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The stratigraphy and structure of the type-area of the Chilliwack group, : southwestern British Columbia Monger, James William Heron 1966

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THE STRATIGRAPHY AND STRUCTURE OF THE TYPE-AREA OF THE CHILLIWACK GROUP, SOUTHWESTERN BRITISH COLUMBIA by James William Heron Monger B. Sc., Reading U n i v e r s i t y , 1959 M. Sc., U n i v e r s i t y of Kansas, 1961 A thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of doctor of philosophy i n the Department of Geology We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May 1966 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree a t the 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 ee t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r 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 ee 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 ran by the Head o f my Depar tment 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 no 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 . Depar tment o f The 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 V a n c o u v e r 8, Canada Date at- ,/u ma. • ( cx%% JAMES WILLIAM HERON MONGER. THE STRATIGRAPHY AND STRUCTURE OF THE TYPE-AREA OF THE CHILLIWACK GROUP, SOUTHWESTERN BRITISH COLUMBIA. ( i i ) Supervisor: Dr. V/. R. Banner. ABSTRACT The stratigraphy and structure of Upper Palaeozoic and Mesozoic sed-imentary and volcanic rocks, and of amphibolitic rocks of unknown age, were studied i n an area of about 14.0 square miles i n the Cascade Mountains of southwestern B r i t i s h Columbia. The amphibolitic rocks are probably of diverse o r i g i n s ; their... s t r a t -igraphic r e l a t i o n s h i p to the other rocks i s not known, although they may, i n part, be equivalent to pre-Devonian rocks i n northwestern Washington. Upper Palaeozoic rocks comprise the Chilliwack Group. The base i s not exposed. Oldest rocks are vo l c a n i c arenites and a r g i l l i t e s which are ov e r l a i n by an arg i l l a c e o u s limestone, about 100 feet t h i c k , i n which E a r l y Pennsylvanian (Morrowan) f u s u l i n i d s occur. Apparently conformably overlying the limestone i s a succession of a r g i l l i t e s , coarse volcanic arenites, minor conglomerate and l o c a l t u f f , which contains both marine and t e r r e s t r i a l f o s s i l s and ranges i n thickness from 450 to 800 feet . A cherty limestone, generally about 300 feet t h i c k , i n which there i s an E a r l y Permian (Leonardian) f u s u l i n i d fauna, i s conformable upon the c l a s t i c sequence. Altered lavas and t u f f s are i n part l a t e r a l l y equivalent to t h i s Permian limestone, and, i n part, o v e r l i e i t ; these v o l c a n i c rocks range i n thickness from 700 to 2,000 feet . Disconformably above the Permian v o l c a n i c rocks are a r g i l l i t e s and vol c a n i c arenites of the Cultus Formation. This formation i s apparently about 4-,000 feet t h i c k , contains Late T r i a s s i c , E a r l y and Late Jurassic f o s s i l s and no s t r a t i g r a p h i c breaks have been recognized within i t . ( i i i ) A l l of these rocks underwent two phases of deformation between Late J u r a s s i c and Miocene time. The f i r s t phase, correlated with mid-Cretaceous deformation i n northwestern Washington, was the most severe., and thrusts and major, northeast-trending recumbent f o l d s were formed. These structures subsequently were folded and fa u l t e d along a northwest trend, possibly i n response to d i f f e r e n t i a l u p l i f t of the Cascade Mountains. (iv) TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS iv. TABLES v i i i ILLUSTRATIONS i x PLATES - x i i ACKNOWLEDGEMENTS x i i i INTRODUCTION 1 Purpose and scope of i n v e s t i g a t i o n 1 Location and a c c e s s i b i l i t y of the type-area of the Chilliwack Group 2 Climate and vegetation 3 Physiography U Orthography 5 Previous work 5 F i e l d work 12 GEOLOGICAL SETTING . 13 STRATIGRAPHY 18 Preliminary statement 18 Amphibolitic rocks 22 North of Chilliwack River 22 Mount Pierce and Nesakwatch Creek V a l l e y 25 Southern end of Slesse Creek V a l l e y 27 Corre l a t i o n 28 Conclusions 29 (v) Devonian rocks of northwestern Washington 30 Pennsylvanian and Permian rocks i n the map-area 31 Lower c l a s t i c sequence 33 McGuire Nappe 33 Autochthon 36 . F o s s i l s 36 Age 37 Environment of deposition . 37 Red Mountain Limestone 38 McGuire Nappe 4-0 Liumchen Nappe 4 2 Autochthon . 4 2 F o s s i l s 43 Age and c o r r e l a t i o n 43 Environment of deposition 44 Upper c l a s t i c sequence 45 On Mount Laughington and Cheam Range 45 McGuire Nappe 4 6 Liumchen Nappe 49 Autochthon 49 F o s s i l s 50 Age and c o r r e l a t i o n 51 Environment of deposition 53 Permian limestone 56 On Mount Laughington and Mount Cheam 59 McGuire Nappe 59 (vi) Liumchen Nappe 6 l Autochthon 61 F o s s i l s 62 Age and c o r r e l a t i o n 6 4 . Environment of deposition 67 Permian v o l c a n i c sequence 6 9 On Mount Laughington and Cheam Range 70 McGuire Nappe 71 Liumchen Nappe 72 Autochthon 79 Metamorphic grade 81 F o s s i l s and age 82 Environment of deposition 83 St r a t i g r a p h i c r e l a t i o n s h i p between Permian and T r i a s s i c rocks BU V a l i d i t y and present status of the term Chilliwack Group 87 Mesozoic rocks of the map-area 91 F o s s i l s and age of the Mesozoic sequence 96 Cor r e l a t i o n 99 Environment of deposition 100 Nomenclature of Mesozoic rocks i n the map-area 102 STRUCTURAL GEOLOGY 1 0 4 Preliminary statement 1 0 4 . S t r u c t u r a l elements ~L0A Planar structures 105 Linear structures 112 ( v i i ) Minor folds 112 S t r u c t u r a l synthesis 113 Subarea 1 113 Subarea 2 118 Subarea 3 125 Subarea 4 129 Subarea 5 130 Subarea 6 133 Subarea 7 136 Subarea 8 • 138 S t r u c t u r a l h i s t o r y of the map-area 14-2 CONCLUSIONS H 9 Geological h i s t o r y of the map-area 149 • BIBLIOGRAPHY 153 APPENDIX A 159 APPENDIX B 164 ( v i i i ) TABLES Table 1: General columnar section of the "Chilliwack Series" according to Daly 8 Table 2: Rock-stratigraphic units 20 Table 3: Tectonic units in the Chilliwack Valley area 21 Table 4: Synopsis of terminology applied to rocks of the Chilliwack.Group units 90 (ix) ILLUSTRATIONS Following page Figure 1 :• Index map showing l o c a t i o n of Chilliwack V a l l e y map-area 2 . Figure 2 : View of ChiiMwack-Valley 3 Figure 3 : Sketch map showing g e o l o g i c a l s e t t i n g of the map-area 13 Figure >'.4 : Form and r e l a t i o n s h i p s of t e c t o n i c units i n the map-area' 21 Figure 5 : Areal d i s t r i b u t i o n of t e c t o n i c units i n the map-area 2 1 Figure 6 : Photomicrograph of amphibolitic rock-from . ": •• . Mount Pierce 26, Figure ,7 : Photomicrograph of fine-grained sandstone of the lower c l a s t i c sequence 4-0 Figure 8 : Large c r i n o i d columnals i n Red Mountain Limestone 4-0 Figure 9 : Photomicrograph of coarse-grained volcanic arenite of the upper c l a s t i c sequencer 48 Figure 10 : Photomicrograph of l i t h i c t u f f at the top of the upper c l a s t i c sequence 4-8 Figure 11 : Photomicrograph of coarse-grained volcanic arenite of the upper c l a s t i c sequence/" : 63 Figure 12 : Parafusulina i n Permian limestone 6-3.--Figure 13 : Pseudofusulinella i n Permian limestone 63 Figure 14 : S i ] , i c i f i e d Schwagerina i n Permian limestone 63 Figure 15 : Photomicrograph of a l t e r e d flow rock of the Permian v o l c a n i c sequence 74 Figure 16 : Photomicrograph of pumpellyite i n v e i n l e t 74 Figure 17 : Photomicrograph of lawsonite i n a l t e r e d plfigioclase feldspar 78 Figure. 18 : Photomicrograph of c r y s t a l v i t r i c t u f f from the Permian v o l c a n i c sequence 78 Figure 19 : Photomicrograph of welded t u f f from the Permian volcanic sequence 83 Figure 20 : Photomicrograph of l i t h i c t u f f containing Permian belemnite 83 Figure 21 : A r g i l l i t e s and sandstones of the Cultus Formation, Liumchen Creek V a l l e y 93 Figure 22 : A r g i l l i t e s and sandstones of the Cultus Formation, Church Mountain 93 Figure 23 : The T r i a s s i c ammonite Hannaoceras, from the Cultus Formation .97 Figure 24 : The T r i a s s i c belemnite Aulacoceras, from the Cultus Formation 97 Figure 25 : S t r a i n - s l i p cleavage i n fine-grained rocks of the Cultus Formation 106 Figure 26 : Minor f o l d i n fine-grained rocks of the Cultus Formation 106 Figure 27 : Photomicrograph showing s l a t y cleavage i n Mesozoic c l a s t i c rock 106 Figure 28 : F o l i a t e d v o l canic arenites, cross-cut by kink-bands 106 Figure 29 : Minor structures 107 Figure 30 : Minor structures ; 107 Figure 31 : Asymmetric minor f o l d 109 Figure 32 : Asymmetric minor f o l d 109 Figure 33 : Relationships between D_2 planar structures 111 Figure- 34 : Relationship of l i n e a r structures to minor folds 112 Figure 35 : Minor f o l d i n rocks of the Cultus Formation 114 Figure 36 : Minor f o l d i n rocks of the Cultus Formation 114 Figure 37 : Recumbent f o l d i n Permian limestone 119 Figure 38 : Recumbent f o l d i n Permian limestone 119 (xi) Figure 39 : Form of hypothetical recumbent f o l d formin the McGuire Nappe Figure 4-0 '• View of east side, north end Slesse Creek V a l l e y Figure 4 1 : Minor f o l d i n t h i n bedded t u f f s and:cherts of the Permian volcanic sequence Figure 4 2 V Relationship between recumbent a n t i c l i n e s on Mounts Mercer and Thurston Figure Wi '• Minor f o l d i n Upper T r i a s s i c rocks on Elk Mountain Figure 4 4 - Postulated development of major structures during Figure 4 5 : Postulated development of D structures (x i i ) PLATES (In Pocket) Plate 1 Geology of the Chilliwack Valley area Plate 2 Geological cross-sections of the Chilliwack Valley area Plate 3 Equal area projections of structural elements ( x i i i ) ACKNOWLEDGEMENTS The writer i s indebted to Dr. W.R. Danner, who suggested the project, supervised the research, and gave advice on numerous occasions; and to Dr. J.V. Ross f o r many stimulating discussions. Both, together with Dr. W.H. Mathews, c o n s t r u c t i v e l y c r i t i c i z e d the manuscript. In addition, assistance and advice were obtained at various times from other members of the s t a f f of the Department of Geology, U n i v e r s i t y of B r i t i s h Columbia and from o f f i c e r s of the C o r d i l l e r a n Section, Geological Survey of Canada. Dr. G.E.G. Westermann, of McMaster U n i v e r s i t y , Dr. E.C. Wilson of the U n i v e r s i t y of C a l i f o r n i a and Doctors H. Frebold, J.A. Jeletzky, and E.T. Tozer of the Geological Survey of Canada, i d e n t i f i e d , and confirmed i d e n t i f i c a t i o n s of f o s s i l s c o l l e c t e d by the writer. The write r was supported during t h i s study by a National Research Council of Canada Studentship. F i e l d expenses were supplied by a National Research Council Grant obtained by Dr. W.R. Danner. • F i n a l l y , the writer wishes to acknowledge the help given i n the f i e l d by D. Whitelaw, R. Poole, and M. Shau, and the encouragement and assistance given by his wife during t h i s study. -1-INTRODUCTION Purpose and scope of i n v e s t i g a t i o n The stratigraphy of many sedimentary and volcanic rock assemblages i n the Western C o r d i l l e r a , p a r t i c u l a r l y those of Palaeozoic age, i s . , very poorly known.' This i s due. to.several f a c t o r s , among which are the p r i o r i t y given by the various g e o l o g i c a l surveys to reconnaissaneemrfi&pping, to t e r r a i n which i s commonly rugged and i n a c e s s i b l e , and to the generally complex structures encountered i n the region. Therefore, W.R. Banner suggested that the w r i t e r make an intensive study of the Upper Palaeozoic .Chilliwack Group, i n the small, r e a d i l y accessible area i n southwestern B r i t i s h Columbia where the group had f i r s t been investigated by R.A. Daly (1912), with the. object of obtaining as much information as possible on i t s s t r a t i g r a p h i c composition. As the i n v e s t i g a t i o n proceeded i t became evident that the s t r u c t u r a l complexity of the area was such that i f any d e f i n i t e statement was. to be made on the stratigraphy of the Chilliwack Group, more emphasis would have to be placed on s t r u c t u r a l geology than was o r i g i n a l l y intended. Consequently, t h i s t hesis i s a study of the stratigraphy and structure of the area i n which the Chilliwack Group was f i r s t described, rather than an account of the Chilliwack Group alone. The general nature and r e l a t i o n s h i p s between rock s t r a t i g r a p h i c units of formational status are described. Palaeontological study i s l a r g e l y r e s t r i c t e d to i d e n t i f i c a t i o n of f u s u l i n i d s i n Palaeozoic rocks, and cephalopods i n Mesozoic rocks, these f o s s i l s providing the most precise s t r a t i g r a p h i c dates. As the i n t e r p r e t a t i o n of the structure of the area i s based p a r t l y on a study - 2 -of minor structures, these are described i n some d e t a i l . Location and a c c e s s i b i l i t y of the type-area of the Chilliwack Group In 1 9 1 2 , Daly described four s t r a t i g r a p h i c sections, which provided the basis f o r his "Chilliwack Series'™, or Chilliwack Group, as i t is. how designated. As these sections were measured i n , and j u s t south of the v a l l e y of Chilliwack River, i t i s j u s t i f i a b l e to regard t h i s v a l l e y as the type-area of the Chilliwack Group. Chilliwack V a l l e y i s located i n southwestern B r i t i s h Columbia, approximately 70 miles east of Vancouver, about 6 miles southeast of the town of Chilliwack, and about 6 miles north of the International Boundary (Figure l ) . I t l i e s within the Skagit Range, on the western' flank of the Cascade Mountains of B r i t i s h Columbia, which are the north-e r l y extension of the Northern Cascade Mountains of northwestern Washington (Smith and Calkins, 1 9 0 4 , p . 1 4 , Fenneman, 1 9 3 1 , p . 4 2 2 , Holland, 1 9 6 4 , p . 4 4 and map). The area investigated by the writer includes much of Chilliwack V a l l e y , and i s bounded on the west by Cultus Lake V a l l e y , on the north-west by Fraser Lowland (Holland, 1 9 6 4 , p . 3 6 ) , on the east by Cheam Range and roughly by the divide between Slesse and Nesakwatch Creeks, and on . the south by the International Boundary. This area i s r e f e r r e d to subse—-. quently as the Chilliwack Valley map-area. Access to most parts of the map-area i s good. A l a r g e l y unpaved a l l -weather road from the settlement of Vedder Crossing, which i s just west . of the map-area, continues p a r a l l e l to Chilliwack River as f a r as C h i l l i -wack Lake, east of.the map-area (Plate l ) . Logging roads, i n various F I G U R E 1 : I n d e x M a p s h o w i n g l o c a t i o n of C h i II i w a c k V a 11 ey M a p A r e a , s o u t h w e s t e r n B r i t i s h C o l u m b i a . - 3 -states of rep a i r , follow most of the major t r i b u t a r y streams of. Chilliwack River and ascend several of the mountains. In the north and northwest parts of the map-area, logging roads go up the mountains, directly, from, the f l o o d p l a i n of Fraser River. A few B r i t i s h Columbia Forest Service t r a i l s run into some of the more inaccessible areas. No permission i s needed to gain access to most of the map-area, as i t l i e s l a r g e l y within Chilliwack P r o v i n c i a l Forest. Climate and vegetation The climate i s mild, with moderate p r e c i p i t a t i o n . At Cultus Lake, on the west side of the map-area, the average annual mean temperature, over a period of 1 0 years, i s 4 9 ° Fahrenheit, and the average annual t o t a l p r e c i p i t a t i o n , over a period of 2 4 years, i s 5 8 inches ( B r i t i s h Columbia Department of Ag r i c u l t u r e , 1 9 5 7 ) . Accumulated winter snow per-s i s t s on some mountain slopes down to an a l t i t u d e of 5 , 0 0 0 f e e t , u n t i l l a t e June or early J u l y . During the two f u l l f i e l d seasons ( 1 9 6 2 , 1 9 6 3 ) spent i n the map-area, steady r a i n and low cloud hampered f i e l d work during much of June, and ea r l y July; f i n e weather predominated i n l a t e July, August and early September. Below 5 , 0 0 0 feet a l t i t u d e f o r e s t vegetation i s p r o l i f i c (see F i g -ure 2 ) . Where v i r g i n f o r e s t . i s present i t contains the t y p i c a l Coast Forest f l o r a with predominant Douglas f i r (Pseudotsuga), hemlock (Tsuga) and cedar (Thuja). Balsam (Abies) i s common at higher a l t i t u d e s . Destruc-t i o n of t h i s f o r e s t by extensive logging operations and f o r e s t f i r e s has resulted i n the development of dense second growth over most of the lower slopes of the mountains. Travel iri t h i s second growth i s extremely Figure 2: Chilliwack V a l l e y . View looking east, from the northeast side of Church Mountain. arduous and time consuming, i n contrast to the r e l a t i v e ease of t r a v e l i n the mature, v i r g i n timber. Above an a l t i t u d e of 5 , 0 0 0 feet alpine, meadowland predominates; above 6 , 0 0 0 feet vegetation i s sparse. Physiography Physiographically the map-area i s i n the southwestern part of the Cascade Mountains of B r i t i s h Columbia (Holland, I 9 6 4 ) . The topography of the map-area is-rugged, with an average r e l i e f of about 5 , 0 0 0 feet., • The mountains r i s e steeply from the f l o o d - p l a i n of Fraser River, of approximately 1 0 0 feet elevation, to heights of about 4 , 5 0 0 feet i n the west and northwestern parts of the map-area, and increase i n height east-ward to a maximum of about 7 , 0 0 0 feet on the eastern margins of the map-area. The map-area, lie's, within the drainage basin of Chilliwack River, with the exception of the slopes of the mountains i n the northwestern part, of- the map-area, which form the south side of Fraser V a l l e y , and which are drained by streams running d i r e c t l y into Fraser River. Orien-t a t i o n of many creeks and the rectangular drainage pattern developed, i n parts of the map-area, r e f l e c t s t r u c t u r a l c o n t r o l . Creeks may run par- . a l l e l , to ..either a northeasterly or a northwesterly s t r u c t u r a l trend. Both v a l l e y and alpine g l a c i a t i o n have had a marked e f f e c t on top-ography. Major stream v a l l e y s are r e l a t i v e l y s t r a i g h t , with truncated spurs, and of modified U-shape (see Figure 2 ) . Daly ( 1 9 1 2 , p . 5 9 5 ) con-sidered the g l a c i e r once occupying Chilliwack V a l l e y to have been the longest v a l l e y g l a c i e r along the International Boundary i n the C o r d i l l e r a , having a length of at l e a s t 30 miles, and a maximum thickness of 4 ? 0 0 0 to 5,000 f e e t . Some minor t r i b u t a r i e s , such as Pierce and Borden Creeks, occupy hanging v a l l e y s . Cirques, some of which contain tarns, are found on the northerly sides of peaks and ridges, and a few higher peaks carry small, permanent snow f i e l d s . V a l l e y f l o o r s are commonly o v e r l a i n by deposits of f l u v i o - g l a c i a l o r i g i n . S u r f i c i a l deposits i n the western part of the map-area have been mapped and c l a s s i f i e d by Armstrong (i960). Orthography In t h i s t hesis the s p e l l i n g s of names of natural and man-made fea-tures follows those given on the Geological Survey of Canada topographic map-sheets 92 H/4, East and West. In some cases such s p e l l i n g s d i f f e r from those.in l o c a l usage or those-used on contiguous United States Geological Survey maps. Previous work Two geologists, G. Gibbs and H. Bauerman, were attached to the Inter-n a t i o n a l Boundary Commission, which determined the boundary between Canada and the United States across the C o r d i l l e r a i n 1859-1861. Gibbs (1874, p.34-2) noted limestone and c o l l e c t e d c r i n o i d fragments and corals of . Devonian or Carboniferous age from'limestone f l o a t i n Chilliwack River. Bauerman ( I 8 8 4 ) published a more d e t a i l e d report i n which he made no d i f -f e r e n t i a t i o n between Palaeozoic and Mesozoic rocks, but estimated that there were 24,000 feet of shaly beds, with limestone i n the higher parts, along Chilliwack Valley, between Schweltza (Cultus) Lake and Chilukweyuk (Chilliwack) Lake. These s t r a t a were considered to be equivalent to shales 'and limestones along the Fort Hope road, and the limestones thought to be - 6 -s i m i l a r to those of Vancouver Island. Bauerman mentioned f i n d i n g Creta-ceous f o s s i l s i n Chilliwack V a l l e y , but gave a ge o l o g i c a l cross-section through t h i s area showing the rocks to be of Palaeozoic age. Smith and Calkins (19.04) made, a ge o l o g i c a l reconnaissance of the Northern Cascade Mountains--in Washington. They.noted the presence of s t r a t a probably ranging i n age from E a r l y Palaeozoic to Ju r a s s i c i n the v i c i n i t y of Mount Baker, a'few miles south of the map-area. The supposed Palaeozoic ..rocks were predominantly sandstones and s l a t e s , with some v o l -canic rocks. Sandstones, le s s metamorphosed than the supposed Palaeozoic rocks, contained Upper J u r a s s i c pelecypods and cephalopods. . During ,190.1. and 1906, R.A. Daly did. g e o l o g i c a l mapping i n the C h i l l i -wack V a l l e y area and his f i n a l report was published i n 1912. Daly's report i s the most d e t a i l e d work-yet published on the geology of t h i s area and he i s responsible f o r a l l s t r a t i g r a p h i c nomenclature, incorporated i n the l i t e r a t u r e , which i s applied to rock u n i t s i n the area. He gave the name "Chilliwack S e r i e s " to sedimentary rocks exposed i n - C h i l l i w a c k , V a l l e y -be-tween the Chilliwack b a t h o l i t h on the east and a point 2 miles, west of the junction of Tamihi Creek with Chilliwack River. Andesitic rocks, which he believed were present i n the upper part of the "Chilliwack S e r i e s " and which crop-out on the International Boundary west of Tamihi Creek he c a l l e d the "Chilliwack Volcanic formation." The term Cultus Formation was applied to f i n e c l a s t i c rocks of supposed T r i a s s i c age, that occur on the west side of Cultus Lake, and, according to Daly (1912, p.516) are i n f a u l t contact with the "Chilliwack Series." Daly described i n some d e t a i l four s t r a t i g r a p h i c sections from..the "Chilliwack Series", measured r e s p e c t i v e l y on Church Mountain, east of -v-Cultus Lake and immediately south of the International Border, on the west slope of Mount McGuire, and on the north side of Chilliwack V a l l e y north of the mouth of Slesse Creek v a l l e y . These four sections were com-bined to give a tentative columnar section f o r the "Chilliwack 'Series",, having a t o t a l thickness of more than 6,780 feet (see Table l).'-Fauna! c o l l e c t i o n s were examined by G i r t y ( i n Daly, 1912, p.515); he considered them.to be c o r r e l a t i v e , i n part, with the fauna of the 1Nosoni-Formation of'.California,.••then-believed to be of Upper Carboniferous age. Daly (1912, p.516, . p.54-4) indicated that he was aware of the str u c -t u r a l complexity of the area, and made a rough i n t e r p r e t a t i o n of the str u c -t u r a l geology. He suggested that the Chilliwack River between Tamihi and and Slesse Creeks flows along the core of a "broken a n t i c l i n e " , whose axis plunges eastward at a low angle. The southern limb of t h i s a n t i -c l i n e i s the northern limb of a "broken syncline" capping Mount McGuire. Probable r e p e t i t i o n of a limestone u n i t on the north side of Chilliwack V a l l e y was ascribed to normal f a u l t i n g . Daly believed that the Cultus Formation was bounded on the east and west by possible normal f a u l t s , and that the volcanic rocks on Liumchen Mountain were overthrust north-, ward (Daly, 1912, p.516, and Map 89A). -8-Table 1: General columnar section of the "Chilliwack Series", according  to Daly (1912, p.514) Top, erosion surface at plane of unconformity, with'. Cretaceous (?) rocks 1. 50+feet Q u a r t z i t i c sandstone. .2. 20 " - — ~ Dark grey a r g i l l i t e . 3'. 50 " L i g h t g r e y limestone, containing corals and c r i n o i d s . 4- 60 ± " ----- Grey calcareous q u a r t z i t e a n d u a r g i l l i t e . 5. 2,000 "-f . w Andesitic flows-,--tuffs, and agglomerates (pillow lava probably i n t h i s member where l o c a l l y developed). • This member may for"convenience be re f e r r e d to as the-Chilliwack Volcanic formation. 6. 200 — — Grey and brownish shale and sandstone, with t h i n con-glomerate bands; shales crumbling and thin-bedded; highly f o s s i l i f e r o u s , with plant fragments,, corals, c r i n o i d s , bryozoans, brachiopods, pelecypods and . cephalopcds ( ? ) . 7. 600-± " ----- Light grey, massive, generally c r y s t a l l i n e limestone, often c r i n o i d a l , with corals and bryozoans.. 8. 90 " —• Shale, sandstone and g r i t . 9 . .110 i . " : — Massive l i g h t grey limestone, with large c r i n o i d stems and brachiopods, bryozoans, and echinoderms. 10. 300± "• Dark grey and brown shales, with f o s s i l s . : 11. 100 " Massive, hard sandstone. 12. 1 , 4 0 0± " Hard sandstones and black and red shales' with bands of g r i t and t h i n beds of conglomerate; thickness very . v.* • • " roughly estimated. 13. 800± • '-"'•'—— Hard, massive sandstone with g r i t t y layers.. 14- 1 , 0 0 0 + " - D a r k grey t o black, often p h y l l i t i c . a r g i l l i t e with q u a r t z i t i c bands. ' . 6,780 feet Base concealed. - 9 -•N.L. Bowen (1914, pp.112-113) noted Chilliwack-type rocks on.both sides of Fraser River, north of the map-area. He suggested that a north-e a s t e r l y trend i n Fraser V a l l e y indicated the existence of a Palaeozoic mountain system oriented i n t h i s d i r e c t i o n . On t h i s e a r l i e r trend north-westerly trending f a u l t s and g r a n i t i c intrusions were superimposed i n Mesozoic time. No further work was published on t h i s area u n t i l 1930, when C.-H. Crickmay (1930a) discussed, the s t r u c t u r a l connection between the Coast and Cascade Mountain systems. ' Crickmay worked mainly on Mesozoic rocks around Harrison Lake, north of the map-area, and gave no d e t a i l e d descrip-t i o n of the Palaeozoic rocks. He traced the structure and some l i t h o l o -g i c a l u nits south across Fraser River to the v i c i n i t y , of Mount Baker i n northern Washington. Unlike Daly, who considered a l l rocks between the Chilliwack b a t h o l i t h on the east and Church Mountain on the west as P a l — aeozoic, Crickmay assigned rocks i n the eastern t h i r d of the Chilliwack V a l l e y area to h i s S l o l l i c u m "Series" of possible T r i a s s i c age. Crickmay described a major f a u l t , the Harrison Lake f a u l t , whose trace l a r g e l y l i e s beneath Harrison Lake. Palaeozoic rocks east of the lake are i n f a u l t contact with Mesozoic rocks to the west. The f a u l t plane dips steeply to the east. The southward continuation of t h i s f a u l t was believed to mark the western l i m i t of Palaeozoic rocks i n the C h i l l i -wack V a l l e y (see map,. Crickmay, 1930a, opp. p.487). Crickmay considered that rocks of the area immediately east of Cultus Lake, described by Daly as Cultus Formation, were schuppen of Carboniferous and Lower Cretaceous rocks. S t r u c t u r a l trends were observed by Crickmay to.be roughly p a r a l l e l -10-to.the boundaries of the "Jurassic Coast Range Ba t h o l i t h " and he suggested that the Cascade Mountains were formed by compression of the geosynclinal sedimentary accumulation against the r e s i s t a n t mass of the b a t h o l i t h . In 194-4 the Geological Survey of Canada published the Hope Sheet. (Map 737A) on a-scale of 4 miles to 1 inch. This g e o l o g i c a l map was. a. compilation by C.E. Cairns?, with the geology shown f o r Chilliwack Valley being, taken d i r e c t l y from Daly's map of 1912. The term Chilliwack Group, rather than Chilliwack S e r i e s , appeared f o r the f i r s t time on t h i s map, but no explanation for the change was made. A b r i e f , general review of the geology of the northern Cascade Moun-tains of Washington State published by P. Misch (1952) was the f i r s t com-prehensive synthesis of the geology of the region, although no d e t a i l e d s t r a t i g r a p h i c information was included. D.N. Hillhouse (1956) studied the geology of the area around Cultus • Lake, and concluded (p.23) that most of the limestones he observed i n the Chilliwack Group are probably of Wolfcampian age, but that an age range from M i s s i s s i p p i a n to T r i a s s i c i s possible. W.R. Danner (1957),. who worked mainly i n northwestern Washington, to the southwest of the map-area, divided the Chilliwack Group into two formations on the basis of l i t h d l o g i e s and extensive faunal c o l l e c t i o n s . These, formations are the Red Mountain Formation of probable' E a r l y Penn-sylvanian to Late M i s s i s s i p p i a n age, and the Black Mountain Formation of Wolfcampian age (Danner, 1957, p.115). The t y p e - l o c a l i t i e s of these pro-posed formations are a few miles southwest of the Chilliwack V a l l e y area. Misch (i960) b r i e f l y described two major westward and northwestward overthrusts i n t h i s region. The lower or Church Mountain t h r u s t - f a u l t -11-transported Palaeozoic rocks over J u r a s s i c and lower Cretaceous rocks. In the Chilliwack V a l l e y map-area t h i s f a u l t i s shown (Map, Geological Discussion Club, I960) to follow approximately the southward extension of Crickmay',s Harrison Lake f a u l t . Recumbent folds within t h i s Palaeo-zoic thrust-plate were observed i n the map-area by Misch (i960). The upper or Shuksan t h r u s t - f a u l t (Misch, I960, 1962) brings low grade met-amorphic rocks of pre-Jurassic age over the Upper Palaeozoic rocks.. Both f a u l t movements are of middle (?) Cretaceous age (see M i l l e r and Misch, 1963, p.107)o The t h r u s t - f a u l t s have been subsequently folded i n T e r t i a r y (early Eocene ?) time (Misch, I960, M i l l e r and Misch, 1963). C.L. Smith (1962) studied the Red Mountain Formation of Danner, and correlated limestone at several l o c a l i t i e s i n northern Washington with t h i s u n i t . W.S. Moen (1962) mapped and described the geology of the northern part of the VanZandt quadrangle, immediately southwest of the map-area in northern Washington. This area contains the t y p e - l o c a l i t i e s of Banner (1957) proposed formations. According to Moen (1962, p.57) the C h i l l i -wack Group was i n i t i a l l y folded and f a u l t e d p r i o r to deposition of Lower Mesozoic rocks, although he presented no evidence to support t h i s con-c l u s i o n . Deformation during middle Cretaceous time produced northeast trending folds and f a u l t s and large-scale thrusts. North trending f o l d s and associated east trending f a u l t s were formed during middle Eocene time Epeirogenic movement i n Pliocene time superimposed structures s i m i l a r l y oriented to those produced i n Eocene time. -12-. F i e l d work F i e l d work by the w r i t e r was done i n 1962, 1963, and 1964. Data was plotted d i r e c t l y on maps of scale 4 inches to 1 mile, enlarged from 1:50,000 Canadian National Topographic Sheets, 92 H/4 West and. East. ;Air photographs, obtained from the B r i t i s h Columbia Department of Lands and Forests, gave almost complete stereographic coverage of the map-area, and were comparable i n scale to the enlarged maps. Locations on the map were determined with-the aid of.the a i r photographs and a Taylor altimeter, c a l i b r a t e d i n 25 foot i n t e r v a l s . In addition to mapping l i t h o l o g i e s and contacts of r o c k - s t r a t i g r a p h i c units of known age, note was made of the geometry, o r i e n t a t i o n , sense of movement and r e l a t i v e age of any secondary structures present. Information from these minor structures, combined with a knowledge of the s p a t i a l d i s t r i b u t i o n of rock units of known age, allows an i n t e r p r e t a t i o n to be made of the geology of the area. The s i z e of the map-area was not f i x e d , but instead governed by two opposing considerations. Mapping had to be done i n s u f f i c i e n t d e t a i l to enable possibly complex structures to be elucidated. On the other hand, the area mapped had to be large enough to allow demonstration of both the continuity, or otherwise, of r o c k - s t r a t i g r a p h i c units and the magnitude of any major structures c o n t r o l l i n g the present d i s t r i b u t i o n of these u n i t s . More f i e l d time was spent i n the c e n t r a l part of the map-area, than towards the periphery. GEOLOGICAL SETTING The Cascade Mountain system i n northwestern Washington and ..southern B r i t i s h Columbia consists of a c e n t r a l , north-northwest trending, gneis-s i c and g r a n i t i c core, flanked on the east and west by b e l t s of sedimen-tary and volcanic rocks which l o c a l l y have been subjected to low-grade regional metamorphism (Figure 3;, Map, Geological Discussion Club, I960; Huntting et al.,'"19.6l).. The type-area of the Chilliwack Group i s s i t u -ated at the northern'end of the western b e l t of sedimentary and volcanic rocks, contiguous to the core of the mountain system, which here consists of the i n t r u s i v e g r a n o d i o r i t i c Chilliwack b a t h o l i t h and the Custer. Gneiss (Daly, 1912). To the north of the map-area, across Fraser River Valley, i n t r u s i v e g r a n i t i c rocks predominate i n the apparent extension of the system, and the Cascade Mountains adjoin the Coast Mountains (Geological Discussion Club, 19.60; L i t t l e , • 1962). The b e l t of sedimentary and vo l c a n i c rocks on the west side of the Northern Cascade Mountains has been the s i t e of intermittent deposition since at l e a s t Middle Devonian time. Volcanic rocks, and sedimentary rocks derived from them, are the predominant deposits, although limestones are of l o c a l importance, Younger sedimentary rocks tend to be arkosic, but s t i l l contain much material of vo l c a n i c o r i g i n (Danner, 1960a, pp.1,2). Middle Devonian rocks l i e unconformably upon an amphibolitic gneiss complex cut by d i o r i t i c rocks i n the San Juan Islands, some 4-0 miles south-west of the map-area (Danner, 1960b). . Amphibolitic and g r a n i t o i d rocks of minor ar e a l extent exposed west and south of the Chilliwack V a l l e y •U p p,rTert. and" ReT seds. and vofc. rx-—\ f o o o'j Lower Tert.pCtfte Crgf: ^ 0 8 - •* se.cl.and vole. nr. Mes. (pre-mi'd-Cretji -—3 sed. and-velc. rx: Pal. Sed. and — _ " ~ _ vole. rx. . . Low grade-met", rx. Mainly sneissic — — rx. N _ — _ mm granitic, no, .7 Ultra basjc, rx. s-i •> y> 'b-i^\ ' ) \ \ \ j \ \ K v I 1 L 8 m i l e s J C Mop taken from guidebook °f G)*oL Di-scussion Club, Vancouver", B. C._, wittn modi ficati'oos } F I G U R E 3 : S k e t c h map s h o w i n g the g e o l o g i c a l s e t t i n g of m a p a r e a . -14-map-area (Moen, 1962, p.49, M i l l e r and Misch, 1963, p . l66) and within, the easternmost part of the map-area are pos s i b l y equivalent to the pre-Xiddle Devonian rocks i n the San Juan Islands. Limestones of Devonian age cropping-out immediately southwest of.the map-area are included by Moen (1962, p.15) within h i s u n d i f f e r e n t i a t e d Chilliwack Group, and correlated by Danner (1960a,- p.3) with Middle Dev-onian v o l c a n i c and c l a s t i c rocks.and limestones of the San Juan Islands (Danner, 1957,p.54)° No M i s s i s s i p p i a n rocks are recognised i n t h i s region (Danner, 1960a, p.3)- Lower Pennsylvanian (?) rocks l i e with apparent conformity (Danner, 1957, p.88) upon Devonian rocks i n the San Juan Islands. Limestones of Ear l y Pennsylvanian age, and associated c l a s t i c rocks present within the map-area and to the-south of i t , form the lower part of the Chilliwack Group as presently established. These Pennsylvanian rocks are widely d i s -t r i b u t e d i n northwestern Washington (Smith, 1962). Lower Permian c l a s t i c rocks, limestones and vo l c a n i c rocks discon-formably o v e r l i e the Pennsylvanian rocks i n and to the southwest of the map-area and comprise the upper part of the Chilliwack Group as presently established. These rocks are ov e r l a i n disconformably i n the map-area by Upper T r i a s s i c rocks. Overlying Lower Permian rocks i n the San Juan Islands, however, are Upper Permian rocks; the l a t t e r are also present f a r t h e r south i n Washington i n the Cascade Mountains (Danner, 1957, 1960a). During Late T r i a s s i c time, v o l c a n i c rocks and limestones were laid-down west of t h i s region on Vancouver Island, and to the east i n the Southern I n t e r i o r of B r i t i s h Columbia (McLearn, 1953). In the map-area predominantly fin e c l a s t i c rocks of marine o r i g i n , belonging to the Cultus -15-Formation, were deposited. These range i n age from Late T r i a s s i c to Early J u r a s s i c , with no recognised break. Middle J u r a s s i c v olcanic rocks crop-out both north and south of the map-area (Crickmay, 1930b, p.35), Danner, 1960a, p.U) and may be present within i t . Upper Ju r a s s i c c l a s t i c rocks are recognised i n the eastern part of the map-area, and c l a s t i c rocks of Upper-Jurassic age grade up into the Lower Cretaceous rocks to the north and south of the map-area (Crickmay, 1930b, p.35, M i l l e r and Misch, 1963, p.167). • . ... Middle Devonian to Lower Cretaceous c l a s t i c rocks of t h i s sedimentary b e l t are derived generally from source areas i n which v o l c a n i c rocks were predominant. The presence of volcanic rocks, not uncommonly accompanied by limestone, and contemporaneous with t h e - c l a s t i c rocks, suggests that many.source areas, were active v olcanic centres, within the mobile b e l t now occupied by the Western C o r d i l l e r a . Although M i l l e r and Misch (1963, p.167) suggested that metamorphism took place during Late Palaeozoic and E a r l y Mesozoic time, i n t h i s region, no evidence of any orogenic a c t i v i t y of t h i s age has been observed within the map-area. Available data, indicates that s t r a t i g r a p h i c breaks between Lower Permian and Upper T r i a s s i c rocks, and possibly between Lower Penn-sylvanian and Permian rocks are due to non-deposition, s u r f i c i a l erosion . and p o s s i b l y non-deformative, epeirogenic (?) u p l i f t . The e a r l i e s t , post-Devonian, evidence of deep, erosion, such as, would presumably accompany orogeny, i s the presence of g r a n i t i c cobbles i n a Lower Cretaceous con-glomerate i n the Harrison Lake area (Crickmay, 1962). The major post-Devonian orogenic event i n the region happened about mid-Cretaceous time ( M i l l e r and Misch, 1963, p.167). Within the Chilliwack V a l l e y map-area, -16-and contiguous areas to the southwest (Moen, 1962,' p.57), northeast trend-ing f o l d s and thrusts were formed, and many of the rocks were^ subjected to very low-grade regional metamorphism. The northeast trend of these structures i s of unknown are a l extent and stands i n marked contrast to the regional north-northwest trend of both Cascade and Coast Mountains. Immediately southwest of the map-area, rocks of Late Cretaceous and Paleocene age l i e with marked unconformity on Palaeozoic and Mesozoic rocks ( M i l l e r and Misch, 1963, p.167). The younger rocks are predomin-antly, .continental arkoses, although they s t i l l contain much v o l c a n i c d e t r i t u s (Danner, 1960a, p.2). To the west, on Vancouver Island, Upper Cretaceous marine rocks are t r a n s i t i o n a l into these c o n t i n e n t a l sediments. Deposition i n t h i s region, from post--;/nid-Cretaceous time to the present, . has occurred i n r e s t r i c t e d basins, whose positions correspond approxim-a t e l y to present day topographic depressions and lowland areas. A second period of deformation took place i n the region i n e a r l y Eocene time ( M i l l e r and Misch, I960, p.170). In the map-area, northwest trending structures normal to the trend of structures "produced during mid-Cretaceous, deformation, were possibly formed at t h i s time. Middle Eocene and younger rocks are continental arkosic rocks which l i e with angular unconformity on the l i t h o l o g i c a l l y s i m i l a r .Paleocene rocks. To the west and southwest of the map-area these rocks are merely t i l t e d or gently, warped (Daly, 1912, p.520, M i l l e r and Misch, 1963, p.171). However, downfaulted middle Eocene (G.E. Rouse, o r a l communication) con-glomerates at Hope, 20 miles northeast of the map-area, have the form of a syncline with steeply dipping limbs (Cairns, 1924, p.70). Intrusion of the Chilliwack b a t h o l i t h , forming a part of the c r y s t a l l i n e -17-core of the Cascade Mountains immediately east of the map-area, appar-ently took place 18 m i l l i o n years ago (Baadsgaard et a l . , 1961, p.697), i n Miocene time (Kulp, 1961). -18-STRATIGRAPHY Preliminary statement Rock-stratigraphic units are described below i n order of decreasing age. Where possible, the descriptions given are of formations or undesig-nated r o c k - s t r a t i g r a p h i c units of comparable status. These r o c k - s t r a t i -graphic u n i t s , t h e i r ages and l i t h o l o g i e s are summarised i n Table 2. S t r u c t u r a l and s t r a t i g r a p h i c data provide evidence f o r the presence within the map-area of at l e a s t three major tectonic u n i t s or nappes, separated by f l a t - l y i n g f a u l t s . These structures were formed by deforma-t i o n subsequent to deposition of a l l rocks i n the'map-area. In some cases, parts of the same.rock-stratigraphic unit are present i n two or more nappes. Such parts were or i g i n a l l y . s e p a r a t e d by unknown distances but are now super-posed. Consequently, unless such a r o c k - s t r a t i g r a p h i c u n i t i s of remark-ably uniform nature, the unit may d i s p l a y quite d i f f e r e n t c h a r a c t e r i s t i c s within the r e l a t i v e l y small dimensions-of the map-area, as the r e s u l t of superposition during deformation. Most descriptions of formations, or undesignated r o c k - s t r a t i g r a p h i c units of comparable status, therefore are subdivided into discussions of the u n i t as present i n d i f f e r e n t tectonic u n i t s . Where t h i s subdivision i s made, the formation i s described i n order of decreasing s t r u c t u r a l level.. To make the subsequent discussion easier to follow, a b r i e f summary of these tectonic units which includes the names given to them and the rocks composing them, i s given below i n Table 3- These structures are discussed i n the structure section of the t h e s i s . A schematic represen-t a t i o n of t h e i r form and r e l a t i o n s to one another i s shown i n Figure -19- , and t h e i r ' d i s t r i b u t i o n within the map-area i n Figure 5« Where possible, c o r r e l a t i o n of ro c k - s t r a t i g r a p h i c u n i t s within a single t e c t o n i c u n i t was achieved by tracing-out l i t h o l o g i e s . C o r r e l a -t i o n of formations exposed i n d i f f e r e n t t e c t o n i c units was made by demon-s t r a t i n g the presence of.a s i m i l a r l i t h o l o g y i n a comparable s t r a t i g r a p h i c succession. - 2 0 -Table 2: Rock-stratigraphic units (S t r a t i g r a p h i c names established i n the l i t e r a t u r e are i n c a p i t a l l e t t e r s ) . Age Name and apparent thickness (feet) Lithology. Late J u r a s s i c Middle J u r a s s i c E a r l y J u r a s s i c Late T r i a s s i c CULTUS FORMATION . 4,000 Fine to medium grained volcanic arenites, arg-i l l i t e s and s l a t e s ; very minor flows disconformity E a r l y Permian (Leonardian) y \ Permian volcanic"sequence F 2,000 - 700 (conformable) Altered basic to i n t e r -mediate flows, t u f f s , minor chert and minor a r g i l l i t e E a r l y Permian (Leonardian) hed) Permian limestone 300 (conformable) Limestone, t y p i c a l l y cherty;- in. part l a t e r -a l l y equivalent to the Permian v o l c a n i c se-quence Permian and (?) Pennsylvanian .CHILLIWACK GROUP 'esently establis Upper c l a s t i c sequence 800-450 (conformable) Coarse to medium-grained v o l c a n i c arenites, arg-i l l i t e s , l o c a l conglom-erates, tuffaceous t o -wards top. This sequence, may include one or more disconformities Lower Pennsyl-vanian (Morrowan)/ M P-to a Red Mountain Limestone ( r e s t r i c t e d from Danner, 1957) 100 (conformable) Limestone, t y p i c a l l y a r g i l l a c e o u s Lower Pennsyl-vanian (?) "V. Unknown age (Possibly equiv- , alent i n part to pre-Middle Dev-onian basement of Danner and Misch) t Lower c l a s t i c sequence 2,500 -BASE NOT RECOGNISED Amphibolitic rocks A r g i l l i t e s , f i n e to med-ium-grained volcanic arenites Rocks of possible diverse o r i g i n and age -21-Table 3'- Tectonic units of the Chilliwack V a l l e y area STRUCTURAL TOP Name of tectonic unit - /" Description Unnamed Permian rocks and amphibo-l i t i c rocks which o v e r l i e Mesozoic rocks i n eastern-most part of the map-area _FLAT LYING FAULT McGuire Nappe Recumbently-folded s e d i -mentary and v o l c a n i c rocks ' which range i n age from Late Jurassic to E a r l y Pennsyl-vanian FLAT LYING FAULT Liumchen Nappe Thrust sheet ( i n part?) com-posed of v o l c a n i c rocks of E a r l y Permian age, with over-l y i n g Mesozoic rocks. In the extreme northeastern part of the map-area, t h i s t ectonic u n i t may include . older sedimentary rocks. • FLAT LYING FAULT Autochthon (No l a t e r a l trans-l a t i o n of these rocks, f o r any great distance, can be demonstrated) Folded sedimentary and v o l -canic rocks of s l i g h t l y lower metamorphic grade • than rocks i n a l l higher tectonic u n i t s . Age of rocks ranges from E a r l y Pennsylvanian to Middle Ju r a s s i c V J c H W K . GP.J A M P H I B . R O C K S McGUIRE N A P P E L I U M C H E N N A P P E U T O C H T H O N , - v A s s u m e d t h r u s t f a u l t s i n d i c a t e d by a r r o w s F o r m of tecton ic units as ou t l i ned by y o u n g e s t P a l a e o z o i c r o c k s F I G U R E 4 : S c h e m a t i c r e p r e s e n t a t i o n of f o r m a n d r e l a t i o n s h i p s of t e c t o n i c u n i t s in t h e m a p - a r e a F I G U R E 5 •* A r e a l d i s t r i b u t i o n of tectonic un i t s in the map a rea -22-Amphibolitic rocks Rocks that vary widely i n texture, l e s s widely i n composition and which are probably of diverse o r i g i n s , but which i n v a r i a b l y contain abun-dant amphiboles, are grouped for the purposes of d e s c r i p t i o n under the heading, of amphibolitic rocks. These rocks have not been completely mapped and p e t r o l o g i c a l examination was r e s t r i c t e d to a few specimens f r o m . s c a t t e r e d l o c a l i t i e s . More work i s necessary to demonstrate whether t h e i r i n c l u s i o n under a common heading i s j u s t i f i e d . The amphibole-bearing rocks - crop-out at the eastern and southeastern l i m i t s of the map-area.. They appear to form a b e l t which extends i n a north-northeasterly d i r e c t i o n from the southern end of Slesse Creek, near the International Boundary, to Airplane Creek Va l l e y , just west of the Cheam Range (Plate l ) . • Present mapping has not established the continuity, or otherwise,.of t h i s b e l t of amphibolitic rocks. As the rocks e x h i b i t somewhat d i f f e r e n t c h a r a c t e r i s t i c s i n the northern, c e n t r a l and southern parts of the b e l t , rocks from each.of these locations are described sep-a r a t e l y o-North of Chilliwack River Amphibolitic rocks form prominent c l i f f s on the east side of Airplane Creek V a l l e y and to the south, at an a l t i t u d e of 4,000 feet,- on the ridge between Foley Creek, and Chilliwack River. At the l a t t e r l o c a l i t y , Daly (1912, p.544) noted the presence of rocks that he described as a s i l l or great dyke, s i m i l a r l i t h o l o g i c a l l y to gabbroic rocks on Mount Pierce to the south of Chilliwack River. Amphibolitic rocks i n these l o c a l i t i e s are t y p i c a l l y fine-grained, even-textured, hard, massive, grey-green weathering, dark greyish-green to black rocks. In a few places, small euhedral feldspars are present, scattered through the:"fine grey-green matrix. R e l a t i v e l y rare coarser equivalents of the above rocks, i n hand specimens, . t y p i c a l l y have an estimated composition of about 70$ amphibole and 30% feldspar. One rock examined i n the f i e l d resembles a fine-grained d i o r i t e , being composed of approximately equal percentages of amphibole and feldspar. A coarse-grained rock of granoblastic texture, composed e n t i r e l y of amphiboles, apparently comprises a dyke within the"predominant fine-grained rocks. A l l coarser grained rocks examined from t h i s area have i s o t r o p i c f a b r i c . M i c r o s c o p i c a l l y , the fine-grained rocks consist of a groundmass of f i n e l y granular epidote (replacing p l a gioclase laths ?), and small sub-hedral to. anhedral hornblende c r y s t a l s e x h i b i t i n g brown to green pleo-chroi|m and comprising 20% to 30% of the whole. C h l o r i t e i s present throughout the groundmass. P y r i t e and p y r r h o t i t e are the most abundant opaque minerals, although ..skeletal iliiienite c r y s t a l s p a r t l y a l t e r e d to semi-opaque leucoxene and f i n e l y granular sphene (?) are common. Rare feldspar, phenocrysts up to 2mm. i n length show-all stages of a l t e r a t i o n to epidote. Fabric of a l l fine-grained rocks examined i s i s o t r o p i c . The composition of the few rocks examined i n d e t a i l suggests that they belong to the q u a r t z - a l b i t e - e p i d o t e - b i o t i t e subfacies of the- green-s c h i s t f a c i e s (Fyfe, Turner and Verhoogen, 1958, p.224-). The amphibolitic rocks on the ridge between Foley Creek and C h i l l i -wack River appear to form a t h i c k , tabular body, roughly conformable - 2 4 -with the underlying, eastward dipping, sedimentary rocks. Apparent t h i c k -ness of these rocks i s nearly 1,000 f e e t . Rocks on the east side o f . A i r -plane Creek V a l l e y may be of even greater thickness. In Airplane Creek V a l l e y , and on the ridge between Foley Creek and Chilliwack River, amphibolitic rocks o v e r l i e Mesozoic s l a t e s , a r g i l l i t e s , and s i l t s t o n e s which are no more metamorphosed than s t r a t i g r a p h i c a l l y equivalent, l i t h o l o g i c a l l y s i m i l a r , rocks further west i n the map-area. The contact has not been observed, but can be located to within about 200 feet i n the lower part of Airplane Creek V a l l e y . Rocks of the Chilliwack Group are exposed above amphibolitic rocks on the east side of Airplane Creek V a l l e y , although the contact has not been investigated. White (1949, p.A215) reported limestones and c l a s t i c rocks of the Chilliwack Group on the southernmost peak of the Cheam Range, about 1,500 feet above the top of the amphibolitic rocks on the east side of Airplane. Creek, and limestone pods and v o l c a n i c rocks probably belonging to t h i s group are present on the west side of the range, f a r t h e r to.the north. The r e l a t i o n s h i p between amphibolitic rocks i n Airplane Creek Valley, and Permian limestones and volcanic rocks that cap Mount Laughington, just west of Airplane Creek i s not known. These Permian rocks o v e r l i e Mesozoic rocks i d e n t i c a l to Mesozoic rocks below the amphibolitic rocks i n Airplane Creek. I f the Permian, rocks on Mount Laughington are the westward exten-sion of the limestones and volcanic rocks i n the Cheam Range, which over-l i e amphibolitic rocks of Airplane Creek, then the amphibolitic rocks must t h i n very r a p i d l y to the west. -25- • . On the ridge south of Foley Creek, a r g i l l i t e s and s l a t e s of unknown age immediately o v e r l i e amphibolitic rocks. The assumed continuation of these rocks i n the bottom of Chilliwack V a l l e y are dark grey to black, quartz-rich s e r i c i t i c s l a t e s and a r g i l l i t e s , l o c a l l y thermally metamor-phosed by the adjacent Chilliwack b a t h o l i t h to c o r d i e r i t e - b i o t i t e horn-f e l s e s . These rocks are somewhat s i m i l a r l i t h o l o g i c a l l y to the "pre-J u r a s s i c p h y l l i t e s " reported by M i l l e r and Misch (1963, p.166). These rocks are possibly the. basal part of the Chilliwack Group, by analogy to the r e l a t i v e positions of the rocks on the east side of Airplane Creek. Mount Pierce and Nesakwatch Creek Va l l e y C l i f f s of amphibolitic rocks on the west side of the northern end of Nesakwatch Creek V a l l e y , were mapped by Daly (1912, p.532) as Slesse D i o r i t e . He regarded the Slesse D i o r i t e as an i n t r u s i v e , s t o c k - l i k e body of post-Carboniferous age, which was cut by the T e r t i a r y C h i lliwack b a t h o l i t h . Amphibolitic rocks at t h i s l o c a l i t y are generally coarser than amphibolitic rocks to the north, although a l l grain sizes are present. They.range from dark grey-green to black rocks, composed"of 100$ amphi-bole, to grey-green rocks containing about 50$ feldspar. Microscopic examination of one coarse-grained specimen, composed of . about equal proportions of feldspar and amphibble, revealed f a i r l y f r e s h andesine associated with large fibrous hornblende c r y s t a l s with ragged terminations and curved cleavage planes. Pleochroism of the hornblende ranges from greenish-yellow to blue-green. Small elongate amphibole c r y s t a l s . w i t h i n the feldspars show very strong blue-green pleochroism and -26-are possibly a c t i n o l i t e . Rocks forming the c l i f f on the west side of Mount Pierce appear to be part of the same body as the amphibolitic "rocks i n Nesakwatch Creek, although continuity i s not d e f i n i t e l y established. Daly (1912, p.543) described from near t h i s l o c a l i t y a body of dyke-like foriji, which was not seen by the writer, composed of serpentine, o l i v i n e , and magnetite and dyke-like bodies of amphibdlite t r a n s i t i o n a l to coarse-grained gabbro. One rock examined by the writer from t h i s l o c a l i t y appears s i m i l a r to the d i o r i t e - l i k e rock from north of the C h i l l i w a c k River (p.20) but has an i n d i s t i n c t l i n e a t i o n produced by roughly aligned hornblende c r y s t a l s . In a t h i n section t h i s rock was seen to be composed of about 1+0% hornblende (with blue-green to greenish-brown pleochroism) set i n a groundmass of f i n e l y granular epidote (Figure 6). Sphene and apatite are present i n minor amounts, the sphene being coarse-grained, drop-like i n shape, and not associated with any opaque minerals. .'. • Ov e r a l l form of the amphibolitic rocks.in t h i s part of the map-area i s not known. The amphibolitic rocks on Mount Pierce appear to have the form of a tabular body, conforming to bedding and f o l i a t i o n i n underlying Mesozoic a r g i l l i t e s and s l a t e s . No rocks were seen to o v e r l i e the amphibolitic rocks i n the Nesak-watch Creek and Mount Pierce l o c a l i t i e s . However, rust-coloured b l u f f s on the east side of Nesakwatch Creek V a l l e y are composed of dark-grey, quartz-rich slates and a r g i l l i t e s ; these rocks are l i t h o l o g i c a l l y s i m i l a r to rocks above amphibolitic rocks on the divide between Chilliwack River and Foley Creek. Figure 6: Photomicrograph (th i n section, plane l i g h t , X^ .0) amphibolitic rock from Mount Pierce, composed l a r g e l y of hornblende and f i n e granular epidote. Sphene (high r e l i e f ) i s v i s i b l e at top centre. -27-i Southern end of Slesse Creek V a l l e y Amphibolite forms c l i f f s on the east side of Slesse Creek Valley, about one mile north of the International Boundary at an .altitude of 3,500 fe e t . These rocks are - fine-grained, massive, hard and s u p e r f i c i a l l y resemble the amphibolitic rocks i n Airplane Creek. However, they are com-posed of an i n t e r l o c k i n g mesh of f i n e , needle-like, blue-green a c t i n o l i t e c r y s t a l s . B i o t i t e i s present i n minor amounts and minute, red-brown gar-nets were observed i n one specimen. Due west of t h i s l o c a l i t y , on the west side of Slesse Creek Valley, at a l t i t u d e s ranging from.2,000 to 2,500 feet, grey to grey-green weather-ing rocks crop-out. Some of these rocks, with a well-developed f o l i a t i o n which i s cut by a l a t e r planar structure, c l o s e l y resemble c e r t a i n rocks i n the a m p h i b o l i t i c - d i o r i t e complex underlying Devonian rocks i n the San Juan Islands (W.R. Danner, o r a l communication). One specimen of t h i s f o l i a t e d rock examined i n t h i n section consists l a r g e l y of an i r r e s o l v a b l e , f i n e l y granular groundmass containing muscovite that i s oriented p a r a l l e l to.the early f o l i a t i o n . . Scattered through the groundmass are a c t i n o l i t e and b i o t i t e c r y s t a l s , mimetic to both the e a r l y f o l i a t i o n and l a t e r planar structures. These rocks crop-out about one mile from the western margin of the Chilliwack b a t h o l i t h , which i s exposed on the east side of Slesse Creek Valley, immediately south of the International Boundary. Contact metamorphism may well be responsible f o r the development of garnet, b i o -t i t e and blue-green a c t i n o l i t e , which cross-eut a l l planar structures. The o v e r a l l form of the bodies of amphibolitic rock at the -southern end of Slesse Creek Va l l e y , and t h e i r r e l a t i o n s h i p to other rock units -28-i n the map-area i s unknown. Cor r e l a t i o n Rocks of s i m i l a r l i t h o l o g y to the amphibolitic rocks i n the map-area have been reported by other workers i n the region, and are b r i e f l y mentioned below. However, u n t i l the amphibolitic rocks i n the map-area have been mapped and described i n d e t a i l , any attempt at c o r r e l a t i o n remains,spec-u l a t i v e . . . Danner (1960b) reported an amphibolitic complex cut by d i o r i t i c rock which.is unconformably o v e r l a i n by Middle Devonian rocks i n the San Juan Islands.. As noted above, amphibolitic rocks from the southern end of Slesse Creek l i t h o l o g i c a l l y resemble c e r t a i n of these pre-Devonian rocks. . The Shuksan. t h r u s t , mapped by Misch (19.60, 1962) i n northern Washing-ton, brings p h y l l i t e s . a n d greenschists. of pre-Jurassic age over Palaeozoic rocks. Underlying the sole of the Shuksan thrust i n the Mount Larrabee area, immediately.southwest of where Slesse Creek crosses the International Boundary, are c r y s t a l l i n e rocks, to which Misch has ascribed a pre-Devonian age,, on the basis of t h e i r l i t h o l o g i c a l s i m i l a r i t y to a m p h i b o l i t i c - d i o r i t i c rocks of the San Juan Islands. These rocks, c a l l e d the Yellow Aster Com-plex ( M i l l e r and Misch, 1963, p.166), are hornblende-rich d i o r i t e and gabbro, amphibolite and a c i d i c g r a n i t o i d rock. Misch ( o r a l communication, February, 1965) has observed amphibolitic rocks on the ridge south of Mount Pierce, which are s i m i l a r l i t h o l o g i c a l l y to some of h i s pre-Devonian c r y s t a l l i n e rocks south of the International Boundary. Daly mapped the Vedder Greenstone on Vedder Mountain, j u s t west of the map-area. He considered i t (Daly, 1912, p.523) to be an a l t e r e d basic -29-d i o r i t e or gabbro, possibly r e l a t e d to volcanic rocks of the Chilliwack Group, although o r i g i n a l l y he believed i t to be part of a basal c r y s t a l -l i n e s e r i e s . The s i m i l a r i t y between the Vedder Greenstone and rocks near the summit of Mount Pierce was remarked on by Daly (1912, p.5UU)• Moen (1962, pp.50-56) described metadiorites, amphibolites... and d i o -p s i d i t e from j u s t southwest of the map-area, i n northern Washington, to the.' south of Vedder. Mountain. He gave a pre-Devonian age to these rocks; presumably because of t h e i r l i t h o l o g i c a l s i m i l a r i t y . t o the rocks i n the. San Juan Islands. Crickmay (1930a, p.4-88) mapped rocks he c a l l e d " T r i a s s i c v o l c a n i c s " , north of the map-area, about 10 miles due north of amphibolitic rocks mapped by the writer i n Airplane Creek. These T r i a s s i c (?) v o l c a n i c rocks cross the Fraser V a l l e y and crop-out to the east of Harrison Lake. Cairns (19UA, Geol. Surv. Canada, Map 737A) showed bodies of serpentine, d i o r i t e , gabbro, amphibolite, hornblendite and pyroxenite i n l o c a l i t i e s correspond-ing to Crickmay's T r i a s s i c (?) v o l c a n i c rocks. Conclusions Further mapping and systematic sampling i s necessary to demonstrate the nature and f i e l d r e l a t i o n s h i p s of these amphibolitic rocks. I t i s not even known whether they form a single u n i t such as could be included under the s t r a t i g r a p h i c term "complex." The following conclusions are to be regarded as speculative. Rocks grouped under the heading "amphibolitic rocks" may well be of completely d i f f e r e n t o r i g i n s . Some, such as the f o l i a t e d rocks exposed at the southern end of the Slesse Creek V a l l e y are possibly of pre-Devonian -30-age, on the basis of t h e i r l i t h o l o g i c a l s i m i l a r i t y to rocks underlying Devonian rocks i n the San Juan Islands. Others, such as the predominantly non-foliated fine-grained rocks north of the Chilliwack River, may corre-spond to the "pre-Jurassic greenschists" of Misch. I t may be possible to obtain.direct evidence of the. age of the l a t t e r rocks from the northeast-ern part of the map-area, where amphibolitic rocks are exposed below Chilliwack Group rocks at the southern end of the Cheam Range. Amphibolitic rocks on Mount Pierce, and to the north on the ridge between Foley Creek and Chilliwack River, and i n Airplane Creek, l i e on top of Mesozoic slates and a r g i l l i t e s . The s p a t i a l r e l a t i o n s h i p of these two l i t h o l o g i e s , and.their geographical p o s i t i o n r e l a t i v e to that of the Shuksan thrust of Misch (i960,.1962) suggests that the amphibolitic rocks may have been emplaced along the northerly continuation of the Shuksan -thrust of Misch. • F i n a l l y , there i s enough doubt about the l i m i t s and nature of the Slesse D i o r i t e , considered by"Daly to be an i n t r u s i v e body, to warrant i t s r e - i n v e s t i g a t i o n . Devonian rocks of northwestern Washington No Devonian rocks have been i d e n t i f i e d i n the Chilliwack V a l l e y area. Middle Devonian volcanic and c l a s t i c rocks, cherts and limestones, designated the President Channel Formation (Danner, 1957, p.54), are pre-sent i n the San Juan Islands, where they apparently l i e unconformably on, an amphibolitic complex cut by d i o r i t i c rock (Danner, 1960b). Danner (1960a, p.3) correlated rocks i n the President Channel Formation with -31-Devonian limestones reported from several l o c a l i t i e s i n northern Whatcom County, immediately southwest of Chilliwack Valley, (Danner, 1960a, p . l ; Moen, 1962, p.15). At one l o c a l i t y i n northern Whatcom County (south end of S i l v e r Lake V a l l e y ) , a conglomerate containing g r a n i t i c cobbles appears to underlie the Devonian limestone. (W.R. Danner, o r a l communication). Some of these. Devonian limestone bodies are i n f a u l t contact with metaT-d i o r i t e s believed to be part.of the basement complex (Moen, 1962, p . l 6 ) . No M i s s i s s i p p i a n rocks are known i n t h i s region (Danner, 1960a, p.3). I t i s not known at present.whether a hiatus e x i s t s , or whether M i s s i s s i p p i a n rocks have not been reported because of the absence of a recognized M i s s i s s i p p i a n fauna. Pennsylvanian and Permian rocks i n the map-area Daly distinguished three separate f o s s i l i f e r o u s limestones within the Chilliwack Group i n the type-area (Table l ) , but made no attempt to d i f f e r e n t i a t e t h e i r ages. . G i r t y ( i n Daly, 1912, p.515) considered these f o s s i l i f e r o u s rocks to be Upper Carboniferous. However, Daly noted that c e r t a i n u n f o s s i l i f e r o u s rocks included i n hi s * C h i l l i w a c k "Series" could well belong to older systems. From investigations of Palaeozoic rocks cropping-out immediately southwest of the Chilliwack V a l l e y map-area Danner (1957, p.113) suggested that the Chilliwack Group was d i v i s i b l e into one formation of Late Miss-i s s i p p i a n to Ea r l y Pennsylvanian age and one of Ea r l y Permian age. His formations were based on two f o s s i l i f e r o u s limestones, and included asso-ciated., but un d i f f e r e n t i a t e d , c l a s t i c and volcanic rocks. The name "Red Mountain Formation" (Danner, 1957, p.113) was applied to the older -32-formation and the name "Black Mountain Formation" (Danner, 1957, p. 11+7) to the younger. These proposed formations have not been formally de-scribed and incorporated i n the l i t e r a t u r e . Two limestone units are distinguished by the writer within the Chilliwack V a l l e y map-area.' F o s s i l content of these limestones indicates t h e i r approximate time-equivalence to the limestones described by Danner. They do not completely correspond t o any two of the limestones i n the com-posite section of Daly reproduced as Table 1 i n t h i s t h e s i s . These two limestones are the only units recognised within the C h i l l -iwack Group as presently established, whose continuity, d i s t i n c t i v e l i t h -ology, and c h a r a c t e r i s t i c f o s s i l content enables them to be used as s t r a t -igraphic markers across much of the map-area. Therefore the s t r a t i g r a p h i c p o s i t i o n of a l l other units in.the Chilliwack Group i s made r e l a t i v e to them. However, these limestones are not. i d e a l marker u n i t s . The upper, Permian, limestone v a r i e s considerably i n thickness and i s , i n part, a f a c i e s equivalent to v o l c a n i c rocks i n the map-area. Fortunately, i t i n v a r i a b l y contains a d i s t i n c t i v e f u s u l i n i d fauna, which enables precise s t r a t i g r a p h i c dating to be made. The lower, Pennsylvanian, limestone i s t h i n and l o c a l l y absent, and E a r l y Pennsylvanian f u s u l i n i d s have been recognised within i t only i n the eastern part of the map-area. However, t h i s limestone generally contains very large c r i n o i d columnals, which are u s e f u l as rock components f o r c o r r e l a t i n g . The c r i n o i d columnals cannot be used to demonstrate time-equivalence of the Pennsylvanian limestone across the map-area, although according to Smith (1962) and Danner ( o r a l communication) they are c h a r a c t e r i s t i c of Pennsylvanian rocks i n the North-ern Cascade Mountains. -33-Lower c l a s t i c sequence A sequence of dominantly fine-grained c l a s t i c rocks which, l i e s s t r a t -i g r a p h i c a l l y below the Pennsylvanian limestone 3 i s c a l l e d ^ f o r reference purposes, the lower c l a s t i c sequence. In i t s l i t h o l o g i c a l homogeneity and mappable nature t h i s sequence i s of formational status, although i t cannot formally.be designated as a formation, p a r t l y because i t s s t r a t i -graphic base i s not recognised. Relative to Mesozoic rocks, t h i s sequence i s of l i m i t e d a r e a l extent within the map-area. Daly (1912,. p.512) described a sequence of sandstones and shales below limestone containing large c r i n o i d stems. Daly regarded t h i s c l a s -t i c sequence as the basal part of his^Chilliwack' Series*(see Table l ) . Danner .(1957, p.119).noted that Pennsylvanian limestone i n northern What-com County conformably o v e r l i e s t h i n bedded cherty a r g i l l i t e s . Smith (1962, p.32) gave a more d e t a i l e d d e s c r i p t i o n of these c l a s t i c rocks. McGuire Nappe C l a s t i c rocks s t r a t i g r a p h i c a l l y (.and s t r u c t u r a l l y ) below the Pennsyl-vanian limestone crop-put i n the south, southeast and northeast parts of the area bounded on the west by Tamihi Creek, on the north by Chilliwack River, on the east by Slesse Creek and on the south by the Int e r n a t i o n a l Boundary. They are also present below Pennsylvanian limestone on the east side of Slesse Creek V a l l e y . These rocks form the s t r u c t u r a l l y lowest part of the core of the McGuire Nappe i n the map-area. The sequence consists of .massive beds of tan-weathering, medium to fine-grained sandstones somewhat sparsely and i r r e g u l a r l y d i s t r i b u t e d through dominant, t h i n l y bedded, rhythmically graded and laminated, hard, -34-very f i n e sandstones, s i l t s t o n e s and . a r g i l l i t e s . The a r g i l l i t e s probably comprise the greater part of the sequence. Conglomerate horizons are present, but are rare. Coarser beds are dark grey to dark grey-green i n colour, hard, and composed of poorly sorted grains, whose maximum size r a r e l y exceeds 3 mm. Determinable c l a s t s i n hand specimens are grey to green chert, rare v o l -canic rock fragments and a r g i l l i t e fragments. Large a r g i l l i t e fragments are common i n some horizons. Although the texture i s preserved i n these rocks, i n hand specimens grain boundaries commonly are i n d e f i n i t e and blurred, and the only c l a s t s with sharp boundaries are a r g i l l i t e f r a g -ments. Very fine-grained sandstones and s i l t s t o n e s commonly form t h i n beds ranging i n thickness from 1 inch to 4 inches, within dominant a r g i l l i t e s . The f i n e g r a n u l a r i t y of these rocks, generally does not allow grading, as shown by overall.range i n grain size within a bed, to be d i r e c t l y observed i n hand specimen, but i t i s apparent as a hue change from medium to dark grey as grain s i z e becomes smaller and a r g i l l i t e content increases. In • some beds grading may be repeated several times, with the formation of i r r e g u l a r l y spaced laminae. Load casts, many of which are minute, and small c u t - a n d - f i l l structures are common. One conglomerate bed about 6 feet t h i c k within t h i s graded sequence i s composed of well-rounded cobbles of feldspar porphyry with euhedral feldspars i n a pale grey to green f e l s i t i c groundmass; the cobbles are scattered through a poorly sorted sandstone matrix. In the coarser c l a s t i c rocks, a crude f o l i a t i o n , roughly p a r a l l e l to bedding,is present. In the fin e rocks t h i s f o l i a t i o n i s present, but i s - 3 5 -extremely d i f f i c u l t to d i s t i n g u i s h from bedding. Microscopic examination of the common f i n e r grained rocks shows, them to be poorly sorted, below a c e r t a i n maximum size of about 0 . 5 mm. Where a l t e r a t i o n i s not extensive, the rocks consist l a r g e l y of plagioclase feldspar, which i s mainly a l b i t e , and low-biref^ingent c h l o r i t i c (?) matrix. Quartz grains are rare or absent, but fragments of a r g i l l i t e are common. In most places, however, a l t e r a t i o n of grains i n these rocks i s so extensive that t h e i r o r i g i n a l composition cannot be d i r e c t l y determined, but can only be i n f e r r e d by analogy with p a r t l y a l t e r e d grains. A l t e r a -t i o n or replacement of plagioclase c l a s t s i s commonly to c a l c i t e , l e s s commonly to brown, semi-opaque clay minerals and r a r e l y to fine-grained aggregates of iquartz (Figure 7 ) . C l a s t i c rocks of t h i s sequence which are coarser than a r g i l l i t e s are c a l l e d a l t e r e d plagioclase arenites or v o l c a n i c arenites ( a f t e r Folk, 1 9 6 1 ; see Appendix A), l a r g e l y on the basis of the composition of the few l i t t l e - a l t e r e d rocks within the sequence. The proportion of f i n e r grained material i n the succession increases towards the s t r a t i g r a p h i c . t o p . Just below the contact with the overlying limestone the sequence i s composed e n t i r e l y of thinly-tedded, black, rusty-weathering, a r g i l l i t e s . Apparent thickness of t h i s succession exposed on the south side of Spencer Peak, above Tamihi Creek, i s more than 2 , 5 0 0 feet; i n Slesse Creek V a l l e y the thickness i s les s than 1 , 0 0 0 f e e t . These, estimates of t h i c k -ness do not take into account d u p l i c a t i o n of bedding by f o l d i n g , vhich i s l o c a l l y d i r e c t l y observed, and commonly indicated by repeated inversions of graded bedding. -36-The upper contact i s well exposed on the south side of Spencer Peak, above Tamihi C reek, at an a l t i t u d e of approximately 5,000 f e e t . In t h i s l o c a l i t y the contact i s gradational. Several t h i n beds of limestone are present within a r g i l l i t e s of the c l a s t i c sequence immediately below the contact with the main limestone body. . The s t r a t i g r a p h i c base, of t h i s sequence has not been seen i n the map-area. On the southwest: side of Spencer Creek, and i n Slesse. Creek V a l l e y the sequence o v e r l i e s Lower Permian v o l c a n i c rocks and minor Lower. Permian limestone. The lower contact has not been observed, but i s the. assumed f l a t - l y i n g f a u l t on the base of the McGuire Nappe. Autochthon One and one h a l f miles southwest of the peak of Church Mountain black cherty a r g i l l i t e s are i n contact with the s t r u c t u r a l base of limestone containing Lower Pennsylvanian f u s u l i n i d s . These rocks are l i t h o l o g i c a l l y s i m i l a r to rocks of the lower c l a s t i c sequence s t r a t i g r a p h i c a l l y below Pennsylvanian limestone i n the McGuire Nappe. However, more d e t a i l e d mapping i s necessary i n t h i s part of the map-area before they can be cor-r e l a t e d with rocks of the lower c l a s t i c sequence i n the.McGuire Nappe, as the s t r u c t u r a l i n t e r p r e t a t i o n of t h i s part of the map-area, based on present mapping, indicates that they are part of the upper c l a s t i c se-quence. S i m i l a r black cherty a r g i l l i t e s are also associated with Pennsyl-vanian limestone i n Liumchen Creek V a l l e y . F o s s i l s F o s s i l s are rare i n t h i s c l a s t i c sequence. Organic hieroglyphs (worm markings) have been observed. Small, acute conic, hollow structures up to about 3 cm. long, r e f e r r e d to as belemnite-like f o s s i l s by Smith. -37-(1962, p.17, p.32 e t c . ) , are present i n c l a s t i c rocks associated with Pennsylvanian limestone on the northeast side of Mount McGuire and to the southwest of the summit of Church Mountain ( F o s s i l L o c a l i t i e s 3_2 and 4-9, Plate l ) . These structures are of unknown o r i g i n ; according to J.A; Jeletzky ( o r a l communication, July 1964) they are not belemnites, but may be r e l a t e d to.pteropods. Poorly preserved, u n i d e n t i f i e d pelecypods and gastropods are present i n rocks of t h i s sequence i n Liumchen Creek, i n the v i c i n i t y of the Pennsylvanian limestone. Daly (1912, p.'5!3) i n h i s Section 3 on the west side of Mount McGuire, reported brachiopods, echihoderms and bryozoans i n shales below the lime-stone, believed by the present writer to be of Pennsylvanian age. None has been found by the writ e r from what appears to be Daly's l o c a l i t y . Age As these rocks underlie limestone of probable" Lower Pennsylvanian age, and are gradational with it.,, they are i n part, of probable Lower Pennsylvanian age. As no s t r a t i g r a p h i c base of the sequence i s seen, the age of rocks i n the lower part of the sequence i s not c e r t a i n . No Miss-i s s i p p i a n rocks are known from the map-area, although Devonian rocks are present immediately to the southwest (Moen, 1962, p.15). Further mapping in the Liumchen Creek area, and to the southwest of i t , may reveal the r e l a t i o n s h i p between t h i s sequence and the Devonian limestones. Environment of deposition No unequivocably marine f o s s i l s have been found by the writ e r within the lower c l a s t i c sequence. The uppermost part, gradational into lime-stone containing c r i n o i d columnals and co r a l s , i s presumably of marine origin.. Daly (1912, p.513, Section 3) reported brachiopods, bryozoans and echinoderms from what i s possibly t h i s sequence, just below c r i n o i d a l -38-(Pennsylvanian ?) limestone. The remainder can only be i n f e r r e d to be of marine o r i g i n . O v e r a l l fineness of grain and poor sorting indicates that..these rocks were l a i d down i n a predominantly low-energy environment. Graded, bedding indicates deposition by t u r b i d i t y currents, and although some f i n e l y lam-inated beds may have been produced by s e t t l i n g - o u t of very f i n e grains widely d i s t r i b u t e d by "normal" marine currents, load casts and cut-and-f i l l structures suggest that most beds were laid-ddwn by the former mech-anism. The rare conglomerate horizons have a high matrix to grain r a t i o , with cobbles suspended i n a poorly sorted matrix whose l a r g e s t grains are sand-sized, a f a b r i c t y p i c a l of t u r b i d i t e sequences. Rounding of cobbles i s presumably due to abrasion p r i o r to f i n a l transport and.deposition. The abundance of plagioclase grains i n the less a l t e r e d rocks, pres-ence of volcanic c l a s t s , and.low quartz content of these rocks suggests that v o l canic rocks predominated i n the source area. No evidence of d i s -tance from source was obtained, although the gradual o v e r a l l decrease of grain size upwards may indicate r e l a t i v e lowering of the source area, or else increase i n distance of the source from the s i t e of deposition. Red Mountain Limestone Limestone of Pennsylvanian age s t r a t i g r a p h i c a l l y o v e r l i e s the c l a s -t i c sequence described above. Although t h i s limestone i s a r e l a t i v e l y t h i n u n i t of minor a r e a l extent within the map-area, i t i s one of the p r i n -c i p a l s t r a t i g r a p h i c markers within the Chilliwack Group as presently de-fine d . It i s proposed that the term "Red Mountain Formation", o r i g i n a l l y - 3 9 -applied by Danner (1957, p.115) to Pennsylvanian limestone and .associated but u n d i f f e r e n t i a t e d c l a s t i c rocks which crop-out just southwest of the map-area be r e s t r i c t e d to Red Mountain Limestone. The Pennsylvanian lime-stone described by Danner i s c o r r e l a t i v e with that i n the map-area. The geographic term "Red Mountain" i s retained as the limestone i s well-devel-oped, e x c e l l e n t l y exposed and r e a d i l y accessible i n a quarry on Red Moun-J' t a i n i n northern Washington. I t has been described i n some d e t a i l from t h i s l o c a l i t y by Smith (1962, p.15-17), who measured a t o t a l thickness of 582-g- f e e t . Danner's o r i g i n a l "Red Mountain Formation" has been r e s t r i c t e d to Red Mountain Limestone as the limestone alone i s a d i s t i n c t i v e and r e a d i l y mappable. u n i t over a wide area. In contrast, the associated c l a s -t i c rocks are r a r e l y f o s s i l i f e r o u s , commonly covered, and so s i m i l a r i n l i t h o l o g y to units of other ages i n the region, that t h e i r r e l a t i o n s h i p to the Pennsylvanian limestone must be seen d i r e c t l y before t h e i r s t r a t i g r a p h i c p o s i t i o n is. c e r t a i n . On the basis of faunal c o l l e c t i o n s , Danner (1957, p.136) ascribed an age of Late M i s s i s s i p p i a n to Early Pennsylvanian to the limestone cropping-out on Red and Black Mountains, which l i e about 5 miles southwest of the map-area. Further studies have lead the above author to believe that an E a r l y Pennsylvanian age i s most probable (Danner, o r a l communica-t i o n , November, 196Z,.) . Smith (1962) described f i v e sections of t h i s limestone at f i v e d i f -ferent l o c a l i t i e s i n northern Washington. He correlated these sections' using l i t h o l o g i e s , s t r a t i g r a p h i c r e l a t i o n s h i p s between the limestone and contiguous u n i t s , and c e r t a i n f o s s i l s used as rock components rather than b i o s t r a t i g r a p h i c a l l y . - 4 0 -Danner ( o r a l communication) c o l l e c t e d f u s u l i n i d s from limestone about one and one h a l f miles southwest of the peak of Church Mountain ( F o s s i l L o c a l i t y 49, Plate l ) , i n the southwestern part of the map-area. These f u s u l i n i d s were considered by J,W. Skinner to be of Morrowan age., and the limestone to. be c o r r e l a t i v e with Pennsylvanian limestone on Black Mountain. As no other f u s u l i n i d s capable of providing a precise age have .been found i n the Pennsylvanian limestone elsewhere i n the map-area, several other c r i t e r i a , s i m i l a r to those employed by Smith (1962) are used i n co r r e l a t i n g t h i s limestone within the map-area. The limestone commonly contains very large c r i n o i d columnals (Figure 8), which seem to be r e s t r i c -ted i n t h i s region to Lower Pennsylvanian rocks (Smith, 1962, p.82, W.R. Danner, o r a l communication). In addition, "belemnite-like" f o s s i l s of Smith, 1962, (possibly pteropods) have only been found i n as s o c i a t i o n with Pennsylvanian limestone i n northern Washington (Smith, 1962, p.82) and are present i n the map area i n s i m i l a r a s s ociation. The limestone i n the map-area i s not uncommonly ar g i l l a c e o u s , i n contrast to the t y p i c a l l y cherty Permian limestone. I t s t r a t i g r a p h i c a l l y o v e r l i e s , and i s p a r t l y gradational with, f i n e c l a s t i c rocks, and i s commonly o v e r l a i n s t r a t i -g r a p h i c a l l y by a coarse c l a s t i c sequence. These c r i t e r i a , when taken t o -gether, enable reasonable confidence to be placed i n c o r r e l a t i o n of t h i s u n i t across the map-area. Cor r e l a t i o n by tr a c i n g out l i t h o l o g y can only be done l o c a l l y as the limestone i n many places occurs as a series of dis c r e t e lenses. McGuire Nappe The Red Mountain Formation i s part of• the core of the McGuire Nappe. The formation i s well-exposed on Spencer Peak, two and one h a l f miles Figure 7: Photomicrograph (th i n section, plane l i g h t , X4.0) of poorly sorted, fine-grained sandstone of the lower c l a s t i c sequence. Most grains v i s i b l e are feldspar, commonly altered to brownish clay minerals (?) and carbonate. Rare quartz grains (Q) are present. Groundmass i s composed of c h l o r i t e , carbonate and wisps of argillaceous material. Note crude ( l e f t to right) f o l i a t i o n . Figure 8: Large c r i n o i d columnals i n Red Mountain Limestone i n Liumchen Creek, about $ mile north of International Boundary. - U -southeast of the summit of Mount McGuire, and crops-out on ridges north and east of t h i s peak, on both sides of Slesse Creek V a l l e y at a l t i t u d e s between 2,000 and 3,000 feet, and at a few l o c a l i t i e s on the north side of Chilliwack River. The Red Mountain Limestone i s t y p i c a l l y medium to dark grey i n colour and weathers tan or grey-white. I t i s l o c a l l y d i v i s i b l e into three units of approximately equal thickness, although commonly deformation.and r e -c r y s t a l l i z a t i o n are too great to allow any d i f f e r e n t i a t i o n to be made. The lowest u n i t i s t h i n to medium bedded with i r r e g u l a r bedding surfaces, which are separated by calcareous shale laminae. Above t h i s there i s a massive u n i t , and the top unit i s s i m i l a r to the lowest one. Chert no-dules are rare i n t h i s limestone, i n marked contrast to t h e i r abundance i n the Permian limestone. R e c r y s t a l l i z a t i o n has u s u a l l y destroyed or obscured o r i g i n a l textures. Where textures are preserved, these rocks are e i t h e r a r g i l l a c e o u s f o s s i l -iferous micrudites ( a f t e r Folk, 1959) or, less commonly, biomicrudites. L o c a l l y , the limestone consists of large c r i n o i d stemsj commonly an inch or more i n diameter and up to almost 1 foot long i n a matrix containing smaller c r i n o i d a l material (Figure 8). Although the matrix of these c r i n -o i d a l limestones i s i n v a r i a b l y r e c r y s t a l l i z e d , the poor s o r t i n g , and the lack of observed o r i e n t a t i o n i n the primary f a b r i c , i n d i c a t e s they are c r i n -o i d a l biomicrudites. Even where the limestone i s coarsely r e c r y s t a l l i z e d , the large c r i n o i d stems remain v i s i b l e . The c r i n o i d stems do not appear to be confined to any p a r t i c u l a r horizon within the limestone. On Spencer Peak they are present i n a separate bed of limestone about 18 inches thick, within a r g i l l i t e s j ust below the main limestone body. Elsewhere they occur - 4 2 -within the massive u n i t . Scattered o o l i t e s have been observed.at the s t r u c -t u r a l base of limestone containing large c r i n o i d stems, on the north bank of Chilliwack River, north of Slesse Creek Valley. The apparent thickness of t h i s limestone i n the McGuire Nappe i s no- . where greater than 200 feet, and i s usually less than 100 f e e t . I t i s l o c a l l y absent, the limestone appearing as a series of d i s c r e t e lenses, which appear t o , l i e - o n the same s t r u c t u r a l plane. I t i s not known at present whether t h i s l a t e r a l d i s c o n t i n u i t y i s a primary d e p o s i t i o n a l fea-ture, or whether i t i s due to subsequent deformation. The lower contact i s p a r t l y gradational with s t r a t i g r a p h i c a l l y under-l y i n g rocks, a few t h i n beds of limestone being present at the top of the underlying f i n e c l a s t i c sequence. The limestone i s s t r a t i g r a p h i c a l l y over-l a i n by a succession i n which coarse c l a s t i c rocks are prominent. Liumchen Nappe About h a l f a mile east of B r i d a l F a l l s i n Fraser V a l l e y , and at the base of the north side of Mount Cheam, i n "the northernmost part of the map-area, c r y s t a l l i n e limestone i s quarried. I t i s b r i e f l y described from t h i s l o c a l i t y by Mathews and McCammon (1957, p . 4 0 ) . The limestone can be traced up the mountain to the west and i s o v e r l a i n and underlain by f i n e c l a s t i c rocks. This limestone i s not s i l i c e o u s and contains c r i n o i d stems. It may be equivalent to the Red Mountain Limestone f a r t h e r south i n the map-area, and i s possibly a part of the Liumchen Nappe. Autochthon An i s o l a t e d outcrop of limestone containing f u s u l i n i d s of Lower Penn-sylvanian age i s present about one and a h a l f miles southwest of the peak of Church Mountain. Limestone containing large c r i n o i d o s s i c l e s i s i n t e r --43-bedded with fin e c l a s t i c rocks i n Liumchen Creek V a l l e y about three-quarters of a mile north of the International Boundary. Further mapping i s necessary before the s t r u c t u r a l r e l a t i o n s h i p between these two lime-stones i s established, although they are believed.to be the same formation. F o s s i l s Small fusulinid's c o l l e c t e d by W.R. Danner and i d e n t i f i e d by J.W. .. Skinner (written communication to W.R. Danner, October, 1964) from the limestone southwest of the summit of- Church Mountain are i d e n t i f i e d as E o s t a f f e l l a and M i l l e r e l l a . Rare endothyroid foraminifera are the only other foraminifera that have been observed i n t h i s limestone elsewhere i n the.map-area. Small, u n i d e n t i f i e d horn corals and rare c o l o n i a l corals are present, and appear to be r e s t r i c t e d to the shaly .phase of the lime-stone, as do rare f u c o i d a l markings on bedding planes. Bryozoan and brach-iopod fragments have been observed i n t h i n sections. C r i n o i d columnals of a l l s i z e s are ubiquitous. Daly (1912, p.513, Section 3) c o l l e c t e d brachiopods and bryozoans from what i s probably the Pennsylvanian limestone on Spencer Peak. These f o s s i l s were not found by the author at t h i s l o c a l i t y . .Girty ( i n Daly, 1912, p.515) noted that t h i s c o l l e c t i o n seemed to d i f f e r considerably from other faunas obtained by Daly from Palaeozoic rocks i n the Chilliwack Va l l e y area. This diff e r e n c e i s presumably because rocks at other l o c a l -i t i e s from which Daly obtained diagnostic f o s s i l s are Permian rather than Pennsylvanian i n age. Age and c o r r e l a t i o n Age of the Red Mountain Limestone i n the map-area i s based on the presence of the f u s u l i n i d s E o s t a f f e l l a and M i l l e r e l l a , which J.W. Skinner -u-considers to be of probable Morrowan, (Early Pennsylvanian) age. Skinner has also i d e n t i f i e d s i m i l a r forms from limestones at the Red Mountain type-l o c a l i t y i n northern Washington, just southwest of the map-area. These f u s u l i n i d s are considered by Skinner to e s t a b l i s h c o r r e l a t i o n of the Penn-sylvanian limestone from the Chilliwack Valley-Red Mountain l o c a l i t i e s with the Coffee Creek Formation of Suplee, Oregon, and with limestones at Har-per Ranch, northeast of Kamloops, B r i t i s h Columbia. Danner (1960a, p.3) and Smith (1962, p.84) correlated Pennsylvanian limestones from the Red Mountain l o c a l i t y with limestone at several other l o c a l i t i e s i n northern Washington, using both palaeontological and rock-s t r a t i g r a p h i c evidence. Limestone containing both large and small c r i n o i d o s s i c l e s crops-out i n the east side of the south end of Harrison Lake, to the north of the map-area (Crickmay, 1930b, pp.35,38) . This limestone was considered by Crickmay to be of Pennsylvanian age,, and i s thus believed by the w r i t e r to be possibly equivalent to the Red Mountain formation i n the map-area. Environment of deposition The marine o r i g i n of the Red Mountain Limestone i s demonstrated by the presence within i t of corals and echinoderm fragments. Sparse o o l i t e s have been observed i n the limestone at only one l o c a l i t y , and the common a r g i l l -aceous content and textures seen i n limestone that has been l i t t l e r e crys-t a l l i z e d , suggests deposition i n a low-energy environment. The base of the limestone i s gradational with the underlying c l a s t i c sequence, and the lower part of the limestone i s a r g i l l a c e o u s ; massive limestone occurs i n the middle part of the u n i t , and the upper i s again a r g i l l a c e o u s . The limestone may have been deposited l a r g e l y because the supply of c l a s t i c -45-sediments ceased, possibly a continuation of the trend evident i n theeunder-l y i n g c l a s t i c sequence, which generally becomes f i n e r upwards. When .clas-t i c deposition was renewed, the carbonate p a r t i c l e s became too. dispersed to form a d i s c r e t e , l i t h o l o g i c a l l y homogenous u n i t . Upper c l a s t i c sequence A sequence of c l a s t i c rocks separating the Pennsylvanian and Permian limestones in Chilliwack V a l l e y area i s c a l l e d , f o r reference purposes, the upper c l a s t i c sequence. I t i s an a r e a l l y extensive, major part of the Chilliwack Group i n the map-area. Although the upper c l a s t i c sequence i s of roughly s i m i l a r composition to the previously described lower c l a s t i c sequence, i t contains a f a r higher proportion of coarse sand-sized c l a s t i c rocks and i s p a r t l y composed of the products of contemporaneous vulcanism. Exact age of t h i s sequence i s problematical. I t i s believed to con-t a i n both. Lower Pennsylvanian and Lower Permian rocks, and to include a hiatus, or hiatuses, possibly representing Middle and Late Pennsylvanian time. D i v i s i o n of the sequence into Pennsylvanian and Permian rocks has not been effected at present because neither diagnostic f o s s i l s , nor an unconformity or unconformities, have been recognized. On Mount Laughington and Cheam Range Alter e d volcanic arenites associated with Permian limestone on Mount Laughington s t r u c t u r a l l y o v e r l i e Mesozoic rocks of the McGuire Nappe. These v o l c a n i c arenites are l i t h o l o g i c a l l y s i m i l a r to rocks s t r a t i g r a p h -i c a l l y below Permian limestone i n the McGuire Nappe, and are considered to be part of the same sequence. Fine cherty a r g i l l i t e s contiguous to Permian limestone on Mount Cheam ( F o s s i l L o c a l i t y 9) may possibly belong - 4 6 -to the same sequence. McGuire Nappe Rocks comprising t h i s sequence are present on Mount McGuire, on the east side of Slesse Creek V a l l e y and on both sides of Chilliwack V a l l e y between the junctions of Slesse Creek and Chipmunk Creek with Chilliwack River. These rocks form the upper part of the core of the McGuire Nappe. . The upper c l a s t i c sequence i n the McGuire Nappe consists of a basal few feet of a r g i l l i t e which i s s t r a t i g r a p h i c a l l y o v e r l a i n by massive to thick-bedded, l o c a l l y c l i f f - f o r m i n g sandstones and minor t u f f and conglom-erate, interbedded with argillaceous rocks. The l a t t e r are much less prominent topographically and are commonly poorly exposed but probably comprise the greater part of the succession. Within t h i s sequence are present three d i f f e r e n t types of c l a s t i c rocks composed of predominantly sand-sized grains; to some extent these three types grade into one another. C l a s t i c rocks of the f i r s t type are quartz-poor v o l c a n i c arenites and are the most common. They are t y p i c a l l y olive-grey to tan weathering, and green, grey-green, or grey i n colour. These rocks are unsorted and com-posed of angular c l a s t s of a l l s i z e s , the larges t c l a s t s being granules or pebbles. There i s no sharp d i f f e r e n t i a t i o n between grains and matrix. The f i n e r grained rocks occur as t h i n , graded beds. More massive and coarser grained beds are of uniform texture for much of t h e i r thickness, with markedly coarser c l a s t s present only at the base of the bed. A l l of these rocks commonly have a crude f o l i a t i o n , with c l a s t s being fl a t t e n e d and g r a i n boundaries blurred and i n d i s t i n c t , as a r e s u l t of l a t e r deforma-t i o n . They are composed of varying proportions of al t e r e d v o l c a n i c rock - 4 7 -fragments, plagioclase feldspars and minor fragments of a r g i l l i t e . The volcanic fragments megascopically resemble grey or green chert, but micro-s c o p i c a l l y have tuffaceous textures or are composed of small, i n t e r - l o c k i n g feldspar l a t h s . Although these fragments are commonly a l t e r e d to saus-s u r i t e , c h l o r i t e , or clay minerals, o r i g i n a l textures are s t i l l d i s c e r n -i b l e . White or pale green a l b i t e or o l i g o c l a s e , showing varying degrees of a l t e r a t i o n to s e r i c i t e , semi-opaque, low-birefringent clay minerals, or, less commonly,, c a l c i t e , i s present i n amounts of up to 30% of the rock. C h l o r i t e i s present throughout and quartz i s very rare, or absent (Figure 9 ) . Rocks of t h i s f i r s t type are l i t h o l o g i c a l l y s i m i l a r to rocks from the Miocene of Papua described as greywackes by Edwards ( 1 9 5 0 , p . 1 4 6 ) . For reasons given i n Appendix A, the writer prefers to use Folk's terminology, and these rocks are c a l l e d a l t e r e d v o l c a n i c arenites. There may be some admixture of effectively-, contemporaneous v o l c a n i c material, but t h i s can-not be demonstrated, and the rocks are considered to have been derived from a pre-existing volcanic terrane. In contrast to the above rocks, i n which quartz i s minor or absent, sandstones of the second type, which are much les s abundant, are maroon, •pale green or silvery-white i n colour and contain up to 10% of angular to rounded, clear quartz grains. Apart from very rare, unaltered a l b i t e c l a s t s , quartz- i s the only unaltered material; the remainder of the grains are completely a l t e r e d to semi-opaque, low-birefringent material or c a l -c i t e , and contain c h l o r i t e , epidote and s e r i c i t e . Some c l a s t s are composed of a l t e r e d shards. The maroon sandstones owe t h e i r colour to disseminated grains of hematite. Origin of these quartz-bearing rocks i s unknown. Quartz-bearing v i t r i c - c r y s t a l t u f f s are common i n the v o l c a n i c sequence -IS-which s t r a t i g r a p h i c a l l y o v e r l i e s the Permian limestone, which i s above t h i s upper c l a s t i c sequence. S i m i l a r t u f f s were possibly produced by vulcanism outside the map-area during the time that the upper c l a s t i c sequence was being deposited. These quartz-bearing t u f f s may have been mixed with the more common volcanic arenites during deposition. . Rocks of the t h i r d type are true l i t h i c t u f f s , composed l a r g e l y of rock fragments, with very, minor amounts of feldspar and quartz (Figure 10). These t u f f s are present l o c a l l y near the top of the upper c l a s t i c sequence. They d i f f e r from the more common volcanic arenites i n having a higher ma-t r i x to grain r a t i o , and i n containing shard-shaped to pumiceous c l a s t s , now l a r g e l y altered to c h l o r i t e . They are interbedded with a r g i l l i t e s containing molds of c r i n o i d columnals and bryozoans and grade v e r t i c a l l y downwards into v o l c anic arenites. A cobble conglomerate, within the upper c l a s t i c sequence and about 20 feet thick, crops-out on the west side of the ridge north of Spencer Peak, above the Pennsylvanian limestone, I t i s composed of rounded cobbles of a l t e r e d basic to intermediate volcanic rocks and cherts, set i n a ma-t r i x of smaller, angular c l a s t s of s i m i l a r composition. The matrix to grain r a t i o of t h i s cobble conglomerate i s high. Apparent thicknesses of the upper c l a s t i c sequence i n the McGuire Nappe are v a r i a b l e . The sequence i s more than 800 feet t h i c k on the east side of Slesse Creek, Due north of Spencer Peak i t i s not more than 450 feet t h i c k . I t i s not known whether t h i s v a r i a t i o n i n thickness i s primary, or i s due to an unconformity within the sequence, or i s the r e s u l t of deformation. The lower contact of the sequence i s conformable with Pennsylvanian Figure 9: Photomicrograph (th i n section, plane l i g h t , X4-0) of coarse-grained volcanic arenite of the upper c l a s t i c sequence, exposed on the east side of Slesse Creek Valley. Most, grains are feldspar (some denoted by F); others are s a u s s u r i t i c v o l c a n i c rock fragments (dark), or "chert" (C); c h l o r i t e i s i n t e r s t i t i a l . F o l i a t i o n i s poorly shown i n t h i n section, but i s apparent from the oriented long axes of grains. Figure 10: Photomicrograph (thin section, plane l i g h t , X4-0) of l i t h i c t u f f at the top of the upper c l a s t i c sequence, exposed 1^ - miles northeast of Mount McGuire Peak. Grains are mainly al t e r e d l i t h i c fragments; rare feldspars (F) and quartz (Q) grains are present. Rock has a much higher matrix to grain r a t i o than the volcanic arenite (see Figure 9). -49-limestone. A few feet of a r g i l l i t e , the basal part of the sequence, sep-arates the limestone from overlying coarse volcanic arenites. Permian lime-stone conformably o v e r l i e s the sequence, with a s i m i l a r t r a n s i t i o n from coarse volcanic arenites, or t u f f s , through a few feet of dark argillaceous rocks, to limestone. This contact i s v i s i b l e and r e a d i l y accessible in-the road at the confluence of Slesse Creek with Chilliwack River. Liumchen Nappe Volcanic arenites, probably part of the Liumchen Nappe, are l i t h o l o -g i c a l l y s i m i l a r to those of the Mount McGuire Nappe and crop-out above Permian limestone at an elevation of 2,000 feet, three miles west of Mount Cheam, and one mile southwest of B r i d a l F a l l s . Due south of t h i s l o c a l i t y at an a l t i t u d e of 4?000 feet s i m i l a r rocks underlie Permian limestone. The a s s o c i a t i o n of these c l a s t i c rocks with Permian limestone, and t h e i r l i t h o l o g i c a l s i m i l a r i t y to rocks of the upper c l a s t i c sequence i n the McGuire Nappe suggest they are part of the same s t r a t i g r a p h i c u n i t . Autochthon Coarse-grained, massive, tan weathering, dark grey to grey-green v o l -canic arenites, conglomerate and interbedded shales s t r u c t u r a l l y o v e r l i e inverted Permian limestone just west of the summit of Church Mountain, and are apparently o v e r l a i n by Pennsylvanian limestone, although further map-ping i s needed to v e r i f y the l a t t e r r e l a t i o n s h i p . The s t r a t i g r a p h i c equivalence of these c l a s t i c rocks to the upper c l a s t i c sequence i n the McGuire Nappe i s shown both by t h e i r l i t h o l o g i c a l s i m i l a r i t y and also by t h e i r r e l a t i o n s h i p to the Permian limestone. The sandstones are composed of vo l c a n i c rock fragments and f a i r l y fresh feldspars ( a l b i t e to o l i g o c l a s e ) , with very minor quartz\ and i n t e r -• -50-granular c h l o r i t e (Figure l l ) . The grains are angular and sorting poor. In contrast to rocks of the equivalent sequence i n the McGuire Nappe, these c l a s t i c rocks are much less altered; the grains are fresher, and there i s no penetrative f o l i a t i o n developed through the rock. A conglomerate bed within the sequence, reported e a r l i e r by Hillhouse, (1956, p. 1 4 ) and Danner (1957, p.119), consists of well-rounded boulders and cobbles of alt e r e d intermediate to basic lavas, chert and some lime-stone, set i n a green to grey volcanic or plagioclase arenite matrix. The grain to matrix r a t i o i s v a r i a b l e , but i n many outcrops rounded cobbles of vol c a n i c rock are dispersed through green to grey volcanic sandstone, and the rock i s a sandstone containing cobbles, rather than a conglomerate. The conglomerate outcrops extensively on Church Mountain, and has a t h i c k -ness, of about 100 f e e t . Thickness of a l l c l a s t i c rocks of t h i s sequence on Church Mountain i s estimated to approach 600 feet . F o s s i l s A r g i l l i t e s of the upper c l a s t i c sequence i n the McGuire Nappe contain molds of small c r i n o i d columnals, f e n e s t e l l a t e bryozoans and brachiopod fragments, but these f o s s i l s are r e l a t i v e l y rare. One graded bed on the northeast side of Mount McGuire ( F o s s i l L o c a l i t y 33) contains belleroph-ontid gastropods, pteropods (?) and fragmental brachiopods. A s i m i l a r faunal assemblage i s reported by Smith (1962, p.29) i n c l a s t i c rocks i n t e r -bedded with Pennsylvanian limestone i n northern Washington. West of Spencer Peak ( F o s s i l L o c a l i t y 4 0 ) shales contain s t r a i g h t n a u t i l o i d s , brachiopod fragments and pteropods ( ? ) . Plant fragments are present i n vo l c a n i c arenites on Church Mountain -51-( F o s s i l L o c a l i t y 50). I d e n t i f i a b l e f o s s i l s are l a r g e l y stem fragments of Calamites and less commonly Lepidodendron. No i d e n t i f i a b l e associated mi c r o f l o r a has been found. Pteropods (?) s i m i l a r to those present i n rocks of the equivalent sequence i n the McGuire Nappe are associated with these plant remains. Age and c o r r e l a t i o n Exact age of the upper c l a s t i c sequence i s not known. No f o s s i l s i d e n t i f i e d are s u f f i c i e n t l y diagnostic to demonstrate whether the sequence i s e i t h e r Pennsylvanian or Permian in age. Plant f o s s i l s found i n the sequence i n the map-area indicate a possible Pennsylvanian or E a r l y Permian age (G.E. Rouse, o r a l communication). In c e n t r a l Oregon, a f l o r a i s pres-ent i n c l a s t i c rocks overlying Pennsylvanian limestone (Merriam and Berthiaume, 1943)- This limestone i s correlated by J.W. Skinner, on the basis of f u s u l i n i d s , with the Pennsylvanian limestone on Church Mountain, which also probably s t r a t i g r a p h i c a l l y underlies plant-bearing rocks of the upper c l a s t i c sequence. However, even i f i t i s assumed that the i d e n t i c a l s t r a t i g r a p h i c positions of f l o r a s i n the Chilliwack V a l l e y and c e n t r a l Oregon allow the f l o r a s to be correlated, the Oregon f l o r a can s t i l l only be dated as Pennsylvanian (Maymay and Read, 1956, p.227). In a l l l o c a l i t i e s i n t h i s region from which plant f o s s i l s are known, they are present i n c l a s t i c rocks associated with E a r l y Pennsylvanian limestone (Danner, .1957, p,127, Smith, 1962). As no report has been made of any plant f o s s i l s i n rocks associated with Permian limestone alone, an E a r l y Pennsylvanian age would seem l i k e l y f o r these c l a s t i c rocks. However, l i t h o l o g i c a l evidence appears to contradict t h i s conclusion. Danner (1960b) suggested that a s t r a t i g r a p h i c break existed i n the region -52-between rocks of E a r l y Pennsylvanian and E a r l y Permian age, with E a r l y Permian coarse c l a s t i c rocks l y i n g disconformably on top of Pennsylvanian limestones. Erosion of possible Pennsylvanian rocks i s indicated by the presence of a rounded limestone cobble containing e i t h e r Pennsylvanian or Permian corals i n conglomerate between Pennsylvanian and Permian limestone on Black Mountain i n northern Washington (Banner, 1957, p . 1 4 7 ) . In the map-area, a s t r a t i g r a p h i c break may be indicated by, the sudden appearance of coarse c l a s t i c rocks, apparently conformable on a few feet of fine c l a s t i c rocks overlying Pennsylvanian limestone, and the continued depo-s i t i o n of si m i l a r coarse c l a s t i c material u n t i l the overlying Lower Per-mian limestone was laid-down. Tuffs i n the upper part of t h i s c l a s t i c sequence may be related to Ea r l y Permian vulcanism, which i s p a r t l y con-temporaneous with the Lower Permian limestone. No d i r e c t evidence f o r a hiatus i n t h i s sequence can be given, a l -though the sequence seems very t h i n to represent a l l of the time between Ea r l y Pennsylvanian and E a r l y Permian, p a r t i c u l a r l y as the type of s e d i -mentation indicated by textures of these rocks i s commonly t y p i c a l of th i c k , r a p i d l y accumulated sequences. As the apparent thickness of t h i s sequence v a r i e s , even within one tectonic u n i t , unconformities may be present within i t . P o ssibly t u r b i d i t y flows and s l i d e s caused erosion of previously deposited unconsolidated material. Available evidence can.only suggest that rocks ranging from E a r l y Pennsylvanian to E a r l y Permian i n age are present i n the sequence, possibly separated by one or several hiatuses,"«rwhich may represent much of t h i s time. C o r r e l a t i o n of these rocks, with s i m i l a r rocks i n northern Washington has been made (Danner, 1957, Smith, 1962), and they may also correlate -53-with plant-bearing rocks i n Oregon (see above). Crickmay (1930b, p..35) reported a c l a s t i c sequence containing conglomerate, from the..Harrison Lake area. Some-pebbles i n the conglomerate are f o s s i l i f e r o u s Pennsylr vanian limestone, and Crickmay dated the conglomerate as post-Pennsylvanian, pre-Early J u r a s s i c . This conglomerate i s possibly equivalent... to... conglom-erate i n the upper c l a s t i c sequence i n the map-area, although .the only basis f o r t h i s c o r r e l a t i o n i s the general l i t h o l o g i c a l s i m i l a r i t y of, these conglomerates. Environment of deposition A marine o r i g i n f o r some of these rocks i s demonstrated by the pre-sence of c r i n o i d columnals and bryozoans i n argillaceous rocks of the sequence i n the McGuire Nappe. Because pteropod-like f o s s i l s , occurring with n a u t i l o i d s and brachiopods i n rocks of t h i s sequence i n the McGuire Nappe, are associated with plant f o s s i l s i n c l a s t i c rocks of the autoch-'-thon, the l a t t e r rocks may well be of marine o r i g i n . Daly (1912, p.511) reported the occurrence of plant f o s s i l s associated with brachiopods, bryozoans, echinoderms, and clams i n what are possibly rocks of t h i s se.-quence i n the autochthon. Available evidence therefore suggests that all., rocks of the upper c l a s t i c sequence are of marine o r i g i n . No current bedding has been observed i n any rocks of t h i s sequence. The presence of graded bedding suggests that t u r b i d i t y flows were the f i n a l transporting mechanism f o r some of the beds. However, t h i s sequence i s not the rhythmic a l t e r n a t i o n of graded beds and shales seen i n t y p i c a l t u r b i d i t e sequences (see Kuenen, 1964-, p.20). Beds composed of coarse c l a s t s are commonly poorly graded, or not graded at a l l , and were possibly deposited by"the mechanism akin to both t u r b i d i t y flows and s l i d i n g proposed -54-by Dzulynski et al.(1959, p.1114)- Conglomerates, containing well-rounded cobbles, generally have a high matrix to grain r a t i o , with cobbles, d i s -persed through a v o l c a n i c arenite matrix. This kind of texture ..can r e s u l t only from transport and deposition by a medium of r e l a t i v e l y high v i s c o s i t y , such as a t u r b i d i t y flow or s l i d e (see Pettijohn, 1957, p.228).. As. round-ing of the cobbles, must have occurred p r i o r to f i n a l transport .by ..such a mechanism, material forming these conglomerates appears to have., been trans-ported i n i t i a l l y and rounded by stream action, temporarily laid-.down and then f i n a l l y deposited by t u r b i d i t y flows or s l i d e s . Stream .transport h i s t o r y was only of s u f f i c i e n t length to allow the largest c l a s t s to become rounded, and sand-sized c l a s t s remained angular (see Pettijohn, 1957, p.63). Such conglomerates, deposited by t u r b i d i t y flows, can be widespread. Dzulynski et a l . (1959, p.1113) report a conglomerate bed which was traced for 30 km. with l i t t l e change i n boulder s i z e , although the thickness of the bed was observed to diminish. Danner (1957, p.119) stated that a cobble conglomerate 150 feet t h i c k separates Pennsylvanian. limestone from Permian limestone on Black Mountain i n northern Washington. The s t r a t i g r a p h i c a l p o s i t i o n .of t h i s conglomerate i s i d e n t i c a l to that of the l i t h o l o g i c a l l y s i m i l a r , but thinner, conglomerate on Church Mountain. I f these conglomerates are the same bed, then the conglomerate bed i s possibly comparable to conglomerates of Dzulynski et a l . , as the Black. Mountain and Church Mountain l o c a l i t i e s are (now) 8 miles apart. These c l a s t i c rooks were derived from a source area composed l a r g e l y of v o lcanic rock, with minor limestone. Absence of any metamorphic, or. g r a n i t i c d e t r i t u s indicates that no deep erosion of the source area took place, and that u p l i f t of the source area was probably not great, and was r e l a t i v e l y short l i v e d . The extent to which vulcanism contemporaneous with deposition contributes to the sequence i s not established..,..although primary t u f f s are present i n the upper part of the sequence in..the McGuire Nappe. Altered quartz-bearing c l a s t i c rocks, interbedded with .volcanic arenites, are possibly the product of d i r e c t deposition from showers of volcanic ejectaon.-The following d e p o s i t i o n a l h i s t o r y i s proposed by the writer. Fine c l a s t i c rocks were l a i d down p r i o r to, and immediately a f t e r deposition of Pennsylvanian limestone, and the limestone may merely represent, a .: cessation of c l a s t i c supply. Conformably above the few feet of. argilla=-: ceous rock overlying the limestone are coarse c l a s t i c rocks, interbedded with argillaceous rocks. The change i n o v e r a l l grain s i z e of these c l a s t i c , rocks, from predominantly fine-grained rocks below the Pennsylvanian lime-stone to coarser c l a s t i c rocks above, indicates accelerated growth of the primary source area above sea l e v e l , following deposition of the Pennsyl-vanian limestone. With t h i s accelerated growth, presumably a d e l t a or sh e l f was repeatedly constructed from material deposited by streams or along-shore currents. This accumulated material was then p e r i o d i c a l l y transported by s l i d e s and t u r b i d i t y flows from t h i s secondary source area to the f i n a l s i t e of deposition. The area above sea l e v e l must have been large enough to allow a primary transport h i s t o r y of length s u f f i c i e n t to enable cobbles and pebbles to. become rounded, and stable enough to permit a f l o r a to become established. Evidence of continued u p l i f t of the source... area i s given by the presence of a rounded limestone cobble, containing e i t h e r Pennsylvanian or Permian corals, i n the conglomerate on Black Moun-t a i n , northern Washington (Danner, 1957, p. 147).. Sediment supply to the -56-basin of deposition was supplemented by sporadic vulcanism, p a r t i c u l a r l y i n the l a t e s t part of the time represented by the sequence. Possibly, up-l i f t of the source area was re l a t e d to subsequent extensive Lower .Permian vo l c a n i c a c t i v i t y i n the region. Permian limestone Lower Permian limestone conformably o v e r l i e s the upper c l a s t i c , s e -quence, and i s i n part a f a c i e s equivalent to, and i n part underlies, v o l c a n i c rocks of the Chilliwack Group. As t h i s limestone i s present i n most parts of the map-area, may r e a d i l y be d i f f e r e n t i a t e d on the basis, of l i t h o l o g y from overlying and underlying rocks, and i s the most prominent single unit i n Chilliwack Valley, forming c h a r a c t e r i s t i c grey-white weather-ing c l i f f s , i t i s the most useful s t r a t i g r a p h i c marker i n the map-area.. In addition, i t i s the only u n i t so f a r recognized i n the Chilliwack Group i n the map-area which contains a widely d i s t r i b u t e d fauna capable of pro-v i d i n g an unequivocable and precise age. As t h i s limestone i s d i s t i n c t i v e , mappable and of l i t h o l o g i c a l homogeneity and i s an important part of the Chilliwack Group i n the map-area, i t i s c l e a r l y of formational status. However,- formal designation of a formation requires the d e s c r i p t i o n of a type-section. Further work i s necessary before t h i s can be done, even though most other d e t a i l s necessary f o r the establishment of a formation are known. Therefore, the writer f e e l s that no useful purpose i s served.in applpifcnginai formational name to t h i s rock unit u n t i l a type-section i s described i n d e t a i l . This unit i s accordingly c a l l e d the Permian limestone i n t h i s report. Daly (1912, p.512) found limestone containing bryozoans, brachiopods and Fusulina elongata Shumard just southwest of the map-area,. in. .northern Washington. G i r t y ( i n Daly, 1912, p.515) suggested that t h i s fauna, pro-bably correlated with that i n the Nosoni Formation of northern. .California, now regarded as Lower Guadalupian i n age (Dunbar et a l . , I960). Thompson et a l . (194-6, p. 11) regard F. elongata Shumard as probably belonging..to. the genus Parafusulina, which would give e i t h e r a Leonardian or.Guadalupian age to t h i s limestone in'the map-area. Therefore, discovery of. F.. elongata Shumard i s the e a r l i e s t recorded evidence of Permian rocks i n the area, although Daly made no attempt to d i f f e r e n t i a t e rocks i n the Chilliwack,. Group on the basis of age. Hillhouse (1956, p.15) noted f u s u l i n i d - b e a r i n g limestone on the south . end of International Ridge i n the southwestern part of the map-area, but gave no d e s c r i p t i o n of the f u s u l i n i d s . Danner (1957, p.153) applied the term Black Mountain Formation to Permian limestone and associated, but u n d i f f e r e n t i a t e d , c l a s t i c and v o l -canic rocks on -Black Mountain i n northern Washington. This limestone, con-tains an abundant f u s u l i n i d fauna, considered by Skinner ( i n Danner, 1957, p.151) to be of Wolfcampian age. The stratigraphy of the Permian limestone i n the map-area has not been studied i n d e t a i l s u f f i c i e n t to e s t a b l i s h whether or not i t contains d i s t i n c t l i t h o l o g i c a l u n i t s . Unfortunately, such units are not apparent from macroscopic i n v e s t i g a t i o n ; they would have to be based on the o r i g i n a l petrology of the limestone, which has commonly been destroyed or obscured by subsequent r e c r y s t a l l i z a t i o n or s i l i c i f i c a t i o n . Therefore a general. . d e s c r i p t i o n can only be given, with more d e t a i l e d information from s p e c i f i c l o c a l i t i e s . -58-Th e Permian limestone i s commonly l i g h t grey i n colour, but.may... l o c a l l y be dark grey, and forms prominent buff, grey or white weathering c l i f f s . In contrast to the Pennsylvanian limestone i t i s only .local 1y__ shaly, and many horizons have a high s i l i c a content, manifested.either..as large black to l i g h t grey chert nodules, oriented p a r a l l e l to bedding., or as a rough weathering surface produced by s i l i c a disseminated through the limestone. F o s s i l s are abundant i n c e r t a i n horizons but are generally sparse or absent, although t h i s absence i s possibly due p a r t l y to subse-quent r e c r y s t a l l i z a t i o n . Although r e c r y s t a l l i z a t i o n has commonly obscured or destroyed the o r i g i n a l texture of the limestone, the texture may i n some cases be i n -fe r r e d from the r e l a t i o n s h i p s of preserved allochems to the r e c r y s t a l l i z e d matrix. F o s s i l s are generally the sole allochems; these were l o c a l l y s i l i c i f i e d , whereas the matrix remained as carbonate, and although sub-sequent r e c r y s t a l l i z a t i o n has destroyed any o r i g i n a l textures and struc-tures i n the matrix, the s i l i c i f i e d f o s s i l s are not a f f e c t e d . I f i t can be assumed that generally a l l f o s s i l s are preserved where s i l i c i f i c a t i o n has taken place, then the common paucity of s i l i c i f i e d f o s s i l s r e l a t i v e to... the abundance of the matrix indicates- that the matrix was o r i g i n a l l y m i c r i t e , rather than sparite and that these rocks were o r i g i n a l l y f o s s i l -i f erous m icrites (see Folk, 1961, p.14.1). A few highly f o s s i l i f e r o u s horizons present i n the upper part of the limestone contain abundant ran-domly oriented f o s s i l s , which show no evidence of size s o r t i n g , i n a micros sparite matrix. These rocks were presumably o r i g i n a l l y biomicrudites. Where no f o s s i l s are present, and a l t e r a t i o n has not progressed beyond r e c r y s t a l l i z a t i o n of the matrix to microsparite, the rocks were presumably -59-o r i g l n a l l y m i c r i t e s . ... On Mount Laughington and Mount Cheam Pods of r e c r y s t a l l i z e d limestone containing poorly preserved, s i l i c i -f i e d , Lower Permian f u s u l i n i d s are present on the summit of Mount Laugh-ington, and on the western ridge of Mount Cheam at an a l t i t u d e of. 6,0.00 feet ( F o s s i l L o c a l i t i e s 9 and 11). As t h i s Permian limestone.overLies Mesozoic rocks which i n turn o v e r l i e Permian rocks of the McGuire. and .... Liumchen Nappes, i t i s considered to belong to a separate and higher t e c -tonic u n i t . Permian, limestone i n the McGuire Nappe i s extremely prominent and i s well exposed over a wide area. I t outlines a large recumbent a n t i c l i n e with an attenuated or missing lower limb. The axis of t h i s major f o l d plunges at a low angle towards the northeast. The peak of Mount McGuire i s composed of limestone forming the hinge of t h i s major structure, and d i g i t a t i o n s on t h i s hinge are exposed as discontinuous limestone c l i f f s . on the north side of the mountain. The limestone c l i f f s appear at pro-g r e s s i v e l y lower a l t i t u d e s towards the northeast, occur by Chilliwack,..River at i t s confluence with Slesse Creek and are present on the north side of Chilliwack V a l l e y on.Mounts Thurston and Mercer. Limestone comprising the upper limb of the recumbent a n t i c l i n e caps ridges due east of Mount McGuire. summit, and i t s eastward continuation crops-out at an a l t i t u d e of about 4,000 feet, on the east side of Slesse Creek V a l l e y . From the l a t t e r l o c a l i t y the limestone outcrops can be traced into Chilliwack V a l l e y where they decrease i n a l t i t u d e to the east, and occur on the v a l l e y f l o o r near the junction of Foley Creek.with Chilliwack River. Northward continuation -60-of limestone forming t h i s upper limb i s present on the south. sids... of Mount Mercer, and i n Chipmunk Creek. Local limestone lenses overlying.-Eermian volcanic rocks southeast of the peak of Mount McGuire, and above Permian, volcanic rocks exposed i n a window at the north end of Slesse. Creek .Valley o u t l i n e the lower limb of t h i s recumbent a n t i c l i n e . . Thickness of Permian limestone i n the McGuire Nappe va r i e s considerably across the' map-area. Below the summit of Mount McGuire i t i s more than 2,000 feet thick, a thickness which i s due i n part to v i s i b l e repe.tition of bedding by f o l d i n g . In l o c a l i t i e s where the limestone i s seemingly, l i t t l e deformed and continuous, such as high on the east side of Slesse Creek Valley, the apparent thickness.is i n the order of 200 to 300 feet. Elsewhere, p a r t i c u l a r l y near the eastern l i m i t of exposure of Permian lime.-, stone i n the McGuire Nappe, the limestone forms d i s c r e t e , commonly t h i n , lenses. I t i s not known whether these lenses are of d e p o s i t i o n a l o r i g i n or r e s u l t from deformation. The Permian limestone i n the McGuire Nappe conformably o v e r l i e s v o l -canic arenites, l i t h i c t u f f s and a r g i l l i t e s . The t r a n s i t i o n from coarse v o l c a n i c arenites, through dark-grey a r g i l l i t e s to limestone i s abrupt, taking place over a few f e e t . I t i s s t r a t i g r a p h i c a l l y o v e r l a i n by Permian., flows, t u f f s , cherts and r a r e l y , a r g i l l a c e o u s rocks. At some l o c a l i t i e s . , such as j u s t north of the peak of Mount McGuire, the f o s s i l i f e r o u s , s t r a t -igraphic top of the Permian limestone contains fragments of v o l c a n i c rock, commonly t u f f , up to one cm. i n diameter. In some cases, the top of the limestone i s marked by a calcareous t u f f composed of v o l c a n i c c l a s t s in.a . calcareous matrix; the l a t t e r contains a few, unbroken f o s s i l s . These tuffaceous limestones and calcareous t u f f s l o c a l l y form a horizon at the -61-extreme top of the Permian limestone, marking the t r a n s i t i o n to overlying volcanic rocks. Liumchen Nappe The Liumchen Nappe i n Chilliwack V a l l e y i s composed l a r g e l y of Per-mian volcanic rocks. A limestone bed, a few feet thick, on the. southwest side of Mount McGuire ( F o s s i l L o c a l i t y . 4-1) l i e s within the dominant lavas and minor t u f f s comprising the Liumchen Nappe. This limestone contains f u s u l i n i d s which although not well preserved, appear to be i d e n t i c a l with f u s u l i n i d s i n the s t r a t i g r a p h i c top of the Permian limestone i n the McGuire Nappe, about 1,000 feet v e r t i c a l l y above t h i s l o c a l i t y . I f t h i s limestone bed can be considered to be time-equivalent to the top of the Permian lime-stone of the McGuire Nappe, then part of the volcanic sequence of the Liumchen Nappe, i s a f a c i e s equivalent to at l e a s t part of the Permian limestone. Pods of Permian limestone, probably belonging to the Liumchen Nappe, are exposed at an a l t i t u d e of 4,000 feet on the south side of Fraser V a l l e y , about two miles west of Mount Cheam ( F o s s i l L o c a l i t i e s 5 and 8). They are ov e r l a i n by chert and c r y s t a l t u f f s and o v e r l i e c l a s t i c sedimentary rocks.. To the north and west of t h i s limestone, at an a l t i t u d e of about 2,000 feet, limestone of probable Permian age o v e r l i e s volcanic rocks and under-l i e s v o l c a nic arenites s i m i l a r to those of the upper unnamed c l a s t i c se-quence . Autochthon Permian limestone of the autochthon i s exposed on the east side of the summit of Church Mountain, i n scattered outcrops west and southwest of the summit and i n Liumchen Creek. -62-Limestone on Church Mountain i s inverted; i t i s overlain..by the upper c l a s t i c sequence, and o v e r l i e s volcanic rocks. At the structural..base of the limestone,tuffaceous limestone and calcareous t u f f mark t h e . t r a n s i t i o n to s t r u c t u r a l l y underlying Permian volcanic rocks. In Liumchen,Creek Valley, i n s u f f i c i e n t mapping has been done to c l a r i f y structure, but.pods of limestone containing Permian f u s u l i n i d s o v e r l i e v o l c a n i c rocks, and. are i n t e r f o l d e d with them. .. A limestone of unknown age i s i n contact with Upper T r i a s s i c . r o c k s i n Liumchen Creek. Because i t i s o v e r l a i n by, and gradational. with,., Per-mian volcanic rocks, and o v e r l i e s Upper T r i a s s i c rocks with a.sharp, con-t a c t , i t i s possibly of Permian age, the succession here being inverted.. Apparent thickness of limestone east of the summit of Church Mountain i s about 500 fe e t . Repetition by v i s i b l e f o l d i n g i s responsible for much of t h i s thickness. Permian limestone west of t h i s l o c a l i t y i s much thinner, possibly less than 100 f e e t . F o s s i l s F o s s i l content of the Permian limestone i n the McGuire Nappe va r i e s considerably. F o s s i l s are abundant in. a few horizons but i n most are. e i t h e r absent or very rare. This paucity may be due, i n part, to destruc-t i o n of f o s s i l s by r e c r y s t a l l i z a t i o n . A well defined fauna found at the s t r a t i g r a p h i c top of the Permian limestone where the limestone i s thick, may p e r s i s t f o r a few feet into overlying tuffaceous beds gradational with the top of the limestone. This same fauna i s also present at some l o c a l i t i e s , such as Chipmunk Creek., where the Permian limestone occurs only as l o c a l , t h i n pods underlying volcanic rocks. F u s u l i n i d s , generally s i l i c i f i e d , are the commonest f o s s i l s - 6 3 -i n t h i s fauna and the genera Parafusulina and Pseudofusulinella.hav.e ..been i d e n t i f i e d (Figures 12, 13). These f o s s i l s , are associated with.rhomhopo-r o i d bryozoans, c r i n o i d columnals and rare gastropods and brachiopod.,.frag-ments. As t h i s fauna i s of r e s t r i c t e d v e r t i c a l range, contains f o s s i l s which enable precise s t r a t i g r a p h i c dating to be made, and i s present almost everywhere i n the map-area at the s t r a t i g r a p h i c contact ...between rocks of markedly d i f f e r i n g l i t h o l o g i e s , i t appears to be an ideal..strat-igraphic marker. However, as the fauna i s found only at the contact, of the limestone with v o l c a n i c rocks some environmental co n t r o l i s possible.; the horizon i t marks may therefore be diachronous, perhaps over a r e s t r i c t -ed time-range. I t s presence only at the s t r a t i g r a p h i c top of the Permian limestone, where i t i s t h i c k , enables s t r u c t u r a l inversion of the lime-stone to be demonstrated i n many, l o c a l i t i e s . Medium sized f u s u l i n i d s of the genus Schwagerina (Figure 14) are present.within the limestone, away from the base and top. The distance, at which they occur above the base of the limestone i s not known, but these forms have only been found where the limestone i s r e l a t i v e l y t h i c k , never i n the t h i n lenses. Associated with t h i s Schwagerina are large horn cor-a l s , s u p e r f i c i a l l y s i m i l a r to Dibunophyllum (E.C. Wilson, written commun-i c a t i o n , J uly, 1962). . An abundant fauna observed h a l f a mile east.of the peak of Mount McGuire ( F o s s i l L o c a l i t y 42) occurs i n a s t r a t i g r a p h i c horizon close to the horizon i n which the medium sized Schwagerina i s found. The fauna contains the tabulate c o r a l M i c h e l i n i a , small poorly preserved horn corals and the brachiopods Rhipidomella (very abundant), Rhynchopora, Ne o s p i r i f e r (?) and some large poorly preserved, fragmental brachiopods with c o s t e l l a t e Figure 11: Photomicrograph (th i n section, plane l i g h t , X4.0) of coarse-grained volcanic arenite of the upper c l a s t i c sequence on Church Mountain. Rock composed of f a i r l y fresh a l b i t e and l i t h i c volcanic fragments, with i n t e r s t i t i a l c h l o r i t e . Note the freshness, and absence of any marked ori e n t a t i o n of the grains, i n comparison to Figure 9. Figure 12: Near a x i a l section of Parafusulina (X7) i n Permian limestone from the southeast side of Mount Thurston. Figure 13: A x i a l section of Pseudofusulinella (X12) i n f u s u l i n i d biomicrudite of Permian age, from Liumchen Creek. Figure 14: Near a x i a l section of s i l i c i f i e d Schwagerina (X10) i n Permian limestone, west side of Pierce Creek. ' , - 64 -ornamentation. C o l o n i a l corals, t e n t a t i v e l y i d e n t i f i e d as Heritschioides by E.C. Wilson (written communication, July, 1964) were found, one mile., northeast of the peak of Mount McGuire ( F o s s i l L o c a l i t y 44), in. what i s probably a s i m i l a r s t r a t i g r a p h i c horizon. Fucoid markings are also pres-ent on some bedding planes. S i l i c i f i c a t i o n i s responsible .for preservation of almost a l L of these f o s s i l s . Quality- of preservation by s i l i c i f i c a t i o n v a r i e s • considerably.. F u s u l i n i d microstructures are . commonly well preserved, whereas many ...large horn corals may only be p a r t l y s i l i c i f i e d and thus poorly preserved. Where s i l i c i f i c a t i o n has not occurred, commonly the only recognizable f o s s i l s are :crinoid columnals, standing out as round patches of coarse white crys-t a l l i n e c a l c i t e against the more f i n e l y c r y s t a l l i n e matrix. Small u n i d e n t i f i e d horn c o r a l s , large horn corals, possibly Dibuno-phyllum, and compound corals,, probably Heritschioddes,are present i n Per-mian limestone of the autochthon. C r i n o i d columnals of various sizes are ubiquitous. Some small s i l i c i f i e d f u s u l i n i d s , probably Schwagerina, were found, i n f l o a t . Calcareous volcanic breccias and tuffaceous limestones., at the s t r u c t u r a l l y lower contact of the limestone on the east side of Church Mountain, summit-(Fossil L o c a l i t y 51), contain well preserved Para-f u s u l i n a and Pseudofusulinella and.some smaller forms which s u p e r f i c i a l l y resemble Parafusulina but are possibly large schwagerinids. Parafusulina and Pseudofusulinella are.present, i n limestones on the east side of Lium^ chen Creek, due west of. Church Mountain. Age and c o r r e l a t i o n . The limestone i s dated on the basis of i t s f u s u l i n i d content. Two horizons containing d i f f e r e n t f u s u l i n i d faunas are known. Fusul i n i d s of -65-the genus Schwagerina occur i n one horizon within the limestone... The other horizon i s at the extreme top of the unit and contains Parafusulina, Pseudofusulinella and possibly some large, u n i d e n t i f i e d schwagerinids.. A l l examples examined of Schwagerina (Figure 1 4 ) are s i l i c i f i a d . , . . and although.some d e t a i l s : of the structure have been destroyed, preservation i s good •enough to allow i d e n t i f i c a t i o n to be made. This i s a. new., specie's, with septal evolution advanced, to a l e v e l where some of the outer ..chamber-l e t s are elongate and appear about to form c u n i c u l i . I t i s similar...to. Sengagerina c r a s s i t e c t o r i a Dunbar and Skinner i n s i z e , general morphology, and evolutionary l e v e l , b u t . d i f f e r e n t i n o v e r a l l shape and i n possession of a smaller proloculus. S. c r a s s i t e c t o r i a occurs i n the lower part, of., the Leonard Formation of Texas :(Ross, 1 9 6 3 , p»13) and i s c l o s e l y r e l a t e d to, and occurs with, S. guembeli, which has reached the.same l e v e l of septal evolution (see Dunbar and Newell, 1 9 4 - 6 , p . 4 0 2 ) . These two genera occur i n Nevada (Knight, 1 9 5 6 , Rich, 1 9 6 1 ) where they are regarded as being, of ..Leo-., nardian age. M i l l s and Davies ( 1 9 6 2 , p . 4 5 ) have described S. missionensis, a form re l a t e d to S. guembeli, from northeastern Washington and believe i t to be of Leonardian-Guadalupian age. McGugan ( 1 9 6 3 ) has described.a schwa-g e r i n i d of s i m i l a r evolutionary l e v e l , from, southeastern B r i t i s h Columbia,., which again he regards' as being on the border of Lower to middle Permian, age. Largely on.the basis of degree of septal evolution, the mediura...sized. Schwagerina from the. Permian limestone of Chilliwack V a l l e y i s regarded, by the w r i t e r as being basal Leonardian i n age. The large Parafusulina (Figure 1 2 ) occurring, with Pseudofusulinella at the extreme top of the Permian limestone i s a new species, i n general morphology close to Parafusulina nosonensis Wheeler and Thompson, but i n -66- . size very s i m i l a r to the larger species, .P. c a l i f o r n i c a ( S t a f f ) . These forms are common in. the lower Guadalupian Nosoni Formation of ..northern C a l i f o r n i a . Therefore t h i s f u s u l i n i d may be as young as Guadalupian i n age. However, the poorly developed c u n i c u l i indicate that i t probably, i s of :Leonardian rather than Guadalupian age. The Pseudofusulinella (Figure 13) occurring with Parafusulina i n Chilliwack V a l l e y i s probably the. form 'described by Skinner (written com-munication to W.R. banner, April,.1964) as Pseudofusulinella danneri . Skinner and Wilde, from the Black Mountain l o c a l i t y i n northern Washington. Although Skinner, ( i n Danner,.1957, p.131) considered the Black Mountain fauna to be of Wolfcampian.age. he has recently recorded a p r i m i t i v e Para-f u s u l i n a from t h i s l o c a l i t y and now considers i t to be pos s i b l y lower • Leonardian i n age (written communication to W.R. Danner, A p r i l , 1964). A t h i r d species occurring with Parafusulina and Pseudofusulinella on Church Mountain appears to be a large Schwagerina or small Parafusulina. Because t h i s form has not been observed elsewhere i n the Chilliwack_..Val 1 ey. . area i t s presence may we l l suggest the cl o s e r r e l a t i o n s h i p of the Church Mountain fauna t° the predominantly schwagerinid fauna of Black Mountain, rather than to those equivalent faunas found elsewhere i n Chilliwack Valley... As the large Parafusulina from the Chi l l i w a c k V a l l e y area appears to be more advanced than any form reported from Black Mountain, the Permian lime-, stone may be diachronous, over a f a i r l y r e s t r i c t e d range. These possible, age differences between parts of the Permian limestone i n different, t e c -tonic units may be enhanced by tectonic.superposition or ju x t a p o s i t i o n of parts of the formation which were l a t e r a l l y separated p r i o r to deformation. No other reported occurrence of t h i s limestone has been made from the -67-region. Mathews and McCammon (1957, p.A3) have reported a limestone near Agassiz, on the north side of Fraser River north of the map-area,, which u n d e r l i e s . l i g h t grey-green.siliceous t u f f . This t u f f i s litholog.i r-.al 1y_. s i m i l a r to c e r t a i n of the volcanic rocks overlying Permian limestone,in. the Chilliwack V a l l e y map-area. On the basis of t h i s a s s o c i a t i o n , the Agassiz limestone i s possibly, a, northerly equivalent of the Permian lime-stone of the Chilliwack V a l l e y . •''•'.'•••' Environment of deposition A l l evidence seen suggests that deposition of the Permian limestone took,place i n a marine low-energy environment, because a l l limestones examined were 'probably, or are, m i c r i t e , f o s s i l i f e r o u s m i c r i t e or biomi-c r u d i t e . Vulcanism,. contemporaneous with deposition of the limestone, maybe p a r t l y responsible for p r e c i p i t a t i o n of m i c r i t i c carbonate by the various mechanisms suggested by Kania (1929) and also a possible cause of the char-a c t e r i s t i c a l l y s i l i c e o u s nature of the limestone (see B i s s e l , 1959, p.'182.).. The following suggestions on conditions extant during deposition of the Permian limestone are l i t t l e more than speculative. More information i s needed on the o r i g i n a l textures of limestone comprising the formation. and.also on Permian stratigraphy from surrounding areas. Available evidence .indicates that-the c l a s t i c : sequence below the Lower. Permian limestone was l a r g e l y deposited by s l i d e s , slumps and t u r -b i d i t y currents. Such mechanisms would tend to deposit sediments i n deeper, parts of the basin. U p l i f t , possibly r e l a t e d to Lower Permian vulcanism, may have elevated i s o l a t e d areas of the sea f l o o r , which previously received, c l a s t i c sediments, to positions s t i l l below wave base, where they were no -68- . longer able to receive sediments by t u r b i d i t y flows or s l i d e s ..(see Heezen, 1963, P.754-J Kuenen, 1964, p.6). .The only materials these elevated, areas could then receive would be p r e c i p i t a t e d carbonates, c l a y - s i z e d . c l a s t s . c a r r i e d i n suspension, and a e r i a l l y transported material such as. v o l c a n i c — ash. Sediments formed by the l a t t e r two agencies are p o s s i b l y represented by the few feet of. shale, and l o c a l l i t h i c t u f f , which.are present s t r a t -i g r a p h i c a l l y below'-the Permian limestone. Subaqueous e f f u s i o n of lavas, by changing the chemical environment i n the sea (see Kania, 1929) might r e s u l t i n chemical p r e c i p i t a t i o n of limestone i n the' v i c i n i t y of a volcanic centre. ' • • . - ' ' v X ' ; ' ' The predominant l i t h o l o g i e s ' o f Permian rocks i n the. autochthon, Liumchen Nappe, and McGuire Nappe are believed to indicate the existence of such a volcanic centre, flanked by areas of limestone deposition. P r i o r t o Cretaceous deformation, during which.rocks of these three tectonic .units were transported to the northwest, rocks of the McGuire Nappe, now s t r u c -t u r a l l y the highest of these three t e c t o n i c u n i t s , l a y southeast of rocks, of the Liumchen Nappe, which i n turn were southeast of rocks of the autoch-thon, the s t r u c t u r a l l y lowest'rocks i n the map-area. The Liumchen Nappe, composed i n large part, of flow rocks and t u f f , with minor lime stone" •contain.-, ing L eonardian.fossils, separated l a t e r a l l y rocks of the autochthon from..', rocks-of the McGuire Nappe. In the l a t t e r t e c t o n i c units Permian rocks are Leonardian limestones, o v e r l a i n by r e l a t i v e l y t h i n lavas and t u f f s . Cessation of limestone deposition possibly was the r e s u l t of a change., from r e l a t i v e l y quiet e f f u s i o n of lavas, to p y r o c l a s t i c a c t i v i t y whose products.so d i l u t e d any carbonate being deposited that i t was no longer, apparent as a d i s c r e t e , homogenous u n i t . -69-Permian volcanic sequence An a r e a l l y extensive sequence of Lower Permian volcanic ro.cks___s_. present i n most parts of the map-area. In some places these vcdcanic_ro.cks l i e conformably, on' the'Permian'limestone; .elsewhere they are a_. p a r t i a l — . , f a c i e s equivalent of t h i s . u n i t . The ..sequence i s o v e r l a i n disconformably by c l a s t i c rocks of Late T r i a s s i c age. L i t h o l o g i e s within the...sequence vary between basic to intermediate flows, t u f f s , and minor cherts and... argi l l i t e s . . ' These rocks prdvide a more s e n s i t i v e index of metamorphio— grade than any other rocks of the map-area. Thicknesses of the di f ferp.nt. l i t h o l o g i c a l types, -and thus the thickness of the sequence as a whole, vary considerably across the map-area. Daly (1912, p.$21) c a l l e d these v o l c a n i c rocks the "Chilliwack V o l -canic formation." : As i t . i s a r e a d i l y mappable, l i t h o l o g i c a l l y d i s t i n c t part of the Chilliwack Group i n the type area i t i s c l e a r l y of formational.'.. status according to modern s t r a t i g r a p h i c p r i n c i p l e s . . However, where these volcanic rocks are t y p i c a l l y developed i n the map-area, (as i n the Lium-chen Nappe) the basal.contact of the sequence i s tectonic and not s t r a t i - , graphic; where both upper.and: lower- s t r a t i g r a p h i c contacts are present ' (as i n the McGuire Nappe) the sequence i s t h i n and somewhat a t y p i c a l . There-fore, as no type section can be given by the writer which.would.adequately represent t h i s succession,"these rocks are not designated a formation and are c a l l e d , instead, the Permian volcanic sequence. Several e a r l i e r workers i n the region have mentioned these rocks. Daly described his "Chilliwack Volcanic formation" as co n s i s t i n g of al t e r e d augite and hornblende andesites, with interbedded. p y r o c l a s t i c s . He believed -70-these rocks were of Upper Carboniferous age, and formed much ofL the., upper part of h i s "Chilliwack S e r i e s " (see Table 1). Crickmay (1930., ,p.4S.&.) mapped Daly's "Chilliwack Volcanic formation" as T r i a s s i c volcanic.rocks, separating the Chilliwack Group from Crickmay's "Slollicum Series--" B r i e f descriptions of some of these volcanic rocks were given by H i l l house (1956,. p..10) and:Danner (1957, p.113), both of whom believed the rocks to be part of the Chilliwack Group. Moen (1962, p.34-) mapped the l a t e r a l continua-t i o n of t h i s - v o l c a n i c sequence, to the southwest of the map-area, and included i t i n the Chilliwack Group. On Mount Laughington and 'Cheam Range .Green, massive, basic flow rocks crop-out on the south side of Mount Laughington at an a l t i t u d e of 4,000 fe e t . These rocks-are amygdaloidal,. consist of a f e l t e d mass of s a u s s u r i t i z e d feldspar m i c r o l i t e s , with augite and a l b i t e phenocrysts,.and are very s i m i l a r to other basic lavas in. the map-area described below. Ch l o r i t e and pumpellyite are present i n ves>- . i c l e s . Thin bedded s i l i c i f i e d t u f f s and.cherts present near the summit of Mount Laughington are associated with Lower Permian limestone. A l l of these rocks s t r u c t u r a l l y , o v e r l i e Mesozoic rocks of the McGuire Nappe. Greenstones cap Lady Peak, near the northern end of Cheam Range. They are composed o f ' c l e a r a l b i t e . l a t h s , minor fibrous hornblende, epidote, minor quartz and c h l o r i t e . , Ilmenite,.leucoxene and. sphene are present i n the groundmass. Vesicles, i n these rocks contain c h l o r i t e . The age of these, greenstones i s uncertain. They o v e r l i e a r g i l l i t e s containing a limestone .  . pod, i n which a few small c r i n o i d stems have been found. Permian limestone containing f u s u l i n i d s , present- to the north of t h i s l o c a l i t y on the western ridge of Mount Cheam, i s possibly part of the same tectonic u n i t , and -71-o v e r l i e s Mesozoic rocks. -McGuire Nappe . Rocks of the Permian volcanic sequence i n the McGuire Nappe, .are.inter-folded with Permian limestone on the north side of Mount McGuire..,.. and over-l i e ' Permian ilmestohe high, on the east side of Slesse Creek Valley,....in_.the Chilliwack V a l l e y east of the junction of Slesse Creek with the, Chi 11 iwac.k. River, and • in. Chipmunk Greek. . .. , Rocks of the Permian volcanic sequence i n the McGuire Nappe, ar.e... of v a r i a b l e . l i t h o l o g y . Thin bedded grey, green to white cherts, jasper, and, s i l i c e o u s , t u f f , l o c a l l y with shaiy interbeds, o v e r l i e the limestone, i n some l o c a l i t i e s . Elsewhere the overlying rock i s a quartz-bearing crystal... t u f f , s i m i l a r to that described more f u l l y below. A dark green, a l t e r e d feldspar porphyry i s present s t r a t i g r a p h i c a l l y above the Permian limestone just west of Pierce Creek, and in. a s i m i l a r s t r a t i g r a p h i c p o s i t i o n north of t h i s l o c a l i t y , on. the- north side of Chilliwack River near i t s junction with Slesse Creek. This, feldspar porphyry i s composed of small, g l a s s -c l e a r a l b i t e phenocrysts i n a very fine-grained, dark green matrix, con-s i s t i n g of .saussuritized feldspar m i c r o l i t e s , small d i o p s i d i c augitesy and c h l o r i t e . /Dark, gabbroic dykes, .cutting the. Pennsylvanian and Permian limestones and c l a s t i c .rocks of the Chilliwack Group, are present on Mount McGuire, and are possibly feeders to the Permian v o l c a n i c sequence. Thickness of volcanic irocks.in the McGuire Nappe i s probably nowhere more than 200 feet, and i s l o c a l l y considerably thinner. The Permian volcanic sequence i s o v e r l a i n by fine-grained s i l t s t o n e s . and . a r g i l l i t e s of Upper T r i a s s i c age. No angular r e l a t i o n s h i p has been -72- • detected between the bedding of the' v o l c a n i c rocks and that of...overlying T r i a s s i c rocks. •Commonly-.a-breccia r a r e l y greater, than 25 feet, thick, and composed o f angular c l a s t s up. to 6 inches long of volcanic rock, chert and minor limestone, marks the contact. .. Composition of volcanic rock claata. i n the breccia i s i d e n t i c a l to that of underlying Permian volcanic-rocks. Poorly, preserved,- silicified,'.medium-sized f u s u l i n i d s of probable E a r l y Permian age were found i n a limestone c l a s t from the b r e c c i a above, the east side of Slesse Creek V a l l e y . As the breccia i s i n v a r i a b l y present., at. t h i s s t r a t i g r a p h i c contact i n the McGuire Nappe, forms a continuous, s t r a t i g r n p h i n . horizon, of r e l a t i v e l y constant thickness, and contains randomly oriented., angular, unsorted, c l a s t s i t i s believed to r e s u l t from a submarine s l i d e . The lower contact of the volcanic sequence i s to some extent grada-t i o n a l with underlying Permian limestone. The contact, where seen,, gener-a l l y " i s marked by an abundant,- f u s u l i n i d . fauna. East of Pierce Creek..and i n Chipmunk .Creek the limestone i s l o c a l l y t h i n and forms.a s e r i e s of d i s -crete lenses'. Where the limestone i s absent the d i s t i n c t i o n of tuffaceous rocks of t h i s volcanic sequence from underlying volcanic arenites i s d i f - . f i c u l t and i n many cases a r b i t r a r y . Liumchen Nappe • ' . ' . " The Liumchen. Nappe i n the map-area i s composed l a r g e l y of the Permian vo l c a n i c sequence. Permian volcanic rocks form, .the summit of Liumchen Mountain and crop-out west of t h i s l o c a l i t y on. the south end of International. Ridge. East of Liumchen Mountain, volcanic, rocks underlie, most of the north and west sides of Mount McGuire and are exposed i n a window at the north . . end of Slesse Creek V a l l e y . Volcanic rocks forming the probable northerly . continuation of the Liumchen Nappe.underlie the south, west and northwest -73- ! slopes of E l k Mountain. Scattered outcrops, northeast of Elk,,Mountain, on the south side of Fraser Valley, are believed to belong to this..volcanic sequence i n the Liumchen Nappe. : . , Permian volcanic rocks are l a r g e l y flow-rocks on Liumchen .Mountain, the west side of Mount McGuire and i n the window at the north end of..,. Slesse. Creek. -Two p r i n c i p a l rock types "are recognized; a domi nant...al tared augite-bearing intermediate to basic rock, and a r e l a t i v e l y rare, hornblende andesite. The augite-bearing flow-rocks are massive and not uncommonly form c l i f f s . Generally,.;it i s not possible to obtain, bedding measurements from these rocks *' l a r g e l y because of t h e i r massive, nature, although., interbedded. p y r o c l a s t i c material/and compositional v a r i a t i o n s ..'enable" bedding to be. discerned l o c a l l y . .Pillow..layas have been.recognized on. the southwest side, of Mount McGuire. These flow rocks are t y p i c a l l y grey-green, but. vary , through yellow-green and brownish-grey to dark green. They are commonly., very fine-grained, and a l t e r e d , so. that accurate f i e l d i d e n t i f i c a t i o n i s not p o s s i b l e . ".Rare, coarse-grained, equivalents, possibly conformable intrusions,, within the sequence,, are of uniform texture and consist of about 70%.ran-domly oriented, "interlocking grey-green a l t e r e d feldspar l a t h s , with i n t e r - . s t i t i a l ferro-magnesiah minerals. C h l o r i t e and c a l c i t e amygdales are com-mon, and c o n c e n t r i c a l l y . a r r a n g e d i c h l o r i t e - f i l l e d : v e s i c l e s have been observed-, at s everal l o c a l i t i e s where no pillows, .were recognized. The composition of these rocks, determined microscopically, varies from about 60% to 80% a l t e r e d plagioclase feldspar, 10% to 20% d i o p s i d i c auglte, at l e a s t 10% c h l o r i t e and various' amounts of ilmenite and i t s a l t e r a t i o n products.^Fig.15). Altered, subhedral, randomly oriented plagioclase feldspar laths are -74-i n v a r i a b l y of uniform si z e i n any one specimen. The longest laths...seen are about 3mm. long, the smallest are m i c r p l i t e s , and the commonest...siZRS . range from 0.4 to 0.2mm,. i n length. Generally, the plagioclase,."! nths...are completely sau s s u r i t i z e d and t h e i r o r i g i n a l nature can only be ..inferred. . from t e x t u r a l r e l a t i o n s h i p s , and by analogy with c r y s t a l s which are part saussurite, and i n part feldspar whose o p t i c a l properties can be determined Optic a x i a l angles of p a r t i a l l y a l t e r e d feldspars are 83° to 84°, and, measurements of. x'A010 give an average of about 15° (obtuse e x t i n c t i o n ) , and-the f e l d s p a r s are'therefore a l b i t e of composition, about Ang. The dio.p-s i d i c augite i s p o r p h y r i t i c or i n t e r s t i t i a l and.may dis p l a y an o p h i t i c o r sub-ophitic relationship: with the a l t e r e d feldspar l a t h s , and i s commonly fres h , but may be highly fractured and show a l t e r a t i o n to c h l o r i t e . Chlor .T i t e , generally with anomalous' blue birefringence, occurs i n t e r s t i t i a l l y , . . . f i l l s v e s i c l e s where i t not;uncommonly, forms r a d i a t i n g aggregates, and i s present i n v e i n l e t s . Pumpellyite i s present in-many of these rocks,, having the form of very f i n e a c i c u l a r c r y s t a l s , often i n r a d i a l c l u s t e r s and occur ri n g t y p i c a l l y with c h l o r i t e i n v e i n l e t s and vesicles (Figure 16). C a l c i t e i s found in v e s i c l e s and r a r e l y as patches i n the.groundmass. S k e l e t a l ilmenite (?.), displaying a l l stages of a l t e r a t i o n to leucoxene and f i n e l y granular^ sphene, occurs i n amounts up to 10%. In some examples small., granules;of sphene are scattered through the rock. Fine-grained hematite i s disseminated through some rocks, these rocks i n hand-specimens being, brownish-grey. A d i s t i n c t i v e feldspar porphyry, within tuffaceous rocks on the north side of Chilliwack River, i s composed of pale green a l t e r e d feldspar pheno-cry s t s , up to 7mm»long, set in. a darker matrix. The feldspars were r Figure 15: Photomicrograph (th i n section, plane l i g h t , X4-0) of t y p i c a l a l t e r e d flow rock i n the Permian volcanic sequence from the north end of Slesse Creek Va l l e y . Groundmass of dark, saussuritized feldspar l a t h s , with d i o p s i d i c augite, opaque grains and c h l o r i t e (C). Figure 16: Photomicrograph (th i n section, plane l i g h t , X100) of pumpellyite c r y s t a l s i n a quartz v e i n l e t i n a l t e r e d flow rock of the Permian volcanic sequence, from the" north end of Slesse Creek Valley. -75-o r i g i n a l l y zoned, but are now e n t i r e l y s a u s s u r i t i z e d and set i n a matrix of f i n e saussuritized feldspars, augite and i n t e r s t i t i a l chlorite... Ilmen-i t e (?), and i t s a l t e r a t i o n products, leucoxene and sphene, are.present. Precise petrographic nomenclature of the flow rocks described.above i s d i f f i c u l t to e s t a b l i s h because of the in v a r i a b l e a l t e r a t i o n of the plagioclase feldspars. . The o r i g i n a l composition of these rocks has to. be in f e r r e d from e x i s t i n g textures and mineral associations. As noted above, augite may display an o p h i t i c and subophitic r e l a t i o n s h i p with a l t e r e d feldspar laths.. In many of these rocks c h l o r i t e i s present between the... feldspar l a t h s , a texture known as i n t e r s e r t a l (Williams, et a l . , 1954, p.22). Williams (1954, p.93) i n r e f e r r i n g . t o andesites, states: " . . . i n t e r s e r t a l and o p h i t i c textures are exceptional save i n v a r i e t i e s t r a n s i t i o n a l to basalts." Well-aligned feldspar laths were not seen i n any specimens from Chilliwack V a l l e y . Moen (1962, p.35) noted t r a c h y t i c texture i n specimens from the l a t e r a l continuation of these volcanic rocks to the southwest of the map-area, although he stated that rocks with t h i s texture were not common. Trachytic texture i s common, i n many andesites, but i s exceptional i n ba-s a l t s . Textures of these a l t e r e d extrusive rocks are therefore i n d i c a t i v e of t h e i r o r i g i n a l b a s a l t i c nature. In addition, Williams, et a l . (1954> pp.95.47) note that ilmenite ( s k e l e t a l c r y s t a l s of which are common i n Chilliwack flow rocks) i s rare i n pyroxene andesites but occurs i n basalts. Moen (1962, p.35) measured e x t i n c t i o n angles of unaltered feldspars i n lavas of the Chilliwack Group from l o c a l i t i e s southwest, of the map-area., obtained compositions intermediate between bligoclase, and andes ine, and c a l l e d these rocks augite andesites. Moen also stated that a l t e r e d -76-feldspars had e x t i n c t i o n angles suggestive of a l b i t e and oligocLase, and mentioned that s p i l i t e s are present i n the volcanic sequence. . Daly. (.19.12, p.52) c a l l e d these rocks augite andesites, noted that they were .altered, but d i d not give any feldspar compositions. A l l feldspar determined ...by the writer from these augite-bearing flow rocks of the Chilliwack Group i s a l b i t e . Although mineralogical assemblages of many of these.-flow, rocks are those of s p i l i t e s , sodium does not appear to have been introduced into the rock. Instead, s a u s s u r i t i c a l t e r a t i o n of the anorthite part...o.£_the plagioclase molecule has l e f t a l b i t e pseudomorphs containing saussurite. Textures and e x i s t i n g mineral associations therefore are believed.by the write r to indicate that these augite-bearing flow' rocks are a l t e r e d basalts, or a l t e r e d a n d e s i t i c basalts. Hornblende andesites, present i n t h i s v o l c anic sequence on Liumchen' Mountain and Mount McGuire, are Very minor i n r e l a t i o n to the augite-bearing... rocks and i n contrast to them are f r e s h . These rocks are p o r p h y r i t i c and. contain elongate hornblende phenocrysts,. and s l i g h t l y a l t e r e d feldspar phenocrysts, some of which show zoning. The composition of the feldspar. . phenocrysts ranges from low andesine to o l i g o c l a s e . The matrix consists, of small, sub-equant c r y s t a l s of feldspar and hornblende. Magnetite and apatite are accessory minerals. Freshness of these rocks suggests that they may be l a t e r than, and i n t r u s i v e into the Permian v o l c a n i c rocks. Volcanic rocks forming the Liumchen Nappe north of C h i l l i w a c k River are l a r g e l y p y r o c l a s t i c rocks, and of these, very pale green to olive-green, quartz-bearing, c r y s t a l v i t r i c t u f f s are probably the most common, and cer-t a i n l y the most prominent. These rocks are hard, massive, and composed of about 4.0$ to 60$ pale green, al t e r e d euhedral to subhedral feldspars, about 5% to 10$ quartz and a va r i a b l e but subordinate amount of l i t h i c and v i t r i c fragments, i n a matrix of s i m i l a r composition. The c l a s t s are. unsorted, but generally have an upper siz e l i m i t of about 2mm.......Maximum. grain s i z e i s commonly uniform throughout a single massive bed, .although grading has been observed i n some medium to t h i n l y bedded c r y s t a l . t u f f s , interbedded with the more common massively bedded rocks. In some o f these graded beds, as the c l a s t s became f i n e r upwards, the c r y s t a l t u f f grades upwards into pale green s i l i c i f i e d t u f f , resembling chert. Quartz c l a s t s are very conspicuous i n t h i n section. Many are euhedral c r y s t a l s , and . show the sub-equant, sub-rectangular o u t l i n e associated with high temper-ature, bipyramidal quartz (see Folk, 1961, p.68). Commonly these grains are p a r t l y rounded and show rounded embayments, suggesting magmatlc. .r.esorb-t i o n . Some quartz grains are both angular and rounded, and are c l e a r l y fragments of euhedral c r y s t a l s . A l l other c l a s t s i n these rocks are invar-i a b l y a l t e r e d i n some degree. Altered plagioclase feldspars are i n .part a l b i t e with compositions ranging from An'^  4o An.g (as determined by X/\010 method), and i n part a semi-opaque very fine-grained material with a fai n t , brown colour. Some of these a l t e r e d feldspars contain various amounts..of a brown fibrous material, with a moderate birefringence masked by the brown colour (Figure 17). This mineral was i d e n t i f i e d as lawsonite on X-ray examination by R.M. Thompson. Remaining c l a s t s are a l t e r e d to c h l o r i t e or semi-opaque clay minerals and have v e s i c u l a r textures or are of shard-l i k e shape, suggesting that they are a l t e r e d v i t r i c fragments. The ground-mass consists of f i n e r c l a s t s of generally s i m i l a r composition to those above, together with c h l o r i t e and chert. Minor amounts of c a l c i t e , e p i -dote and pumpellyite are present. Rarely, the whole rock, with the -78-exception of the quartz grains, may be c a l c i t i z e d . Epidote and,pumpell-y i t e are rare, the l a t t e r , when present, occurring as a c i c u l a r . c r y s t a l s i n v e i n l e t s . Owing to a l t e r a t i o n of the feldspars, the nomenclature of these..rocks i s d i f f i c u l t to e s t a b l i s h . The presence of lawsonite together.with, .albite i n the feldspar c r y s t a l s , suggests the c r y s t a l s were o r i g i n a l l y p l a g i o -clase more c a l c i c than a l b i t e . Moen (1962, p.4-0) described s i m i l a r v o l -canic rocks from the Chilliwack Group to the southwest of the map^area, and c a l l e d them dacites. Textures and mineral-associations suggests...that these quartz-bearing rocks i n Chilliwack V a l l e y are a l t e r e d dacite c r y s t a l t u f f s . L i t h i c t u f f s appear to be more common i n other t e c t o n i c units and are described i n d e t a i l under the appropriate headings. They may be more abundant i n the Liumchen Nappe than i s r e a l i z e d at present, as they are commonly r e l a t i v e l y s o f t and more e a s i l y eroded than the massive lavas and quartz-bearing c r y s t a l t u f f s with which they are interbedded,. and tend to be covered. S i l i c i f i e d f i n e t u f f s , resembling grey to pale green cherts are • present i n the volcanic sequence but are nowhere abundant. A l l gradations e x i s t between these rocks and coarser grained quartz-bearing c r y s t a l t u f f s (Figure 18). Thin bedded to massive jasper i s l o c a l l y present. No t y p i c a l ribbon cherts have been seen i n the v o l c a n i c sequence i n the Liumchen Nappe. Apparent thickness of volcanic rocks of the Liumchen Nappe exposed on Liumchen Mountain i s nearly 2,000 f e e t . Volcanic rocks exposed i n the window at the north end of Slesse Creek are about 700 feet t h i c k . Although Figure 17: Photomicrograph (th i n section, crossed n i c o l s , X100) of an al t e r e d plagioclase feldspar c r y s t a l containing lawsonite (L), i n c r y s t a l t u f f of the Permian volcanic sequence, from the southeast side of Mount Thurston. Figure 18: Photomicrograph ( t h i n section, plane l i g h t , TU+Q) of base of c r y s t a l v i t r i c t u f f bed, from Permian v o l c a n i c sequence, ju s t west of B r i d a l F a l l s . The t u f f i s composed l a r g e l y of volcanic quartz and semi-opaque a l t e r e d v i t r i c fragments. Note fine-grained s i l i c i f i e d t u f f at base, which i s the top of the underlying t u f f bed. - 7 9 -the base of volcanic rocks on E l k Mountain i s not seen, the exposed t h i c k -ness approaches that on Liumchen Mountain. • Quartz-bearing c r y s t a l t u f f s of the Liumchen Nappe are o v e r l a i n , . apparently disconformably, by f i n e c l a s t i c rocks of Upper T r i a s s i c age on E l k Mountain. Other contacts of the v o l c a n i c sequence i n the.Liumchen Nappe In Chilliwack V a l l e y are s t r u c t u r a l rather than s t r a t i g r a p h i c . On Mount McGuire and at the north end of Slesse Creek V a l l e y these v o l c a n i c rocks are o v e r l a i n by Upper Palaeozoic limestones and c l a s t i c rooks, of the. McGuire Nappe. This contact i s assumed to be a f l a t - l y i n g fault... Daly (1912, Map 89A) showed vo l c a n i c rocks of h i s Chilliwack volcanic formation to be overthrust upon both Mesozoic and Palaeozoic rocks., i n the Church Mountain area, and Moen (1962), working to the southwest of .the mapr-area mapped the continuation of Daly's thrust i n northern Washington. Be-cause volcanic rocks of the Liumchen Nappe l i e on Mesozoic rocks.at the south end of International Ridge, on Palaeozoic rocks on Church...Mnnntflin,, and o v e r l i e Mesozoic rocks on the northwest side! of Mount McGuire,, the! lower contact of v o l c a n i c rocks i n the Liumchen Nappe i s believed t° he a thrust f a u l t . Autochthon Lavas and t u f f s s t r u c t u r a l l y below and part l y , g r a d a t i o n a l with Lower Permian limestone are exposed on the north and east sides of the summit_..of Church Mountain, and p y r o c l a s t i c rocks, cherts and minor flows are present i n Liumchen Creek V a l l e y . Permian flow rocks i n the autochthon are s i m i l a r i^ o those described previously, being grey-green to maroon, amygdaloidal, a l t e r e d basic lavas. Pillow lavas are exposed i n Liumchen Creek V a l l e y . -80-The p y r o c l a s t i c rocks vary i n size from coarse v o l c a n i c breccias, with c l a s t s up to 6 inches i n diameter, to very fine-grained tuffs.,. and..range i n colour from various shades of green to maroon. They are compo.aed.-of v a r i a b l e percentages of a l t e r e d v i t r i c to l i t h i c fragments. The. v i t r i c ' fragments are commonly a l t e r e d to semi-opaque clay minerals and- c h l o r i t e , and t h e i r o r i g i n a l composition can only be i n f e r r e d by the vesicular_.natur.e or shard-like outlines of the c l a s t s . The l i t h i c fragments t y p i c a l l y , con-t a i n r e l i c t m i c r o l i t e s , or r a r e l y , large, randomly oriented, altarecLl'eld-spar l a t h s , set i n a c h l o r i t e matrix and some l i t h i c fragments contain c h l o r i t e amygdales. Quartz i s absent or rare i n these rocks. A l t e r a t i o n of these' rocks i s commonly so extensive, that microscopic examination is. made under plane polarized l i g h t alone, as with crossed n i c o l s the rocks appear as a mass of c h l o r i t e and carbonate i n which textures cannot be., distinguished. W.R. Danner c o l l e c t e d a fine-grained, dark grey to green, banded rock from Liumchen Creek, composed e n t i r e l y of a l t e r e d shards, or-iented and f l a t t e n e d p a r a l l e l to bedding (Figure 19). The texture suggests, that i t i s a welded t u f f . On Church Mountain t h i s v o l c anic sequence s t r u c t u r a l l y underlies Lower Permian limestone. The contact i s gradational, and marked by calcareous p y r o c l a s t i c rocks containing f u s u l i n i d s . The volcanic rocks s t r u c t u r a l l y o v e r l i e Mesozoic rocks on the east side of Church Mountain and are i n t e r -folded with them to the north of the summit. Rocks on both sides of t h i s folded contact appear to be conformable. Volcanic rocks i n Liumchen Creek are o v e r l a i n p a r t l y by Lower Permian limestone and p a r t l y by older c l a s t i c rocks, and pass s t r u c t u r a l l y downwards into limestone of unknown age, which conformably o v e r l i e s Upper T r i a s s i c s i l t s t o n e s and a r g i l l i t e s . Elsewhere -81-i n Liumchen Creek V a l l e y , volcanic rocks are i n t e r f o l d e d with T r i a s s i c rocks, but the sequence appears to be conformable. Metamorphic grade The only altered basic volcanic rocks composed of a well-defined... met-amorphic mineral assemblage are the greenstones forming the summi t_of..Lady Peak, which- belong to the quartz-albite-muscovite-chlorite subrr.facias_.of the greenschist f a c i e s o f Fyfe, Turner arid Verhoogen (1958, p.219). In other volcanic rocks of the Chilliwack Group, p a r t i c u l a r l y the massive lavas and c r y s t a l t u f f s , t e x t u r a l and mineral reorganization r e s u l t i n g from metamorphism appears to be r e l a t i v e l y s l i g h t and s u p e r f i c i a l l y l i t t l e more than diagenetic. Feldspars i n the al t e r e d basic lavas r e t a i n t h e i r o r i g i n a l form, although a l t e r e d to saussurite and a l b i t e , and augite phenocrysts. . are generally unaltered. In the quartz-bearing c r y s t a l t u f f , the f e l d -spars are p a r t l y a l t e r e d to i n c i p i e n t lawsonite, so fine-grained and o f such a t y p i c a l form that i t could only be determined using X-rays. C h l o r i t e i s ubiquitous and pumpellyite i s present i n many rocks. Z e o l i t e s or preh-ni t e have not been found i n these rocks. As Fyfe, Turner and Verhoogen (1958, p.226) state that lawsonite i s known only i n the glaucophane s c h i s t f a c i e s , some of these rocks belong t o . . t h i s f a c i e s as defined by these authors. Lawsonite has been found only .in a l t e r e d feldspars i n c r y s t a l t u f f s and not i n feldspars i n al t e r e d basic lavas, even whej»e these rock types are apparently l a t e r a l equivalents and.. present i n the same s t r u c t u r a l horizon. This, together with the a t y p i c a l form of the mineral, suggests that the lawsonite present i n these rocks was formed very close to the lower l i m i t s of i t s s t a b i l i t y range and that i t s presence i n the c r y s t a l t u f f i s due to s l i g h t l y more favourable i n t e r n a l -82-physico-chemical conditions i n the t u f f rather than to any differences i n external conditions. True glaucophane s c h i s t s have been reported from the Northern Cascades i n Washington by Smith and Calkins (1904, p.52) and. P. Misch ( o r a l communication) but t h e i r s t r u c t u r a l and stratigraphic, re l a -t i onships to rocks i n the Chilliwack V a l l e y i s not known at present.. . .. Seki (1961) demonstrated that pumpellyite i s a u s e f u l indicator, of metamorphic grade i n low-temperature regional metamorphism. He believed that metamorphism producing pumpellyite could be divided into two types., the glaucophanitic and non-glaucophanitic type, the former representing "higher s o l i d pressure" during metamorphism than the l a t t e r . Pumpellyite i n a l t e r e d volcanic rocks i n Chilliwack V a l l e y has been produced by the former type of metamorphism. Seki also suggested that four mineral f a c i e s , the pumpellyite-chlorite, pumpellyite-prehnite, c h l o r i t e and z e o l i t e facies... span the gap between the greenschist and diagenesis. Metamorphism at r e l -a t i v e l y "low s o l i d pressure" would cause successive changes from diagen-e s i s , r e s p e c t i v e l y through the z e o l i t e , pumpellyite-prehnite and green-s c h i s t f a c i e i and at r e l a t i v e l y higher s o l i d pressure through the zeolite., . c h l o r i t e , pumpellyite-chlorite and glaucophane s c h i s t f a c i e s . Metamorphic mineral assemblages suggest that metamorphism i n Chilliwack V a l l e y area has followed the • l a t t e r path, and that these rocks belong to Seki's pump-, e l l y i t e - c h l o r i t e f a c i e s , t r a n s i t i o n a l to the glaucophane s c h i s t facies.. F o s s i l s and age. ' : " " Fusu l i n i d s of Leonardian age are found i n calcareous p y r o c l a s t i c rocks at the base of the volcanic sequence present i n the autochthon, i n t h i n limestones i n t e r c a l a t e d with v o l c a n i c rocks i n the Liumchen Nappe,, and i n limestone associated with volcanic rocks on Mount Laughington. -83-Belemnites, s i m i l a r to Dictyoconites groenlandicus Fischer, ..from.-the Late Permian of Greenland ( s i m i l a r i t y confirmed by J.A. Jeletzky, o r a l communication, July, 196-J are present i n l i t h i c t u f f s of the sequenaa. i n Liumchen Creek (Figure 20). No other diagnostic f o s s i l s are known. This volcanic sequence i s therefore p a r t l y Leonardian i n age, and as the upper age limit, is....not.' known, some l a t e r Permian rocks may be included. Environment of deposition F o s s i l s i n v o l c a n i c rocks comprising the Pertnlannylijliaa'hicnsequ'.n'beon and i n contiguous rock units- gradational into these v o l c a n i c rocks,. to_-gether with rare pillow lavas, suggests that some of these rocks were laid-, down i n a marine environment. The welded t u f f texture of an a l t e r e d vitric... t u f f from Liumchen Creek indicates that t h i s and perhaps other volcanic rocks of t h i s sequence were deposited s u b a e r i a l l y . I t has been suggested i n the discussion on environment of deposition . of the Permian limestone that basic lavas were q u i e t l y extruded and con-so l i d a t e d around the vent(s) of a v o l c a n i c centre, whilst contemporaneous limestone deposition took place p e r i p h e r a l l y to t h i s . Rocks of the vol-: canic centre now form the Liumchen Nappe, whereas the s i t e s of limestone deposition are now the subjacent autochthon and superjacent McGuire Nappe. A subsequent change to a more s i l i c e o u s magma resulted i n explosive ejec-t i o n of predominantly quartz-bearing c r y s t a l t u f f which spread over the area, terminating limestone deposition. This t u f f was possibly p a r t l y a e r i a l l y transported d i r e c t l y to the s i t e of deposition. Unconsolidated c r y s t a l t u f f s on the flanks of the v o l c a n i c centre may have been transported to the f i n a l s i t e of deposition by subaqueous p y r o c l a s t i c flows (Fiske, Figure 19: Photomicrograph (th i n section, plane l i g h t , X4.0) of welded t u f f (?) composed e n t i r e l y of fl a t t e n e d , a l t e r e d v i t r i c fragments. Specimen c o l l e c t e d by W.R. Danner from Liumchen Creek. Figure 20: Photomicrograph (th i n section, plane l i g h t , X18) showing a cross-section of a ribbed belemnite s i m i l a r to Dictyoconites groenlandicus Fischer, i n a l i t h i c t u f f of Permian age from Liumchen Creek Val l e y ( F o s s i l L o c a l i t y 55). -84-1963). This mode of transport would be compatible with the massive, un-sorted, non-graded nature of much of the c r y s t a l t u f f . Grading...in_..some of these t u f f s suggests they were possibly deposited by turbidity, flows-In the Liumchen Nappe, an apparent l a t e r a l t r a n s i t i o n takes .place., from a sequence of predominant lavas to a sequence of c r y s t a l tuff...with, minor lava. Although no precise time horizon can be drawn through both of these f a c i e s , that they are at l e a s t p a r t l y contemporaneous i s shown by interbedded lavas and c r y s t a l t u f f s on the north side of Mount McGuire, and therefore the change from a sequence of basic lavas, to an overlying. sequence of quartz-bearing c r y s t a l t u f f appears to have been gradationa! rather than abrupt. S t r a t i g r a p h i c r e l a t i o n s h i p between Permian and T r i a s s i c rocks As conditions i n the basin of deposition during and following Permian vulcanism have some bearing on the s t r a t i g r a p h i c r e l a t i o n s h i p between Permian and T r i a s s i c rocks, t h i s t o p i c i s introduced here, rather than i n the discussion of Mesozoic rocks. Although Moen (1962, p.67) stated the Chilliwack Group southwest of the map-area i n northern Washington, was.. . i n i t i a l l y folded and f a u l t e d p r i o r to deposition of Lower Mesozoic rocks, he gave no d i r e c t evidence to support h i s statement. No evidence of Permo-T r i a s s i c deformation i s recognized in,the map-area. The Permian v o l c a n i c sequence i s s t r a t i g r a p h i c a l l y o v e r l a i n by rhyth-m i c a l l y graded, f i n e v o l c a n i c arenites and a r g i l l i t e s of Upper Triassic. age. Existence of a s t r a t i g r a p h i c break between these sequences i s i n d i - . cated by the following f a c t o r s . At some l o c a l i t i e s i n the map-area less than 100 feet of c r y s t a l t u f f separates lower limestone with Leonardian -85-f u s u l i n i d s from overlying Upper T r i a s s i c rocks. The l i t h o l o g y of ..the T r i — • a s s i c sequence above the contact i s markedly d i f f e r e n t from that of-under-l y i n g Permian rocks, with no gradation between the two. The contact.As. marked by a breccia horizon, composed of c l a s t s of i d e n t i c a l lithology. to underlying Permian rocks. E a r l y Permian f u s u l i n i d s were found, .in one ..clast i n the b r e c c i a . This b r e c c i a i s believed to r e s u l t from a submarine-slide, and although not n e c e s s a r i l y marking erosion of Permian rocks in_the. map-area, represents erosion of Permian rocks i n the region. A l l evidence indicates that a disconformity e x i s t s between Permian and T r i a s s i c rocks i n the map-area. Bedding of contiguous Permian and T r i a s s i c rocks i s conformable. Although rocks within the map-area covered a much wider area p r i o r to tectonic superposition, everywhere the s t r a t i -graphic Permo-Triassic contact i s seen, i t i s underlain by Permian volcanic rocks. V a r i a t i o n i n thickness of the Permian volcanic sequence may be p a r t l y due to erosion, but from the nature of the sequence, t h i s v a r i a t i o n could well be o r i g i n a l . S t r u c t u r a l evidence shows that both Permian and T r i a s s i c rocks have undergone the same number of periods of deformation, and that any differences i n degree of metamorphism are between rocks of d i f f e r e n t tectonic units and not between Permian and T r i a s s i c rocks of.the same t e c t o n i c u n i t . The b r e c c i a at the contact demonstrates that erosion of Permian rocks d i d take place and therefore t h i s s t r a t i g r a p h i c break i s probably a regional unconformity, although only a disconformity can be demonstrated i n the map-area. Dott (1961) has .discussed the existence of extensive Late Permian and., probable E a r l y T r i a s s i c vulcanism and the common lack of recognition of Lower and Middle T r i a s s i c rocks over much of the Western C o r d i l l e r a . He -86-linked these two f a c t o r s , suggesting: ". . . as a working hypothesis that the rate of Permian sedimentary and volcanic accumulation exceeded subsidence and so b u i l t up to or s l i g h t l y above sea l e v e l by E a r l y T r i a s s i c I sostatic. adjustment to t h i s v o l c anic p i l e by slow subsidence lagged until.. Late T r i a s s i c when vulcanism had diminished somewhat. The b e l t then again subsided more uniformly below sea l e v e l , or sea l e v e l rose e u s t a t i c a l l y allowing widespread marine transgression." A modified form of Dott's hypothesis i s adopted to explain' the nature of the contact between Permian and T r i a s s i c rocks i n the Chilliwack V a l l e y . During Permian time, rate of accumulation of v o l c a n i c rocks i n the map-area may have exceeded the sum of t h e i r rates of erosion and subsidence, r e s u l t i n g i n the growth of a volcanic i s l a n d above sea l e v e l . Support f o r t h i s proposal i s provided by the welded t u f f from Liumchen Creek, as i t i s d i f f i c u l t to conceive how such a texture could be formed i n a subaqueous environment. Once the supply of v o l c a n i c material had ceased, erosion and subsidence would lower the volcanic i s l a n d below wave base. The breccia, at the.contact between Permian and T r i a s s i c rocks, may r e s u l t from erosion of a s t i l l - e l e v a t e d contiguous part of the volcanic i s l a n d , deposited by submarine s l i d i n g (also causing erosion?) on the already submerged Per_Lan_. v o l c a n i c rocks of the map-area. By Late T r i a s s i c time, volcanic a c t i v i t y i n southwestern B r i t i s h C o l -umbia was concentrated west of the map-area on Vancouver Island and to the * .northeast, i n the N i c o l a area i n the I n t e r i o r of B r i t i s h Columbia. Upper T r i a s s i c sediments i n the map-area, mainly graded bedded v o l c a n i c arenites and a r g i l l i t e s , appear to have been deposited by t u r b i d i t y currents i n a trough between these v o l c a n i c centres. Following the reduction of the v o l c a n i c i s l a n d to wave base, i t would stand as a slowly subsiding i s o l a t e d high area Jon the sea-floor, surrounded -87-by the lower sea-floor on which material was being deposited by, t u r b i d i t y currents. I t would be able to receive only pelagic sediments.nnti1 i t . reached the general l e v e l of the basin by subsidence and possibly by the accumulation of t u r b i d i t e s i n the surrounding lower areas, i f , accumulation exceeded subsidence i n these areas, (see Heezen, 1963, p.754, Kuenen,... 1964, p.6). By Late T r i a s s i c time, there was l i t t l e or no di f f e r e n c e i n .elevation between the l e v e l of the old volcanic centre and the general level, ofVthe basin f l o o r and t u r b i d i t e s were deposited over the whole area. As no pelagic sediments have been recognized, the i n t e r v a l between general cessation of vulcanism and subsequent erosion, and deposition of Upper T r i a s s i c rocks, may have been r e l a t i v e l y short. V a l i d i t y and present status of the term Chilliwack Group The term Chilliwack Group i s derived from Daly's Chilliwack Series, which i s informally defined by modern standards. Because s t r a t i g r a p h i c • names are now defined according to the Code of S t r a t i g r a p h i c Nomenclature '(1961) an examination of the v a l i d i t y and present status of the term Chill-r iwack Group i s e s s e n t i a l . The geographical name Chilliwack must be retained f o r reasons of prior.-,,.. i t y and usage although the term Chilliwack V a l l e y would be more applicable by modern standards. The change from Series to Group f i r s t appeared i n 1944 on'the g e o l o g i c a l map of the Hope area (Geol. Surv. Canada Map 737A) although no explanation was given f o r t h i s a l t e r a t i o n . Danner, (1957, p.113) observed that the usage of Group here i s correct according to. modern s t r a t i g r a p h i c a l p r a c t i c e . As defined by the S t r a t i g r a p h i c Code, a group consists of two or more -88-associated formations and i s defined i n order to demonstrate the natural r e l a t i o n s h i p between formations with s i g n i f i c a n t features i n common.. A l -though formations within the Chilliwack Group were proposed by.Danner (1957, p.114) not enough was known of the composition, of these, units, to define them formally, and they have not been incorporated within the l i t -erature, and the present usage of the term Chilliwack Group i s informal. Temporary use of "group" i n t h i s instance i s presumably acceptable as the S t r a t i g r a p h i c Code notes noncommittally that i t has been used f o r recon-naissance work f o r sequences that appear d i v i s i b l e into formations but which have not as yet been divided. Therefore the term Chilliwack Group provides a u s e f u l interim s t r a t i g r a p h i c c l a s s i f i c a t i o n and w i l l eventually become formal when a l l formations within i t have been defined. As noted above, a group i s established formally i n order to demonstrate the natural r e l a t i o n s h i p between formations. The Permian limestone and the Permian volcanic sequence, both of which are of formational status,, are gradational into one another and are possibly g e n e t i c a l l y related., e i t h e r d i r e c t l y by chemical p r e c i p i t a t i o n of the limestone by contempor-aneous vulcanism, and/or i n d i r e c t l y , by vulcanism elevating part of the sea f l o o r above the general l e v e l and thus making i t a s u i t a b l e s i t e f o r limestone deposition. R e s t r i c t i o n of the term Chilliwack Group to include these u n i t s alonfe would emphasize such r e l a t i o n s h i p s and would also allow the group to be defined formally. In addition, t h i s r e s t r i c t e d usage would be i d e a l as these two formations are the predominant Palaeozoic rocks i n the Chilliwack V a l l e y . However, the upper c l a s t i c sequence, under-l y i n g the Permian limestone may be p a r t l y or almost wholly Lower Permian i n age and i s possibly separated from the underlying Lower Pennsylvanian -89-rocks by a hiatus of unknown duration. I f such a s t r a t i g r a p h i c break can be demonstrated, then a more l o g i c a l d i v i s i o n might be to include, all__>f the c l a s t i c rocks above the hiatus i n the Chilliwack Group; the presence of t u f f s i n t h i s c l a s t i c sequence indicates a possible genetic..relation-ship between these rocks and the Permian volcanic sequence. Older .rocks would be combined into a new group composed of c l a s t i c rocks below such a s t r a t i g r a p h i c break, the Red Mountain Limestone ( r e s t r i c t e d from. Danner, 1957) and c l a s t i c rocks below the Pennsylvanian limestone. These.older rocks are a minor part of the Chilliwack Group as presently established i n the type-area and are seemingly better exposed j u s t southwest of. the map-area i n northern Washington. These changes i n terminology are summarized on the following page, i n Table 4.. TABLE _[.: Synopsis of terminology a p p l i e d to rocks of the C h i l l i w a c k Group and contiguous u n i t s AGE Daly,1912 Crickmay,1930a,1962 (mainly H a r r i s o n Lake area) Danner,1957,1960a (mainly north-west Washington) This t h e s i s C r e t -aceous Tamihy S e r i e s V a r i o u s Nooksack NW p a r t of SE p a r t of map-area map-area J u r a -s s i c near j Group H a r r i s o n Lake i H a r r i s o n Lake voles j, Nooksack v o l c a n i c s sandstones M.Jurass? v o l e s . T r i a -s s i c C u l tus f o r m a t i o n S l o l l i c u m S e r i e s T r i a s s i c v o l c a n i c s ^ . Formation Permian ' • / // • P . o r—1 H Limestone of Black Htn. Pm. b e a r i n g e l a s t i c s Limestone of ,Bed .Mtn. r—! 6 .Pi c o •H rH H £ -Permian v o l c a n i c sequ. Permian limestone upper c l a s t i c sequence "Red Mountain Limestone Penns-y l v a n i a n •Chilliwack . Iseries ', • C h illiwack / ^ V o l c a n i c fm, ca o • i — ' C h i l l i w a c k S e r i e s M i s s i s s -i p p i a n --(none known i n region) sequence -91-Mesozoic rocks of the map-area In contrast to the l i t h o l o g i c a l l y diverse Palaeozoic rocks, Mesozoic rocks are of r e l a t i v e l y uniform l i t h o l o g y , r a r e l y have any strong topo-graphic expression and are generally poorly exposed. They therefore can-not be r e a d i l y subdivided into smaller r o c k - s t r a t i g r a p h i c units... More-over, although Upper T r i a s s i c , Lower J u r a s s i c and Upper Jurassic,.fossils, have been found, these f o s s i l s are too scarce to allow b i o s t r a t i g r a p h i c . units to be defined. Therefore the Mesozoic rocks are discussed under one heading. Several previous workers have described these rocks. Daly (1912, pp.516-518) reported a r g i l l i t e s and associated coarser, c l a s t i c rocks, con-t a i n i n g T r i a s s i c cephalopods, from the east side of Cultus Lake, and named these rocks Cultus Formation. He also gave the name Tamihy Series to c l a s -t i c rocks present near the south end of Tamihi Creek, j u s t south of the map-area)and on the basis of f i e l d r e l a t i o n s concluded that these rocka, were younger than both the Chilliwack Group and the Cultus Formation., and believed t h e i r age to be possibly Cretaceous. Crickmay (1930a, map) showed T r i a s s i c rocks overlying Palaeozoic rocks i n the eastern part of the map-area, where Daly and other authors (e.g. Cairns, 19UU) believed rocks, of Palaeozoic age to occur. Crickmay named these rocks the S l o l l i c u m Series, c o r r e l a t i n g them with s i m i l a r rocks on the east side of Harrison Lake, north of the map-area. Frebold (1953, p.1232) considered that Daly's T r i -a s s i c ammonites probably belonged to the lower part of the Lower J u r a s s i c , although he stated 'that beds, of T r i a s s i c age may be present i n the Cultus Formation. Hillhouse (1956) mapped Mesozoic rocks around Cultus Lake, and -92-followed Frebold i n concluding they were of Lower Jurassic age. Misch. (1963, p.167) used the term Nooksack Group f or c l a s t i c rocks .varying..in age from Late Jurassic to E a r l y Cretaceous which crop-out south ..of ...the. ' map-area; these rocks include some of those i n Daly's Tamihy Series..... Mesozoic rocks are widespread i n the map-area. They form,J_nternational Ridge, the north side of Church Mountain, and crop-out both i n the north-ern part of Tamihi Creek Valley, and i n Chilliwack River two miles .east of i t s confluence with Tamihi Creek. Five miles northeast of Cultus Lake, Mesozoic rocks are exposed i n road cuts i n the Ryder Lake area. To the north of Chilliwack V a l l e y and on the east side of Slesse Creek Valley, Mesozoic rocks crop-out above Palaeozoic rocks. The eastward continuation of these Mesozoic rocks on Mount Laughington and west of Mount Cheam i s ov e r l a i n by Palaeozoic rocks. Mesozoic rocks of Chilliwack V a l l e y map-area are t y p i c a l l y rusty-brown, dark grey or buff weathering shales, a r g i l l i t e s , s l a t e s , s i l t s t o n e s and very fine-grained sandstones. Of these, argillaceous rocks are probably predominant. Coarser sandstones and f i n e breccias are present i n t h i s se-quence but are r e l a t i v e l y uncommon. Thicknesses of i n d i v i d u a l beds range from s i l t s t o n e laminations i n predominant a r g i l l i t e s up to about U inches i n beds composed p a r t l y of coarse sand-sized c l a s t s . Rarely, bedding.thick-nesses are much greater. Graded bedding i s t y p i c a l of these rocks, with regular alternations taking place between shales and coarser c l a s t i c rocks. V a r i a t i o n i n grain s i z e may be d i f f i c u l t to see i n f i n e r beds but may be recognized by hue changes from l i g h t grey to dark grey to black as the • grain size becomes f i n e r and the content of arg i l l a c e o u s material increases. Small load casts are common at the base of i n d i v i d u a l graded beds and -93-convoluted and cross-bedded laminae are observed r a r e l y at the top of some beds. These rocks form a t y p i c a l t u r b i d i t e sequence (see Kuenen, 196/0 of graded, r e g u l a r l y a l t e r n a t i n g f i n e sandstones and a r g i l l i t e s (Figures 21, 22). Sand-sized rocks of t h i s sequence are unsorted, with no sharp d i s -t i n c t i o n into grains and matrix. They are composed of various proportions of angular volcanic rock fragments, plagioclase feldspars, shale chips and minor amounts of limestone fragments. Rocks i n which feldspar.grains are more abundant than v o l c a n i c rock fragments tend to be l i g h t . g r e y i n colour, and where v o l c a n i c fragments predominate the rocks are dark, grey or grey-green. Some rocks with sand-sized textures contain s h a l a "micro-breccias" or intraformational conglomerates. Mic r o s c o p i c a l l y , some volcanic fragments show r e l i c t tuffaceous tex-tures and are commonly a l t e r e d to low b i r e f r i n g e n t , semi-opaque cla y min-e r a l s , c h l o r i t e or less commonly c a l c i t e ; others are fragments of alte r e d basic or intermediate lavas and consist of an alte r e d ( s a u s s u r i t i z e d ?) groundmass of feldspar m i c r o l i t e s that encloses plagioclase phenocrysts. Clasts which are single feldspar c r y s t a l s are. common, and show varying degrees of a l t e r a t i o n . Unaltered feldspars are a l b i t e , and a l t e r e d f e l d -spars., p a r t i c u l a r l y i n Mesozoic rocks of the autochthon,- are composed of a l b i t e associated with c a l c i t e or, by analogy with p a r t l y a l t e r e d grains,, a l t e r e d e n t i r e l y to c a l c i t e . In Mesozoic rocks of tec t o n i c units higher than the autochthon a t y p i c a l a l t e r a t i o n product of the feldspar laths i s a brownish, fine-grained mineral ( i n c i p i e n t lawsonite ?) or fibrous law-sonite ( i d e n t i f i e d by X-ray methods). Some c l a s t i c c a l c i t e grains are of organic o r i g i n , f o r they possess the microstructure c h a r a c t e r i s t i c of Figure 21; T y p i c a l exposure of rocks of the Cultus Formation i n the autochthon, showing thin-bedded a r g i l l i t e s , i n t e r -bedded with t h i c k e r bedded, graded volcanic arenites. Exposure i n logging road, west side of Liumchen Creek V a l l e y . Figure 22: Thin-bedded altered v o lcanic arenites and a r g i l l i t e s of Norian age; Cultus Formation, north side of Church Mountain. -94-echinoderm skeletons (see Moore. L a l i c k e r and Fischer, 1952, p..575). T y p i c a l l y , quartz i s absent or rare, but rounded, clea r , volcanic, .quartz grains are l o c a l l y common i n the groundmass, and epidote i s present, but rare. These rocks are t y p i c a l v o l c anic arenites. Fine-grained Mesozoic rocks i n the autochthon e x h i b i t a.fracture-cleavage developed during^." probable mid-Cretaceous deformation and. the coarser-brained rocks are joi n t e d but otherwise unaffected. By ..contrast, fine-grained rocks of the Mesozoic sequence i n a l l higher t e c t o n i c units possess a s l a t y cleavage, with marked mineral and t e x t u r a l aniao.tro.pism being developed, and coarser rocks have a crude, penetrative f o l i a t i o n . There i s some v a r i a t i o n of l i t h o l o g y i n t h i s sequence of predominantly graded volcanic arenites and a r g i l l i t e s . Hard argillaceous cherts and. cherty a r g i l l i t e s , which are generally thin-bedded but oc c a s i o n a l l y massive, are present near the contact with Palaeozoic rocks on the north side of Chilliwack Valley, west of Mount Cheam, on Church Mountain and i n the v i c i n i t y of Pierce Creek. These rocks are i n v a r i a b l y fine-grained and. no . graded bedding has been observed i n them. On the southwest side of Elk-Mountain, at an a l t i t u d e of 4,000 feet, a t h i n , sparsely f o s s i l i f e r o u s , shaly limestone to calcareous shale bed i s interbedded with these cherty a r g i l l i t e s ( F o s s i l L o c a l i t y 2). Minor a r g i l l a c e o u s limestones i n Mesozoic . rocks also crop-out on the Foley Creek road, and are exposed i n creek beds on the south side of Mount Laughington. V a r i o l i t i c lavas i n the extreme northwestern part of the map-area, at an a l t i t u d e of 500 feet on the Ryder Lake road, o v e r l i e f i n e c l a s t i c rocks which contain Lower Jurassic f o s s i l s and are themselves o v e r l a i n by massive, micaceous sandstones. These lavas occur as p i l l o w - l i k e masses, -95-with dark green c h l o r i t i c material between the pillows. Pale g r e e n . v a r i — o l i t e s set i n dark green c h l o r i t i c material are v i s i b l e near the-borders of the pillows; these v a r i o l i t e s become more numerous and coales.ce.towards the centre of the pillows, where the whole rock i s pale green. Thin,.sec-tions reveal that the rock i s composed of r a d i a t i n g aggregates, up to;, one mm. i n diameter, of o l i g o c l a s e or a l b i t e . C h l o r i t e patches,.within., the rock simulate the shape of pyroxene phenocrysts and contain r e l i c t pyroxene cleavages. C h l o r i t e occurs i n v e s i c l e s , and with calcite.,, f i l l s , v eins. Minor amounts of pumpellyite are associated with the c h l o r i t e . The massive micaceous sandstone overlying the variolitic,..la_ras_..con=-t a i n s up to 10$, angular quartz fragments, feldspars, v o l c a n i c rock f r a g -ments and f a i r l y abundant muscovite and b i o t i t e . Its composition d i f f e r s , by the presence of d e t r i t a l micas, from a l l other known Mesozoic c l a s t i c rocks i n the map-area, but resembles c l a s t i c rocks cropping-out on the. east side of Vedder Mountain, j u s t west of the map-area (W.J. McMillan, o r a l communication, February, 1965). The lower s t r a t i g r a p h i c contact of these rocks was described previously i n the discussion of the Permo-Triassic boundary. Bedding at the base of the Mesozoic sequence i s conformable with that i n the s t r a t i g r a p h i c a l l y underlying Permian rocks. The contact i n many places i s marked by a brec-c i a , derived l a r g e l y from underlying Permian volcanic rocks. No upper s t r a t i g r a p h i c contact of the Mesozoic sequence i s known from the map-area. Although rocks of l a t e s t Cretaceous or possible Paleocene age crop-out on the north side of Chilliwack River, immediately west of the map-area (Crickmay and Pocock, 1963, p.1933), exposure i s so poor at . t h i s l o c a l i t y that the s t r u c t u r a l and s t r a t i g r a p h i c r e l a t i o n s h i p s of these -96-rocks to older Mesozoic rocks was not determined. The youngest ,,Me.so_oic rocks known are of Late J u r a s s i c age; these rocks crop-out i n the. south-eastern part of the map^-area and are o v e r l a i n s t r u c t u r a l l y by. amphibolitic rocks of uncertain age. The apparent thickness of Mesozoic rocks i n the map-area.,probably exceeds 4,000 f e e t . Lack of d i s t i n c t i v e marker horizons, folding, and— r e l a t i v e paucity of outcrops makes i t impossible to give any.estimate, of the o r i g i n a l thickness. F o s s i l s and age of the Mesozoic sequence F o s s i l s are not very common i n Mesozoic rocks from Chilliwack V a l l e y . Bottom dwelling forms are represented by rare clams, s n a i l s and crinoid-o s s i c l e s , the l a t t e r being found only i n the shaly limestone bed on Elk-Mountain, or as d e t r i t a l fragments of unknown age i n c l a s t i c rocks. Trace f o s s i l s , such as worm borings and t r a i l s , are present throughout the se-quence but are never abundant. Ammonites and belemnites have been found at a few, scattered l o c a l i t i e s . F o s s i l s diagnostic of the Upper T r i a s s i c (upper Karnian and ea r l y Norian), E a r l y Jurassic (Sinemurian) and Late J u r a s s i c ( l a t e Oxfordian-. early Kimmeridgian) have been c o l l e c t e d from Mesozoic rocks i n the map-area. Daly (1912, p.517) obtained f o s s i l s from a l o c a l i t y j u s t south of the Inte r n a t i o n a l Boundary to the southwest of the map-area which were consid-ered to be of T r i a s s i c age. These f o s s i l s were i d e n t i f i e d as the ammon-i t e A r n i o t i t e s vancouverensis Whiteaves? and Aulacoceras ? sp., a belemnoid. resembling A.Carlottense Whiteaves. Ammonites of l a t e E a r l y J u r a s s i c or - 9 7 -e a r l y Middle J u r a s s i c age were found on the Ryder Lake road by. J.E.... Arm-strong (Hillhouse 1956, p.33). A molluscan fauna was found by the writ e r i n Mesozoic rocks on the east side of Liumchen Creek, not f a r from the contact of these..rocks with Palaeozoic rocks ( F o s s i l L o c a l i t y 53) . The most abundant f o s s i l - i s . . t h e small ammonite Hannaoceras c.f. H. (Sympolycyclus) nodifer (Hyatt.and Smith) (Figure 23 ) . Fragments of a larger ammonite, possibly D i s c o t r o p i t e s, and a large Halobia' (H.superba ?) were found associated with Hannaoceras... E.T. Tozer (written communication, December, 1964.) confirmed t h i s i d e n t i -f i c a t i o n of Hannaoceras but stated that the i d e n t i f i c a t i o n s of Discotro- p i t e s and Halobia are not very s a t i s f a c t o r y owing to t h e i r poor preserva- . t i o n . From near t h i s l o c a l i t y a belemnite, possibly A t r a c t i t e s c.f. A. drakei Smith, some small u n i d e n t i f i e d pelecypods and a medium-sized, orthostropic gastropod were c o l l e c t e d . This fauna appears to be repre-sentative of the Tropites subbulatus zone, and i s uppermost Karnian in.age. Poorly preserved Halobias were c o l l e c t e d on the north side of Church Mountain ( F o s s i l L o c a l i t y 52). These were t e n t a t i v e l y i d e n t i f i e d by G.E.G. Westermann (written communication, February, 1964) as Halobia  d i l a t a K i t t l ?, probably of lower, possibly of middle, Norian age. Fragmentary ammonites and large, ribbed, belemnites were found i n shaly limestone on the southwest side of E l k Mountain ( F o s s i l L o c a l i t y 2 ) . The belemnites (Figure 21+) were i d e n t i f i e d as Aulococeras c.f. A. C a r l o t -tense Whiteaves. J.A. Jeletzky ( o r a l communication, July, 1964.) confirmed t h i s i d e n t i f i c a t i o n and considers that Aulacoceras i s r e s t r i c t e d to the Upper T r i a s s i c . The ammonites from t h i s l o c a l i t y were too poorly preserved to be i d e n t i f i e d . Figure 23: Hannaoceras c.f. H. (Sympolycyclus) nodifer (Hyatt and Smith), X3, an ammonite of upper Karnian age, from lower part of Cultus Formation, Liumchen Creek ( F o s s i l L o c a l i t y 53). Figure 24: Cross-section of Aulacoceras c.f. A. Carlottense Whiteaves, X3, a ribbed belemnite of Upper T r i a s s i c age, from shaly limestone of the lower part of the Cultus Formation, on E l k Mountain ( F o s s i l L o c a l i t y 2). -98-The Upper T r i a s s i c age of Aulacoceras r a i s e s some doubt as.to the age of Daly's c o l l e c t i o n (1912, p.517) which contained, i n addition to Aula-coceras , ammonites i d e n t i f i e d as Lower J u r a s s i c by Frebold (1953, p.1232). A poorly preserved ammonite, c o l l e c t e d from Mesozoic rocks on. the logging road between Mount Mercer and Mount Thurston, was i d e n t i f i e d , by H. Frebold (written communication, November, 1963) who writes: "The poorly preserved specimen resembles specimens c o l l e c t e d by Dr. Armstrong some years ago, and by me i n the summer of 1963. I am including these specimens i n the Arnioceratidae and w i l l , probably i d e n t i f y them with Melanhippites. I have also made c o l l e c t i o n s from the Harrison Lake area some years ago and l a s t summer, which indicate the presence of the same genus. The age of the beds concerned, which also includes pelecypods, i s Sinemurian.". S i m i l a r forms to t h i s were found i n the Ryder Lake road, probably from the l o c a l i t y where they were f i r s t c o l l e c t e d by J.E. Armstrong (o r a l communication, 1964.). No Middle J u r a s s i c f o s s i l s are known from the map-area. Daly (1912., p.519) noted that Stephanoceras ? and Auc e l l a e r r i n g t o n i , r e s p e c t i v e l y of Middle and Upper Jurassic age, had been obtained from a l o c a l i t y not f a r south of Tamihi Creek i n northern Washington. Poorly preserved pelecypods found i n talus below the north face of Mount McFarlane i n the upper part of Pierce Creek V a l l e y ( F o s s i l L o c a l i t y 29) were i d e n t i f i e d by J.A. Jeletzky as Buchia ex. gr. concentrica (Sower-by). .Jeletzky i n a written communication (August, 1964) states: "Most specimens are d i s t o r t e d beyond recognition. However, two l e f t valves are strongly suggestive of Buchia ex. gr. concentrica (Sowerby) (~ B. bronni Lahusen, non ? R o u i l l i e r , 18/+7). A l l rep-resentatives of t h i s species group are r e s t r i c t e d to the upper Oxfordian-lower Kimmeridgian stages of the Upper J u r a s s i c through-out North America and northern Eurasia. This i s , accordingly, the most probable age of t h i s s l a t y f a c i e s of the Nooksack Group. The same Buchia fauna, although much better preserved, occurs i n -99-the lower part of the type Nooksack Group i n northwestern Washington." Correlation Rocks of Upper T r i a s s i c age are common i n t h i s region. To. the south-west of the map-area, the Karnian to Norian Haro Formation of the San Juan Islands consists of c l a s t i c sedimentary rocks, derived largely, from v o l -canic sources, and some limestones (Danner, 1957, p.304.) • 0n...Texada. Island, i n the S t r a i t of Georgia, about 130 miles west-northwest.of the map-area, the ammonite Hannaoceras i s present i n limestones i n t e r s t r a t -i f i e d with volcanic rocks (Mathews, 194-7, p.36). Crickmay (1930b, p.35) noted possible T r i a s s i c sedimentary rocks on the west side of Harrison Lake and also (Crickmay, 1930a, p.4-88) showed T r i a s s i c a r g i l l i t e s , s c h i s t s and greenstones, which he c a l l e d the S l o l l i c u m Series, cropping-out on the east side of Harrison Lake, and continuing to the south across Fraser.. River, into the eastern part of Chilliwack V a l l e y map-area. No f o s s i l s were reported as evidence of age of the S l o l l i c u m S e r i e s . About 80 miles to the northeast, on the east.side of the Cascade Mountains, the Nicola Group contains f o s s i l s of Late T r i a s s i c age, and consists mainly of v o l - , canic rocks, with l e s s e r amounts of limestone and c l a s t i c sedimentary, rocks, (McLearn, 1953, p.1217). The only known rocks from near the map-area which contain Lower Jur- . as s i c f o s s i l s are from Harrison Lake (see Frebold, written communication, above). Lower Jurassic rocks are known from Vancouver Island, from Parson Bay^which i s about 200 miles northwest of the map-area, (Jeletzky, 19.54-5 Crickmay, 1928) and from the Tyaughton Lake area, over 100 miles north of -100-t the map-area (Cairns, 1943). Volcanic rocks of Middle Jurassic age, the Harrison Lake Formation of Crickmay (1962, p.3), crop-out on the west side of Harrison Lake. These rocks are correlated by Danner (1960a, p.4) with volcanic rocks, at ..the .base of the Upper Ju r a s s i c to Lower Cretaceous Nooksack Group which, cr.o.ps-out south of the map-area i n northern Washington. V a r i o l i t i c flow rocks.over-l i e rocks containing Lower Jurassic f o s s i l s i n the northwestern..part,of the map-area. Possibly these volcanic rocks can be correlated with the other Middle J u r a s s i c v o l canic rocks i n the region. Upper Jurassic c l a s t i c rocks of Chilliwack V a l l e y map-area are dom-in a n t l y fine-grained, and are of s i m i l a r l i t h o l o g y to Crickmay's Agassiz P r a i r i e Formation (1962, p.6) of comparable age. According to Jeletzky (written communication, above) these rocks i n the map-area are a slaty, f a c i e s of the Nooksack Group. Misch and Armstrong ( i n Hillhouse, 1956, pp.38-39) have suggested that sedimentary rocks on the east side of Vedder Mountain immediately west of the map-area are equivalent to Misch's. Upper Jurassic-Lower Cretaceous Nooksack Group. The mica-bearing sandstone above the (Middle Jurassic ?) volcanic rocks i n the northwestern part-of the .map-area i s l i t h o l o g i c a l l y s i m i l a r to some of the rocks on the east side of Vedder Mountain. Environment of deposition A l l evidence suggests that Mesozoic c l a s t i c sedimentary rocks i n Chilliwack V a l l e y map-area were deposited by t u r b i d i t y currents, or r e -lated processes, well below wave base. These rocks are t y p i c a l l y graded; the only cross-bedding laminations observed are confined to the uppermost - 101 -part of i n d i v i d u a l graded beds, and according to Kuenen. (1964, p.27) these may be produced by f l u c t u a t i o n s of t u r b i d i t y currents. The presence, of worm borings and t r a i l s i n these c l a s t i c rocks, indicates that .the s e d i -ments possibly accumulated at a depth of water greater than that. to. which l i g h t can penetrate (Seilacher, i n Trumpy, I960, p.874). Cherty a r g i l l i t e s i n the sequence near the contact with Palaeozoic rocks may have been formed i n the following manner. The s i l i c a content of the sea water i n the basin may have been high as the r e s u l t of ...contempor-aneous (Upper T r i a s s i c ) vulcanism. Unless c l a s t i c sedimentation were r e s t r i c t e d to very f i n e material, slowly deposited from suspension,, then p r e c i p i t a t e d s i l i c a would be so d i l u t e d by c l a s t i c material r a p i d l y depos-ited, from t u r b i d i t y currents, that i t s presence would not be obvious. These cherty a r g i l l i t e s may have been deposited on l o c a l highs on the sea f l o o r , possibly remnants of the Permian volcanic i s l a n d , on which material could not be laid-down by t u r b i d i t y currents (see Heezen, 1963, p.754, Kuenen, 1964, p - 6 ) , but which could be covered by very f i n e c l a s t i c mat-e r i a l o r i g i n a l l y c a r r i e d i n d i l u t e suspension by "normal" marine currents. With the possible exception of m"ica-bearing sandstone i n the extreme . northwest of the map-area, Mesozoic rocks i n Chilliwack V a l l e y area were l a r g e l y derived from v o l c a n i c rocks. As noted above, Upper T r i a s s i c v o l -canic rocks are present, both to the west on Vancouver Island, and to.the northeast, on the other side of the Cascade Mountains. I t i s suggested that during Late T r i a s s i c time conditions i n these areas northeast and west of the map-area were analogous to conditions i n the map-area during E a r l y Permian time. The- areas were highs on the sea f l o o r r e s u l t i n g from volcanic accumulation exceeding subsidence. Upper T r i a s s i c rocks i n the -102- . . map-area, composed l a r g e l y of c l a s t s of v o l c a n i c o r i g i n and deposited, by t u r b i d i t y currents, probably accumulated i n a trough between the. highs, and were derived from them. The l i t h o l o g y of Upper T r i a s s i c and...Lower Jur a s s i c rocks i n the map-area i s i d e n t i c a l , and no s t r a t i g r a p h i c break can be detected between them. Presumably conditions extant i n Late T r i -a s s i c time continued into the J u r a s s i c . Volcanic rocks within the map-area of possible Middle J u r a s s i c age., and Middle J u r a s s i c v o l canic rocks j u s t to the north of the map-area, near Harrison Lake, record the migration of v o l c a n i c centres back to the v i c i n -i t y of the map-area again, during Middle J u r a s s i c time. L i t t l e can be said of the source of the slates containing the only Upper Ju r a s s i c f o s s i l s known i n the map-area. The mica-bearing sandstone . above the (Middle J u r a s s i c '?) volcanic rocks i n the Ryder Lake area i s l i t h o l o g i c a l l y s i m i l a r to rocks on Vedder Mountain, some of which were reported to contain g r a n i t i c c l a s t s (Hillhouse, 1956, p.34). Therefore the mica-bearing sandstone i n the map-area may be p a r t l y derived from gran-i t i c or high-grade metamorphic rocks. Lower Cretaceous conglomerate con-t a i n i n g g r a n i t i c c l a s t s has been reported from north of the map-area i n the Harrison Lake area (Crickmay, 1962, p.7). Nomenclature of Mesozoic rocks i n the map-area Daly (1912, p.516) gave the name Cultus Formation to presumed T r i a s s i c rocks east of Cultus Lake. Later work has shown both Upper T r i a s s i c and Lower J u r a s s i c f o s s i l s to be present i n the sequence. No s t r a t i g r a p h i c . break or marked l i t h o l o g i c a l v a r i a t i o n i s known i n t h i s sequence and the term Cultus Formation i s retained. Although "Slollicum S e r i e s " was applied - 1 0 3 -by Crickmay (1930a) to rocks of supposed T r i a s s i c age cropping^out.in the eastern part of the map-area, these rocks are l a t e r a l equivalents of. the :Cultus Formation i n the Cultus Lake area and the term "Slollicum. Series" can be rejected on grounds of p r i o r i t y , i n s u f f i c i e n t l i t h o l o g i c a l - d e s c r i p -t i o n and lack of f o s s i l s c i t e d as evidence of age. As no stratigranhic.. break or l i t h o l o g i c a l v a r i a t i o n has been detected between Upper ...Jurassic.. rocks i n the southeastern part of the map-area and Upper T r i a s s i c . a n d Lower Ju r a s s i c rocks elsewhere, these rocks can only be regarded..as. part of the Cultus Formation, s t r a t i g r a p h i c a l l y equivalent to the Agass_Lz_For-mation of Crickmay (1962) or part of the Nooksack Group of Misch ( M i l l e r and Misch, 1963). In the northwestern part of the map-area, three d i s -t i n c t rock types are present. These are, Lower Jurassic a r g i l l i t e s of the Cultus Formation, v o l c a n i c rocks, which, i f of Middle J u r a s s i c age, are possibly part of the Harrison Lake Formation of Crickmay (1962), and mica-ceous sandstones, which crop-out above the lavas and may be equivalent to the Nooksack Group or the Peninsula Formation of Crickmay (1962). -104-STRUCTURAL GEOLOGY Preliminary statement^ The e f f e c t s of what appear to be two phases of one period... of., defor-mation are recognized i n rocks whose ages range from Pennsylvanian to. Late J u r a s s i c . ' The f i r s t phase, hereafter denoted D]_, took place a f t e r Late Ju r a s s i c time and before the Miocene, and i t i s correlated with..the pro-bable mid-Cretaceous deformation of Misch ( M i l l e r and Misch, 1963, p.l67). Major northeast-trending overturned and recumbent folds and thrus.ts~wer.e formed at t h i s time. Minor f o l d s , denoted F-^ , and associated structures formed during D^ are used i n est a b l i s h i n g the s t y l e , sense of movement., and o r i e n t a t i o n of the major structures. During the second phase, denated D^, northwest-trending structures were superimposed upon the e a r l i e r , .struc-tures. The time during which the second period of deformation took place can only be established as post-D^ and pre-Miocene. Major structures formed during D^ are not prominent r e l a t i v e to those formed during D^, but . minor structures produced during t h i s period of deformation are common. A general d e s c r i p t i o n of s t r u c t u r a l elements i s given below; t h i s i s followed by more s p e c i f i c descriptions of both minor and major structures. S t r u c t u r a l elements Any one or combination of the following s t r u c t u r a l elements may be present i n a single outcrop. -105-Planar structures Bedding, denoted S , i s comnionly an e a s i l y recognized planar ...struc-ture, which, acting as a marker i n folded rocks, enables the style, of.... folds formed during to be distinguished. Bedding i s discerned, i n — i n d i -v i d u a l outcrops of c l a s t i c sedimentary rocks by v a r i a t i o n s i n grain., s i z e , or, i n the fine-grained c l a s t i c rocks such as interbedded silts.t.c_ie.s...and. a r g i l l i t e s , 1 by v a r i a t i o n s i n hue. C l a s t i c sedimentary rock sequences in. which neither of the above can be seen are not common. Bedding i s recog-nized i n limestone outcrops, even where r e c r y s t a l l i z a t i o n has been exten-sive, from the presence of chert nodules p a r a l l e l to bedding, or from shaly. interbeds. However, bedding i n massive lavas and some c r y s t a l t u f f s may not be distinguishable i n single outcrops and i n many cases can only, he determined by mapping l i t h o l o g i c a l u n i t s . Planar structures, denoted S p are those produced during D^. Their presence i n a p a r t i c u l a r rock and t h e i r exact nature depend i n part upon both the competancy of the rock during deformation and also the metamor-r. phic environment i n which deformation has taken place (see De S i t t e r , 1956, p.77). The e a r l i e s t secondary planar structure recognized which r e s u l t s from deformation of both Palaeozoic and Mesozoic fine-grained c l a s t i c rocks i n the western parts of the map-area (Subarea 1, Plate 3) i s e i t h e r a f r a c -ture or s t r a i n - s l i p cleavage. In outcrops both of these cleavages are v i s -i b l e t y p i c a l l y as a set of c l o s e l y spaced fractures commonly oriented at low angles to bedding. S t r a i n - s l i p cleavage i s developed when bedding., S , i s c l o s e l y and r e g u l a r l y spaced and the rock i s fine-grained, as i n -106-laminated silts'tone and a r g i l l i t e sequences (Figure 25), whereas fracture cleavage occurs when S^ i s more widely and l e s s r e g u l a r l y spaced and/or the rocks are coarser grained (Figure 26). In a single graded bed...this f r a c -ture cleavage may be i n the upper part, composed- of clay-to s i l t - s i z e d c l a s t s , but not the lower part containing medium or coarse sand-sized c l a s t s . Both fracture cleavage and s t r a i n - s l i p cleavage are oriented roughly . p a r a l l e l to the a x i a l planes of minor folds of the same s t y l e i n t h i s (western) part of the map-area. For t h i s reason, and because bedding is. the only planar • structure cut by e i t h e r the fracture or s t r a i n - s l i p , c l e a v -age, they are considered to be equivalent planar structures which were formed during D , and both are denoted by the same symbol, S|. Their d i f -f e r i n g c h a r a c t e r i s t i c s are seemingly due to differences of the primary nature of the rocks i n which they are developed. Sl a t y cleavage, denoted by S£, i s the e a r l i e s t secondary planar struc-ture recognized which r e s u l t s from deformation i n a l l fine-grained c l a s t i c rocks i n the remaining, major, eastern part of the map-area. In the field., i t i s d i f f i c u l t l o c a l l y to d i s t i n g u i s h t h i s cleavage from bedding, as the two are commonly nearly p a r a l l e l . However, microscopic examination invar-i a b l y reveals that s l a t y cleavage, S|', has been developed (Figure 27). A penetrative planar structure of metamorphic o r i g i n i s also* present i n ' coarse-grained c l a s t i c rocks i n t h i s part of the map-area. In volcanic arenites containing granule or coarse sand-sized grains, t h i s planar struc-.. ture i s a somewhat i r r e g u l a r f o l i a t i o n (Figure 28), which becomes more reg-u l a r as grain s i z e decreases, and appears to grade into s l a t y cleavage. Individual grains i n the coarse c l a s t i c rocks appear f l a t t e n e d and many Figure 25: S t r a i n - s l i p cleavage, S', i n laminated s i l t s t o n e s and a r g i l l i t e s of the Cultus Formation; exposed i n Liumchen Creek. Dip of cleavage i s to southeast. Figure 26: F fo.ld i n medium to thin-bedded^ fine-grained clastic-Tocks showing- poorly developed a x i a l plane fracture cleavage, £U» ( p a r a l l e l to dashed l i n e ) . Cultus Formation, i n side of logging road, north side of Church Mountain. Dip of a x i a l plane of f o l d i s to the southeast. Figure 27: Photomicrograph, ( t h i n section, plane l i g h t , X30) of fine-grained c l a s t i c rock from basal part of the Mesozoic sequence i n Foley Creek showing s l a t y cleavage, S" ((parallel to dashed l i n e ) , p a r a l l e l to compositional banding, SU. and SQ have both been gently folded. Figure 28: Coarse volcanic arenite of the upper c l a s t i c sequence on the south side of Mount Mercer, showing the penetrative f o l i a t i o n , 5^, ( p a r a l l e l to dashed l i n e ) cross-cut by kink-bands ( p a r a l l e l to dotted l i n e ) . Dip of plane of kink-bands i s to the southwest. -107-grain boundaries are i n d i s t i n c t (Figure 30B). This f o l i a t i o n ,ia. approxi-mately p a r a l l e l to s l a t y cleavages i n contiguous fine-grained.rocks, and i s the e a r l i e s t recognized planar structure of metamorphic or i g i n . in_.the coarse-grained rocks. I t i s therefore considered to be an anal_.g-_us-..struc-ture to the s l a t y cleavage, and i s also denoted by the symbol S". Where the r e l a t i o n s h i p i s seen between s l a t y cleavage in.fine-grained c l a s t i c rocks, and i t s seeming equivalent, the f o l i a t i o n i n coarser, c l a s -t i c rocks,-and minor F^ f o l d s , these planar structures are a x i a l plane... cleavages (e.g. Figure 29A). Both S | and are the e a r l i e s t planar structures r e s u l t i n g from, .de-formation and bear the same r e l a t i o n s h i p to minor folds i n t h e i r respec-t i v e parts of the map-area, and are thus considered to be analogous struc-tures, both of which were produced during D^. In addition, c l a s t i c rocks, i n both parts of the map-area are s t r a t i g r a p h i c a l l y equivalent and were o r i g i n a l l y of s i m i l a r character. Therefore, the d i f f e r i n g natures of and are due presumably to d i f f e r e n t metamorphic conditions extant during t h e i r production. As S!^  involves reorganization of rock-material (to pro-duce s l a t y cleavage), i n contrast to S | , and as i t i s also developed. i n . .... coarse c l a s t i c rocks, unlike S | , i t appears to have been produced under more intense metamorphic conditions /than S | . Planar structures, denoted by S£ and SJJ, cut SQ, S | and and were formed during D^. Unlike the e a r l i e r two secondary planar structures which are ubiquitous, i n c e r t a i n rock types, i n t h e i r respective parts of the map-area, planar structures formed during are i r r e g u l a r l y d i s t r i b u t e d on outcrop scale, although present throughout the map-area. Planar structures designated by S' are t y p i c a l l y associated with f i n e FIGURF, 29: Minor structures. With the exception of B, a l l examples shown of minor structures were traced d i rec t ly from sawn surfaces of hand specimens* The specimens are oriented i n a near-vertical plane, with the azimuth of the plane indicated approximately!. A Isoc l ina l ly folded laminations i n a slate/sil tstone rocki Slaty cleavage, i s effectively paral lel to the axial planes of these minor folds. Specimen i s from lower c las t ic sequence, east side of Slesse Creek* B Conjugate fo ld , i n thin but irregularly bedded argillaceous rocks of the Cultus Formation, northeast side of Church Mountain• Conjugate fold, i n cherty a r g i l l i t e , developed on limb of pre-exipting fold . Triassic rocks, near summit of Elk Mountain, FIGURE 30s Minor structures. All examples are traced directly from sawn surfaces of hand specimens* The specimens are oriented in a near vertical plane with the azimuth of the plane indicated approximately* A Planar fractures (Si) associated with crinkles,, in a slate. Specimen from basal part of Mesozoic s equence, Foley Creek• B Crudely foliated volcanic arenite, showing flatt-ening of clasts parallel to S", cross-cut by kink bands, parallel to S', Specimen from upper clastic sequence, south side£ Mount Mercer* C Curved fractures (Si) in a foliated fine tuff or volcanic arenite. Variation in grain size across specimen is responsible for curving of fracture planes. Specimen from upper clastic sequence, Slesse Creek gorge* D Minor Dg fold, associated with kink bands, in fol-iated tuff or volcanic arenite of upper clastic seq-uence, Slesse Creek, F I G U R E 30 : M i n o r s t r u c t u r e s -108-p a r a l l e l c r i n k l e s l o c a l l y developed on SQ and S^. These crinkles, are com-mon i n rocks, i n which SQ and generally s u b p a r a l l e l , dip eastwards...at low to moderate angles, and i s described below as i t occurs.. in...racks_. with t h i s eastward dip. The fin e p a r a l l e l c r i n k l e s are irregularly...dis.-r.. t r i b u t e d and may be e i t h e r s o l i t a r y or i n groups i n which they, are spaced as c l o s e l y as 10 c r i n k l e s per inch. Where c l o s e l y spaced, the. ..cr±nklas_. . t y p i c a l l y have the form of r e g u l a r l y repeated, minute, asymmetric,. s t e p r r . l i k e f o l d s , with a short limb generally dipping steeply eastwards,...a..1 nnger limb dipping e i t h e r gently eastwards, h o r i z o n t a l or gently westwards_,_.and.. an angular hinge. Fractures, denoted S^, may be present i n s t e a d .afLihe steep short limb, and are approximately normal to the general dip of SQ or S j and thus dip steeply westwards (Figure 3 0 A ) . In rocks of uniform ... l i t h o l o g y , these fractures are planar (Figure 3 0 A ) but i n rocks where, the grain s i z e varies they are curved (Figure 3 0 C ) . The fractures divide the rock into a ser i e s of s l i c e s , with each s l i c e elevated successively above i t s eastern neighbour, so that the o v e r a l l dip to the east of SQ and...S£ i s apparently steepened. Apart from t h i s l o c a l apparent steepening and. warps-ing of SQ and S!^  where c r i n k l e s associated with S^ are well developed., no .. folds have been observed associated with.this planar structure. Structures developed i n rocks other than fine-grained c l a s t i c rocks cut SQ and S!^  planes, are s i m i l a r l y oriented to SJ, planes i n contiguous., fine-grained rocks and are believed to be analogous. J o i n t drags ( F l i n n , 1952, p.266) or kink bands (Ramsay, 1962, p.523) are developed i n less w e l l - f o l i a t e d and generally coarser grained rocks than the f i n e c l a s t i c rocks i n which the c r i n k l e s .occur. Geometry of these kink bands i s simi- . l a r to that of the c r i n k l e s i n the fine-grained rocks, but they, are of - 1 0 9 -greater amplitude, more angular, and are not as c l o s e l y spaced or as. reg-u l a r l y repeated (Figures 28, 30B). The kink bands are t y p i c a l l y present i n rocks that dip gently eastwards. Orientation of the plane..oil. kirJcing-i s roughly normal to S or S" and i s approximately p a r a l l e l to .SI. in...con?-0 1 *~ tiguous fine-grained rocks. Local, c l o s e l y spaced fractures in...shaly...lime-stones are p a r a l l e l to S^ i n adjacent shales. In massive rocks., p a r t i c u -l a r l y massive, hard, quartz-bearing c r y s t a l t u f f s , zones of en-echelon q u a r t z - f i l l e d f r a c t u r e s , with each fra c t u r e up to 1 foot long, are l o c a l l y present. The plane of the zone containing these fractures i s . roughly..par-a l l e l to S^ planes i n associated f o l i a t e d rocks. Planar structures designated S^ occur t y p i c a l l y i n fine-grained c l a s -t i c rocks and are developed on the short limb of asymmetric f o l d s (Figure 31), which s u p e r f i c i a l l y resemble the oblique-shear or chevron folds of De S i t t e r (1956, p.183). Commonly, these f o l d s are oriented so that SQ or S", defining the longer, plane, limb, dips east at low to moderate, an-gles. SJJ i s oriented at about U5° to SQ or S!^  and thus dips eastward., at. a f a i r l y steep angle. The shorter, western limb i s divided into a series of s l i c e s by S^ planes; SQ and S!^  i n each s l i c e i s folded, and the overall, e f f e c t i s to produce a "limb" which dips westward or i s nearly horizontal-. Less common are fo l d s believed analogous to those described above i n which SQ and S^ are deformed and i n which SJJ i s poorly developed (Figure 30D) or absent (Figure 32). Furthermore, SJJ planes are displayed i n some rocks, with no recognizable fold-forms. Rarely folds s i m i l a r i n form to those described above occur where SQ or S^ dip steeply westwards, and S^ i s nearly h o r i z o n t a l . Although S' and S" have never been seen at the same l o c a t i o n , and Figure 31: Asymmetric " f o l d " produced during D 2, with east-ward dipping, longer limb, and short western "limb" cut by S" ( p a r a l l e l to dashed l i n e ) . In upper c l a s t i c sequence (?) by logging road, west side of Mount Cheam. Figure 32: Asymmetric f o l d , with eastern dipping longer limb, believed analogous to f o l d i n Figure 31, but with no development °f _>o p i a n e s « Lower c l a s t i c sequence, i n logging road, south end of Slesse Creek. -110-thus t h e i r r e l a t i o n s h i p cannot be d i r e c t l y observed, several .lines-.Q.f evidence suggest they are re l a t e d structures produced during .the.same phase of deformation, D^. The main differ e n c e between them appears...to. be t h e i r angular r e l a t i o n s h i p with e a r l i e r planar structures; SI,"'!"3 or-iented at roughly 90° to S _ or S ' , and at about 4-5°. U 1 l~ Both SJ, and have been formed under s i m i l a r metamorphic.conditions. They both cut S^ and S j or and are associated with f o l d forms_.which commonly have angular hinges and which appear to r e s u l t from deformation... under which the rocks generally behaved i n a b r i t t l e manner. In every.ex- .. ample of and SIJ studied microscopically, the r e o r i e n t a t i o n of minerals p a r a l l e l to £P and S^ i s mechanical and r e s t r i c t e d ' t o the immediate vici=. n i t y of the planar structures. Because there i s no reorganization of. rock. .. material, these structures were presumably produced at a lower metamorphic grade than that under which s l a t y cleavage (S!p was formed. To allow for. such a decrease i n metamorphic grade there must have been a r e l a t i v e l y long i n t e r v a l between the time when S!^ was produced (D-^ ) and the time.when. S£ and were formed (p_2) . Conjugate folds (Figure 29B) are present i n the map-area and appear., to have been produced under s i m i l a r metamorphic conditions, and at a simi-l a r time to Si, and S^, as both S Q and S| or S!^  are deformed i n these con-jugate f o l d s , and as the folds have angular hinges and seem to be the r e -s u l t of b r i t t l e deformation. The r e l a t i o n s h i p between conjugate folds and planar structures formed during T)^ has not been observed by. the writer i n the map-area, but the r e l a t i o n s h i p s between these structures may be i n f e r r e d , from the studies done elsewhere by Paterson and Weiss (1962) and Ramsay (1962). - I l l -Conjugate folds and kink bands have been produced experimentally by compression of p h y l l i t e . Where the d i r e c t i o n of compression is_contained within the f o l i a t i o n of the p h y l l i t e so conjugate folds are formed ..by. the symmetrical i n t e r s e c t i o n of two sets of kink planes. The sets, of..kink, bands are asymmetric where the d i r e c t i o n of compression i s not.contained i n the f o l i a t i o n , and only one set i s developed when the d i r e c t i o n ...of ..com-pression i s at 25° to 45° to the f o l i a t i o n (Paterson and Weiss, 1962, pp. I O 4 . 6 - I O 4 . 7 ) . Ramsay (1962) discussed the form and geometry of conjugate folds and t h e i r r e l a t i o n to stress d i r e c t i o n s , and noted that bedding planes f r e -quently contain the maximum stress d i r e c t i o n (Pmax) where conjugate folds, have been formed i n t h i n l y bedded rocks. Where the maximum (and minimum stress) d i r e c t i o n s are oriented at about 4-5° to bedding planes, then kink, bands or j o i n t drags are produced (Ramsay, 1962, pp.521-522). In the Chilliwack V a l l e y area conjugate folds are rare, but were presumably produced when Pmax was contained i n SQ or S^ (Figure 33A). The angular r e l a t i o n s h i p s of the a x i a l planes of these folds to SQ or S^ are the same or very s i m i l a r to the angular r e l a t i o n s h i p s between S" and S —2 —0 or S-^  i n the "oblique-shear" type f o l d s . I t i s suggested that S^ i s formed when Pmax was nearly but not quite contained within the plane of SQ or S,, thus producing an asymmetrical f o l d , corresponding to one of the folds of a conjugate p a i r (Figure 33B) . Pmax oriented at about 4-5° to the f o l i a t i o n , however, produced S^ i n fine-grained rocks, and kink bands i n coarser and less w e l l - f o l i a t e d rocks oriented at roughly 90° to the f o l i -a t ion (Figure 33C). Thus, the d i f f e r e n t S^ planar structures are believed to have been formed during the same phase of deformation (D ) by stress A FjL 0 v FOR D 2 CONTAINED WITHIN S p OR 5, .may ™r\ i=!Z X T / C O N J U G A T E F O L D B ' A S S U M E I N A L L C A S EL 5 T H A T T H E P O T E N T I A L P L A N E S O F F A I L U R E A R E O R I E N T E D A T 45° T O PmaK ff,qvFOR A T A L O W A N G L E T O 5 0 O R S , .Ruin s! ' O B L I Q U E S H E A R T > P E F O L D C 3>a* F O f ? O R I E N T E D A P P R O X I M A T E " ~ 4-5° F R O M S 0 O R S , F I G U R E 33 : Suggested re la t ionsh ip b e t w e e n D- p l a n a r s t r u c t u r e s -112-f i e l d s oriented d i f f e r e n t l y with respect to the e a r l i e r planar, structures, S 0 o r S r Linear structures Linear structures denoted L^ were produced during and are. the.,, i n t e r s e c t i o n of S^ or with S Q , or the r a r e l y observed c r i n k l i n g of.S^ i n the s l i c e s associated with s t r a i n - s l i p cleavage, S^. L^ i s p a r a l l e l , to the axes of minor folds', denoted F^, formed during (Figure 34A) . Linear structures produced during are of several types. Crinkles or crests of kink bands, p a r a l l e l to the i n t e r s e c t i o n of SJ, with SQ or S-^ , are denoted L^ (Figure 34-B). Both the crests of chevron f o l d s , denoted F^, and the i n t e r s e c t i o n of with S Q or are denoted L^ (Figure 34C.). The crests of conjugate f o l d s are denoted L^. Intersecting sets of L , each set being p a r a l l e l to the f o l d axes of the small paired monoclinic folds and producing a rhombic pattern of kinks on SQ or S^ have been ob-served at a few l o c a l i t i e s (Figure 34-D). Minor f o l d s The following c r i t e r i a d i s t i n g u i s h F^ from -F folds i n the f i e l d . F-^  f o l d s are the r e s u l t of deformation of SQ alone. They are commonly t i g h t with angular to rounded hinges, and, i n rocks of s u i t a b l e composi-t i o n , have an a x i a l plane cleavage S' or S" which i s present throughout 1 <~-the f o l d (e.g. Figures 26, 35, 37). F_2 f o l d s deform S Q and and are e i t h e r conjugate or are of asymmetric "oblique-shear" type. Cleavage, . SJj, where present, i s r e s t r i c t e d to the short limb of these folds (Figures 29B, 31, 32). F. f o l d axi s A x i a l p l ane ( p a r a l l e l to s;,s; B t V L's para l le l V- on ly w h e n i n t e r s e c t i o n of c o n j u g a t e p l a n e s c o n t a i n e d in S 0 or S, F I G U R E 3 4 : Re lat ionship of l i n e a r s t ruc tu re s to m inor s t ruc tu re s other -113-It i s sometimes d i f f i c u l t to r e l a t e f o l d s with the s t y l e .of. those shown i n Figure 36 and 4-0 to e i t h e r or D^, when these f o l d s .are. present i n rocks i n which S^ i s poorly developed, such as the cherts in_Figure../.CL Where such folds cannot be re l a t e d to the complimentary f o l d of,.a_ conjug-ate p a i r and where t h e i r axes are conformable with those of neighbouring F^ f o l d s , they are considered to be F^ f o l d s . S t r u c t u r a l synthesis The map i s divided into eight subareas, from each of which the.orien-t a t i o n of the above s t r u c t u r a l elements i s plotted on a equal-ar.ea-.net... (Plate 3)» Choice of these subareas i s i n part a r b i t r a r y , depending upon outcrop d i s t r i b u t i o n , and i n part based on tectonic u n i t s , p a r t i c u l a r tec-, tonic units being further subdivided perpendicular to the d i r e c t i o n of plunge o Subarea 1 This subarea i s bounded on the west by Cultus Lake V a l l e y , on the north by Chilliwack River, and on the east by the eastern l i m i t of Meso-zoic rocks i n the northern part of Tamihi Creek V a l l e y (Plate 3). The southern l i m i t i s the contact between both Palaeozoic and Mesozoic rocks_ and overlying Permian, volcanic rocks of the Liumchen Nappe. Rocks of t h i s subarea are less metamorphosed than those elsewhere i n the map-area, and the fine-grained c l a s t i c rocks contain fr a c t u r e c l e a -» vage or s t r a i n - s l i p cleavage (S|) rather than the s l a t y cleavage (S") present i n equivalent rocks i n the remainder of the map-area. No cleavage formed during p, has been observed i n coarse sand-sized rocks of the Cultus - 1 H -Formation, i n coarse c l a s t i c rocks of the Chilliwack Group, or. in-Palaeo-zoic limestones and v o l c a n i c rocks of t h i s subarea. Minor folds (denoted F ) i n medium-to-thin-bedded, prfttiominwritly fina c l a s t i c rocks of the Cultus Formation on the east side of the- south....end of Cultus Lake are overturned to the northwest, and have h o r i z o n t a l . ^ o l d -axes trending 050° and a x i a l planes dipping 35° to the southeast. ., These-folds are generally t i g h t , with rounded hinges, and fine-grained, rocks have a well-developed fracture cleavage, S j , approximately parallel...to t h e i r a x i a l planes. Many F^ folds occur i n thin-bedded rocks . of....the..Cultus Formation and thin-to-medium-bedded v o l c a n i c rocks at the stratigraphic. top of the Chilliwack Group i n Liumchen Creek Va l l e y . These f o l d s are t i g h t to nearly i s o c l i n a l (Figure 35), have angular to rounded hinges, and fold-axes of v a r i a b l e o r i e n t a t i o n . Because.fold-hinges are commonly angu-l a r i n t h i n l y bedded rocks and rounded i n more massive rocks,, t h e i r form appears to be l a r g e l y a function of competancy. The folds are overturned i n a northerly or northwesterly d i r e c t i o n , with a x i a l planes dipping gen-e r a l l y southerly at moderate angles but r a r e l y as steeply as 80°. Tight F^ folds present i n rocks of the Cultus Formation on the north sides of Church Mountain (Figures 26, 36), are i n v a r i a b l y overturned to the north., Wo f o l d s have been observed i n coarse c l a s t i c sedimentary rocks of the Chilliwack Group exposed to the west of the summit of Church Mountain.. Permian limestone, forming c l i f f s east of and immediately below the summit.. of Church Mountain, i s deformed into large f o l d s , also overturned to the north. Minor structures produced during are commonly chevron folds or kinks re l a t e d to these, but the planar structure, SJJ, which i s associated Figure 35: Tight to nearly i s o c l i n a l F f o l d , with sputh-. east dipping a x i a l plane, and f o l d axis plunging north-eastward at a low angle, i n fine-grained c l a s t i c rocks of the Cultus Formation, not f a r above the contact with Permian limestone exposed in i n l i e r , east side of Liumchen Creek. Figure 36: Tight (£,?) f o l d , with southeast dipping a x i a l plane and f o l d axis plunging southwest at a low angle, i n thin-bedded c l a s t i c rocks of the Cultus Formation, i n side of logging road, north side of Church Mountain. -115-with chevron folds elsewhere i n the map-area, apparently i s not well-de-veloped i n t h i s subarea. Crenulations or structures r e l a t e d to SJ, and conjugate folds are r e l a t i v e l y rare. A l l of these l a t e r structur.es_.in t h i s subarea are of very i r r e g u l a r form, i n comparison to analogous-struc-tures elsewhere i n the map-area. Ramsay (1962, p.517) has noted that., con-jugate folds are most commonly developed i n t h i n bedded or' closely. .1 ami rated rocks and only r a r e l y i n s t r a t a where the beds exceed 10 cm. i n . thickness... Possibly the more regular form of structures found i n rocks elsawher.e i n the map-area i s the consequence of the s l a t y cleavage (S!^) ..in-these—., rocks being a more perfect f o l i a t i o n than the fracture cleavage (Sj.). char-;., a c t e r i s t i c of rocks of Subarea 1. Stereographic p r o j e c t i o n of the above s t r u c t u r a l elements shows the e f f e c t s of more than one period of deformation, as plots of l i e on a. (poorly defined) great c i r c l e and poles to SQ are scattered (Plate 3)- I f i t can be assumed that p r i o r to D^, SQ was h o r i z o n t a l , D-^  deformation, would. then produce F-^  f o l d s with h o r i z o n t a l f o l d axes. The o r i e n t a t i o n of L^ ., when h o r i z o n t a l , i s 060°, and presumably indicates the trend of F^ f o l d s . p r i o r to deformation. Poles to SQ form a d i f f u s e maximum corresponding to a s t r i k e of 060°, and a dip of 4-0°; possibly t h i s i s some r e f l e c t i o n . of the o r i e n t a t i o n of the average limbs, and thus.the a x i a l plane p r i o r to deformation. During D^ deformation D^ structures were deformed, so. that L-^  l i n e a t i o n s when plotted l i e on a great c i r c l e , and poles to S^ no longer form a regular pattern. The presence of even a d i f f u s e concentra-t i o n of poles to SQ remaining a f t e r t h i s deformation may ind i c a t e a bias i n sampling, and/or that the e f f e c t s of the second period of deformation... were l o c a l i z e d , and the o r i e n t a t i o n of many early structures were l i t t l e -116-a l t e r e d by the l a t e r period of deformation. The i r r e g u l a r d i s t r i b u t i o n on outcrop scale of minor structures produced during ( i n contrast to the ubiquitous fracture or s t r a i n - s l i p cleavage 'formed during D^*in all... f i n e c l a s t i c rocks) gives some basis to the l a t t e r suggestion. Most planar structures formed during which were measured from t h i s subarea are SJJ structures; they are thus of l i t t l e value i n determining the o r i e n t a t i o n of axes of the stress system which produced them (see Figure 33B). How-ever the or i e n t a t i o n of stress axes can be determined from r a r e l y observed conjugate f o l d s . In one conjugate f o l d (Figure 29B), the i n t e r s e c t i o n of the a x i a l planes of the pa i r of asymmetric folds comprising the conjugate f o l d i s approximately h o r i z o n t a l , with an azimuth of 150°. This i n t e r -section i s p a r a l l e l to the intermediate stress axis (Pint) of the stress system producing the f o l d . According to Ramsay (1962, p.520) the correct b i s e c t o r giving Pmax can always be determined from the shape of the f o l d . In the case of the f o l d i n Figure 29B, Pmax i s approximately horizontal.. and has an azimuth of 2^0° (60°). The possible o r i e n t a t i o n of F^ f o l d axes p r i o r to deformation was' 060° and h o r i z o n t a l ; t h i s corresponds to Pint fo r D . Thus Pmax f o r D 0 appears to coincide with the possible o r i e n t a t i o n 4- I <~ of Pint f o r D^. In summary, minor folds formed during p o s s i b l y had ho r i z o n t a l f o l d axes, trending about 060°, and a x i a l planes dipping 4.0° to. . the southeast. These folds were deformed during D^. The o r i e n t a t i o n ..of Pmax during was p a r a l l e l to the possible p o s i t i o n of undeformed F^ fold.- . axes, or Pmax during was p a r a l l e l to Pint for D^. Further mapping of l i t h o l o g i c a l units i s necessary before the major structure of Subarea 1 i s known. Permian'volcanic rocks i n the bottom of Liumchen Creek V a l l e y are i h t e r f o l d e d with Mesozoic rocks. The contact -117-i s probably s t r a t i g r a p h i c ; rocks are conformable on both sides of .it—a'nd f o s s i l s of• Upper Karnian age, the oldest known Mesozoic fossils,. 1 n the . map-area, are found close to the contact. Palaeozoic rocks capping,....,. Church Mountain are inverted. The s t r u c t u r a l succession, from, the tap down, consists of the upper c l a s t i c sequence, exposed west of. the peak, Permian limestone t r a n s i t i o n a l downward to Permian volcanic rocks, exposed, below the east.side of the peak, and f i n a l l y , Mesozoic rocks. North of the peak of Church Mountain, Permian rocks are i n t e r f o l d e d with M e s o z o i c — rocks, with a s t r a t i g r a p h i c contact between them. This i n t e r f o l d i n g .of... Mesozoic and Permian rocks and the overturned sequence on Church Mountain suggests that overturned f o l d i n g rather than thrusting i s responsible for, the presence of Palaeozoic rocks on top of Mesozoic rocks. Possibly the Palaeozoic rocks on Church Mountain form the inverted limb of a large r e -cumbent a n t i c l i n e , with a southerly (?) dipping a x i a l plane. The str u c -t u r a l r e l a t i o n s h i p "between the inverted Palaeozoic sequence capping Church. Mountain and the rocks i n Liumchen Creek i s not known. As Pennsylvanian. ... limestone i s present i n Liumchen Creek, not f a r north of the International Boundary and also 3,000 feet higher, roughly along s t r i k e , southwest of the summit of Church Mounta i n , the r e l a t i o n s h i p between the two may be. complex. In degree of metamorphism (including development of frac t u r e cleavage) no detectable difference e x i s t s between rocks i n Liumchen Creek and those on Church Mountain. This uniformity i s i n contrast to the higher-degree of metamorphism (including development of s l a t y cleavage) i n a l l , . . .. s t r u c t u r a l l y higher, rocks i n the map-area, and suggests that rocks of Subarea 1 should be considered as a sing l e u n i t . Rocks i n Subarea 1 are considered to be autochthonous. There i s no -118-evidence that rocks i n the western part of t h i s subarea have undergone, any considerable l a t e r a l t r a n s l a t i o n . The a x i a l planes of F^ folds~.near Cultus Lake and i n Liumchen Creek dip at moderate ( r a r e l y steep) angles.to.the., southeast. I f the a t t i t u d e of these overturned minor folds r e f l e e t s - t h a t a t t i t u d e of large-scale structures, as i n the overlying McGuire. Nappe^- . where the minor recumbent folds r e f l e c t the a t t i t u d e of the majox..stmc_=_.. ture, then i t i s u n l i k e l y that these rocks have been displaced ..lateral l y . to any great extent. However^Palaeozoic rocks o v e r l i e Mesozoic racks in „. the eastern part of the map-area. As a l l rocks i n Subarea 1 have undergnne. the same amount of metamorphism, and as there i s evidence of f o l d i n g o,f. the rocks on Church Mountain rather than overthrusting^the Palaeozoic/rocks are possibly parautochthonous. The hypothetical r e l a t i o n s h i p of rocks i n t h i s subarea to each other and to other rocks i n the map-area i s i n d i -cated i n Figure 4- and Plate 2, section 8 - 8 . Subarea 2 Subarea 2 l i e s south of Chilliwack River and east of Borden Creek. . It i s bounded on the west by Mesozoic rocks of Subarea 1, and includes volcanic rocks l y i n g west of Tamihi Creek and south of Subarea 1. Its . . southern boundary i s the l i m i t of mapping. This subarea i s composed mainly of v o l c a n i c rocks and limestones .of .. . Permian' age, and also includes older c l a s t i c rocks and Pennsylvanian lime-stone^. Massive Permian volcanic rocks are exposed on the west and north- .  west slopes of Mount McGuire and o v e r l i e rocks of Subarea 1. S t r u c t u r a l l y overlying the volcanic rocks and forming the peak of the mountain i s Per-mian limestone, which i s p a r t l y s t r a t i g r a p h i c a l l y equivalent to the under- , -119-l y i n g rocks. Minor v o l c a n i c rocks, s t r a t i g r a p h i c a l l y above the Permian limestone, are exposed on the north side of the peak. The upper..clastic-sequence, Pennsylvanian limestone and the lower c l a s t i c sequence, a l l . . s t r a t - . i g r a p h i c a l l y below the Permian limestone, crop-out southeast of the peak. Minor structures produced during are common i n sedimentary rocks of t h i s subarea. Large, recumbent, n e a r - i s o c l i n a l f o l d s , overturned to the northwest, with northeast trending axes, are v i s i b l e i n Permian limestone c l i f f s northeast of the peak of Mount McGuire (Figures 37, 38)... Tuffs, thin-bedded cherts and a r g i l l i t e s of the volcanic sequence strat.-. i g r a p h i c a l l y overlying the Permian limestone, are infolded into the lime- . stone west of the peak, and form angular, t i g h t , recumbent, "zig-zag" F^ f o l d s , of a smaller scale than the F^ fo l d s i n the limestone. Few F^ folds have been recognized, however, i n the extensive area of limestone., outcrops east of the peak of Mount McGuire because such f o l d s i n massive limestone are too large to be v i s i b l e i n most outcrops. No F^ folds have .. . been seen i n massive volcanic rocks possibly because SQ planes are d i f f i - . . c u l t to recognize i n these rocks,and no S^ planes have been seen i n these rocks. The massive v o l c a n i c rocks nonetheless are l o c a l l y h i g h l y faulted, and contain shear zones which i n a few cases are p a r a l l e l to t u f f horizons., i n the predominant flow rocks. C l a s t i c rocks, southeast of the peak of Mount McGuire show a crude S | f o l i a t i o n but folds are not common i n these, rocks. Repeated inversion of graded bedding i n graded rocks of the lower c l a s t i c sequence s t r a t i g r a p h i c a l l y below Pennsylvanian limestone, south- •  east of Mount McGuire peak, i s due to small-scale F^ f o l d i n g . Minor structures formed during are not common i n rocks of t h i s subarea, possibly because of the massive nature of most rocks i n the Figure 37: Recumbent F^ f o l d , overturned to the northwest, i n c l i f f s of Permian limestone on the north side of the north ridge of Mount McGuire. Axis of f o l d i s nearly-p a r a l l e l to c l i f f - f a c e . Figure 38: Recumbent F f o l d , overturned to the northwest, i n c l i f f s of Permian limestone i n cirque north of peak of Mount McGuire. Arrow points to f o l d ; dashed l i n e indicates contact between limestone and s t r a t i g r a p h i c a l l y higher, s t r u c t u r a l l y lower, t u f f s and cherts of the Permian volcanic sequence. -120- . . subarea. Crinkles occur i n some (rare) f o l i a t e d volcanic rocks_in Tamihi Creek, and rare F "chevron 1 1 folds i n fine-grained c l a s t i c rocks..sporth.-2 east of the summit of Mount McGuire. Steep, closely-spaced, l o c a l point-ing i n Permian limestone i s approximately p a r a l l e l to S^ planes i n .fine c l a s t i c rocks of the subarea east of Subarea 2. Information recorded of a l l s t r u c t u r a l elements, except. SQ, is. sparse. . from t h i s subarea. The few recorded l i n e a t i o n s trend O4.O0, and have.. shallow plunges to the northeast or are h o r i z o n t a l . Poles to S l i e on ^ B ~0 a great c i r c l e , whose pole corresponds approximately to the o r i e n t a t i o n of L l i n e a t i o n s . Too few D s t r u c t u r a l elements have been recorded to. • "1 "2 be of any value. Two explanations f o r the structure of Subarea 2. are considered below. The f i r s t i s that the structure consists of two nappes, major tectonic units separated from each other and from underlying rockjs.by thrust (?) f a u l t s . The lower t e c t o n i c unit i s a thrust sheet and i s c a l l e d the Lium-chen Nappe. The upper u n i t i s characterized by a recumbent anticline,, with-, a t h i n , p a r t l y preserved lower limb cut out by a thrust or lag f a u l t , and i s designated the McGuire Nappe. The second explanation i s that the structure consists of a single recumbent f o l d , with the lower limb being the Liumchen Nappe proposed above. Rocks forming the proposed Liumchen Nappe i n t h i s subarea underlie, the lower parts of the west and northwest sides of Mount McGuire and ex-, tend westwards across Tamihi Creek to Liumchen Mountain. The nappe i n t h i s subarea i s composed of massive Permian volcanic rocks, mainly flows. Evidence that the basal contact of t h i s nappe i s a low-angle thrust f a u l t i s provided by the map-pattern. A continuous body of Permian volcanic -121-rocks extends from about 9 miles southwest of the map-area (Moen, 1962,. Plate l ) and crosses the International Boundary at the south end. of Inter-nation a l Ridge, where i t l i e s on Mesozoic rocks. East of t h i s locality,.. the v o l c a n i c rocks continue p a r a l l e l to, and j u s t south of the .Boundary, s t i l l l y i n g on Mesozoic rocks (Daly, 1912, Map 89A) and recross_.the..Boun-dary again, to form the summit of Liumchen Mountain, north of. which-.they, l i e on Palaeozoic rocks. The volcanic rocks of Liumchen Mountain extend to the east across Tamihi Creek and are exposed on Mount McGuire, where they again o v e r l i e Mesozoic rocks. Overthrusting would account f o r the overstepping of t h i s Permian volcanic u n i t from Mesozoic v o l c a n i c rocks... . i n the west, on to Palaeozoic rocks north of Liumchen Mountain, and back on to Mesozoic rocks on Mount McGuire, and seemingly provides the basis' f o r Daly's (1912, Map 89A) and Moen's (1962, p.61, and map) interpreta-. t i o n of the lower contact of t h i s body of Permian volcanic rocks as a thrust. Supporting evidence f o r overthrusting i s provided by the d i f f e r -ing nature of S^ planar structures i n c e r t a i n rocks, apparently o r i g i n a l l y , of the same composition, below and above t h i s f a u l t . S l a t y cleavage .is... developed i n a l l fine-grained c l a s t i c rocks and a f o l i a t i o n i n coarser c l a s t i c rocks above t h i s overthrust, whereas below the overthrust, s t r a i n -s l i p cleavage or f r a c t u r e cleavage i s present i n fine-grained c l a s t i c . rocks, with no corresponding cleavage i n coarser rocks. De S i t t e r (1956, p.98) concluded that fracture cleavage could develop into s l a t y cleavage. The apparent lack of any t r a n s i t i o n between the two i n the map-area, is. a d d i t i o n a l support f o r a s t r u c t u r a l d i s c o n t i n u i t y . The upper contact of t h i s t e c t o n i c unit w i l l be discussed i n the following d e s c r i p t i o n of the McGuire Nappe. -122-Rocks forming the McGuire Nappe i n t h i s subarea underlie the summit of Mount McGuire and extend eastwards as f a r as the limb of the..subarea-The nappe i s composed of Permian limestone, o v e r l a i n stratigraphinally.... by minor Permian v o l c a n i c rocks and underlain by c l a s t i c rocks and-.Penn-r. sylvanian limestone. Permian limestone forming the peak of Mount..McGuire outlines a large recumbent a n t i c l i n e , overturned to the northwest.,, whosa. lower limb i s p a r t l y missing (Plate 1, Plate 2, section 6 - 6 ' ) . The axis . of t h i s major structure trends 04.0° and plunges northeast at about 5°, and the a x i a l plane dips generally eastward at shallow angles. The conformity, of the geometry of f o l d s i n c l i f f s north of the summit of Mount McGuire (Figure 38) with that of the major structure demonstrates that the major . structure was formed during the same period of deformation, D^, as the minor f o l d s . Permian limestone at the peak of Mount McGuire i s the hinge... of t h i s major recumbent a n t i c l i n e and forms d i g i t a t i o n s , which north of the peak enfold younger t u f f s and a r g i l l i t e s of the Liumchen Mountain For-mation. Limestone o u t l i n i n g the upper limb of the major f o l d forms a prom-.. inent ridge east of the peak of Mount McGuire; t h i s upper limb may extend at l e a s t 4-jjr miles to the southeast as Misch ( o r a l communication, February.,.. 1965) has mapped limestone o v e r l a i n by v o l c a n i c rocks on Border Peak. The lower limb of t h i s major recumbent f o l d i s t h i n and represented only by Permian limestone forming a low east-west ridge southeast of the peak.of Mount McGuire and scattered limestone pods, further south, which l i e on Permian volcanic rocks of the underlying Liumchen Nappe. C l a s t i c rocks, s t r a t i g r a p h i c a l l y below the Permian limestone, together with Pennsylvanian. limestone form the core of t h i s recumbent a n t i c l i n e and crop-out southeast, of the peak of Mount McGuire. Rocks of the upper c l a s t i c sequence are i n -123-contact with Permian limestone and extend s t r a t i g r a p h i c a l l y down...to Penn-sylvanian limestone exposed near Spencer Peak, below which are rocks ..of the lower c l a s t i c sequence. This l a t t e r sequence contains the oldest. rocks of reasonably c e r t a i n age i n the map-area; these l i e d i r e c t l y , on. Permian volcanic rocks of the Liumchen Nappe (Plate 2, section 6-6'). The f a c t that no rock sequences i n the core of the McGuire Nappe are.inverted and that the oldest rocks i n the nappe l i e d i r e c t l y on Permian volcanic., rocks, i s evidence f o r the existence of a f l a t - l y i n g f a u l t between the. McGuire Nappe and the underlying Liumchen Nappe. The a l t e r n a t i v e explanation f o r the structure of t h i s subarea, which i s . e q u a l l y compatible with the evidence from minor structures, i s that rocks of t h i s subarea are part of one t e c t o n i c u n i t , a large recumbent a n t i c l i n e overturned to the northwest, instead of the two t e c t o n i c u n i t s postulated above. The lower limb of the si n g l e tectonic unit i s composed of the Permian volcanic sequence, and the hinge and upper limb consists p a r t l y of Permian limestone and minor v o l c a n i c rocks, together with Meso-zoic rocks which s t r a t i g r a p h i c a l l y and s t r u c t u r a l l y o v e r l i e Permian rocks, east of t h i s subarea. Older rocks l i e i n the core of t h i s recumbent fold.. As the Permian volcanic sequence i s at l e a s t p a r t l y s t r a t i g r a p h i c a l l y equivalent to the Permian limestone, a rapid f a c i e s change must take place across the hinge of t h i s postulated major f o l d , from a sequence composed of Permian volcanic rocks to a predominantly sedimentary sequence. How^ -ever, i f these rocks do form a large recumbent f o l d , i t i s d i f f i c u l t t ± f not impossible jto give any s t r u c t u r a l l y consistent explanation f o r the absence of an inverted sequence of Pennsylvanian to Permian c l a s t i c rocks.,., with interbedded Pennsylvanian limestone, i n the core of the f o l d , as the -124-oldest known rocks i n t h i s tectonic u n i t are c l a s t i c rocks, s t r a t i g r a p h -i c a l l y and s t r u c t u r a l l y below Pennsylvanian limestone, which lie..on..Permian v o l c a n i c rocks of the postulated lower limb. No evidence f o r or...against inversion of the volcanic sequence i n the lower limb has been obtained... from t h i s subarea, and good evidence e x i s t s that the p o s i t i o n .of. the..,... v o l c a n i c sequence above rocks of Subarea 1 i s due to overthrusting, ..rather than overturned f o l d i n g . However, the hinge of t h i s postulated major.re.-cumbent f o l d as marked by Permian .limestone on Mount McGuire, i s at...least.. 5 miles southeast, i n a d i r e c t i o n normal to the trend, and contained ..within. . the a x i a l plane, of any possible hinge marked by the contact between the Permian volcanic rocks and s t r a t i g r a p h i c a l l y overlying Mesozoic rocks. Maximum thickness of the Permian volcanic rocks immediately below Permian... limestone marking the hinge i s 2,000 feet . I f i t i s assumed that no t h i c k -ening occurs at the hinge of the major recumbent f o l d , then the contact... between Mesozoic rocks and Permian v o l c a n i c rocks on the hinge would only be 2,000 feet northwest of the hinge as marked by Permian limestone. The ac t u a l distance to any possible hinge i s ten times t h i s , which strongly... suggests that there i s a s t r u c t u r a l d i s c o n t i n u i t y between the lower, v o l -canic sequence and the upper, predominantly sedimentary sequence (Figure 39). However, there are c e r t a i n objections to the s t r u c t u r a l interpretation, proposed by the w r i t e r that there are two separate t e c t o n i c u n i t s , each underlain by a f l a t - l y i n g f a u l t . North of t h i s subarea, north of the Chilliwack River, Mesozoic rocks s t r a t i g r a p h i c a l l y and s t r u c t u r a l l y over-l i e Permian volcanic rocks which are the northerly continuation of the Liumchen Nappe i n Subarea 2. Therefore, i f the McGuire Nappe had been thrust over the Liumchen Nappe, as suggested by i t s geometry, Mesozoic FIGURE 3 9 : C o m p a r i s o n of h y p o t h e t i c a l a n d actua l fo rms of postu lated recumbent f o l d f o r m i n g McGuire Nappe -125-rocks should separate the two tectonic units i n Subarea 2, which-...is-.not the case. A possible explanation f o r t h i s apparent anomaly is. tha.t_.the f l a t - l y i n g f a u l t separating the two t e c t o n i c units i s a lag or. lagj-fault rather than a thrust. A lag, as o r i g i n a l l y defined by Bailey (193-n P./+67.) i s a f a u l t formed i n close causal connection with f o l d i n g , which... replaces the normal.(upper) limb of a recumbent structure. A l a g — f a u l t ( H i l l s , . 1963, p.191) i s a low angle f a u l t with normal f a u l t displacement, which . originates from the upward movement of the footwall block i n a general region of t h r u s t i n g . In t h i s case, the hanging wall i s the McGuire Nappe which has lagged behind the movement of the footwall, or Liumchen Nappe. (A lag, as used i n Bailey's sense, cannot be proven i n t h i s example.) The geometry of the overlying f i r s t order nappe i s apparently anomalous, but may be a r e l i c t of i t s i n i t i a l form (see below). This lagging behind of the McGuire Nappe, i n the general forward movement could account for the absence of Mesozoic rocks between the two tectonic u n i t s , and i s compatible, with the presence of Permian volcanic rocks of the Liumchen Nappe at least..... 6 miles northwest of the hinge of the McGuire Nappe. Subarea 3 This subarea i s bounded on the west by a north-south l i n e along Borden Creek, on the north by the Chilliwack River and on the least by Slesse Creek. The southern l i m i t i s the l i m i t of g e o l o g i c a l mapping in. t h i s d i r e c t i o n (Plate 3). Most rocks i n t h i s subarea are s t r a t i g r a p h i c a l l y below the Permian limestone, with the exception of Permian limestone and minor volcanic rocks which crop-out i n the north of the subarea, Permian limestone i n -126-th e centre, and Permian volcanic rocks i n the bottom of Slesse. .Creek. . V a l l e y , Minor folds formed during are v i s i b l e i n the limestone,, bluff..at the confluence of Slesse Creek with Chilliwack River, and i n f i n e c l a s t i c rocks on the west side of Slesse Creek V a l l e y about 3 miles south of-...the above l o c a l i t y . S l a t y cleavage S^ i s developed i n the f i n e c l a s t i c -recks but as. t h i s cleavage i s su b - p a r a l l e l to bedding i n t h i s subarea, ,it.,is_.. d i f f i c u l t to d i s t i n g u i s h the two. Coarse c l a s t i c rocks, particularly.. those which are tuffaceous, show a crude f o l i a t i o n , p a r a l l e l to S!^  in., f i n e r , contiguous rocks. Structures formed during are very well developed i n t h i s subarea, possibly because of the predominance of w e l l - f o l i a t e d f i n e c l a s t i c rocks. Crinkles and associated planar structures (S^), "oblique shear" type f o l d associated with S^, and folds probably r e l a t e d to "oblique shear" type folds with no development of SJJ (Figure 32), are common, p a r t i c u l a r l y i n the v i c i n i t y of Pennsylvanian limestone on the west side of Slesse Creek V a l l e y . L o c a l l y t h i s limestone, which i s shaly, shows c l o s e l y spaced fractures p a r a l l e l to S^. Proj e c t i o n of the above information shows the e f f e c t s of two periods of deformation. Most poles to S^ are concentrated i n a s i m i l a r area to those i n the plot of Subarea 2, but an a d d i t i o n a l weak maximum i s devel-oped i n the northeast quadrangle. Orientation of the few L^ l i n e a t i o n s i s v a r i a b l e , but they are confined to the northeast-southwest quadrangles and vary i n plunge from h o r i z o n t a l to 4-5°. Structures r e l a t e d to provide more information. According to Ramsay (1962, p.521) structures s i m i l a r to kink bands are produced when -127-Pmax and Pmin are oriented at about 45° to bedding planes (or. f o l i a t i o n ) ' and of the two shears produced one w i l l cut the bedding planes ..at .a,high angle, and the other may l i e so close to bedding that shear movements are diss i p a t e d by s l i p on bedding surfaces. Where i s present, ..assiiciated with c r i n k l e s or kink bands, and oriented at about 90° to (or...S^.), . then i f i t can be assumed that the other conjugate shear i s nearly....para-l l e l to SQ (or S^), i n t e r s e c t i o n of S' with SQ (or S^) w i l l give a.rough approximation of the o r i e n t a t i o n of Pint (Figure 33C). Direction, o f , d i s -placement along S^ w i l l indicate which b i s e c t o r of the angle between Sj (and S^) and S^ contains Pmax. The average Pint determined from the i n t e r -section of SQ (S^ i s e f f e c t i v e l y p a r a l l e l to S^) with S^ i s oriented at about 170° and plunges at 10° to the south, Pmax plunges 25° i n a d i r e c t i o n 075°, and Pmin plunges at 65° i n a d i r e c t i o n 260°. The development of a west dipping limb, (Plate 3) i s presumably due to the imposition during . I)^ of the above stress f i e l d on previously folded rocks. Most rocks i n t h i s subarea l i e i n the core of the McGuire Nappe. The. limestone b l u f f at the confluence of Slesse Creek with Chilliwack River i s the hinge of a syncline overturned to the west-northwest, which l i e s be-tween d i g i t a t i o n s of Permian limestone on the nose of the McGuire Nappe. The general northeasterly trend and plunge of these d i g i t a t i o n s from..the peak of Mount McGuire to t h i s limestone b l u f f i s r e a d i l y apparent from the s p a t i a l d i s t r i b u t i o n of Permian limestone, forming c l i f f s , on the north side of Mount McGuire. Permian limestone i n the cent r a l part of the sub-area, north of Spencer Peak,' and possibly limestone o v e r l a i n by volcanic rocks on Canadian Border Peak south of the subarea (P. Misch, o r a l commun-. i c a t i o n , February, 1965), are part of the upper limb of t h i s nappe. -128-Strongly f o l i a t e d , amphibolitic rocks cut by S planes crop-out.in the 2 west side of the Slesse Creek Valley, about 2 miles south of.this..subarea. Their p o s i t i o n r e l a t i v e to the d i s t r i b u t i o n of dated rock units..as-pres-ently known, suggests they l i e i n the core of the McGuire Nappe-. ...Further mapping i n the southern end of the Slesse Creek Va l l e y and on... Border. Peak i s necessary before t h i s i s confirmed. Volcanic rocks, l a r g e l y lavas, are exposed i n the bottom of. the north end of the Slesse Creek V a l l e y . These v o l c a n i c rocks l i e be low ...fina c l a s -t i c rocks which are s t r a t i g r a p h i c a l l y below Pennsylvanian limestone exposed on both sides of Slesse Creek V a l l e y . The composition, degree..of. a l t e r -a t i on, and s t r u c t u r a l p o s i t i o n of these v o l c a n i c rocks i s i d e n t i c a l to "that volcanic rocks of the Liumchen Nappe which s t r u c t u r a l l y underlie f i n e c l a s T -t i c rocks s t r a t i g r a p h i c a l l y below Pennsylvanian limestone to the south of. the peak of Mount McGuire. The volcanic rocks exposed at the northern end of Slesse Creek; V a l l e y are therefore believed to belong to the Liumchen Nappe, and are exposed i n a window or fenster i n the McGuire Nappe (Plate" 1., Plate 2, section 4--V). As the dip of the rocks immediately west of. t h i s window i s predominantly to the west, the present exposure of these lavas i s believed to be p a r t l y due to t h e i r p o s i t i o n i n the core of an antif.orm. rel a t e d to the second period of deformation, which trends roughly p a r a l l e l . , to Slesse.Creek (Plate 2, section D-D'). Apart from t h i s antiform, the present s p a t i a l d i s t r i b u t i o n of these rocks i n t h i s subarea i s governed l a r g e l y by structures formed during, the f i r s t period of deformation and the present topography. -129-Subarea 4 Subarea 4 i s bounded on the west by Slesse Creek, on the .north by Chilliwack River and to the east and south by the l i m i t of mapping-(Plate 3 ) . The steep sides of Chilliwack V a l l e y and the Slesse CreeJc„Va11 ey-, r e s p e c t i v e l y on the north and west of t h i s subarea, are underlain, by...Pal-aeozoic rocks, and the t i p s of the ridges by Mesozoic rocks (Figure. 4-0). S l a t y cleavage (S^) i s ubiquitous i n fine-grained c l a s t i c rocks and. i s p a r a l l e l to the f o l i a t i o n of coarser c l a s t i c rocks; both generally nearly p a r a l l e l to bedding (S^). C r i n k l i n g and associated S^ cleavage and kink bands are l o c a l l y common. Stereographic p r o j e c t i o n shows that most poles to S^ form a single . maximum, corresponding to bedding o r i e n t a t i o n of s t r i k e 155° and dip 25° to the southwest. A second, weak maximum, located i n the northeast quad-rangle, corresponds i n r e l a t i v e p o s i t i o n to a weak maximum developed i n a s i m i l a r p o s i t i o n i n the projection from Subarea 3- Plots of are located i n the northeast quadrant, and the majority trend about 060° and plunge about 4.0°. ' Stress axes f o r D ^ , as approximately determined from the i n t e r s e c t i o n of SQ (and S'j) with SJ, are, Pmax trending 150° and h o r i z o n t a l , Pmin t r e n d -ing 140° and plunging at 7 0 ° and Pint at 320° and plunging 20° . The pos-. i t i o n of Pint indicates that the presence of two maxima of poles to S^ i n the northeast, and southwest quadrants i s due to D . Rocks i n Subarea 4 l a r g e l y belong to the McGuire Nappe; exceptions, are volcanic rocks of the underlying Liumchen Nappe which are exposed i n Figure 4-0: View of east side, north end, Slesse Creek V a l l e y with Chilliwack V a l l e y to l e f t ; most of these rocks are part of the McGuire Nappe; exceptions are, rocks below the dashed l i n e A, which are Permian volcanic rocks of the Liumchen Nappe exposed i n a window, and rocks above the dashed l i n e B, which are amphibolitic rocks on Mount Pi e r c e . Contact between Mesozoic and underlying Palaeozoic rocks i n the McGuire Nappe i s indi c a t e d by the dotted l i n e ; with f a i r l y continuous c l i f f s of Permian limestone exposed not f a r below the contact. -130-a window at the bottom of Slesse Creek and amphibolitic rocks..structurally overlying Mesozoic rocks of the McGuire Nappe on Pierce Mountain. (Figure 4.0). Thickness of Palaeozoic rocks forming the McGuire Nappe .,is about 2,000 feet; thickness of Mesozoic rocks i n the McGuire Nappe is..about. 3,000 feet between the top of the Palaeozoic rocks, and the overlying am-p h i b o l i t i c rocks. The contact between Palaeozoic and Mesozoic rocks i s higher on,the. east side of Pierce Creek than the west side. As no l o c a l marked.change of o r i e n t a t i o n of structures has been found along t h i s creek,,.this d i f -ference i n elevation i s believed to be due to high-angle reverse, f a u l t i n g which occurred during (Plate 2, Section D-D'). Subarea 5 Subarea 5 i s bounded on the west by a l i n e southward from the summit of Mount Thurston, on the south by Chilliwack River, on the east by .Chip-munk Creek and to the north by the Mount Thurston-Mount Mercer ridge. , Palaeozoic rocks occupy'the southern slopes, and Mesozoic rocks.the upper parts of Mounts Mercer and Thurston. Folds developed during D^ are r e a d i l y recognized i n many rocks i n , t h i s subarea. On the southeast side of Mount Thurston, v o l c a n i c rocks and cherts are i n t e r f o l d e d with Permian limestone. The t h i n bedded cherts are l o c a l l y deformed i n t i g h t , overturned, zig-zag, folds with.planar limbs and sharp, angular hinges (Figure 4-1), which are "in marked contrast to the f a r l e s s regular deformation present i n contiguous limestones. As the cherts overlay the limestone p r i o r to deformation, and so presumably had the same i n i t i a l o r i e n t a t i o n , and as both have been subjected to the same Figure Ul: Minor F^ f o l d on southeast side of Mount Thurston, i n thin-bedded s i l i c i f i e d t u f f and chert. -131-metamorphic conditions, the d i f f e r i n g s t y l e s of deformation are .seemingly due to the d i f f e r i n g competancies of the cherts and limestones-. . Else.-where, n e a r - i s o c l i n a l recumbent f o l d s , commonly of small s i z e , ..occur, i n cherts and a r g i l l i t e s ; a s l a t y cleavage (S^) i s present i n f i n a c l a s t i c rocks; t h i s i s p a r a l l e l to the penetrative f o l i a t i o n i n contiguous coarse c l a s t i c rocks shown i n Figure 28. Structures produced during are w e l l developed i n the c l a s t i c rocks. Gradations e x i s t from c r i n k l e s associated with S^ planes i n fine.-grained c l a s t i c rocks, to kink bands i n the coarse c l a s t i c rocks. Planes .which contain kink bands are roughly p a r a l l e l to S' planes i n associated fin e 2 c l a s t i c rocks. Chevron folds are present but do not appear to be as com-mon as other structures produced during D . Projection of poles to S^ shows a sca t t e r . A maximum i s developed corresponding to bedding with a s t r i k e of 120° and dip of 25° to the north-east. Plots of'L are present i n both northeast and southwest quadrants 1 and trend about 060°. Poles to S^ are scattered, but are i n the v i c i n i t y of the maximum of poles to S . Stress axes, approximately determined from the i n t e r s e c t i o n of S (and the p a r a l l e l Sip with SJJ give the trend and plunge of Pmax as 225° at 15°, of Pmin as 010° and 70°, and Pint as 130° and 15°. I f i t i s as-sumed that p r i o r to D^, was h o r i z o n t a l , then the p o s i t i o n of Pint f o r D r e l a t i v e to that of L and poles to S on the projection, suggests .that the p o s i t i o n of and poles to S^ r e s u l t from r o t a t i o n of these s t r u c -tures about Pint for D . _ 2 Rocks i n Subarea 5 are part of the McGuire Nappe. Permian limestone on the southeast side of Mount Thurston and northwest of the junction of -132-Slesse Creek with Chilliwack River i s deformed into a large recumbent a n t i -c l i n e with tuffaceous c l a s t i c rocks i n the core. This fold,.farmed during D_^ , has a northeast trending axis, and i s the northeasterly continuation of the recumbent, a n t i c l i n e outlined by Permian limestone on Mount... McGuire. D i g i t a t i o n s outlined by Permian limestone on the hinge of this...fold, on. Mount Thurston i n t e r f i n g e r with s t r a t i g r a p h i c a l l y overlying cherts, .crystal t u f f s and minor a r g i l l i t e , and the limestone i t s e l f i s both o v e r l a i n .and underlain by lavas and c r y s t a l t u f f s . . . . A second recumbent f o l d , again delineated by Permian limestone, ..is v i s i b l e on the south side of Mount Mercer, about 2 miles east of the. f o l d on Mount Thurston and appears to be an a d d i t i o n a l recumbent structure developed during which,structurally o v e r l i e s that f o l d on the south-east side of Mount Thurston. Mesozoic rocks, present to the south of! the saddle between Mounts Mercer and Thurston thus seem to l i e i n a recumbent syncline between the two recumbent a n t i c l i n e s formed of Permian rocks. However, f i e l d r e l a t i o n s between rock units on the south side of Mount Mercer and the present s p a t i a l d i s t r i b u t i o n of rock u n i t s along the. trend of these f o l d s , on Mount McGuire to the southwest, and Chipmunk Creek, to the northwest make t h i s explanation improbable. The second recumbent fold, on Mount Mercer i s believed to be the northeastward extension of the fold, on Mount Thurston, elevated to i t s present p o s i t i o n during and thus simulating a second higher recumbent structure formed during which ap-pears to s t r u c t u r a l l y o v e r l i e the northeast projection, along plunge, of the f o l d on Mount Thurston (Figure 1+2, Plate 2, Sections 3-3', C - C ) . The nature of t h i s displacement i s not c e r t a i n but i s believed to be due to f a u l t i n g during D . No predominant dip of bedding i n a westward d i r e c t i o n O r i g i n a l f o r m FIGURE 42: Relation between recumbent anticlines on Mounts Mercer and Thurston -133-has been seen on the southwest side of Mount Mercer, which would... be. ex-pected i f f o l d i n g was the mechanism. In addition, Mesozoic rocks...which l i e i n the apparent recumbent syncline noted above, structurally, and.strat-i g r a p h i c a l l y o v e r l i e Permian volcanic rocks on Mount Thurston and., are. i n contact with both Permian volcanic rocks and the s t r a t i g r a p h i c a l l y . lower Permian limestone on Mount Mercer. The l a t t e r contact can only. ..he. ex-r plained by a f a u l t between Mesozoic and Palaeozoic rocks. De S i t t e r . (1956, p.223) has discussed the as s o c i a t i o n of chevron-folding ..with .thrus.tr- . ing. In the map-area "chevron" or "oblique shear" type folds, are one. .man?:, i f e s t a t i o n of D , and as the s p a t i a l d i s t r i b u t i o n of rocks associated.with the probable f a u l t suggests that i t i s a high-angle thrust with an eastr. ward-dipping f a u l t plane which s t r i k e s i n a s i m i l a r d i r e c t i o n as Pint f o r D , t h i s f a u l t i n g i s believed to have taken place during D . The contin-uation of t h i s f a u l t to the south may be responsible f o r the elevation of Palaeozoic rocks on the east side of Pierce Creek above those on the west described under Subarea Subarea 6 , Subarea 6 i s the western part of Mount Thurston and E l k Mountain. Its eastern l i m i t i s a l i n e south from the summit of Mount Thurston, and i t i s l i m i t e d to the northeast and southwest by d r i f t covered areas. Permian volcanic rocks, mainly t u f f s with minor flows and i n t e r c a l -ated limestones outcrop on the lower, southwestern slopes of Mount Thurs-ton and Elk Mountain and are ov e r l a i n by predominantly fine-grained c l a s -t i c rocks of Mesozoic age. S l a t y cleavage (S"), generally p a r a l l e l to bedding, i s developed i n -134-the f i n e c l a s t i c rocks of Mesozoic age on Mount Thurston and Elk, Mountain, and coarser c l a s t i c rocks i n t h i s sequence are f o l i a t e d . Minor F folds have not been recognized i n the volcanic rocks of t h i s subarea.,.. but are present i n overlying f i n e c l a s t i c rocks near the summit of Elk..Mountain. Crinkles and chevron folds' produced during are present but are .not-common. The s t r u c t u r a l data which has been obtained i s mainly.£r,om...a few widely scattered outcrops of Mesozoic rocks, a n d . l i t t l e data has been obtained from the predominant, commonly massive, Permian volcanic rocks. . The pro j e c t i o n of poles to shows a spread, i n which bedding correspond-ing to the p r i n c i p a l maximum, s t r i k e s due north and dips 15° east. Re-corded L l i n e a t i o n s s t r i k e almost due east or northeast. Small conjugate 1 J folds (Figure 29C) l o c a l l y developed on the limbs of minor, upright F^ folds (Figure 43) have an intermediate stress axis which trends 102° and plunges 5°> almost p a r a l l e l to the axis of the e a r l i e r f o l d s . These con-jugate folds presumably r e s u l t from the tightening of the e a r l i e r F^ ..folds along the same axis, under metamorphic conditions of lower grade than.those at which the o r i g i n a l f o l d i n g took place. Rocks of t h i s subarea are believed to be part of the Liumchen Nappe. In both l i t h o l o g y and age the volcanic sequence, representing the Palaeo-zoic i n t h i s subarea, i s f a r closer l i t h o l o g i c a l l y to the t h i c k Permian volcanic sequence.of the Liumchen Nappe than to the Pennsylvanian-Permian, limestone, c l a s t i c rock and volcanic rock sequence of ei t h e r the overlying McGuire Nappe or the underlying autochthon. The differences between the Permian volcanic rocks of t h i s subarea and those of the Liumchen Nappe are believed to be the r e s u l t of f a c i e s changes. A t r a n s i t i o n takes place from Liumchen Mountain and the west side of Mount McGuire, where the rocks Figure 4-3: Upright F-]_ f o l d with east trending, h o r i z o n t a l axis i n thin-bedded cherty a r g i l l i t e s on Elk Mountain, with s t i l l smaller F^ f o l d on southern (right) limb. The f o l d has been tightened by l a t e r deformation, producing f r a c t u r i n g at hinge, and the small conjugate folds ( i l l u s t r a t e d i n Figure 29C) on the limbs. Minor f l a t -l y i n g shears are v i s i b l e j u s t above pens. -135-are l a r g e l y flows, through interbedded flows and quartz-bearing .crystal t u f f s on the north side of Mount McGuire and south side of Mount .Thurston to the predominant t u f f s on E l k Mountain. The lower contact of the Liumchen Nappe on the north side of C h i l l i -wack River can only be located approximately, owing to lack of. exposure, and i s the northerly extension of the t h r u s t - f a u l t separating ...Permian, volcanic rocks from underlying Mesozoic rocks on the northwest...side ..of. Mount McGuire. Supporting evidence f o r existence of the t h r u s t - f a u l t - i n t h i s subarea i s provided by the presence of s l a t y cleavage (S!j)...in.Meso.-. zoic rocks on Elk Mountain; fine-grained c l a s t i c Mesozoic rocks, on.the south side of Fraser V a l l e y , west of E l k Mountain contain fr a c t u r e cleav-age, and underlie Permian volcanic rocks of t h i s nappe. The upper contact of t h i s nappe i s drawn below the lowest d i g i t a t i o n of Permian limestone marking the hinge of the McGuire Nappe on the south-east side of Mount Thurston, l a r g e l y by analogy with the contact at the base of t h i s nappe south of the summit of Mount McGuire, 5 miles to the southwest along the trend of the structure. This basal contact of the McGuire Nappe descends the north side of Mount McGuire, crosses the C h i l l i -wack River j u s t west of i t s confluence with Slesse Creek and comes into contact with Mesozoic rocks south of the summit of Mount Thurston (Plate l ) . I t i s to be emphasized that although the nose of the McGuire Nappe., and the. underlying Liumchen Nappe are v i s i b l e i n cross-section on the southeast side of Mount Thurston, no Mesozoic rocks separate these s t r u c t tures, and there i s no great difference i n a l t i t u d e between the upper part of the McGuire Nappe as marked by the t h i n Permian volcanic sequence above the Permian limestone, and the s t r u c t u r a l l y underlying Permian volcanic -136-rocks of the Liumchen Nappe (Plate 2, section 4—4')" As there, is.evidence on Mount McGuire that a s t r u c t u r a l d i s c o n t i n u i t y does e x i s t between ...these two proposed nappes, the absence of Mesozoic rocks between these struc-tures can only be explained i f the s t r u c t u r a l d i s c o n t i n u i t y between, the nappes i s a l a g - f a u l t . This explanation i s compatible with the presence of Permian volcanic rocks of the Liumchen Nappe 5 miles northwest of the hinge of the McGuire Nappe marked by the Permian limestone on the south-east side of Mount Thurston. Subarea 7 Subarea 7 includes Foley Creek V a l l e y , from i t s confluence with Chilliwack V a l l e y to as f a r as Foley Lake, Mount Laughington and the d i -yide between Foley Creek and Chilliwack River. Fine-grained Mesozoic rocks predominate i n t h i s subarea. They s t r a t -i g r a p h i c a l l y o v e r l i e Palaeozoic rocks i n the western part of the map-area, and are o v e r l a i n by amphibolitic rocks on top of the ridge between Foley Creek and Chilliwack River and on the east side of Airplane Creek near Foley Lake. Permian rocks o v e r l i e Mesozoic rocks on top of Mount Laugh-ington. The fine-grained Mesozoic c l a s t i c rocks have well developed s l a t y cleavage (S!p commonly nearly p a r a l l e l to bedding (Figure 27), with L^ produced by the i n t e r s e c t i o n of these two surfaces. Although repeated, inversion of bedding suggests the presence of folds i n the sequence, only, a few (F^) folds have been seen. These are n e a r - i s o c l i n a l , recumbent., structures, whose axes plunge northeast, p a r a l l e l to L^ l i n e a t i o n s . Coarr-ser Palaeozoic c l a s t i c rocks are f o l i a t e d , the f o l i a t i o n being approxim-at e l y p a r a l l e l to S" i n the f i n e r rocks. No structures have been .observed -137-i n massive amphibolites i n t h i s subarea. Structures produced during are w e l l developed, and are. predomin-antly l o c a l , c l o s e l y spaced c r i n k l e s ( L ^ ) , and planar structures. (S^) associated with these. Poles to S are scattered and l i e on a great c i r c l e , whose.pole .cor-0 responds to the maximum concentration of L^. A maximum on this,great-... o o c i r c l e corresponds to bedding oriented at s t r i k e 14-0 with dip. 25... to,the northeast. An i s o l a t e d second concentration i s present i n the. northeast quadrangle, and i s analogous i n p o s i t i o n to s i m i l a r l y isolated-concentra-tions i n projections f o r Subareas 3 and U- L^ l i n e a t i o n s are scattered,, but the average o r i e n t a t i o n of the greatest concentration trends 050° and . plunges 30°. Presumably the spread of poles along the great c i r c l e , cen-tred on L^ i s due to the f i r s t period of deformation. Intersections of S^ and S^ gives the approximate o r i e n t a t i o n of stress axes f o r D,-,, with Pmax trending 238°, and plunging 6°. I f i t i s assumed that f o l d axes or l i n e a t i o n s were o r i g i n a l l y h o r i z o n t a l , then the o v e r a l l northeast dip of bedding, with a few beds dipping to the southwest i s believed to r e s u l t from the r o t a t i o n of S . about Pint f o r D . "0 " ~2 Mesozoic and minor Permian rocks of the McGuire Nappe are o v e r l a i n i n t h i s subarea by amphibolitic rocks and Permian rocks which presumably belong to a higher t e c t o n i c u n i t . The Mesozoic rocks and minor Permian .. rocks i n Foley Creek Va l l e y and i n the sides of Mount Laughington are the f a r t h e s t known extension to the northeast of the McGuire Nappe. Permian rocks on the summit of Mount Laughington, amphibolitic rocks i n Airplane. Creek V a l l e y and on the ridge between Foley Creek and Chilliwack River appear to occupy the same s t r u c t u r a l plane and thus to belong to the same -138-tectonic u n i t , which s t r u c t u r a l l y o v e r l i e s the McGuire Nappe. . To...the north, Palaeozoic rocks near the summit of Mount Cheam and Lady..Pefl.k_.are possibly part of t h i s u n i t . The r e l a t i o n s h i p between the Permian ..rocks, on Mount Laughington, to amphibolitic rocks i n Airplane Creek, is..not. known, although the l a t t e r are o v e r l a i n by Palaeozoic rocks at the south, end., of Cheam Range. Possibly the Palaeozoic rocks form a p a r t i a l envelope..around a core of amphibolitic rock. Further mapping i s necessary to ..establish—., r e l a t i o n s and to determine whether the emplacement of these rooka...above-Mesozoic rocks of the McGuire Nappe i s due to thrusting related, to or Subarea 8 Subarea 8 includes the northwest side, summit, and south side of Mount Cheam, Lady Peak, and the northern part of the Mount Laughington ridge. The subarea i s i s o l a t e d as there i s a paucity of exposures between i t and other subareas. Palaeozoic volcanic rocks, limestones and c l a s t i c sedimentary rocks., crop-out on the northeast side of Mount Cheam. These are o v e r l a i n by Mesozoic rocks, which are i n turn o v e r l a i n by Palaeozoic rocks near the. summit of Mount Cheam. Rare recumbent i s o c l i n a l F^ folds are v i s i b l e i n Palaeozoic rocks i n the northwest side of Mount Cheam. S l a t y cleavage, commonly s u b p a r a l l e l to bedding, occurs i n fine-grained c l a s t i c rocks, and coarser c l a s t i c rocks are f o l i a t e d . Chevron f o l d s , j o i n t drags and c r i n k l e s are present l o c a l l y . P rojection of poles to bedding shows a lack of recognizable pattern., apart from a general eastward dip of bedding. The few L l i n e a t i o n s -139-o o obtained have an average azimuth of 025 and plunge about 20 . .....Not .enough measurements of and S^ in t e r s e c t i o n s have been made to determine..the o r i e n t a t i o n of D stress axes. However, the orientations of S. . and ..L ~2 ~2 ~2 are not very d i f f e r e n t from that i n the r e s t of the map-area; the D^..stress system i s probably s i m i l a r to that elsewhere. The s p a t i a l d i s t r i b u t i o n of Palaeozoic rocks exposed on the ...south side of Fraser Valley, 2 miles west of Mount Cheam, suggests they form part of a recumbent f o l d . Permian limestone and minor volcanic.rocks..... exposed to the west of Mount Cheam at an a l t i t u d e of 4-,000 feet., are, over^ l a i n s t r a t i g r a p h i c a l l y by Mesozoic rocks, and themselves o v e r l i e a ..sequence of coarse to fine-grained c l a s t i c rocks, i n part l i t h o l o g i c a l l y , , s i m i l a r .ta,. the upper c l a s t i c sequence elsewhere i n the map-area. A bed of limestone of possible Pennsylvanian age i s present i n t h i s c l a s t i c sequence. S t i l l lower on the mountain side, coarse-grained c l a s t i c rocks o v e r l i e probable . Permian limestone, which i s s t r u c t u r a l l y above volcanic rocks exposed at. the base of the mountain, west of B r i d a l F a l l s . I f these rocks do form a recumbent f o l d , i t s r e l a t i o n s h i p to other te c t o n i c units i n the map-area i s not known. ' Trend of l i n e a t i o n s i n rocks forming t h i s possible f o l d , suggests that i t was formed during D . It i s proposed that the Palaeozoic rocks on the west side of Mount Cheam are part of the Liumchen Nappe, although t h i s suggestion i s to be regarded as t e n t a t i v e . Volcanic rocks of the Liumchen Nappe on E l k Moun-t a i n , are of s i m i l a r l i t h o l o g y to those at the base of the west side of Mount Cheam, 5 miles northeast of E l k Mountain. Rocks at both l o c a l i t i e s .. are predominantly pale green, quartz-bearing c r y s t a l - v i t r i c t u f f s and s i L - . i c i f i e d t u f f s . Although exposures on the south side of Fraser Va l l e y - H O -between Elk Mountain and Mount Cheam are extremely poor, a few scattered outcrops of pale green s i l i c i f i e d t u f f near the v a l l e y floor.indicate.. that there i s continuity between the two areas. I f t h i s i s so, volcanix rocks at the base of Mount Cheam belong to the Liumchen Nappe... In.addi=. t i o n , the Liumchen Nappe i s the only one of the three lower nappes-in.-. which Palaeozoic rocks are d i r e c t l y observed to extend as far,.north...as_ Fraser V a l l e y . As the trend of the south side of. Fraser V a l l e y ...between . E l k Mountain and Mount Cheam i s roughly p a r a l l e l to the northeast-smith-west trend of structures i n the map-area, the Liumchen Nappe., could. ex= tend northeast from Elk Mountain to Mount Cheam, with no major .change .of . trend. ...... . On the other hand, i n l i t h o l o g y , stratigraphy and structure, the Palaeozoic succession on the west side of Mount Cheam, above the basal. v o l c a n i c rocks, resembles that of the McGuire Nappe rather than the Lium-chen Nappe- Furthermore, the contact between Permian and Mesozoic rocks... at an a l t i t u d e of 4>000 feet to the west of Mount Cheam can be traced, almost continuously along Chipmunk Creek, as f a r as Chilliwack V a l l e y , where i t appears as the contact between Permian and Mesozoic rocks of the McGuire Nappe. However, the s t r u c t u r a l continuity between_rocks on Mount Cheam and those of the McGuire Nappe i n Chilliwack V a l l e y may be more apparent than r e a l , as no marked break has been observed between rocks, of . the Liumchen Nappe and the McGuire Nappe where they are p a r t i c u l a r l y w e l l -exposed on the southeast side of Mount Thurston. Also, the hinge of the McGuire Nappe-as delineated by Permian limestone on'Mounts Thurston and Mercer i s at l e a s t 5 miles due south of any possible hinge as marked by Permian limestone i n the apparent recumbent f o l d on Mount Cheam. Assuming - U l -the rocks on Mount Cheam belong to the McGuire Nappe, then the. .only pos-s i b l e explanation f o r such a discrepancy i s that l a t e r deformation ...was responsible f o r a northwesterly t r a n s l a t i o n of the hinge of the recumbent f o l d , from a p o s i t i o n i t occupied on the northeasterly extension.along . . s t r i k e of the McGuire. Nappe, to i t s present p o s i t i o n on Mount .....Cheam. , -If f o l d i n g were responsible f o r such a t r a n s l a t i o n anl abrupt change..of,trend of l i n e a t i o n would be expected i n the area between Mounts. Thurston. and Mercer and Mount Cheam. No such change has been recorded; the ...rare.. L '., . "1 l i n e a t i o n s trend northeasterly with no marked change of d i r e c t i o n . I f s t r i k e - s l i p f a u l t i n g were responsible, l a t e r a l movement would have to be considerable; no evidence of such movement i s evident from the map-pattern. Therefore, available evidence suggests that the predominantly sedimentary Palaeozoic succession above volcanic rocks on the west side of Mount Cheam.. .. can only belong to the Liumchen Nappe. I f t h i s i s i n f a c t so, a rapid, f a c i e s change must occur from the predominantly volcanic sequence on E l k Mountain to the predominantly sedimentary sequence on Mount Cheam. Evidence f o r a reverse f a u l t r e l a t e d to D 2 has been found i n the v i -c i n i t y of Pierce Creek, and i n the saddle between Mounts Mercer and Thur-ston? (Plate l ) ; the northwesterly extension of t h i s f a u l t i s believed to be responsible f o r the elev a t i o n of Permian rocks cropping-out two and .a h a l f miles east-northeast of E l k Mountain above contiguous Mesozoic rocks to the west. Major structures formed during have a general plunge to. . the northeast i n Chilliwack V a l l e y . However, Permian rocks of the Liumchen. Nappe crop-out at an a l t i t u d e of 3>000 feet on Elk Mountain; equivalent Permian rocks of presumably the same te c t o n i c unit are present to the norths east at an a l t i t u d e of 4,000 feet on Mount Cheam. This apparent anomaly - U 2 -i s believed to be due to f a u l t i n g which has elevated Palaeozoic.,rac.ks_. to the northeast above t h e i r western equivalents. L i t h o l o g i e s . a f L s c a t -tered outcrops indicate that the trace of t h i s f a u l t crosses the., ridge. 2-jJt- miles east-northeast of Elk Mountain. I f t h i s i s so, then, the fault, appears to be the northerly continuation of the reverse f a u l t ..present.. further south i n the map-area between Mounts Thurston and Mercer.. As. the s t r i k e of the f a u l t plane i s approximately p a r a l l e l to Pint f o r as_... determined from minor structures, i t was possibly formed during, D ...... . Permian rocks crop-out above Mesozoic rocks near the summit .,of-Ma.unt Cheam and are present further south i n Cheam Range. The structural. xela=-. t i o n s h i p of these rocks to underlying rocks i s not known at present; .they may l i e above a thrust, and presumably belong to the same tec t o n i c unit as the Permian rocks overlying Mesozoic rocks on Mount Laughington, further south i n the map-area. S t r u c t u r a l h i s t o r y of the map-area A l l recognized deformation i n the map-area took place a f t e r deposir-t i o n of Upper Jurassic rocks and p r i o r to i n t r u s i o n of the Chilliwack . b a t h o l i t h , an event, dated radio-metrically ? which took place 18 m i l l i o n years ago (Baadsgaard. et a l . , 1961, p. 697), i n Miocene time (Kulp, 1961.). The same maximum number of s t r u c t u r a l elements i s developed i n rocks rang-ing i n age from E a r l y Pennsylvanian to.,Late J u r a s s i c . E a r l i e r rocks are not noticeably more metamorphosed than l a t er ones, and i n c i p i e n t metamor-: phism of the glaucophane-schist type i s present i n both Palaeozoic and Mesozoic rocks. S t r a t i g r a p h i c breaks between Permian and T r i a s s i c rocks, and probably between Lower Pennsylvanian and Lower Permian rocks, are - H 3 -believed to r e s u l t from u p l i f t with no associated deformation,... non-deposi-t i o n , and possibly erosion. C l a s t i c rocks of known E a r l y Pennsylv.anian to Late Jurassic age are derived from v o l c a n i c and sedimentary ..rocks.;... there has been no deep erosion, with c l a s t i c " d e t r i t u s derived, .from... p l u -tonic or high-grade metamorphic rocks, such as would be expected.to accom-pany a major period of mountain b u i l d i n g . Misch, working j u s t south of the map-area i n northern Washington., has recognized two periods of post-Upper J u r a s s i c deformation.. According t o Misch, thrusting to the west fend northwest took place along two.major thrust f a u l t s i n about mid-Cretaceous time i n t h i s region (Misch.,. I960, M i l l e r and Misch, 1963). The-: lower, Church Mountain thrust, corresponds i n part to that thrust below the Liumchen Nappe of the wr i t e r , and was considered to carry Upper- Palaeozoic rocks over Jurassic and Lower Cret-aceous rocks; the upper, Shuksan thrust, brought low-grade metamorphic rocks over Palaeozoic rocks; i t s northerly continuation i n the map-area may correspond to that contact mapped by the writer between amphibolitic. rocks and underlying Mesozoic rocks i n the eastern part of the map-area... Following t h i s deformation, continental arkosic rocks of l a t e s t Cretaceous-Paleocene age were deposited i n the region and subsequently folded into moderately t i g h t to open folds ( M i l l e r and Misch, 1963, p»l67, p.171). These rocks are o v e r l a i n with angular unconformity by middle and/or upper Eocene rocks of s i m i l a r l i t h o l o g y , which have been subsequently warped rather than folded ( M i l l e r and Misch, 1963, p.167, p.173). The e f f e c t s of two phases of deformation have been recognized by the writer i n Pennsylvanian to J u r a s s i c rocks i n the map-area. There i s l i t t l e , doubt that the structures formed during the f i r s t phase, D-, , p a r t l y corre-r . spond to the mid-Cretaceous thrust plates of Misch. The second-phase of deformation, D^, took place p r i o r to i n t r u s i o n of the Miocene Chil 1 iwack b a t h o l i t h , as unoriented b i o t i t e and c o r d i e r i t e porphyroblasts, , i n ..ther-mally metamorphosed rocks close to the contact, grow across minor .struc-tures (S" planes) produced during D P. This dates D as pre-Miocene. and <• ^ 2 i s the only way of obtaining a minimum age f o r both periods of.deforma-r-. t i o n . Further work i s necessary to demonstrate whether corresponds to the e a r l y Eocene deformation of M i l l e r and Misch. The following,.struc-t u r a l h i s t o r y of the map-area i s t e n t a t i v e l y suggested. Palaeozoic and Mesozoic rocks were i n i t i a l l y deformed into northeast trending f o l d s . During f o l d i n g , s l a t y cleavage (S^) was developed i n rocks of appropriate composition towards the middle of the orogenic belt.,, and now i n the McGuire Nappe, and fr a c t u r e cleavage (Sj) i n rocks of simi-,.. l a r composition to the northwest, now forming the autochthon. Nothing, has been observed to r e l a t e the i n c i p i e n t glaucophane-schist type meta-morphism present i n both Palaeozoic and Mesozoic rocks i n the map-area, to any period of deformation. Following Fyfe et a l . (1958, p.177), t h i s metr-amorphism may have resu l t e d from the deep b u r i a l of sediments with high water content i n a region of low thermal gradient; i n the map-area metar-morphism of the glaucophane-schist type therefore may have taken place before or i n the e a r l i e s t stages of D^ deformation. The cause of the northeast trend of D structures, which are oriented "1 nearly normal to the C o r d i l l e r a n trend i n the region, i s not known. This, northeast trend i s extensive; Bowen (19L4, p.112) reported northeast trends from north of Fraser River, north of the map-area, and Moen (1962, plate 1.) has shown t h i s trend continuing for several miles southeast of the map-area. - H 5 -Crickmay (1930a) suggested that t h i s anomalous trend was due to ...the.,geo-s y n c l i n a l accumulation being wrapped around the southern end o£ .the. "Coast Range Bat h o l i t h . " As g r a n i t i c rocks were present north of the map.-area in Lower Cretaceous time (Crickmay, 1962), they may have acted as a but-tress during mid-Cretaceous deformation and thus controlled t h i s anomalous trend. A l t e r n a t i v e l y , i f structures were formed i n response to base-ment deformation, then possibly the o r i e n t a t i o n of these structures may. be c o n t r o l l e d by an old, pre-Devonian, northeasterly trend i n the basement rocks. Although the l o c a t i o n of probable basement rocks at the southern end of Slesse Creek suggests they Ire i n the core of the recumbent a n t i -c l i n a l structure which i s the McGuire Nappe, and thus possibly controlled.. the formation of t h i s nappe, further mapping i s needed before the r e l a -t i o n s h i p of these basement rocks to the sedimentary rocks i s known. Misch (1962).suggested that s i m i l a r rocks, mapped south of the l o c a l i t y i n Slesse Creek, are part of a pre-Devonian basement complex, which moved up along the root of h i s Shuksan t h r u s t - f a u l t , and became imbricated with Palaeo-zoic rocks i n the upper part of his Church Mountain thrust p l a t e . The upper part of Misch's Church Mountain thrust plate seemingly i s roughly equivalent to the McGuire Nappe. As deformation continued, so the northeast-trending f o l d s became overturned to the northwest, thrusting took place, and the Liumchen. Nappe and Mount McGuire Nappe were formed. Presumably these two nappes were i n i t i a l l y d i s c r e t e f o l d s , r e l i c t s of which are preserved as the recumbent a n t i c l i n e on Mount McGuire, and the recumbent a n t i c l i n e i n the possible northeasterly extension of the Liumchen Nappe, to the west of Mount Cheam. Rocks of the McGuire Nappe, closer to ;the centre of the orogenic be l t than - H 6 -rocks of the Liumchen Nappe, were i n i t i a l l y thrust over rocks,of_the.Lium-chen Nappe, and became a recumbent a n t i c l i n e whose lower limb. was. p a r t l y removed by t h r u s t - f a u l t i n g . With continuing deformation, the...greater com-petancy of the thick volcanic sequence forming the Liumchen Nappe, resulted i n t h i s underlying nappe being moved r e l a t i v e l y further forward.; ..the..s.tr,ucT t u r a l d i s c o n t i n u i t y separating the Liumchen and McGuire Nappes...is....thus a lag f a u l t rather than a thrust. The postulated development of, these„struc-tures i s shown i n Figure Structures formed during were then superimposed upon the. earlier., structures. Deformation during D^ i s believed to be responsible..for...the. common dip of bedding to the northeast at low to moderate angles^ for. .the production of large-scale open folds such as the antiformal structure... a t the north end of Slesse Creek, and for reverse f a u l t s with northeast-dipping f a u l t planes. The s t y l e of minor structures formed during this, period of deformation suggests they are the r e s u l t of b r i t t l e deformation; t h i s contrasts with the folds produced during D^. In addition, D^ planar .. structures do not involve the reorganization of rock material necessary to produce the s l a t y cleavage formed during D^ i n parts of the map-area. Therefore, structures formed during D^ appear to have been formed at a somewhat lower metamorphic grade than that extant during D^ i n parts of the., map-area. This lowering of metamorphic grade indicates that there i s some, time difference between D^ and D^ structures. The genetic r e l a t i o n s h i p between D and D structures i s not known. X £ I f i t i s assumed that p r i o r to D^, bedding was h o r i z o n t a l , then the f o l d axes of F^ f o l d s , ( p a r a l l e l to L^), produced during D^ would be h o r i z o n t a l and p a r a l l e l to Pint f o r D . I f t h i s i s so, then Pint f o r D , p r i o r to Dp F I G U R E 4 4 " P o s t u l a t e d d e v e l o p m e n t of D f m a j o r s t r u c t u r e s - H 7 -deformation appears to have coincided with Pmax f o r D , and was_..narmal. to Pint f o r (compare diagrams B and C, Plate 3). Orientation o f Pint f o r appears to coincide with the d i r e c t i o n of tectonic transport, during. Dn as indicated by the form and o r i e n t a t i o n of structures. Similar....rela-tionships .p i n v a r i a b l y developed i n environments where thrusting, i s . impor-tantjhave been discussed by other workers. Cloos (194-6, pp. 127-128) gave examples of l i n e a t i o n s and f o l d i n g normal to the regional trend,., developed i n areas i n which thrusting i s important i n Scotland and Scandinavia. Kvale (1953) discussed l i n e a r structures and t h e i r r e l a t i o n s h i p to move-ment i n the Caledonides of Western Europe, and concluded (p.6l) that where compression and resultant f o l d i n g predominate i n orogenic b e l t s , so axes of the folds are perpendicular to the d i r e c t i o n of compression and l i n e a -tions p a r a l l e l to the f o l d axes; where overthrusting i s the predominant process, l i n e a t i o n s and small scale folds are formed p a r a l l e l to t h e . d i r -ection of movement. Johnson (1956, 1957) described conjugate and mono-c l i n i c f o l ds with fold-axes p a r a l l e l to the d i r e c t i o n of movement on the Moine Thrust. Style of these folds (Johnson, 1956, p.34-6, Text-fig.1, 1957, p.252, f i g . 5 , i n part) i s d i r e c t l y comparable to that of minor folds formed during i n the Chilliwack V a l l e y map-area. Johnson (1956, p.34-9) considered these folds to be accomodation structures formed by stresses... within the thrust zone during movement, and not a r e f l e c t i o n of the d i r -ection of forces applied e x t e r n a l l y to the whole rock mass. However, as these structures were produced concomitantly with thrusting, and as the... P_2 structures i n the map-area appear to be l a t e r than D-^  movements, they do not appear to be analogous. There does not appear to be any d i r e c t genetic r e l a t i o n s h i p between D and D structures i n the map-area. - U S -Structures produced during may be the r e s u l t of d i f f e r e n t i a l .up-l i f t of the Cascade Mountain system, which resulted i n the earlier, s t r u c -tures s l i p p i n g sideways with the production of antiforms, reverse, .faults and b r i t t l e type minor structures, as suggested i n Figure US- The sense of movement indicated by most of the "oblique shear" type minor, f.o.1 ds i s to the southwest, and the reverse f a u l t i n g a t t r i b u t e d to has. the. same sense. The apparent symmetry of these structures with respect to..D^ structures may r e s u l t from t h e i r o r i e n t a t i o n being i n part controlled-by the e a r l i e r structures. As indicated e a r l i e r , deformation of. this...type probably ceased before i n t r u s i o n of the Chilliwack b a t h o l i t h . A compar-ison of structures i n the map-area, with those produced during the early Eocene deformation of M i l l e r and Misch (1963) might enable the D„ movements to be dated more p r e c i s e l y . NNW F I G U R E 45:Postulated d e v e l o p m e n t of Q 2 s t r u c t u r e s - U S -CONCLUSIONS Geological h i s t o r y of the map-area Late Palaeozoic and Mesozoic h i s t o r y of t h i s region i s dominated by migrating volcanic centres, whose proximity to the map-area have r ' g O¥e_ned to a large extent the type of deposition within i t . No evidence.has been found to demonstrate that any deformation took place i n the map.-area_.be-tween E a r l y Pennsylvanian and Late J u r a s s i c time, and the majo_.,..p.eriod .. . of deformation was i n mid-Cretaceous time, subsequent to deposition of. a l l rocks i n the map-area. The l i t h o l o g i c a l s i m i l a r i t y between some amphibolitic rocks exposed i n the eastern part of the map-area to Devonian rocks i n the San Juan Islands suggests they are of t h i s age, and are thus basement rocks on which a l l l a t e r rocks i n the map-area were deposited. However, the s t r a t -igraphic r e l a t i o n s h i p between these rocks i n the map-area and the Palaeo-zoic and Mesozoic rocks i s not known. The oldest rocks of reasonably c e r t a i n age are predominantly f i n e -grained c l a s t i c rocks of the lower c l a s t i c sequence, which were derived, from a source area composed l a r g e l y of vo l c a n i c rocks, and deposited i n part by t u r b i d i t y currents, presumably i n a marine basin. Lower Pennsylvanian limestone, the Red Mountain Formation, was l a i d down on top of t h i s c l a s t i c sequence. I t i s l o c a l l y gradational with.the underlying sequence and i t s presence as a di s c r e t e l i t h o l o g i c a l l y homo-genous unit may be p a r t l y due to a cessation of c l a s t i c supply to the basin, a trend indicated by the o v e r a l l decrease i n grain s i z e towards -150-the top of the underlying c l a s t i c sequence. The limestone is.lnn.wl 1y shaly and preserved textures indicate that i t was l a i d down in...a .1 ow-.,.. energy environment. As t h i s limestone i s r e g i o n a l l y widespread,., occurring i n a l l tectonic units i n the map-area and at several l o c a l i t i e s ...in. north-ern Washington, i t s presence i s perhaps i n d i c a t i v e of a period, of..tec-tonic quiesence. C l a s t i c rocks of the upper c l a s t i c sequence were l a i d down on top of the Red Mountain limestone. I n i t i a l l y , fine-grained c l a s t i c sediments... accumulated to a depth of a few feet; these were succeeded by. coarse—... grained unsorted sandstones, minor conglomerates and a r g i l l i t e s . , derived l a r g e l y from a volcanic terrane and deposited by sub-aqueous s l i d i n g and. t u r b i d i t y currents. This sediment supply was supplemented by sporadic vulcanism outside of the map-area, which contributed l i t h i c and crystal, t u f f s , p a r t i c u l a r l y to the upper part of the sequence. The coarse nature of sediments i n the sequence i s possibly the r e s u l t of rapid u p l i f t r e -lated to t h i s vulcanism. A sparse, marine fauna was present i n the basin... of sedimentation. Fragmental plant m a t e r i a l , found i n rocks of t h i s , s e -quence i n the autochthon, demonstrates the presence of land i n the region at t h i s time. The source area of t h i s c l a s t i c sequence was large enough to permit a primary transport h i s t o r y of s u f f i c i e n t length to enable cob-bles to become rounded, and stable enough to permit a f l o r a to become es-t a b l i s h e d . Age of t h i s c l a s t i c sequence i s not cer t a i n ; i t appears to. span E a r l y Pennsylvanian to E a r l y Permian time, as no s t r a t i g r a p h i c breaks are known. By E a r l y Permian time, a volcanic centre, represented by basic lavas i n the Liumchen Nappe, had migrated to the map-area. Permian limestone, -151-now i n the autochthon and Liumchen Mountain Nappe, was deposited,.in a low-energy environment northwest and southeast of the volcanic....centre, on top of the upper c l a s t i c sequence. T r a n s i t i o n between the underlying.,coarse c l a s t i c rocks l a i d down by t u r b i d i t y flows and s l i d e s , and the, overlying limestone, takes place over a few feet, and i s marked by fi n e ...clastic....... rocks and l i t h i c t u f f s . Possibly the sea f l o o r was l o c a l l y elevated above the general basin l e v e l by the advent of vulcanism, to a p o s i t i o n s t i l l below wave base, but where i t could no longer receive c l a s t i c sed-iments c a r r i e d by t u r b i d i t y flows or s l i d e s . Cessation of Permian limestone deposition may have been caused by a change of magma from a basic one, which was r e l a t i v e l y q u i e t l y extruded,, to a more s i l i c e o u s magma which resulted i n p y r o c l a s t i c a c t i v i t y , , the products of which blanketed the area of limestone deposition. Quartz-, bearing c r y s t a l t u f f s with minor flows o v e r l i e the Permian limestone; these t u f f s were probably deposited both d i r e c t l y , and also by sub-aqueous . . s l i d i n g and t u r b i d i t y currents. The vol c a n i c centre was possibly elevated above sea l e v e l during t h i s period of p y r o c l a s t i c a c t i v i t y . Cessation of vulcanism resulted i n erosion of t h i s v o l c a n i c p i l e to wave base, where i t stood as an elevated area above the general l e v e l of the sea f l o o r , and was possibly surrounded by a low area i n which sediments were deposited by t u r b i d i t y flows. By Late T r i a s s i c time t h i s l o c a l high . no longer existed and f i n e c l a s t i c rocks were deposited by t u r b i d i t y curr-rents r i g h t across the map-area. Deposition of rocks by t u r b i d i t y currents continued from Late T r i a -s s i c to Late Jurassic time across much of the map-area, with no detected .... st r a t i g r a p h i c break. Rocks of Late T r i a s s i c and E a r l y J u r a s s i c age derived -152-l a r g e l y from pre-existing volcanic rocks, which apparently accnmnlatari i n a trough or basin between volcanic highs then e x i s t i n g to the west, nn .. Vancouver Island and to the northeast i n the I n t e r i o r of B r i t i s h ..Columbia. Volcanic centres were located just north and south of the mapL-area-in... Middle Jurassic time, and one may be represented by flows of. passih.1 e Middle J u r a s s i c age i n the northwestern most part of the map-area. .  In... the eastern part of the map-area, sedimentation of the type.present i n . the E a r l y J u r a s s i c continued u n t i l the Late J u r a s s i c . Sometime a f t e r deposition of the Upper Ju r a s s i c sediments, probably, in mid-Cretaceous time, a l l of these rocks were strongly deformed. North-east trending folds were i n i t i a l l y produced and were overturned to the northwest. With continuing deformation they developed into recumbent structures and r e l a t e d t h r u s t s . No evidence has been found to demonstrate that minerals c h a r a c t e r i s t i c of glaucophane-schist type metamorphism found, in c e r t a i n rocks i n the map area i s r e l a t e d to t h i s deformation and the.. metamorphism may merely be the r e s u l t of deep b u r i a l p r i o r to t h i s period... of deformation. Following t h i s f i r s t period of deformation these rocks were again deformed. Structures produced trend northeast and may be the r e s u l t of movement to the southwest, caused by d i f f e r e n t i a l u p l i f t of" the Cascade Mountain system. .. .. Outside of the map-area, arkosic Late Cretaceous to Paleocene sed-.. . . iments of molasse-type were deposited, and sedimentation of t h i s type has e f f e c t i v e l y continued u n t i l the present day i n the region. -153-BIBLIOGRAPHY Armstrong, J.E., I960, S u r f i c i a l geology, Chilliwack (west h a l f ) ; Geol. Surv. Can., Map 53-1959-Baadsgaard, H., F o l l i n s b e e ^ , R»E»^ and Lipson, J.-,.-, 1961, Potassium argon dates of b i o t i t e s from C o r d i l l e r a n granites; B u l l . Geol. Soc. Amer., v o l . 72, p. 689-701. Bailey, E.B., 1934, West Highland tec t o n i c s : Loch Lomen to Glen Roy; Geol. Soc. London Quart. Jour., v o l . 78, p. 82-131. Bauerman, H., 1884, Report on the geology of the country near the f o r t y - n i n t h p a r a l l e l of north l a t i t u d e , west of the Rocky Mountains; Geol. and Nat. H i s t . Surv. Can., Rept. Prog. 1882-83-84. 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M i l l s , J.W., and Davies, J.R., 1962, Permian f o s s i l s of- the Kettle. F a l l s area, Stephens County, Washington; Contr. Cush.Found. Foram. Research, v o l . 13, p. 41-51. Misch, P., 1952, Geology of the Northern Cascades of Washington; The Mountaineer, v o l . 45, p.No. 13, p. 4-22. Misch, P., I960, Large overthrusts i n the northwestern Cascades near the 49th P a r a l l e l , Whatcom and Skagit Counties, Washington.,, and Lower Tomyhoi. Creek area, B r i t i s h Columbia; (abstract) B u l l . Geol. Soc. Amer., v o l . 71, p. 2069. Misch, P., 1962, Unusual imbrication patterns displayed by pre-Devonian c r y s t a l l i n e s and Upper Palaeozoic rocks below Mount Shuksan overthrust i n Mount Larrabee (Red Mountain)-Tomyhoi Peak area of northwestern Cascades, Whatcom County, Washington; Geol. Soc. Amer., sp. pap., Abstracts f o r 1962, p. 53. Moen, W.S., 1962, Geology and mineral deposits of the north h a l f of the Van Zandt Quadrangle, Whatcom County, Washington; Washington Div. of Mines and Geology, B u l l . 50. Moore, R.C., L a l i c k e r , C.G., and Fischer, A.G., 1952, Invertebrate F o s s i l s ; McGraw H i l l Book Co. Inc., New York, Toronto, London. O r i e l , S.S., 1949, D e f i n i t i o n s of arkose; Amer. Jour. S c i , , v o l . 247, p. 824-829. Packham, G.H., 1954> Sedimentary structures as an important f a c t o r i n the c l a s s i f i c a t i o n of sandstones; Amer. Jour. S c i . , v o l . 252, p. 466-476, Paterson, M.S., and Weiss, L.E., 1962, Experimental f o l d i n g i n rocks; Nature, v o l . 195, p. IO46-IO48. -158-Pettijohn, F.J.,1957, Sedimentary Rocks; Harper and Brothers, Mew York. Ramsay, J.G., 1962, The geometry of conjugate f o l d systems; Geol. Mag., v o l . 99, p. 516-526. Rich, M., 1961, S t r a t i g r a p h i c section and f u s u l i n i d s of the Bi r d Spring Formation near.Lee Canyon, Clark County, Nevada; Jour. Paleontology, v o l . 35, p. 1159-1180. Ross, C.A., 1963, Standard Wolfcampian Series (Permian), Glass Mountains, Texas.; Geol. Soc. Amer., Mem. 88. Seki, Y», 1961, Pumpellyite in low-grade metamorphism; Jour. Petrology, v o l . 2, p. 4.07-423. Smith, C.L., 1962, Stratigraphy of the Red Mountain Formation (Lower Pennsylvanian?) of rldrthwestern Washington; unpub. M. 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 Columbia. Smith, G.O., and Calkins, F.C., 1904, A g e o l o g i c a l reconnaissance across the Cascade Range near the f o r t y - n i n t h p a r a l l e l ; U.S. Geol. Surv., B u l l . 235. Thompson, M.L., Wheeler, H.E., and Hazzard, J.C., 1946, Permian f u s u l i n i d s of C a l i f o r n i a ; Geol. Soc. Amer., Mem. 17. Trumpy, R., I960, Paleotectonic evolution of the Central and Western Alps; B u l l . Geol. Soc. Amer., v o l . 71, p. 893-908. , Van Andel, T.H., 1958, Origin and c l a s s i f i c a t i o n of Cretaceous, Paleocene. and Eocene sandstones of Western Venezuela; Am. Assoc. Petroleum Geologists B u l l . , v o l . 4 2 , p. 734-76.3. Williams. H., Turner, F.J., and G i l b e r t , CM., 1954, Petrography; W.H. Freeman and Company, San Francisco. White, W.H., 1949, M i n i s t e r Mines, B r i t i s h Columbia; Annual Rept., p. A214-A216. -159-APPENDIX A Choice of c l a s t i c sedimentary rock c l a s s i f i c a t i o n Where the o r i g i n a l composition of the c l a s t i c sedimentary rocks of the Chilliwack Group and Cultus Formation can be determined, then, these rocks are seen to consist mainly of fragments of volcanic rocks and plag-iocl a s e feldspars. Quartz grains and fragments of. sedimentary and.meta-morphic rocks are r a r e l y abundant and commonly absent. T h e s e ' c l a s t i c rocks are quite v a r i a b l e i n hue, generally being dark when vo l c a n i c f r a g -ments predominate and l i g h t when feldspar fragments are more abundant. Sorting i s poor and rhythmically graded sequences are common. These, rocks present two problems, the f i r s t being one of nomenclature and c l a s s i f i c a -t i o n , and the second, the d i f f i c u l t y of d i s t i n g u i s h i n g some of them, from-true p y r o c l a s t i c deposits. Most workers i n the region (e.g. Misch, 1952, Danner, 1957, and Moen, 196l) have c a l l e d these rocks greywackes. The term "greywacke" has been v a r i o u s l y defined by d i f f e r e n t modern a u t h o r i t i e s and has no u n i v e r s a l l y accepted meaning at present. According to Boswell (i960, p.154-) the. term greywacke o r i g i n a l l y had a l a r g e l y t e x t u r a l connotation, although. Naumann' c l a s s i c a l d e f i n i t i o n (1858, i n K l e i n , 1963, p.571) included both composi-t i o n a l and t e x t u r a l elements. I f i t i s believed that a very general conce of the term "greywacke" i s s u f f i c i e n t l y exact, then the c l a s t i c rocks of the Chilliwack Group and Cultus Formation could well be c a l l e d greywackes. Their somewhat r e s t r i c t e d compositional nature would allow the term "grey-wacke" to be q u a l i f i e d by the adjective "volcanic" as i s done by Edwards (194.7a) f o r rocks very s i m i l a r i n composition to these. Boswell (i960, -160-p.154) suggested that the term greywacke should be abandoned completely, or else given a precise connotation; and Pettijohn, (i960, p.627) has s i m i l a r l y recommended that the meaning should be r e s t r i c t e d to be of any value, and should take into account the o r i g i n a l or type material (re-cently described by Helmhold, translated by Van Houten, 1958). Modern a u t h o r i t i e s have made two-fold attempts to obtain both .a uni v e r s a l sandstone c l a s s i f i c a t i o n and p r e c i s i o n i n d e f i n i t i o n . Modern sandstone c l a s s i f i c a t i o n s u sually include both the term "arkose", c l a s s -i c a l l y defined on the basis of mineralogical composition ( O r i e l , 1949), and also "greywacke", i n which, c l a s s i c a l l y , texture i s an important f a c t o r , i f not the main one. Therefore, i n order to r e t a i n some semblance of the o r i g i n a l meaning of the terms "greywacke"and "arkose", these c l a s s i f i c a t i o n s must be based on both t e x t u r a l properties and mineralogical composition. Krynine (194-8), Dapples, Krumbein and Sloss (195.3) have employed the concept of mineralogical composition p a r a l l e l i n g t e x t u r a l maturity i n t h e i r c l a s s i f i c a t i o n s . Folk (1956, p.170) and Van Andel (1958, p.745) have demonstrated that t h i s i s too simple an..approach, and have shown that as texture and mineralogical composition are s t r i c t l y two independent parameters, only one of these parameters can be chosen as a basis f o r c l a s s i f i c a t i o n , and the two cannot be combined.' Two objections can be made to the choice of texture as a basis f o r c l a s s i f i c a t i o n . One i s demonstrated by the c l a s s i f i c a t i o n of Pettijohn (1957) and Packham (1954) who placed primary emphasis on texture,., or genetic factors interpreted l a r g e l y from texture, but apparently found i t necessary to include the mineralogical c l a s s i f i c a t i o n as texture alone i s too imprecise a property on which to define a sandstone c l a s s . However, -161-the main objection to texture as a basis f o r c l a s s i f i c a t i o n i s that raised by Folk (1954, p.352) who states, "Rock types, , must be set up on the firm basis of mineral composition, not on the insecure basis of clay content of the sediment, which i s a r e f l e c t i o n l a r g e l y of the v i c i s s i t u d e s of the l o c a l environment." and both Folk (1954) and Van Andel (1958) base t h e i r c l a s s i f i c a t i o n soley on the mineralogical composition of the rock. G i l b e r t s ' c l a s s i f i c a t i o n (1954) bas both a t e x t u r a l and mineralogical basis, and the nomenclature applied to the rock w i l l thus p a r t l y depend on 4 ,the v i c i s s i t u d e s of. the l o c a l environment." For a complete d e s c r i p t i o n Folk (1954) proposes a t r i p a r t i t e nomen-clatu r e , with a rock name derived from the mineralogical composition, and separate terms for t e x t u r a l maturity and grain s i z e . K l e i n (1963., p.572) recommends that Folk's approach to sandstone c l a s s i f i c a t i o n be follxiwed but has also stated (1963, p.572) that the c l a s s i c a l conceptions of the various types w i l l not be invalidated by t h i s approach. This i s .incorrect, the greywacke of Folk being very d i f f e r e n t from the c l a s s i c a l greywacke, so d i f f e r e n t that possibly the term should not be used i n the c l a s s i f i -cation and should be abandoned, as suggested by Boswell (I960,, p.1,54) • The ternary diagram f o r mineral composition proposed by Folk,, (1954> p.354) and extended by Folk (1961, p . I l l ) i s used i n t h i s report. The three poles, each with t h e i r respective mineral and rock fragmenthgroups, derived from source areas of igneous, sedimentary and metamorphic. rocks, give r i s e , r e s p e c t i v e l y j t o arkoses, orthoquartzites and greywackes. Sed-iments at the igneous pole are d i f f e r e n t i a t e d into "arkose" derived from plutonic (predominantly g r a n i t i c ) source rocks, which i s close to the -162-c l a s s i c a l arkose, and volcanic or plagioclase arenites derived from...vol-canic sources (Folk, 1961, p.117). Moen (1962, p .L4) has noted that grey-wackes (composed l a r g e l y of rock fragments) grade into arkoses (composed l a r g e l y of feldspars) i n Chilliwack Group rocks southwest of the map-area. A l l evidence indicates that these rocks were derived from the same v o l -canic source-area, and the use of Folk's c l a s s i f i c a t i o n thus avoids, the necessity of using two terms, c l a s s i c a l l y of very d i f f e r e n t meaning., f o r g e n e t i c a l l y r e l a t e d rocks. Unfortunately, these volcanic arenites are very susceptible to a l t e r a t i o n by diagenetic or metamorphic processes and i n many cases the exact composition cannot be determined. I d e n t i f i -cation can then only be made by comparison with less a l t e r e d but i d e n t i -f i a b l e rock, i n the same sequence. There may be considerable d i f f i c u l t y i n d i s t i n g u i s h i n g these volcanic arenites, derived from pre-existing, but probably nearly contemporaneous volcanic terranes, from true p y r o c l a s t i c rocks, p a r t i c u l a r l y when the p y r o c l a s t i c rocks have been deposited by submarine p y r o c l a s t i c flows. (Fiske, 1963, p.392). Hay (1952) considers that a l l reworked pyroclastic. material,, even though the remaking may be e s s e n t i a l l y contemporaneous with deposition, as i s the case with submarine p y r o c l a s t i c flows, should be designated v o l -canic sandstone. The opposite view i s taken by Fisher (1961) who believes a l l m aterial moved p r i o r to l i t h i f i c a t i o n , from i t s o r i g i n a l place-.of deposition, should be c a l l e d p y r o c l a s t i c . Carozzi (I960, p.112) believes shards or pumiceous fragments constitute d i r e c t proof of p y r o c l a s t i c o r i g i n , but these would tend to be r e a d i l y removed by any so r t i n g processes,. and are e a s i l y destroyed by metamorphism. Generally t u f f s tend to be greener i n colour than v o l c a n i c arenites -163-and the l a t t e r are commonly graded. In p r a c t i c e , there i s probably l i t t l e chance of a t u f f being recognized i n a sequence of volcanic arenites, unless shards are found, and conversely, i n a sequence of flows, most vol c a n i c arenites would probably be c a l l e d t u f f s , even though shards.are not seen. -164-APPENDIX B F o s s i l l o c a l i t i e s of the Chilliwack V a l l e y Map-Area F o s s i l l o c a l i t i e s are given on Plate 1. The b r i e f descriptions below indicate l i t h o l o g y of the f o s s i l i f e r o u s . r o c k s and t h e i r f o s s i l content. Most l o c a l i t i e s known are l i s t e d ; others not l i s t e d occur i n the immed-iate v i c i n i t y of given l o c a l i t i e s , and can be found by t r a c i n g out the' same horizon. L o c a l i t y 1: A r g i l l i t e s i n side of road ascending plateau south of the settlement of Ryder Lake, a l t i t u d e 100 feet* F o s s i l s : Poorly preserved, a r n i o c e r a t i d ammonite of E a r l y Jurassic age; s i m i l a r specimens were c o l l e c t e d e a r l i e r from t h i s l o c a l i t y by J.E.. Arm-strong and H. Frebold. At an a l t i t u d e of 4-00 feet on the. same road, just north of the f i r s t . road junction, u n i d e n t i f i e d clams are present i n coarse c l a s t i c rocks i n roadside. L o c a l i t y 2: Shaly-- limestone within dominant cherty a r g i l l i t e s , on the southwest side of E l k Mountain, a l t i t u d e j u s t over 4.000 feet . F o s s i l s : Aulacoceras c f . A. garlottense Whiteaves, 1889, of Late T r i -a s s i c age, and two u n i d e n t i f i e d , poorly preserved ammonite genera. L o c a l i t y 3: Limestone, s i l i c e o u s , on ridge top, 2^ - miles northwest of Elk Mountain, a l t i t u d e 4,800 feet. F o s s i l s : Rare, medium sized f u s u l i n i d s , c l o s e l y resembling, .the common Schwagerina seen elsewhere, of E a r l y Permian age. L o c a l i t y 4: Limestone, i n side of logging road on south side of ridge mentioned i n L o c a l i t y 3, about 1 mile northwest of L o c a l i t y 3, a l t i t u d e -165-4,000 fe e t . F o s s i l s : Large, r e c r y s t a l l i z e d f u s u l i n i d s , probably Parafusulina. of Ear l y Permian age. L o c a l i t y 5: Limestone, i n side of logging road, just north of saddle., 2^ - miles south of B r i d a l F a l l s , a l t i t u d e 4,000 feet. F o s s i l s : Poorly preserved Parafusulina, and Pseudofusulinella of Leonardian age, both well and poorly preserved, with large horn corals (Dibunophyllum?) and c r i n o i d columnals. L o c a l i t y 6: Limestone, i n side of, and below, logging road on top of b l u f f , 1 mile southwest of settlement of B r i d a l F a l l s , a l t i t u d e 2,200 feet. F o s s i l s : Small c r i n o i d columnals; limestone f l o a t containing poorly preserved f u s u l i n i d s was found i n the bed of the logging road, near, t h i s l o c a l i t y . L o c a l i t y 7: Limestone, i n creek, at end of old logging road, about. 1 mile southeast of B r i d a l F a l l s , a l t i t u d e 1,650 fe e t . F o s s i l s : Abundant medium sized c r i n o i d columnals. L o c a l i t y 8: Limestone, s i l i c e o u s , interbedded with chert and jasper, above logging road, about 2 miles south-southeast of B r i d a l F a l l s , -altitude 3,800 fe e t . F o s s i l s : Abundant, f a i r l y well preserved, p a r t l y s i l i c i f i e d , Para-f u s u l i n a and Pseudofusulinella?, rhomboporoid bryozoans, and sma l l . c r i n o i d columnals, of Leonardian age. . . About 1 mile north of t h i s l o c a l i t y , at an a l t i t u d e of 3,200 feet, limestones containing poorly preserved Parafusulina and small c o l o n i a l c o r a l s , are the northerly extension of the limestone at Locality..8. L o c a l i t y 9: Limestone on south side of western ridge of Mount Cheam, just -166-below ridge top, a l t i t u d e 5,850 feet . F o s s i l s : Rare, poorly preserved Parafusulina, of Leonardian age.. L o c a l i t y 10; Limestone pod, on the west side of Lady Peak, a l t i t u d e 6,250 feet. . . F o s s i l s : Small crinoid. columnals. L o c a l i t y 11: Limestone, cherty, on ridge of Mount Laughington, a l t i t u d e 5,500 feet . F o s s i l s ; Poorly preserved, s i l i c i f i e d Parafusulina, rare horn co r a l s , c r i n o i d columnals, of Leonardian age. L o c a l i t y 12: Limestone pod, on west side of Chipmunk Creek, a l t i t u d e 1,900 fe e t . F o s s i l s : Medium sized, r e c r y s t a l l i z e d f u s u l i n i d s (Schwagerina?.). of E a r l y Permian age. L o c a l i t y 13: Limestone, by logging road leading into Foley Creek. F o s s i l s : • Rare, r e c r y s t a l l i z e d large f u s u l i n i d s (Parafusulina?) of Ea r l y Permian age. L o c a l i t y 14: North side of limestone k n o l l above Chilliwack River.. F o s s i l s : Medium sized to small c r i n o i d columnals. L o c a l i t y 15: Talus, below limestone c l i f f on the southeast side of.Mount Mercer, a l t i t u d e of 3,000 feet . F o s s i l s : Abundant, medium sized Schwagerina?, completely s i l i c i f i e d or r e c r y s t a l l i z e d , of E a r l y Permian age. L o c a l i t y 16: Shaly; base of limestone c l i f f , on the southeast side of Mount Mercer, a l t i t u d e 3,750 feet . F o s s i l s : Poorly preserved but i d e n t i f i a b l e Parafusulina, large horn corals (Dibunophyllum?) and rhomboporoid bryozoans, of Leonardian age. - 1 6 7 -L o c a l i t y 1 7 : Limestone, southeast of summit of Mount Mercer, a l t i t u d e 4 , 6 0 0 f e e t . F o s s i l s : P a r t i a l l y s i l i c i f i e d , poorly preserved horn c o r a l s , small c r i n o i d columnals, and r e c r y s t a l l i z e d medium sized f u s u l i n i d s (Schwagerina.?) of E a r l y Permian age. L o c a l i t y 1 8 : Talus, below limestone c l i f f , and above old logging road, on south side of Mount Mercer, a l t i t u d e 2 , 3 0 0 f e e t . F o s s i l s : Abundant s i l i c i f i e d Schwagerina, large horn corals (Dibuno-phyllum?), of E a r l y Permian age. L o c a l i t y 1 9 : Shales i n side of logging road ascending to saddle between Mounts Mercer and Thurston, a l t i t u d e 4 , 0 0 0 f e e t . F o s s i l s : Poorly preserved a r n i o c e r a t i d ammonite, i d e n t i f i e d by H. Frebold as Melanhippites of Sinemurian age. L o c a l i t y 2 0 : Limestone on north bank of Chilliwack River, j u s t over 1 mile east of the junction of the Chilliwack River with Slesse C r e e k s .. F o s s i l s : Large c r i n o i d stems. L o c a l i t y 2 1 : Contact of limestone with underlying shales and v o l c a n i c rocks, just north of old logging road, and ijr mile northwest of the con-fluence of Slesse Creek with the Chilliwack River, a l t i t u d e 1 , 2 0 0 . f e e t . F o s s i l s : Parafusulina, Pseudofusulinella and rhomboporoid bryozoans, of Leonardian age. L o c a l i t y 2 2 : Volcanic arenites, t u f f s ? and shales below limestone, c l i f f s , above and to north of L o c a l i t y 2 1 , a l t i t u d e 2 , 6 0 0 feet. F o s s i l s : Molds of c r i n o i d columnals, f e n e s t e l l a t e bryozoans. L o c a l i t y 2 3 : Limestone, on south side of Mount Thurston, altitude. 2 , 3 0 0 f e e t . -168-F o s s i l s : Parafusulina, Pseudofusulinella of Leonardian age. L o c a l i t y 2U' Limestone, i n creek bed, a l t i t u d e 2,300 feet . F o s s i l s : Parafusulina. L o c a l i t y 25: Beds of limy chert, within dominant t h i n bedded cherts, on divide between two creeks, just above t h e i r junction, south side of ...Mount Thurston, a l t i t u d e 1,850 feet . F o s s i l s : Abundant, p a r t l y s i l i c i f i e d Parafusulina, rhomboporoid bryozoans, small c r i n o i d columnals, of Leonardian age. Several other f o s s i l l o c a l i t i e s containing the same fauna, occur i n limestone i n the v i c i n i t y of L o c a l i t i e s 21, 23, 2U, 25, but are not l i s t e d , as they are r e a d i l y located by t r a c i n g out the same horizon along the h i l l s i d e . L o c a l i t y 26: Limestone, ar g i l l a c e o u s and cherty, on the west side of k n o l l , east side of Borden Creek, near i t s confluence with Chilliwack River and immediately south of the main road i n Chilliwack Valley,. a l t i t u d e 850 f e e t . , r  F o s s i l s : Parafusulina, of Leonardian age. L o c a l i t y 27: Limestone pods, on the east side of Pierce Creek, a l t i t u d e 3,500 feet . . . . F o s s i l s : Large, poorly preserved f u s u l i n i d s , probably Parafusulina. L o c a l i t y 28: In limestone t a l u s , at base of large north-facing limestone c l i f f , west side of Pierce Creek, a l t i t u d e 3,600 feet . F o s s i l s : S i l i c i f i e d Schwagerina, of E a r l y Permian age. L o c a l i t y 29: A r g i l l i t e s , i n talus slope below north face of Mount McFarlane, a l t i t u d e 5,000 feet . F o s s i l s : Distorted clams, i d e n t i f i e d by J.A. Jeletzky as Buchia ex. gr. -169-concentrica Sowerby, of Late Oxfordian-Early Kimmeridgian age. L o c a l i t y 30: Limestone, i n creek on east side of Slesse Creek Va l l e y , a l t i t u d e 1,74-0 fe e t . F o s s i l s : Large c r i n o i d stems. L o c a l i t y 31: Limestone, i n creek bed on northeast side of Mount McGuire, a l t i t u d e 3,100 feet. F o s s i l s : Large c r i n o i d columnals. L o c a l i t y 32: Limestones and c l a s t i c sedimentary rocks i n side of old logging road, northeast side of Mount McGuire, a l t i t u d e 2,900 feet . F o s s i l s : Large c r i n o i d columnals i n limestone; pteropods? i n c l a s t i c rocks i n contact with the limestone. L o c a l i t y 33: Calcareous, badly weathered, c l a s t i c rock i n side of. old logging road, northeast side of Mount McGuire, a l t i t u d e 2,750 feet . F o s s i l s : Bellerophontid gastropods, brachiopod fragments, pteropods? L o c a l i t y 34-: Limestone f l o a t , below limestone c l i f f , north end of ridge on east side of Borden Creek, a l t i t u d e 4-,000 fe e t . F o s s i l s : Poorly preserved Schwagerina, E a r l y Permian age. Just below t h i s l o c a l i t y , f e n e s t e l l a t e " bryozoans and c r i n o i d columnal molds, are present i n a r g i l l i t e s . ... L o c a l i t y 35: Shales i n side of Borden Creek, a l t i t u d e 3,4-50 f e e t . F o s s i l s : Molds of small c r i n o i d columnals and f e n e s t e l l a t e bryozoans. L o c a l i t y 36: Shaly horizon i n limestone c l i f f , northwest of Spencer Peak, a l t i t u d e about 5,000 feet . F o s s i l s : Brachiopod fragments, f e n e s t e l l a t e bryozoans, crinoid. colum-nals, and endothyroid foraminifera of Lower Pennsylvanian? age. L o c a l i t y 37: Limestone, on ridge, northwest of Spencer Peak, a l t i t u d e -170-5,000 fe e t . F o s s i l s : Large c r i n o i d columnals, of Lower Pennsylvanian? age. L o c a l i t y 38: Limestone c l i f f southwest side of Spencer Peak,, a l t i t u d e 5,100 f e e t . F o s s i l s : Small horn corals; large c r i n o i d columnals are present i n bed below main body of limestone on north side of t h i s peak; of Lower Pennsylvanian? age. L o c a l i t y 39: Limestone c l i f f , due north of Spencer Peak. F o s s i l s : Large c r i n o i d columnals; small horn corals i n c l i f f on south-west side; of Lower Pennsylvanian? age. L o c a l i t y 4.0: Tuffaceous?, shales on north side of ridge, below limestone. F o s s i l s : Orthoconic n a u t i l o i d s , bellerophontid gastropods, pelecypods?, pteropods?. L o c a l i t y 41: Limestone bed, i n predominant volcanic rocks, i n creek, bed on southwest side of Mount McGuire, a l t i t u d e 4,000 feet . F o s s i l s : Parafusulina of Leonardian age. L o c a l i t y 42: Limestone, due east of peak of Mount McGuire, and j u s t north-west of saddle i n c e n t r a l east-west ridge, a l t i t u d e 5,100 f e e t . F o s s i l s : Small horn co r a l s , tabulate corals ( M i c h e l i n i a ) , compound co r a l s , and brachiopods, the most abundant being Rhlpidomella; a l l f o s s i l s are s i l i c i f i e d and preservation v a r i e s considerably; of E a r l y Permian age. L o c a l i t y 43: Below c l i f f on the east side of the peak of Mount McGuire, a l t i t u d e 5,700 feet . F o s s i l s : S i l i c i f i e d , medium sized Schwagerina of E a r l y Permian age. L o c a l i t y 44: Limestone, south side of north ridge of Mount McGuire, a l t i t u d e , 4,800 feet . - 171 -F o s s i l s : C r i n o i d columnals, c o r a l Heritschioides , of E a r l y Permian age L o c a l i t y 45: Limestone, northwest ridge of Mount McGuire, a l t i t u d e .5,000 feet. F o s s i l s : S i l i c i f i e d brachiopods. L o c a l i t y 4.6:. Rock composed of volcanic fragments i n a calcareous matrix, north side of north ridge of Mount McGuire, base of limestone c l i f f . , , a l t i t u d e 4,800 feet . F o s s i l s : Parafusulina, of Leonardian age. L o c a l i t y 47: Tuffaceous and agglomeratic limestone, b i o c l a s t i c limestone, at contact with infolded cherts, a r g i l l i t e s and volcanic rocks, north of peak of Mount McGuire, a l t i t u d e 6,000 feet . F o s s i l s : Parafusulina, Pseudofusulinella, schwagerinid?, rhombopo-r o i d bryozoans of Leonardian age. L o c a l i t y 48: Shales, s h a l y r limestone on ridge 1 mile north of the summit of Liumchen Mountain. This i s possibly the l o c a l i t y from which Daly (1912, p.510) made his c o l l e c t i o n s # 1512, 1514. F o s s i l s : Abundant brachiopods, f e n e s t e l l a t e and rhomboporoid bryo-zoans, clams?. L o c a l i t y 49: L imestone, capping k n o l l about 1^ - miles southwest o f the summit of Church Mountain. F o s s i l s : Fucoid markings, f u s u l i n i d s E o s t a f f e l l a , M i l l e r e l l a c o l l e c t e d by W.R. Danner from t h i s l o c a l i t y , and i d e n t i f i e d by Skinner; poorly preserved co r a l s , c r i n o i d columnals, of Lower Pennsylvanian age. L o c a l i t y 50: C l a s t i c rocks, on east side of k n o l l about 3/4 miles due west of the summit of Church Mountain. F o s s i l s : Fragments of Calamites, Lepidodendron, pteropod ? — l i k e f o s s i l -172-L o c a l i t y 51: Tuffaceous limestone, base of limestone c l i f f on east side of summit of Church Mountain. F o s s i l s : Parafusulina, Pseudofusulinella, large Schwagerina? and . rhomboporoid bryozoans; Dibunophyllum? and c r i n o i d columnals are present i n limestone c l i f f above t h i s l o c a l i t y ; of Leonardian age. L o c a l i t y 52: Shales, i n side of logging road, northeast side of Church Mountain, a l t i t u d e 2,900 feet . F o s s i l s : Pelecypods c o l l e c t e d from t h i s l o c a l i t y were i d e n t i f i e d by G.E.G. Westermann as Halobia d i l a t a t a K i t t l ? of Norian age. L o c a l i t y 53: Shales, i n side of old logging road, above and to east of main logging road i n Liumchen Creek. F o s s i l s : Hannaoceras nodifer (Hyatt and Smith), Discotropites?, Halobia? of Upper Karnian age. Just north of t h i s l o c a l i t y , above creek flowing northwestwards into Liumchen Creek, belemnites, A t r a c t i t e s cf. A.drakei^small clams and a gastropod were found i n s i m i l a r shales. L o c a l i t y 54-: Coarse c l a s t i c rocks, i n side of old logging road above fork i n Liumchen Creek. F o s s i l s : Plant fragments. L o c a l i t y 55: Tuff, i n ,Liumchen Creek. F o s s i l s : Belemnite, c f . Dictyoconites groenlandicus Fischer 194-7, and c r i n o i d columnals; of Permian age. L o c a l i t y 5b: Limestone, on east side of Liumchen Creek V a l l e y . F o s s i l s : Parafusulina, Pseudofusulinella, of Leonardian age. L o c a l i t y 57: Limestone, i n bed of Liumchen Creek. F o s s i l s : Large c r i n o i d columnals. -173-L o c a l i t y 58: Limestone, i n volcanic rocks on the south end of International Ridge. F o s s i l s : F u s u l i n i d s , Parafusulina?, of E a r l y Permian age. L o c a l i t y 59: Shales, i n dominant volcanic arenite sequence, on north side of north ridge of Mount McGuire, a l t i t u d e 4,900 feet. F o s s i l s : Fenestellate bryozoans, small brachiopods, Hustedia? PLATE 1 : Geological map of Chilliwack Valley area E X P L A N A T I O N SYMBOL CULTUS FOri»!ATION Upper Jurassic Liddle Jurassic? Lower Jurassic Upper Triassic • J L a r g e l y f i n e v o l c a n i c a r „ : , : t ea nr;d I "* 7 " r K l l U t e a , w i t h minor f l o w s i n ' I Kyder Lake area Leonardian CHILLTWACK GROUP PERMIAN VOLCANIC SEQUENCE a. Largely altered basic to intermediate flow rocks b. Largely tuffs c. Largely cherts and argillites PERMIAN LIMESTONE Leonardian Limestone, typically cherty f'.orrowan UPPER CLASTIC SEQUENCE I - -?-0- - J Coarse to medium grained volcanic L '. '. 1 arenites and argillites, with r • ~ " "j local conglomerates and tuffs RED MOUNTAIN LIMESTONE Limestone, typically argillaceous LOWER CLASTIC SEQUENCE Largely fino grained volcanic arenites and argillites UNDIFFERENTIATED CHIL!.IWACK GROUP? uncertsIn Age uncertain Includes quart-rich phyllitic rocks, locally above amphibolitic rocks and c J h « r f m e . 3 r 0 . n e r f U o s r . c rocks ' I I B O L I T I C hoc?; Rocks of possible diverse origins in which amphiboles are Important constituents r B PLATE 2: Geological cross-sections of Chilliwack Valley area LINES OP SECTIONS AND COLOUR KEY GIVEN ON PLATE 1 SECTIONS 1—1' TO 8—8' ARE ROUGHLY NORMAL TO THE TREND OP STRUCTURES FORMED DURING D -1 SECTIONS A—A' TO D—D' ARE ROUGHLY PARALLEL TO THE TREND OP STRUCTURES PORMED DURING D — l 

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