strike and plunge of the fold axes. A scattering of the points of intersection and the production of two or more maxima in dicate that the area has undergone more than one period of deformation. Examination of figures 47 to 52 shows that part of the area, at least, has undergone more than one period of White, ibid, p. 60. d e f o r m a t i o n . The amount o f s c a t t e r i n g o f p o i n t s o f i n t e r  s e c t i o n d e c r e a s e s f r o m west t o e a s t i n t h e s o u t h e r n p a r t o f t h e a r e a . T h e r e a p p e a r s t o be l i t t l e o r no s c a t t e r i n g i n t h e n o r t h e r n p a r t o f t h e map a r e a , w h i c h c a n be i n t e r p r e t e d as i n d i c a t i n g e i t h e r (1) t h a t t h e n o r t h e r n a r e a was i n v o l v e d i n o n l y one p e r i o d o f d e f o r m a t i o n o r (2) t h a t i n t h i s a r e a t h e e f f e c t o f t h e l a s t s t r o n g p e r i o d o f d e f o r m a t i o n i s so s t r o n g as t o o b l i t e r a t e t r a c e s o f any e a r l i e r d e f o r m a t i o n . The maxima i n f i g u r e s 50 and 51 i n d i c a t e t h a t t h e a z i m u t h o f t h e f o l d axes formed d u r i n g t h i s l a s t s t r o n g d e f o r m a t i o n i s n o r t h 50° west t o n o r t h 55° n o r t h w e s t . T h i s s t e e p p l u n g e p r o b a b l y i n d i c a t e s r e - f o l d i n g o f a l r e a d y f o l d e d s t r a t a as i t i s u n l i k e l y s u c h s t e e p l y p l u n g i n g f o l d axes c o u l d d e v e l o p d u r i n g one p e r i o d o f f o l d i n g . Most o f t h e t r a c e s o f e a r l i e r d e f o r m a t i o n have been o b l i t e r a t e d , however, p a r t i c u l a r l y i n t h e n o r t h e r n p a r t o f t h e i s l a n d . The a z i m u t h s and p l u n g e s o f d r a g f o l d s ( f i g u r e 52) a l t h o u g h q u i t e v a r i a b l e , a r e a l s o i n d i c a t i v e o f an a z i m u t h o f a p p r o x i m a t e l y n o r t h 50 west t o n o r t h 55° west and a p l u n g e o f 50° t o 55° n o r t h w e s t f o r t h e m a j o r f o l d a x e s . However, an i n s u f f i c i e n t number o f d r a g f o l d s were measured t o p u t any i n t e r p r e t a t i o n b a s e d on them on a sound s t a t i s t i c a l b a s i s . When t h e a z i m u t h and p l u n g e o f t h e m a j o r f o l d axes d e r i v e d f r o m t h e d a t a on t h e i n t e r s e c t i o n s o f p l a n e s o f f o l i a t i o n i s p l o t t e d on f i g u r e 46, and a g r e a t c i r c l e i s drawn a t 90° t o t h i s p o l e i t i s f o u n d t o p a s s t h r o u g h t h e c e n t r e o f t h e s t r o n g e s t maxima on t h i s f i g u r e . T h i s i n d i c a t e s t h a t an 140 a z i m u t h o f n o r t h 50 west n o r t h 55° west and p l u n g e o f 50° t o 65° n o r t h w e s t f o r t h e f o l d axes r e s u l t i n g f r o m t h e d o m i n a n t p e r i o d o f d e f o r m a t i o n i s s u b s t a n t i a l l y c o r r e c t . The f a i l u r e o f t h i s g r e a t c i r c l e , o r any o t h e r g r e a t c i r c l e b a s e d on t h e i n t e r s e c t i o n o f p l a n e s o f f o l i a t i o n , t o p a s s t h r o u g h t h e s e c o n d maxima o f f i g u r e 46 i s p r o b a b l y due t o t h e e f f e c t s o f t h e two o r more p e r i o d s o f d e f o r m a t i o n w h i c h have a f f e c t e d t h i s a r e a . To summarize, t h e m e t a m o r p h i c r o c k s o f Hawkesbury I s l a n d have p r o b a b l y u n d e r g o n e two o r more p e r i o d s o f d e  f o r m a t i o n . The f o l d a x e s r e s u l t i n g f r o m t h e s t r o n g e s t (? and l a t e s t ) p e r i o d o f d e f o r m a t i o n have an a z i m u t h o f n o r t h 50 west t o n o r t h 55° west and p l u n g e o f 50° t o 6 5 ° n o r t h w e s t a p p r o x  i m a t e l y . I f t h e f o l d i n g i s due t o c o m p r e s s i o n a l o n e t h i s p r o b  a b l y i n d i c a t e s a n o r t h e a s t - s o u t h west d i r e c t i o n o f g r e a t e s t c o m p r e s s i o n i . e . t h e d i r e c t i o n i n d i c a t e d by t h e g e n e r a l t r e n d o f t h e C o a s t I n t r u s i o n s . The p r e s e n c e o f a s h e a r com ponent w o u l d m o d i f y t h e p i c t u r e somewhat. 141 F i g u r e 46. P o l e s of F o l i a t i o n o f the Metamorphic Rocks of Hawkesbury I s l a n d 142 N Figure 47. Intersection of the Planes of F o l i a t i o n of the Metamorphic Rocks in Area I (bounded by the l i m i t of mapping on the south, upper Angle Valley on the east, Ice Cake Lake to Backbacon Lake on the north and Douglas Channel on the west.) 143 Figure 48. Intersection of the Planes of Foliation of the Metamorphic Rocks in Area II (bounded by the limit of mapping on the south, Verney Passage on the east, lower Angle Valley on the north, and upper Angle Valley on the west). 144 F i g u r e 49. I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c R o c k s i n A r e a I I I ( b o u n d e d b y V e r n e y P a s s a g e o n t h e s o u t h , E v e l y n C r e e k o n t h e e a s t , E v e l y n L a k e t o I c e C a k e L a k e o n t h e n o r t h a n d l o w e r A n g l e V a l l e y o n t h e w e s t . ) 145 F i g u r e 50. I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c R o c k s i n A r e a I V ( b o u n d e d b y t h e s e a o n t h e s o u t h a n d e a s t , R o y L a k e t o E v e l y n L a k e o n t h e n o r t h , a n d E v e l y n C r e e k o n t h e w e s t ) . 146 F i g u r e 5 1 . I n t e r s e c t i o n o f t h e P l a n e s o f F o l i a t i o n o f t h e M e t a m o r p h i c Rocks i n A r e a V ( c o m p r i s i n g a l l t h e m e t a m o r p h i c r o c k s n o r t h o f a r e a s I t o I V i n  c l u s i v e ) 147 N F i g u r e 52. T h e A z i m u t h a n d P l u n g e o f D r a g F o l d s i n t h e M e t a m o r p h i c R o c k s o f H a w k e s b u r y I s l a n d . 148 Owing t o t h e n a t u r e o f t h e mapping p r o b a b l y many s m a l l f a u l t s and s h e a r z o n e s e s c a p e d d e t e c t i o n . The f o l l o w i n g a r e t h e o n l y f a u l t s s e e n t h a t e x t e n d more t h a n a few f e e t : 1. A s h e a r zone a t l e a s t 5000 f e e t l o n g i n l o w e r A n g l e V a l l e y w i t h a s t r i k e o f n o r t h 50° e a s t , a v e r t i c a l d i p (110°) and d r a g f o l d i n g w h i c h i n d i c a t e s an up ward and s o u t h w a r d movement o f t h e west s i d e o f t h e s h e a r r e l a t i v e t o t h e e a s t s i d e . 2. A number o f f a u l t s i n t h e v i c i n i t y o f I c e Cake L a k e , t h e l o n g e s t o f w h i c h i s some 5000 f e e t l o n g , w i t h s t r i k e s v a r y i n g f r o m n o r t h 1 0 ° e a s t t o n o r t h 4 0 ° e a s t and s t e e p d i p s . Most o f t h e s e have d i s p l a c e d t h e k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t bands a few f e e t . One v e r y l o n g f a u l t west o f I c e Cake l a k e has o f f s e t t h e k y a n i t e bands some h u n d r e d s o f f e e t . I n a l l c a s e s t h e r e has b e e n l e f t h and s e p a r a t i o n . As t h e map u n i t s so d i s p l a c e d moved have n e a r l y v e r t i c a l d i p s , t h i s p r o b a b l y i n d i c a t e s l e f t l a t e r a l s t r i k e - s l i p movement. Some o f t h e f a u l t s have r e s u l t e d f r o m movement a l o n g t h e a x i a l p l a n e o f l a r g e d r a g f o l d s w h i c h i n v o l v e t h e w h o l e o f t h e k y a n i t e band. 3. A s i n g l e f a u l t j u s t t o t h e west o f t h e above s e r i e s w i t h a known l e n g t h o f some 300 f e e t . T h i s s t r i k e s n o r t h 50° w e s t , d i p s v e r t i c a l l y and had a n unknown amount o f v e r t i c a l movement, as i n d i c a t e d by s l i c k e n s i d e s . 4. A s h e a r z o n e , a n d / o r f a u l t z o n e i n and n e a r West T r e n c h B r o o k w i t h a known l e n g t h o f some 4000 f e e t . T h i s s t r i k e s n o r t h 60o west and d i p s v e r y s t e e p l y . S l i c k e n s i d e s i n d i c a t e v e r t i c a l movement. 5. A f a u l t o r n a r r o w s h e a r zone o f unknown l e n g t h ( g r e a t e r t h a n 200 f e e t ) c u t t i n g t h e N o r t h M o u n t a i n q u a r t z m o n z o n i t e a t e l e v a t i o n 600 f e e t above G a u d i n P o i n t . T h i s has a s t r i k e o f due n o r t h , a d i p o f 85° west and an unknown d i r e c t i o n o f movement. The s t r i k e and d i p o f t h e A n g l e V a l l e y s h e a r z o n e and t h e I c e - C a k e Lake a r e a f a u l t s i n d i c a t e s t h a t t h e i n t e r  m e d i a t e s t r e s s a x i s was n e a r l y v e r t i c a l . A s s u m i n g an a n g l e o f 3 0 ° between t h e d i r e c t i o n o f f a u l t i n g o r s h e a r i n g and t h e g r e a t e s t s t r e s s a x i s , and t h a t a l l t h e movement n o t e d i s s i n i s t r a l , t h e s e f a u l t s w o u l d have been formed d u r i n g a p e r i o d d u r i n g w h i c h t h e a x i s o f g r e a t e s t s t r e s s v a r i e d between n o r t h o o 20 west and n o r t h 20 e a s t . The v a r i a t i o n i n d i r e c t i o n o f maximum s t r e s s may be l e s s t h a n i s i n d i c a t e d , as p a r t o f t h e v a r i a t i o n i n s t r i k e o f t h e f a u l t s may be due s i m p l y t o t h e inhomogeneous c h a r a c t e r o f t h e r o c k s i n v o l v e d . The n o r t h 50° west t o n o r t h 60° west f a u l t s ( (3) and (4) ) have v e r t i c a l o r n e a r l y v e r t i c a l movement and a r e p a r a l l e l o r s u b - p a r a l l e l t o t h e f o l i a t i o n p l a n e s i n t h e meta m o r p h i c r o c k s . As t h e s e f a u l t s p r o b a b l y o c c u r on f o l i a t i o n p l a n e s t h e d i r e c t i o n o f f a u l t i n g , a l t h o u g h t o some d e g r e e i n d i c a t i v e o f t h e s t r e s s e n v i r o n m e n t , i s p r o b a b l y c o n s i d e r a b l y m o d i f i e d by t h e weakness o f t h e s e r o c k s p a r a l l e l t o t h i s p l a n e . A d i r e c t i o n o f g r e a t e s t s t r e s s f a i r l y c l o s e t o v e r t i c a l i s i n d i c a t e d , however. T h e s e f a u l t s do n o t seem t o f i t t h e o v e r a l l r e g i o n a l p a t t e r n . They may p e r h a p s s i m p l y be t h e r e s u l t o f m i n o r s l i p p a g e a l o n g f o l i a t i o n p l a n e s . SMALL-SCALE STRUCTURES (1) I n t h e m e t a m o r p h i c r o c k s S m a l l - s c a l e s t r u c t u r a l f e a t u r e s o b s e r v e d i n t h e meta m o r p h i c r o c k s i n c l u d e s c h i s t o s i t y o r f o l i a t i o n , l i n e a t i o n , d r a g f o l d s , s e g r e g a t i o n b a n d i n g , m i n o r c r e n u l a t i o n s o f f o l  i a t i o n , c a t a c l a s t i c s t r u c t u r e s , and p s e u d o c a t a c l a s t i c s t r u c t u r e s o f t e x t u r e s . 150 S e g r e g a t i o n b a n d i n g , c a t a c l a s t i c s t r u c t u r e s and p s e u d o c a t a c l a s t i c s t r u c t u r e s have b e e n d i s c u s s e d p r e v i o u s l y and w i l l n o t be c o n s i d e r e d f u r t h e r . Most o f t h e r o c k s o f t h e E c s t a l l s e r i e s have a w e l l d e v e l o p e d f o l i a t i o n , a s has b e e n p r e v i o u s l y m e n t i o n e d . A n o t a b l e f e a t u r e o f t h i s f o l i a t i o n i s t h a t i t i s p a r a l l e l o r n e a r l y p a r a l l e l t o r e l i c t s e d i m e n t a r y b e d d i n g i n a l l t h e l o c a l i t i e s i n w h i c h t h e l a t t e r was s e e n . T h i s may be due t o ease o f r e c r y s t a l l i z a t i o n p a r a l l e l t o o r i g i n a l b e d d i n g . L i n e a t i o n was n o t e d i n a few p l a c e s I n t h e a m p h i b o l i t e s and i s v e r y p r o m i n e n t I n t h e k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a IS s c h i s t s . The l i n e a t i o n i n t h e a m p h i b o l i t e s A e x p r e s s e d by an a l i g n m e n t o f h o r n b l e n d e p r i s m s w i t h i n t h e p l a n e o f f o l i a t i o n . I t was n o t e d i n s p e c i m e n s o f p a r t i c u l a r l y c o a r s e - g r a i n e d a m p h i b o l i t e s , e s p e c i a l l y f r o m t h e E v e l y n Lake a r e a . One v e r y c o a r s e - g r a i n e d a m p h i b o l i t e has two d i s t i n c t l i n e a t i o n s , one w i t h a v e r t i c a l d i p and t h e o t h e r w i t h a d i p o f a b o u t 50° E a s t w i t h i n a f o l i a t i o n p l a n e t h a t s t r i k e s n o r t h 65° west and d i p s s t e e p l y n o r t h . The l i n e a t i o n i n t h e k y a n i t e - s t a u r o l i t e - a l m a n d i n e m i c a s c h i s t s i s e x p r e s s e d by a p a r a l l e l a l i g n m e n t o f e l o n g a t e k y a n i t e c r y s t a l s . T h i s l i n e a t i o n i s g e n e r a l l y about h o r i z o n t a l . D r a g f o l d s and m i n o r c r e n u l a t i o n s a r e common and t h e a t t i t u d e s o f a number were m e a s u r e d . U n f o r t u n a t e l y many o u t c r o p s were f l a t and no good i d e a o f p l u n g e c o u l d be ob t a i n e d , so t h a t o n l y 49 r e a d i n g s were made w h i c h c o u l d be p l o t t e d a c c u r a t e l y on t h e s t e r e o - n e t . The g r e a t v a r i a t i o n 151 i n a z i m u t h and p l u n g e i s i n d i c a t e d by f i g u r e 6. T h e r e a r e u s u a l l y one o r two d i r e c t i o n s o f m a j o r d r a g f o l d i n g i n a g i v e n e x p o s u r e , but s m a l l e r c r e n u l a t i o n s i n s e v e r a l d i r e c t i o n s a l s o o c c u r . I n t h e n o r t h e r n p a r t o f t h e E c s t a l l s e r i e s , t h e g r e a t m a j o r i t y o f t h e m a j o r d r a g f o l d s were f o u n d t o have a z i m u t h s o f s o u t h 85° west t o n o r t h 50° west and s t e e p w e s t e r l y p l u n g e s . T h i s i n d i c a t e s t h a t t h e beds t o t h e n o r t h have moved e a s t r e l a t i v e t o t h e beds t o t h e s o u t h . (2) The i g n e o u s r o c k s Of t h e a r e a o f i g n e o u s r o c k s e xamined, o n l y t h e N o r t h M o u n t a i n i n t r u s i o n has w e l l d e v e l o p e d f o l i a t i o n a n d / o r l i n  e a t i o n . Weak l i n e a t i o n s were n o t e d i n o t h e r p l u t o n s . The f o l i a t i o n o f t h e d i o r i t e and q u a r t z d i o r i t e o f t h e N o r t h M o u n t a i n i n t r u s i o n i s e x p r e s s e d by a s u b - p a r a l l e l a l i g n m e n t o f i n d i v i d u a l h o r n b l e n d e c r y s t a l s , b i o t i t e f l a k e s , c l o t s o f m a f i c s and i n c l u s i o n s o f m a f i c - r i c h r o c k s . T h i s f o l i a t i o n s t r i k e s n o r t h 50° w e s t t o n o r t h 65° west and d i p s f r o m n o r t h 70° n o r t h t o v e r t i c a l l y . T h i s f o l i a t i o n , as p r e v i o u s l y n o t e d , may be due t o i n j e c t i o n o f a p a r t i a l l y c r y s t a l l i n e magma o r o f g r a n i t i z a t i o n o f p a r t o f t h e E c s t a l l s e r i e s r o c k s , as i t i s s u b - p a r a l l e l t o b o t h t h e f o l i a t i o n i n t h e E c s t a l l s e r i e s r o c k s and t h e c o n t a c t o f t h e N o r t h M o u n t a i n i n t r u s i o n . I n t h e q u a r t z m o n z o n i t e a much weaker f o l i a t i o n p r o b a b l y some f o r m o f f l o w b a n d i n g , i s common. T h i s i s p a r a l l e l t o t h e f o l i a t i o n i n t h e d i o r i t e and q u a r t z d i o r i t e . I n t h e Danva p l u t o n t h e a t t i t u d e o f t h e f o l i a t i o n 152 v a r i e s f r o m a s t r i k e o f n o r t h 15° west and v e r t i c a l d i p t o a s t r i k e o f n o r t h 45° ciast and d i p o f 8 0 ° n o r t h - w e s t . T h i s f o l i a t i o n i s p r o b a b l y n o t c a u s e d by f l o w b u t r a t h e r b y a s s i m i l a t i o n i n s i t u o f t h e m e t a m o r p h i c r o c k s . I t i s due t o a l i g n m e n t o f c l o t s o f m a f i c m i n e r a l s and i n some p l a c e s o c c u r s n e a r l y p e r p e n d i c u l a r t o t h e n e a r e s t m a r g i n o f t h e p l u t o n . The f o l i a t i o n u s u a l l y p a r a l l e l s t h e s t r i k e o f t h e m e t a m o r p h i c r o c k s i m m e d i a t e l y o u t s i d e t h e p l u t o n . The B e a v e r L a k e p l u t o n r a r e l y has any n o t i c e a b l e l i n e a t i o n o r f o l i a t i o n . T h e s e a r e c o n f i n e d t o t h e m a r g i n s o f t h e p l u t o n and a r e marked p r i n c i p a l l y by a p a r a l l e l a l i g n m e n t o f m a f i c m i n e r a l s . A l l t h e l i n e a t i o n and f o l i a t i o n n o t e d had s t r i k e s p a r a l l e l t o t h e f o l i a t i o n o f t h e a d j a c e n t m e t a m o r p h i c r o c k s and a r e p r o b a b l y a l s o a r e s u l t o f a s s i m  i l a t i o n i n s i t u o f t h e s e r o c k s . The S i d e b a c o n L a k e p l u t o n a p p e a r s t o l a c k l i n e a t i o n o r f o l i a t i o n . However, most o f i t s c o n t a c t w i t h t h e m e t a  m o r p h i c r o c k s was n o t examined and i t may have t h e same m a r g i n a l t y p e o f l i n e a t i o n o r f o l i a t i o n as t h e o t h e r p l u t o n s . 153 CHAPTER V I CONCLUSIONS The metamorphosed, s e d i m e n t a r y and p y r o c l a s t i c ( ? ) r o c k s o f t h e E c s t a l l s e r i e s were l a i d down i n a eugeo- s y n c l i n a l t r o u g h . The q u a r t z i t e s o f t h e Q u a a l R i v e r - E c s t a l l R i v e r a r e a may be an e x c e p t i o n as t h e y may h a v e been l a i d down i n a s t a b l e e n v i r o n m e n t p r i o r t o t h e f o r m a t i o n o f t h e e u g e o s y n c l i n e . The s o u r c e a r e a f o r t h e s e d i m e n t s was p r o  b a b l y one o r more i s l a n d a r c s , w h i c h must have b e e n t h e s i t e o f c o n s i d e r a b l e l o c a l v o l c a n i c a c t i v i t y . The age o f t h e s e s e d i m e n t s i s somewhat d o u b t f u l b u t t h e y a r e most l i k e l y t o be O r d o v i c i a n t o D e v o n i a n . The metamorphosed i g n e o u s r o c k s o f t h e E c s t a l l s e r i e s may h a v e b e e n i n p a r t f l o w s a s s o c i a t e d w i t h t h e v o l c a n i c a c t i v i t y o f t h e i s l a n d a r c s . I n p a r t , however, t h e y a r e i n t r u s i v e b o d i e s , p r o b a b l y o r i g i n a l l y g a b b r o i c i n compos i t i o n , w h i c h may have been a s s o c i a t e d w i t h t h e above men t i o n e d v o l c a n i c a c t i v i t y o r p e r h a p s have b e e n i n t r u d e d d u r i n g t h e o r o g e n y w h i c h r e s u l t e d i n t h e metamorphism o f t h e E c s t a l l s e r i e s r o c k s . The main metamorphism o f t h e E c s t a l l s e r i e s i s r e g i o n a l i n t y p e . I t t o o k p l a c e u n d e r s t r o n g c o m p r e s s i o n and p r o b a b l y a t t e m p e r a t u r e s i n t h e r a n g e o f 4 0 0 ° C t o 700° C. I t p r e c e d e d t h e i n t r u s i o n o f t h e C o a s t I n t r u s i o n s . The g r a d e 154 o f metamorphism g e n e r a l l y r e a c h e d i s t h e a l m a n d i n e a mphi b o l i t e f a c i e s , s t a u r o l i t e - q u a r t z and p o s s i b l y k y a n i t e - m u s c o v i t e - q u a r t z s u b f a c i e s , i n d i c a t i v e o f q u i t e a h i g h g r a d e o f r e g i o n a l metamorphism. S m a l l amounts o f l a t e . , s e r i c i t e , c h l o r i t e and e p i d o t e a r e common t h r o u g h o u t t h e E c s t a l l s e r i e s . T h e s e a r e due t o r e t r o g r e s s i v e metamorphism. R e t r o g r e s s i v e metamorphism i s v e r y i n t e n s e i n s h e a r z o n e s where s e r i c i t e - e p i d o t e a s s e m b l a g e s a r e d e v e l o p e d w h i c h i n c o m p o s i t i o n a p p r o a c h t h e g r e e n s c h i s t f a c i e s . The s e r i c i t i z e d r o c k s o f t h e s h e a r z o n e s may be due t o h y d r o t h e r m a l s o l u t i o n s w h i c h u s e d t h e s h e a r z o n e s as p a s s a g e w a y s . The C o a s t I n t r u s i o n s and r e l a t e d r o c k s i n t h i s a r e a have r e a c h e d t h e i r p r e s e n t p o s i t i o n s by i n t r u s i o n w i t h some a s s i m i l a t i o n o f t h e c o u n t r y r o c k . A l t h o u g h n o t r e s p o n s i b l e f o r most o f t h e metamorphism o f t h e E c s t a l l s e r i e s r o c k s , t h e y may have c a u s e d an i n c r e a s e i n m e t a m o r p h i c g r a d e w i t h i n 300 f e e t or l e s s o f t h e i r c o n t a c t s w h i c h has r e s u l t e d i n t h e f o r m a t i o n o f r o c k s b e l o n g i n g t o and a p p r o a c h i n g t h e s i l l i m  a n i t e - a l m a n d i n e s u b f a c i e s o f t h e a l m a n d i n e a m p h i b o l i t e f a c i e s . The m e t a m o r p h i c r o c k s o f t h e E c s t a l l s e r i e s i n t h e map a r e a have u n d e r g o n e a t l e a s t two p e r i o d s o f d e f o r m a t i o n . The d i r e c t i o n o f c o m p r e s s i o n d u r i n g t h e d e f o r m a t i o n w h i c h a p p e a r s t o have had t h e s t r o n g e s t e f f e c t on them was p r o b a b l y n o r t h  e a s t - s o u t h w e s t . Some t i m e a f t e r ( o r b e f o r e ? ) t h e i n t r u s i o n o f t h e C o a s t I n t r u s i o n s e r o s i o n began i n t h i s a r e a and has c o n t i n u e d t o t h e p r e s e n t t i m e . The f e a t u r e t h a t has had t h e most ' 155 e f f e c t i n s h a p i n g t h e p r e s e n t t o p o g r a p h y i s P l e i s t o c e n e g l a e i a t i o n . The g l a c i e r s o f t h i s p e r i o d , a t one s t a g e , c o m p l e t e l y c o v e r e d t h e i s l a n d . T h e r e was l i m i t e d d e p o s i t i o n o f m a r i n e c l a y s i n t h e v a l l e y s s h o r t l y a f t e r r e t r e a t o f t h e g l a c i e r s and d e p o s i t i o n o f t a l u s , e t c . , i s c o n t i n u i n g and i s g r a d u a l l y f i l l i n g t h e g l a c i a l v a l l e y s . The p o s i t i o n o f t h e m a r i n e c l a y s a t a l t i t u d e 330 f e e t p r o b a b l y i n d i c a t e s an i s o s t a t i c r e c o v e r y o f t h i s amount s i n c e t h e i r d e p o s i t i o n . 1 5 6 BIBLIOGRAPHY Anderson, G.H. ( 1 9 3 7 ) , Granitization, Albitization and Related Phenomena in the Northern Inyo Range of California- ' Nevada, G.S.A. Bulletin, vol. 4 8 , pp. 1-74. Bacon, R.W. ( 1 9 5 7 ) 5 Geology of Lower Jervis Inlet, B r i t i s h Columbia, B.C. Dept. of Mines, Bulletin No. 3 9 . Barth, T.F.W. ( 1 9 5 2 ) , Theoretical Petrology, John Wiley and Sons, Inc., New York. Bil l i n g s , M.P. ( 1 9 5 4 ) , Structural Geology, Second edition, Prentice-Hall, Inc., New York, Bostock, H.S. (1948), Physiography of the Canadian Cordillera with Special Reference to the Area North of the F i f t y - f i f t h Parallel, Geol. Survey of Canada Memoir 247. Bowen, N.L., (1940), Progressive Metamorphism of Siliceous Limestone and Dolomite, Jour. Geol. 48, pp. 2 2 5 - 2 7 4 . Bressler, CT. ( 1 9 5 0 ) , Garnet Deposits near Wrangell, South eastern Alaska, U.S.G.S. Bull. 9 6 3 - C Buddington, A.F. and Chapin, T. ( 1 9 2 9 ) , Geology and Mineral Deposits of Southeastern Alaska, U.S.G.S. Bull. 800. Compton, R.R. ( 1 9 5 8 ) , Significance of Amphibole Paragenesis in the Bidwell Bar Region, California, Am. Min., Sept., pp. 8 9 0 - 9 0 7 . Dana, S.A. ( 1 9 3 2 ) , A Textbook of Mineralogy (revised by Ford) John Wiley and Sons, New York. Dolmage, V. ( 1 9 2 1 ) , Coast and Islands of Brit i s h Columbia Between Burke Inlet and Douglas Channel, Can. Dept. of Mines, G.'S.C. Summary Report, Part A, pp. 2 2 - 4 9 . . — ( 1 9 2 2 ) , Coast and Islands of Br i t i s h Columbia Between Douglas Channel and the Alaskan Boundary, G.S.C, Summary Report, Part A, pp. 9-34. Eardley, A.J. ( 1 9 4 7 ) , Paleozoic Cordilleran Geosyncline and Related Orogeny, Jour. Geol. 5 5 , pp. 309-342. Eskola, P. (1914), Petrology of the Orijarvi Region, Bull. Comm. Geol. Finlande, No. 40. Fyfe, ¥ . 3 . , Turner, F.J. and Verhoogen, J. ( 1 9 5 8 ) , Meta morphic Facies and Metamorphic Reactions, G.S.A. Memoir 7 3 . 157 G i l l , J.E., and Byers, A.R. (194-8), Surf Inlet and Pugsley Mines, Structural Geology of Canadian Ore Deposits, C.I.M. Jubilee Volume, pp. 99-104. Hanson, G. (1922), Reconnaissance Between Kitsault River and the Skeena River, B.C. G.S.C. Summary Report, Part A, pp. 35A-50A. (1923) } Reconnaissance Between Skeena River and Stewart, G.S.C. Summary Report Part A pp. 29-45 (1935), Portland Canal Area, B r i t i s h Columbia, G.S.C. Memoir 175. Harker, A. (1932), Metamorphism, Metheun, London. Hietenen, Anna (1958), Kyanite, Andalusite and Sillimanite in the Schists in Boehls Butte Quadrangle, Idaho, Am. Min. vol. 41, pp. 1-27. Ingerson, E. (1955), Geologic Thermomentry, Crust of the Earth, G.S.A. Special Paper 62 , pp. 465-488. Irvine, W.T. (1948), Britannia Mine, Structural Geology of Canadian Ore Deposits, C.I.M. Jubilee Volume, pp. 105-109 James, H.T. (1929), Britannia Beach Map Area, Bri t i s h Columbia, G.S.C. Memoir 158. Kennedy, ¥.Q. (1949), Zones of Progressive Regional Meta morphism in the Moine Schists of the Western High lands of Scotland, Geol. Mag. vol. 86, pp. 43-56. Kindle, E.D. (1937), Mineral Resources of the Terrace Area, Coast Distr i c t , B r i t i s h Columbia, G.S.C. Memoir 205. Knopf, E.B. and Ingerson, E. (1938), Structural Petrology, G.S.A. Memoir 6. Larsen, E.S. (1948), Batholith of Southern California, G.S.A. Memoir 29. Lobeck, A.K. (1939), Geomorphology, McGraw-Hill Book Co. Inc. Lord, C.S., Hage, CO., and Stewart, J.S. (1947), The Cor- dilleran Region, Geology and Economic Minerals of Can ada, Third Edition, G.S.C. Economic Geology Series 1. Mayo, E.B. (1941), Deformation in the Internal Mount Lyell- Mount Whitney, California, G.S.A. Bulletin vol 52. pp. 1001-1084. 158 McConnell, R.G. ( 1 9 1 2 ) , Geological Section Along the Grand Trunk Pacific Railway from Prince Rupert to Alder- mere, B.C.G.S.C. Summary Report, pp. 55-62. Nelson, N.E. (1948), Hidden Creek Mine, Structural Geology of Canadian Ore Deposits, C.I.M. Jubilee. Volume, pp. 125-128 . Padgham, W.A. (1958) Geology of the Ecstall-Quaal River Area, British Columbia, Unpublished M.A.Sc. Thesis, Univer sity of British Columbia. Peacock, M.A. ( 1 9 3 5 ) , The Fiord-land of British Columbia, G.S.A. Bull. 46, pp. 633-696. Perrin, R. ( 1 9 5 4 ) , Granitization, Metamorphism and Volcanism, Am. Jour, of Science, vol. 252 , pp. 449-465. Pettijohn, F.J. ( 1 9 5 7 ) , Sedimentary Rocks, Second edition, Harper and Brothers Phemister, T.C. ( 1 9 4 5 ) , The Coast Range Batholith near Van couver, B.C. Quarterly Jour. Geol. Soc. of London, vol. CI, parts 1 and 2 , pp. 3 7 - 8 8 . Ramberg, H. ( 1 9 4 9 ) , The Facies Classification of Rocks : A Clue to the Origin of Quartzo-feldspathic Massifs and Veins, Jour. Geol. Vol. 57 , PP« 18-54. ( 1 9 5 2 ) , The Origin of Metamorphic and Metasomatic Rocks, University of Chicago Press, Chicago. Read, H.H. ( 1 9 5 6 ) , The Granite Controversy, Interscience Publishers Inc., New York. Rogers, A.F. and Kerr, P.F. (1942), Optical Mineralogy, Second Edition, McGraw-Hill Book Co. Inc., Smith, F.G. ( 1 9 5 2 ) , Decrepitation Characteristics of Garnet, Am. Min. Vol. 37 , pp. 470-491. Thornbury, W.D. ( 1 9 5 4 ) , Principles of Geomorphology, John Wiley and Sons. Turner, F.J. (1948), Mineralogical and Structural Evolution of the Metamorphic Rocks, G.S.A. Mem. 30. ( 1 9 5 1 ) , Observations of Twinning of Plagioclase in Metamorphic Rocks, Am. Min., July-August, pp. 581-589 . and Verhoogen, J. ( 1 9 5 D, Igneous and Metamorphic Petrology, McGraw-Hill Book Co., 159 Twenhofel, W.H. (1950), Principles of Sedimentation, Second Edition, McGraw-Hill Book Co. Inc., Ty r r e l l , C.W. (1926), The Principles of Petrology, Tenth Edition 1946, Methuen and Co. Ltd., London. Williams, H., Turner, F.J., Gilbert, CM. (1955), Petrography, W.H. Freeman and Co. Winchell, A.N., Winchell, H. (195D, Elements of Optical Mineralogy Part II, Descriptions of Minerals, John Wiley and Sons, Inc., White, W.H. (1959), Cordilleran Tectonics in Bri t i s h Columbia, A.A.P.G., Bull., January, pp. 60G100. Yoder, H.S. Jr. (1955), Role of Water in Metamorphism, Crust of the Earth, G.S.A. Special Paper 62, pp. 505-524. 

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
Canada 27 1
China 13 37
United States 8 0
Unknown 2 0
Republic of Korea 2 0
Austria 2 0
Japan 2 0
Russia 1 0
City Views Downloads
Unknown 19 4
Beijing 11 2
Ashburn 5 0
Vancouver 3 0
Tokyo 2 0
Montreal 2 0
Shenzhen 2 35
Burnaby 2 0
Mountain View 2 0
Victoria 2 0
Edmonton 2 0
Calgary 1 1
Moscow 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}
Download Stats

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0053044/manifest

Comment

Related Items