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The geology of a portion of the Skagit delta area, Skagit County, Washington Hopkins Jr., William Stephen 1962

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THE GEOLOGY OP A PORTION OF THE SKAGIT DELTA AREA SKAGIT COUNTY, WASHINGTON by WILLIAM STEPHEN HOPKINS, JR B.S. U n i v e r s i t y o f Washington, S e a t t l e , Washington  A Thesis submitted i n p a r t i a l f u l f i l m e n t o f the requirements f o r the degree o f MASTER OF SCIENCE i n the Department of GEOLOGY  We accept t h i s t h e s i s as conforming to the r e q u i r e d standards  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1962  TJI presenting  t h i s thesis 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 an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference  and study.  I further agree that permission  for extensive copying of t h i s thesis f o r scholarly purposes may granted by the Head of my Department or by his  be  representatives.  It i s understood that copying or publication of this thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  Geology  The University of B r i t i s h Columbia, Vancouver 8, Canada. Date  19  April  1962  ABSTRACT  Northwest-southeast  Miocene u p l i f t  with  subsequent  e r o s i o n has bared r o c k s o f P a l e o z o i c , Mesozoic and Cenozoic ages in  the western S k a g i t D e l t a r e g i o n .  Pleistocene glaciation  f o l l o w e d by r e c e n t a l l u v i a t i o n has b u r i e d much o f the bedrock l e a v i n g rock exposures o n l y on i s l a n d s i n S k a g i t Bay or as low h i l l s p r o j e c t i n g through the a l l u v i u m . A low-grade  metamorphosed sequence o f graywacke, con-  glomerate, b r e c c i a , a r g i l l i t e ,  and s p i l i t e ,  a l l o f probable  P a l e o z o i c age, make up the o l d e s t rocks o f the a r e a . Mesozoic r o c k s , composed o f graywacke and a r g i l l i t e , out i n h i l l s northwest  crop  and southeast o f the town o f L a Conner.  The c o n t a c t between P a l e o z o i c and Mesozoic r o c k s i s not exposed but an unconformity i s b e l i e v e d to separate the two. were found i n e i t h e r sequence.  No f o s s i l s  Because P a l e o z o i c ( ? ) and  Mesozoic(?) rocks can not be c o r r e l a t e d with any other known u n i t s , new names have been assigned by the w r i t e r .  The P a l e o z o i c ( ? )  sequence i s c a l l e d the Goat I s l a n d Formation and the Mesozoic(?) sequence i s c a l l e d the L a Conner  Formation.  A l o n g the North Fork o f the S k a g i t R i v e r a sequence with i n t e r b e d d e d sandstones  conglomerate  and s i l t s t o n e s makes up  d i s c o n n e c t e d , low, t r e e covered h i l l s .  Lithologically  t h i s se-  quence can be d i v i d e d i n t o two formations separated by a probable unconformity.  M i c r o f o s s i l s i n the upper u n i t i n d i c a t e a Lower  T e r t i a r y age but other  d e f i n i t e c o r r e l a t i o n with d e s c r i b e d u n i t s i n  areas i s not p o s s i b l e .  designated  The  lower formation  i s here  the D e l t a Rocks Formation while the upper i s c a l l e d  the Ika Formation. S e r p e n t i n i t e s make up jacent p a r t s of F i d a l g o s e r p e n t i n i t e encloses cite,  c e l e s t i t e , and  considered Triassic  the whole of Goat I s l a n d and  Island.  On  ad-  southern F i d a l g o I s l a n d another  an unusual hydrothermal v e i n c o n t a i n i n g strontianite.  These u l t r a b a s i c rocks  p a r t o f the F i d a l g o Formation and  are  are of probable  age. A small outcrop of marine P l e i s t o c e n e o c c u r s at the  end  of Goat I s l a n d and  Vashon t i l l  and  contains  an assemblage o f  outwash cover most of F i d a l g o  east  invertebrates.  I s l a n d and  Pleasant  Ridge. P r e - T e r t i a r y deformation has Paleozoic  been i n t e n s e w i t h both  and Mesozoic sequences f o l d e d , sheared and  Cenozoic deformation has been r e s t r i c t e d to Miocene folding.  cal-  faulted. concentric  Axes of both p r e - T e r t i a r y and T e r t i a r y f o l d i n g are  a l i g n e d e s s e n t i a l l y east-west.  CONTENTS Chapter  Page  1.  Introduction L o c a t i o n and access P r e v i o u s g e o l o g i c a l work F i e l d work Acknowledgments  2.  Geography Surface features Mainland Ika I s l a n d Goat I s l a n d Bald Island Martha and Whitman Islands S e a l Rocks Deadman and L i t t l e Deadman I s l a n d s Hope I s l a n d Skagit Island D e l t a Rocks McGinn I s l a n d . . . . . . . Climate . . . . . . . Vegetation . . . . . Culture . . . . . Water supply and drainage  3.  . . . . . . . .  1 1 2 2 4  •. .  . . . . .  4 4 5 7 7 8 8 9 9 9 10 10 11 11 12 12 14  Geology 20 General Features . 20 T a b l e " o f Formations . . . . 22 Pre-Upper Cretaceous sedimentary rocks 23 Occurrence . . . . . . . . . . 23 Stratigraphy . 23 P a l e o z o i c (?) Goat I s l a n d Formation 24 F i n e - g r a i n e d rocks . . . . . . . . 25 Medium-grained rocks . . . . . . . . . . . . 27 Coarse-grained rocks . . . . . 28 Mesozoic(?) La Conner Formation 30 Summary o f p r e - T e r t i a r y s t r a t i g r a p h y 33 Origin 38 V o l c a n i c Rocks 40 Occurrence . . . . . . . . . . . . . . . . . . 40 Field description" . 41 Petrography 43 L i t t l e Deadman I s l a n d . 44 V o l c a n i c rocks south o f La Conner' 44 V o l c a n i c rocks from Hope I s l a n d 45 V o l c a n i c rocks from Southern F i d a l g o I s l a n d . 47 Summary o f greenstone p e t r o l o g y 47 Volcanic breccia 48  Page Origin 50 Age 53 Late Cretaceous-Early T e r t i a r y Sediments 54 Occurrence 54 Stratigraphy 55 Delta Rocks Formation 55 Ika Formation 57 Sedimentary structures 62 Age and c o r r e l a t i o n 64 Origin 68 Delta Rocks Formation 68 Ika Formation 71 Paleobotany 73 General 73 A n a l y t i c a l Procedure 74 Identification 75 Environmental s i g n i f i c a n c e 77 Marine P l e i s t o c e n e 79 I n t r u s i v e Rocks 82 Occurrence 82 Petrology 85 Field description 85 Thin-section d e s c r i p t i o n . . 86 Origin '. . . 87 Serpentinization 91 Steatization . . . . . . . . . . . . . . . . . . 92 Age . . . . . . . . . . . . . . . . . 93 Structure . . . . . . . . . . . . . . . . . . . . 94 Regional 94 Local 95 Economic geology 99 Strontium' . : 99 Occurrence . . . . . . . . . . . . . . . . . . 99 Local geology . . . . . . . . . . 100 Vein mineralization 102 Serpentinite . . . . . . . . . . . . 105 - O r i g i n of deposit . 109 Serpentinite . . . . . . 109 Strontium vein 110 General 112 Gravel and crushed rock' 112 Glaciation 114 G l a c i a t i o n i n the Puget Sound trough . . . . . . 114 G l a c i a l e f f e c t s i n the map area 117 Geomorphology 120 Skagit D e l t a 120 Shorelines of mainland and i s l a n d s 121 Coves, sea c l i f f s and caves 123 "Deeps" i n Skagit Bay 126 Summary of post-Vashon h i s t o r y as i n d i c a t e d by physiography 128 Bibliography 130  ILLUSTRATIONS Plate 1. 2. 3. 4. 5. 6. 7.  Page G e o l o g i c map o f r e p o r t area Index map Measured s e c t i o n o f p o r t i o n o f the Ika Formation N o r t h - s o u t h c r o s s - s e c t i o n through Ika I s l a n d S t r u c t u r a l i n t e r p r e t a t i o n o f P a l e o z o i c C ? ) rocks on b a s i s o f s t e r e o g r a p h i c a n a l y s i s S t r u c t u r a l i n t e r p r e t a t i o n o f T e r t i a r y rocks on b a s i s o f s t e r e o g r a p h i c a n a l y s i s S k e t c h map o f La Conner Strontium mine  i n pe-etee^~K\L^ 3 . . . 61 69 96 97 101  Figure 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.  View east toward Ika I s l a n d Southwest s i d e o f Ika I s l a n d South end o f Swinomish Channel View n o r t h up S k a g i t Bay View south down S k a g i t Bay S k a g i t I s l a n d from n o r t h shore o f Hope I s l a n d . . . . F o l d e d graywacke on S k a g i t I s l a n d F a u l t i n g i n sheared graywacke Photomicrograph o f P a l e o z o i c C ? ) sheared graywacke . . Photomicrograph o f ' s h e a r e d P a l e o z o i c C ? ) pebble conglomerate Graywacke cut by m u l t i t u d e o f r a m i f y i n g quartz ve i n l e t s Photomicrograph o f MesozoicC?) a r g i l l a c e o u s l i m e stone nodule Photomicrograph o f MesozoicC?) sheared graywacke . . Photomicrograph o f MesozoicC?) f e l d s p a t h i c graywacke. S p i l i t e v o l c a n i c r o c k s ' d i p p i n g s t e e p l y toward the observer P o o r l y developed p i l l o w l a v a s at southeast end o f Fidalgo Island Photomicrograph o f s p i l i t e showing h i g h degree o f saussuritization Photomicrograph o f m i c r o p o r p h y r i t i c s p i l i t e from flow b r e c c i a on Ika I s l a n d Photomicrograph o f conglomerate from D e l t a Rocks Formation Photomicrograph o f conglomerate m a t r i x , D e l t a Rocks Formation T y p i c a l conglomerate o f Ika Formation, i n h i l l s near mouth o f N o r t h Fork o f the S k a g i t R i v e r T y p i c a l conglomerate o f Ika Formation, i n h i l l s near" mouth o f N o r t h Fork o f the S k a g i t R i v e r Conglomerate o f the D e l t a Rocks Formation Photomicrograph o f sandy s i l t s t o n e o f the Ika Formation  6 6 15 15 18 18 26 26 29 29 34 34 37 37 43 43 46 46 56 56 59 59 63 63  Figure  Page  25. 26. 27.  Small f a u l t i n Ika Formation on I k a Island 65 C o a l i f i e d l o g i n sandstone of the I k a Formation . . . 65 Invertebrate-bearing marine P l e i s t o c e n e conglomerate at east end of Hope Island 81 G l a c i a l s t r i a t i o n s and grooving; south side of K i k e t Island 81 J o i n t e d s e r p e n t i n i t e on north shore of Hope I s l a n d . . 8 4 View west along south shore of Hope Island 84 Photomicrograph of serpentinized dunite w i t h c h a r a c t e r i s t i c mesh texture 89 Two o f the three a d i t s driven to c e l e s t i t e strontianite vein 103 S e r p e n t i n i t e c l i f f s above a d i t s shown i n f i g u r e 32 . . 103 Photomicrograph of s e r p e n t i n i t e enclosing celestite-strontianite vein 108 Photomicrograph of serpentinite"adjacent to c e l e s t i t e - s t r o n t i a n i t e vein 108 Quarry i n conglomerate of the D e l t a Rocks Formation . 113  28. 29. 30. 31. 32. 33. 34. 35. 36.  INTRODUCTION  LOCATION AND ACCESS This report describes the geology of an area of about 45 square m i l e s , l o c a t e d i n Western Skagit County,  northwestern  Washington, about 20 miles due south o f Bellingham and 40 miles south o f the Canada-United States border.  The area i s bordered  on the east by Skagit D e l t a a l l u v i u m , on the north by alluvium and g l a c i a l d e b r i s , while to the west and south i t i s d e l i m i t e d by Skagit Bay. La Conner, a town of about 600 population l i e s close to the geographical center of the map area. Most of the mainland and southern Fidalgo I s l a n d are r e a d i l y a c c e s s i b l e by road, but many of the outcrops o c c u r r i n g along the coast can be v i s i t e d only on foot and at low t i d e . The i s l a n d s o f Skagit Bay, comprising the western p o r t i o n of the map area, can be reached only by boat and then only with some d i f f i c u l t y .  Skagit Bay, when whipped by southerly winds,  can become unpleasantly rough, and hazardous f o r a small boat. Shoal areas and mud f l a t s are n a v i g a t i o n hazards, even f o r shallow d r a f t outboard v e s s e l s .  At low t i d e i t i s not p o s s i b l e to cross  most of the mud f l a t areas, hence I k a , Whitman and Martha Islands are i n a c c e s s i b l e at low water. high t i d e .  Other d i f f i c u l t i e s a r i s e at  Several i s l a n d s , i n p a r t i c u l a r Hope and Seal Rocks,  are p a r t i a l l y bordered by wave cut benches, which are b a r e l y water covered at high t i d e .  The unwary navigator can e a s i l y  lose a shear p i n or even hole h i s boat unless he approaches these i s l a n d s with considerable c a u t i o n .  2  PREVIOUS GEOLOGICAL WORK  McLellan (1927) i n h i s work on the San Juan Islands b r i e f l y describes the rocks o f the northern end of F i d a l g o I s land, some s i x miles northwest of the area described i n t h i s report.  More r e c e n t l y W.R.Danner, while doing d e t a i l e d geology  i n the San Juan I s l a n d s , has had occasion to v i s i t the area. Various p u b l i c a t i o n s of the "Washington D i v i s i o n of Mines and Geology," and predecessor agencies, r e f e r to d i f f e r e n t aspects of the general r e g i o n without much s p e c i f i c reference to t h i s p a r t i c u l a r area.  Included are p u b l i c a t i o n s byJ B r e t z (1913?  1920); Cambell (1953); Daly (1912); Glover (1935, 1947) and W i l l i s (1898). Landis (1929) reported on the strontium occurrence at the southeast end of Fidalgo I s l a n d .  Sceva (1950) discussed the  geology and ground water resources o f the Skagit D e l t a .  FIELD WORK  F i e l d work was s t a r t e d i n December I960 and continued at i n t e r m i t t e n t i n t e r v a l s through November 1961.  F i e l d data f o r  the eastern p o r t i o n of the area was p l o t t e d on U.S. G e o l o g i c a l Survey topographic sheets with a s c a l e o f 2 inches equal one m i l e . The western part was p l o t t e d on topographic sheets of s c a l e one inch equal one m i l e .  Although l a c k i n g recent c u l t u r a l changes,  these maps were found g e n e r a l l y adequate and accurate.  4  ACKNOWLEDGMENTS  S e v e r a l people o f f e r e d c o n s i d e r a b l e a s s i s t a n c e the p r e p a r a t i o n o f t h i s r e p o r t .  during  Mr. A l a s t a i r S i n c l a i r o f f e r e d  much c o n s t r u c t i v e c r i t i c i s m and made many h e l p f u l s u g g e s t i o n s . Dr. Glen Rouse o f the Botany Department was o f i n d i s p e n s i b l e h e l p w i t h methods, i d e n t i f i c a t i o n and p r e s e n t a t i o n o f the p a l e o b o t a n i c a l data.  Dr. P.A.Dehnel, o f the zoology  department,  k i n d l y i d e n t i f i e d the marine P l e i s t o c e n e i n v e r t e b r a t e s .  Special  thanks are due Dr. W.R.Danner under whose s u p e r v i s i o n t h i s t h e s i s was w r i t t e n .  Dr. Danner o f f e r e d much h e l p f u l advice both  i n the l a b o r a t o r y and the f i e l d .  GEOGRAPHY  SURFACE FEATURES  The  e n t i r e map area i s t o p o g r a p h i c a l l y low, with  ele-  v a t i o n s r a n g i n g from s e a l e v e l to a maximum height o f 440 f e e t on I k a I s l a n d .  F l a t and immensely f e r t i l e r i v e r a l l u v i u m o f the  Skagit D e l t a covers the western p o r t i o n o f the map a r e a . Bay  Skagit  and b o r d e r i n g mud f l a t s comprise the western p a r t o f the  area.  The North Fork o f the Skagit R i v e r flows westward through  the southern  p a r t o f the map a r e a .  Bedrock p r o j e c t s through the  a l l u v i u m as rounded h i l l s and i n Skagit Bay forms islands.  steep-sided  5  MAINLAND On the mainland, bedrock occurs along the North Fork of the Skagit River and northward along Pleasant Ridge, mostly as low, r o l l i n g h i l l s with maximum e l e v a t i o n s of 100 to 150 f e e t . A l l h i l l s are surrounded by a l l u v i u m , the surface of which slopes gently from sea l e v e l near F i s h Town to about 10 f e e t above sea l e v e l at the eastern border of the map area.  Except where  c l e a r e d f o r a g r i c u l t u r a l purposes, vegetation on the h i l l s i s dense, and includes c o n i f e r s , deciduous trees and under brush. The west and south sides of these h i l l s are o f t e n marked by v e r t i c a l to near v e r t i c a l , 20 to 30 foot high c l i f f s . Much of the town of La Conner i s b u i l t on and around bedrock h i l l s r i s i n g to s i m i l a r e l e v a t i o n s as those along the Skagit R i v e r .  These are o c c a s i o n a l l y steep-sided and are densely  covered with vegetation except where c l e a r e d by man. Within the map area, Fidalgo I s l a n d can be d i v i d e d into two d i s t i n c t geographical d i s t r i c t s : (a) A southeast promentory bordering Swinomish Slough and (b) the remainder of the i s l a n d north o f the promentory.  The northern and western p a r t s of the  i s l a n d form a r o l l i n g upland surface, a t t a i n i n g an average e l e v a t i o n of 100 to 300 feet but s h o r e l i n e s are bordered by 50 to 75 foot high b l u f f s . depressions.  The upland surface contains s e v e r a l closed  Thick f o r e s t and underbrush cover the i s l a n d .  Some of the most rugged t e r r a i n w i t h i n the map area l i e s at the southeast end of Fidalgo I s l a n d . R e l i e f i s approximately 400 f e e t with numerous steep slopes and c l i f f s , e s p e c i a l l y  Figure 1. View east toward Ika I s l a n d . Notice opposed d i p s . West end of Goat Island to l e f t .  Figure 2. Southwest side of Ika I s l a n d . Contact between Delta Rocks Formation (below) and Ika Formation (above) l i e s h a l f way up slope. Both units dip north ( l e f t ) .  7  around the margin.  The area i s h e a v i l y covered with second growth  timber and underbrush.  Several overgrown l o g g i n g roads are  present, and the remains o f two abandoned sawmills i n d i c a t e former extensive l o g g i n g operations. In the northwest corner of the map area a sandspit connects Fidalgo and K i k e t I s l a n d s . Kifeet Island has an area o f about 80 acres and a maximum e l e v a t i o n o f 160 f e e t .  Vegetation  i s t h i c k except on the eastern and western e x t r e m i t i e s of the island.  A p r i v a t e road t r a v e r s e s the i s l a n d from east to west.  IKA ISLAND Ika Island has an area of 115 acres, and w i t h the exception of a permanent 32 acre s a l t water swamp, has a steep, p r e c i p i t o u s land s u r f a c e .  I t i s t o p o g r a p h i c a l l y asymmetrical  with a northern high p o i n t of 155 feet and a southern high of 440 f e e t separated by a saddle l e s s than 30 feet high.  Soil  cover i s t h i n over most o f the i s l a n d but vegetation i s t h i c k except on v e r t i c a l rock faces.  These tend to be separated by  benches covered with a t h i c k tangle of v e g e t a t i o n .  The I s l a n d  i s completely surrounded by mud f l a t s and i s a c c e s s i b l e only at high t i d e .  GOAT ISLAND Goat I s l a n d , covering 109 acres, l i e s adjacent to the Swinomish Ship Channel, consequently i t s north side can be reached by boat at any time.  I t i s lowest at the west end,  g r a d u a l l y r i s i n g to i t s maximum e l e v a t i o n of 225 feet at the  8  northeast edge.  The i s l a n d i s steep-sided, being bounded on  the east, north and south by c l i f f s of v a r y i n g height. route of convenient  The  access to i t s top i s from the west.  only  During  the second World War Goat I s l a n d was the home of a small army detachment, based i n what was c a l l e d Fort Whitman.  Subsequently  the Fort was abandoned and vegetation overgrew the c l e a r e d areas making ground traverses d i f f i c u l t .  Numerous barbed wire en-  tanglements are s t i l l present and can be hazardous. now  Goat I s l a n d ,  the property of the Washington State Game Department, i s  set aside as a game preserve.  BALD ISLAND Bald I s l a n d , located near the mouth of the North Fork of the Skagit River covers 12.5 103 f e e t .  acres with a maximum height of  I t i s a rounded grass and tree covered knob, used  by i t s owners f o r c a t t l e g r a z i n g .  MARTHA AND  WHITMAN ISLANDS  Martha and Whitman I s l a n d s , a r b i t r a r i l y named by the author i n l i e u of o f f i c i a l names, are two adjacent rocky knobs, each about an acre i n extent, l y i n g north of Goat I s l a n d . Martha I s l a n d i s about 35 feet high, barren of trees or shrubs but supports some grass i n f r a c t u r e s or depressions.  Whitman  I s l a n d , perhaps 50 feet high, i s almost c i r c u l a r and bounded by almost v e r t i c a l c l i f f s . mud  Both i s l a n d s are surrounded by  f l a t s which are exposed at low t i d e .  9  SEAL ROCKS . S e a l Rocks i s a group of s h o a l rock areas i n the middle of S k a g i t Bay. A seaward s l o p i n g rocky t e r r a c e surrounds the "Rocks" which are more or l e s s uncovered at low t i d e but l a r g e l y awash at h i g h , vessels.  so are a d e f i n i t e menace t o c l o s e l y p a s s i n g  A n a v i g a t i o n beacon i s i n s t a l l e d at the h i g h e s t  of Seal Rocks.  Vegetation  point  i s l i m i t e d to l i c h e n s , moss and  grasses.  DEADMAN AND LITTLE DEADMAN ISLANDS Deadman and L i t t l e Deadman I s l a n d , l o c a t e d between Goat and Hope I s l a n d s , are r e s p e c t i v e l y , s i x and three acres i n area.  Except f o r s i z e they are s i m i l a r and both support a  f l o r a o f c o n i f e r s and underbrush.  Both a r e f a i r l y  but a c c e s s to t h e i r summits i s easy.  Deadman I s l a n d r i s e s to  50 f e e t while L i t t l e Deadman i s perhaps one-half number o f l a r g e eagle n e s t s L i t t l e Deadman  steep-sided  that.  A  were observed i n the few t r e e s o f  Island.  HOPE ISLAND Except f o r F i d a l g o  I s l a n d , Hope I s l a n d i s the l a r g e s t  i s l a n d w i t h i n the map area, h a v i n g an area o f about 180 acres and  an east-west dimension o f n e a r l y one m i l e .  I t i s almost  f l a t - t o p p e d with average e l e v a t i o n o f about 125 f e e t but near the east end i s more than 160 f e e t above s e a - l e v e l .  The i s l a n d  i s mostly bounded by steep c l i f f s which a t the southwest and  10 west end plunge at h i g h angles i n t o deep water. n o r t h , east and southeast  shores are bordered  Much of the  by sand beaches.  Care must be e x e r c i s e d i n l a n d i n g on the southern shores because o f l a r g e boulders  and  and  irregularities  t e r r a c e b o r d e r i n g these p o r t i o n s o f the I s l a n d .  The  eastern  on the  rocky  cove on  the n o r t h shore appears to have only a g r a d u a l l y s h a l l o w i n g sandy bottom making l a n d i n g a "wet-boot" a f f a i r but with danger to boat or motor.  Except  i s l a r g e l y grass covered,  the I s l a n d i s f o r e s t e d with a dense  growth of c o n i f e r s and  at the extreme west end,  no  t h i c k underbrush.  which  Hope I s l a n d i s State  p r o p e r t y and a p a r t o f Deception Pass S t a t e Park.  SKAGIT ISLAND L y i n g to the n o r t h o f Hope I s l a n d , Skagit I s l a n d i s a mound-like rock r i s i n g to 110  f e e t and  i s bounded by near v e r t i c a l c l i f f s rocky,  wave-cut t e r r a c e .  c o v e r i n g 26 a c r e s .  dropping  It  down to a narrow,  Access to the I s l a n d summit i s  p o s s i b l e only at the n o r t h e a s t end where a s m a l l sandy beach a l l o w s a boat l a n d i n g and where c l i f f s the grass covered brush  covered.  southwest end  are l a c k i n g .  Except  for  the I s l a n d i s c o n i f e r and  Along with Hope I s l a n d , Skagit I s l a n d i s a p a r t  of Deception Pass S t a t e Park.  DELTA ROCKS D e l t a Rocks i s a c o l l e c t i v e  term f o r a s m a l l group of  rocky k n o l l s south o f the mouth of the North Fork of the S k a g i t  11  R i v e r and the only outcrop south of the Skagit River w i t h i n the map area.  This outcrop i s separated from diked dry land by one-  h a l f mile of s a l t water swamp, impassable at high t i d e .  Even  at low water h i p boots are necessary because of the soggy, unpredictable surface.  The maximum e l e v a t i o n at D e l t a Rocks i s  86 f e e t .  McGINN ISLAND Across Swinomish Slough from the southeast t i p of Fidalgo I s l a n d i s s i t u a t e d a small i s l a n d of 38 acres.  Known as McGinn  I s l a n d , and t i e d to the Skagit D e l t a by a sand bar, i t forms the east border of "Hole-in-the-Wall", or southern entrance to the Swinomish Ship Channel.  The i s l a n d i s h e a v i l y f o r e s t e d and  i s the s i t e of s e v e r a l p r i v a t e homes. A quarry has been opened i n i t s north s i d e .  CLIMATE  The climate w i t h i n the map area i s equitable and m i l d . Average p r e c i p i t a t i o n on the Skagit D e l t a i s 36 inches, with the greatest r a i n f a l l i n December and the l e a s t i n J u l y .  Pre-  v a i l i n g winds are from the southwest, and though these may a t t a i n considerable force over Skagit Bay, winds over the d e l t a are r a r e l y strong.  Temperatures are moderate with winter lows  seldom below 30°F and summer highs r a r e l y above 80°F.  12 VEGETATION  H i l l y areas have been logged i n times past and are now densely covered with secondary growth timber which, among the evergreens includes Douglas F i r , Grand F i r , Cedar and Hemlock.  In the more r e c e n t l y logged areas w i l l o w , w i l d cherry,  western b i r c h , dogwood, cottonwood, alder and b i g l e a f maple are common. Shrub vegetation includes s t i n g i n g n e t t l e s , Oregon grape, blackberry, salmon berry, s a l a l , w i l d rose and buckbrush. The " f l a t l a n d s " made up almost e n t i r e l y of Skagit R i v e r alluvium i s e x c e p t i o n a l l y r i c h and i n t e n s i v e l y farmed. Major crops are g r a i n s of various s o r t s , e s p e c i a l l y oats with a record 175 bushels per acre.  Other crops include hay, hops,  vegetables and sugar beets, as w e l l as much of the cabbage, t u r n i p beet and c a u l i f l o w e r seed used i n the United S t a t e s .  CULTURE  The Skagit D e l t a Country has long been occupied by several d i f f e r e n t Indian t r i b e s .  The time of a r r i v a l of the  f i r s t indians i s unknown but presumably they have been i n the area f o r s e v e r a l thousands of years.  A s i t e i n eastern  Washington was occupied about 8,000 years ago and i t seems reasonable  to assume that occupation west of the Cascades was  13  e s s e n t i a l l y contemporaneous.  The moist c l i m a t i c conditions of  Western Washington are not, however, conducive to p r e s e r v a t i o n of c u l t u r a l s i t e s . Evidence f o r recent i n d i a n occupancy i s very s t r i k i n g w i t h i n the map  area.  Many of the h i l l s and lowlands along  the Skagit R i v e r are mantled with human-created d e b r i s , especi a l l y clam and mussel s h e l l s , which make up impure, man-made coquinas up to 3 feet t h i c k .  Presumably these middens were the  garbage dumps f o r adjacent i n d i a n v i l l a g e s .  A most s t r i k i n g  example of t h i s i s on Swinomish Slough across the r i v e r from La Conner where an e n t i r e f l a t meadow surface i s b u i l t on a s h e l l base.  Another occurrance i s near the mouth of the Skagit  R i v e r on the north shore.  Excavations by an a r c h e a l o g i c a l team  penetrated more than 3 f e e t of s h e l l and interbedded m a t e r i a l s without reaching a base.  soil  Because a cover of large  c o n i f e r s covers t h i s l a t t e r s i t e , i t s age must be at Least s e v e r a l hundred years.  Within the past year an i n d i a n skeleton  was uncovered i n b u r i a l p o s i t i o n from t h i s area. The f i r s t known v i s i t of a white man L t . Joseph Whidbey, commander of HMS  to the area was  by  Chatham, accompanying the  George Vancouver e x p e d i t i o n which explored Puget Sound i n 1792. whidbey f i r s t s a i l e d north through Saratoga Passage to the v i c i n i t y of the mouth of the Skagit R i v e r .  Several weeks l a t e r ,  i n June 1792, he discovered the true nature of Deception Pass when he t r a v e r s e d i t from west to east, again p e n e t r a t i n g to the region of the Skagit D e l t a .  14  During the next 50 years the i n e v i t a b l e western c y c l e of trappers and t r a d e r s , followed by s e t t l e r s , was enacted i n the Puget Sound Country.  By the middle of the 19th century the  r i c h farmlands of the Skagit D e l t a were a t t r a c t i n g homesteaders while the waters of Skagit Bay, somewhat l a t e r , a t t r a c t e d commercial fishermen. La Conner, the only town w i t h i n the map settlement of about 600 persons.  area, i s a  I t was f i r s t s e t t l e d i n 1867  as a f i s h i n g and a g r i c u l t u r a l v i l l a g e and f u l f i l l s a s i m i l a r r o l e today. The surrounding country i s almost completely and s u p p l i e d by a c l o s e l y spaced network of roads.  agricultural Much of the  farmland i s on reclaimed s a l t t i d e marsh, with the waters of Skagit Bay and the Skagit R i v e r being held back by a complex p a t t e r n of d i k e s .  WATER SUPPLY AND DRAINAGE  The major drainage feature of the area i s the North Pork of the Skagit which i s the p r i n c i p a l d i s t r i b u t a r y of the Skagit R i v e r .  Drainage area of the west f l o w i n g Skagit R i v e r  i s 3,060 square miles of which 400 square miles are i n Canada. The average discharge of the r i v e r i s 16,260 cubic feet per second and i s maintained  at a rather steady flow by a s e r i e s  of upstream dams and r e s e r v o i r s . Because the r e g i o n a l water t a b l e i s only s l i g h t l y above  F i g u r e 3. S o u t h end o f S w i n o m i s h C h a n n e l , between F i d a l g o and McGinn I s l a n d s  F i g u r e 4. V i e w n o r t h up S k a g i t B a y . Hope I s l a n d t o l e f t , L i t t l e Deadman I s l a n d c e n t e r , Deadman I s l a n d right.  16 s e a - l e v e l , ground water i s found at shallow depths over the e n t i r e Skagit D e l t a .  Lenses of sand and g r a v e l , the p r i n c i p a l  a q u i f e r s are capable of producing large q u a n t i t i e s o f water. Wells 40 to 70 feet deep pump 125 to 600 g a l l o n s per minute. These are pump y i e l d s and o f t e n below t h e i r t h e o r e t i c a l p o t e n t i a l . (Sceva, 1950). Deep w e l l s , below 110 f e e t , and those near the margin of the d e l t a penetrate only f i n e - g r a i n e d sediments and consequently are poor producers. Recharge o f a q u i f e r s i s thought to be p r i n c i p a l l y from p r e c i p i t a t i o n with small amounts cont r i b u t e d l o c a l l y by the Skagit R i v e r . As of 1950 only seven water analyses had been run o f ground waters on the Skagit D e l t a and these gave diverse results.  T o t a l hardness ranged from high to low; two water  samples were very high i n bicarbonates.  Most ground water from  the d e l t a r e q u i r e s no treatment f o r domestic use, but l o c a l l y i t i s high i n i r o n or carbonaceous m a t e r i a l which r e q u i r e s chemical treatment f o r removal. Pleasant Ridge, composed of u n d i f f e r e n t i a t e d P l e i s t o cene sediments, and capped by Vashon t i l l contains s e v e r a l perched water t a b l e s .  These, while u s u a l l y adequate f o r dom-  e s t i c use, are too l o c a l and r e s t r i c t e d f o r the heavier pumping r e q u i r e d f o r stock use.  Wells, penetrating to depths of 100  to 200 f e e t , supply s u f f i c i e n t q u a n t i t i e s of water f o r stock and domestic use from sand or gravel lenses l y i n g below the r e g i o n a l water t a b l e .  Two logged w e l l s are located w i t h i n the  map area and are named below. also tabulated.  A water a n a l y s i s f o r one w e l l i  Data from Sceva (1950).  Well 5H-1 - West side Pleasant Ridge. Ground l e v e l , 90«; T.D.  112'; B i t 4"; Casing 112';  depth to producing zone 90*; Thickness of producing i n t e r v a l , 22'; Producing i n t e r v a l rock type, f i n e - g r a i n e d sand; Date d r i l l e d , 1946; Water use, domestic and stock purposes. Sample D e s c r i p t i o n  Thickness  Depth  A l l u v i u m and t i l l of Vashon age: S o i l and hardpan  50  50  P l e i s t o c e n e Deposits, u n d i f f e r e n t i a t e d : Sand Clay  30 10  80 90  Sand, f i n e - g r a i n e d , water bearing  22  112  Chemical A n a l y s i s of water, w e l l 5H-1 (U.S.Navy) P a r t s per M i l l i o n I r o n , Fe Bicarbonate, HCO, S u l f a t e , SO, C h l o r i d e , CI Fluoride, F N i t r a t e , N0 7  ?  Hardness as CaCO,  total non-carbonate 7  0.05 358.0 20.0 6.0 0.2 18.0 320.0 190.0  Well 9H-1 - Southeast end of Pleasant Ridge. Ground l e v e l , 25'; T.D.  60'; B i t , 6"; Casing l e n g t h  60*; Date d r i l l e d , 1944; Use of water, domestic. No analyses, but water i s known to be high i n i r o n .  Figure 5- View south down Skagit Bay. Seal Rocks, right; Goat Island, center; Fidalgo Island, l e f t .  Figure 6. Skagit Island from north shore of Hope Island.  19 As regards  water supply from w e l l s d r i l l e d on F i d a l g o  I s l a n d or other areas less predictable. and p r o v i d e  o f p r e - T e r t i a r y r o c k s the r e s u l t s  are  Most h o l e s are from 6 to 60 f e e t i n depth  an adequate source  of domestic water.  Presumably  t h i s water i s e x t r a c t e d from f r a c t u r e s because s u r f a c e  outcrop  suggest there i s no e f f e c t i v e p o r o s i t y or p e r m e a b i l i t y i n p r e Tertiary  rocks. Another minor source  c a t c h b a s i n s and  cisterns.  of water f o r d w e l l i n g use, People who  use,  i s by  or have used, t h i s  system r e p o r t i t p r o v i d e s more than an adequate supply of f r e s h , s o f t r a i n water. The age  and  s m a l l e r i s l a n d s have no  s i g n i f i c a n t surface drain-  to the w r i t e r ' s knowledge no w e l l s have been  on them.  The  army, when occupying  drilled  Goat I s l a n d , p i p e d f r e s h  water from the mainland. An almost u n l i m i t e d q u a n t i t y of f r e s h water i s a v a i l able w i t h i n the area covered  by t h i s r e p o r t .  Only a very  percentage o f a v a i l a b l e ground water i s b e i n g u t i l i z e d and much g r e a t e r supply watertable  c o u l d be o b t a i n e d without  small a  appreciable  drawn down.  In the u n l i k e l y event ground water s u p p l i e s became inadequate, water c o u l d be d i v e r t e d from the S k a g i t R i v e r . With p u r i f i c a t i o n t h i s would be and  stock purposes.  s a t i s f a c t o r y f o r a l l domestic  20  GEOLOGY  GENERAL FEATURES  The western Skagit Delta area i s underlain by rocks of PaleozoicC?), MesozoicC?) and Cenozoic ages.  Included are  igneous, sedimentary and low-grade metamorphic rocks. Low grade, regionally metamorphosed PaleozoicC?) sedimentary rocks are exposed i n the southwest part of the map area.  This i s a sequence composed of graywacke, p h y l l i t e s ,  conglomerates,  breccias, slates and interbedded volcanic rocks.  Deformation has been intense and the rocks are highly deformed. MesozoicC?) rocks, e s s e n t i a l l y graywacke and p h y l l i t e , crop out i n a northwest-southeast and Kiket Islands i n the northwest  belt extending from Skagit to a h i l l north of Dodge  Valley i n the southeast part of the map area. Volcanic rocks, largely s p i l ^ i t e s , occur at the very southeast end of Hope Island and crop out at spotty i n t e r v a l s southward to the region just west of La Conner.  Alteration i s  intense and c a t i c l a s t i c deformation i s present at the Hope Island outcrop. the northwest  A flow-breccia of similar material crops at  end of Ika Island.  The PaleozoicC?) and  MesozoicC?) sequences with contained volcanic rocks are c a l l e d the Goat Island Formation and La Conner formations respectively. Poorly sorted Tertiary conglomerates  with interbedded  21 sandstones and s i l t s t o n e s are present i n the south p o r t i o n of the map area.  These sedimentary rocks have been preserved i n  an e s s e n t i a l l y east-west trending s y n c l i n e . I d e n t i f i a b l e m a c r o f o s s i l s were not found but a n a l y s i s of f i n e r - g r a i n e d p o r t i o n s o f the sequence revealed the presence of plant microf o s s i l s , e s p e c i a l l y spores and p o l l e n .  An e a r l y T e r t i a r y age  i s suggested by t h i s assemblage, but i t i s not p o s s i b l e to c o n c l u s i v e l y equate t h i s sequence with described rocks from other areas.  However on the b a s i s of l i t h o l o g y i t i s p o s s i b l e  to subdivide these rocks i n t o two formations probable unconformity.  separated by a  The older i s c a l l e d the D e l t a Rocks  formation while the younger i s termed the Ika Formation. P l e i s t o c e n e deposits are represented discontinuous  outwash and t i l l u n i t s .  by abundant though  These are the deposits  of the l a s t stage of P l e i s t o c e n e g l a c i a t i o n (Vashon).  A  l i m i t e d s u i t e of marine i n v e r t e b r a t e remains were found i n P l e i s t o c e n e outwash or beach deposits at the east end of Hope Island. U l t r a b a s i c i n t r u s i v e rocks make up Hope I s l a n d and adjacent p a r t s of Fidalgo I s l a n d .  A s i m i l a r u l t r a b a s i c rock,  with a contained hydrothermal v e i n of strontium  minerals,  occurs at the southeast end of Fidalgo I s l a n d .  These u l t r a -  basic i n t r u s i o n s , now s e r p e n t i n i t e , are assigned to the Fidalgo Formation of McLellan  (1927).  Skagit River alluvium c o n s t i t u t e s the youngest and a e r i a l l y the l a r g e s t l i t h o l o g i c u n i t of the western Skagit  22  Delta area. deposited River.  The e n t i r e S k a g i t D e l t a i s composed  of alluvium  s i n c e the P l e i s t o c e n e by the west f l o w i n g  The D e l t a i s i n the process  Skagit  o f being b u i l t westward and  i s g r a d u a l l y t i e i n g many o f the i s l a n d s to the mainland. Following i s a table of formations.  TABLE OF FORMATIONS SEDIMENTARY-VP LOANIC ROCKS ERA Cenozoic  PERIOD  NAME  LITHOLOGY  QuaternaryRecent  Skagit d e l t a a l l u vium and beach deposits  Pleistocene  G l a c i a l t i l l and outwash. Some marine d e p o s i t s  EoceneC ? )  Ika Formation  Conglomerate with interbedded sandstones and s i l t stones. Much carbonaceous material.  Paleocene(?) EoceneC?)  D e l t a Rocks Formation  Conglomerate composed l a r g e l y o f metamorphic rocks  MesozoicC?)  l a Conner Formation  Graywacke, a r g i l l ite, argillaceous limestone nodules,/  PaleozoicC ?)  Goat I s l a n d Formation  Graywacke, conglomerate, b r e c c i a , a r g i l l i t e , pillow lavas, s p i l i t e .  INTRUSIVE ROCKS MesozoicC?)  Upper TriassicC?)  Fidalgo Formation  Ultrabasic intrusions, serpentinite, celestite-strontianite vein.  23 PRE-UPPER CRETACEOUS SEDIMENTARY ROCKS  OCCURRENCE  The pre-Upper Cretaceous r o c k s o f the S k a g i t Bay a r e a are an u n f o s s i l i f e r o u s sequence o f graywackes with t h i n of i n t e r b e d d e d s l a t e s , a r g i l l i t e s and conglomerates. crops occur i n h i l l s surrounded as i s l a n d s i n S k a g i t Bay.  layers  Out-  by r e c e n t d e l t a i c d e p o s i t s or  Where s u b j e c t e d to wave e r o s i o n  c l i f f s are prominent and are f r e q u e n t l y marked by d i f f e r e n t i a l e r o s i o n a l o n g cleavage or bedding The  w r i t e r i s unable  pre-Upper Cretaceous  planes.  to a s s i g n d e f i n i t e ages to the  sedimentary  rocks o f the Skagit Bay a r e a ,  or to c o r r e l a t e them with r o c k s d e s c r i b e d from other a r e a s . They w i l l be d i s c u s s e d a c c o r d i n g to a broad and t e n t a t i v e twof o l d d i v i s i o n as o u t l i n e d i n the f o l l o w i n g s e c t i o n on stratigraphy.  STRATIGRAPHY  On a l i t h o l o g i c b a s i s , u s i n g e s p e c i a l l y c o l o r , s i z e , degree o f deformation, presence  or absence o f v o l c a n i c  r o c k s , and content o f c a l c i t e , the pre-upper sedimentary  grain  Cretaceous  r o c k s have been d i v i d e d i n t o two broad  t e n t a t i v e l y c o n s i d e r e d P a l e o z o i c and Mesozoic.  groups,  The two groups  w i l l be c o n s i d e r e d independently; t h i s w i l l be f o l l o w e d by a  24 resume o f s i m i l a r i t i e s and d i f f e r e n c e s which l e d to the present sub-division.  A d i s c u s s i o n o f s t r u c t u r e has been d e f e r r e d t o  a l a t e r chapter so the e n t i r e g e o l o g i c  column can be d i s c u s s e d  as an e n t i t y , PALEOZOICC?) - GOAT ISLAND FORMATION The  sequence, here c o n s i d e r e d  Paleozoic  i n age,  crops  out a t S e a l Rocks, on Goat I s l a n d , the southeast end of F i d a l g o I s l a n d , McGinn I s l a n d , s e v e r a l small h i l l s south o f La Conner, B l d a  I s l a n d and a t the northwest end o f Ika I s l a n d  where i t i s exposed below l a t e Cretaceous or T e r t i a r y sediments. The  best  exposures o f t h i s sequence are seen a l o n g  the margins  o f Goat I s l a n d , consequently the U n i t i s , i n t h i s r e p o r t , named the Goat I s l a n d Formation. The  predominant rock type i s thin-bedded graywacke but  i n c l u d e d are prominent i n t e r b e d s l o c a l l y r e a c h boulder s i z e .  o f pebble conglomerate which  Argillite  i s common and s l a t e  with p o o r l y developed cleavage i s r a r e .  V o l c a n i c rocks  w i t h i n the sequence at s e v e r a l d i f f e r e n t  localities.  occur  Color on weathered outcrop i s u s u a l l y b u f f to g r e e n i s h gray.  Fresh  even b l a c k .  s u r f a c e s are v a r i o u s The rocks  shades o f green to gray or  are h i g h l y i n d u r a t e d ,  no p o r o s i t y or p e r m e a b i l i t y .  r e s i s t a n t and have  S i l i c i f i c a t i o n i s common,  e s p e c i a l l y prominent as r a m i f y i n g v e i n l e t s and o f t e n and  c a l c i t e occur intergrown w i t h i n the same v e i n l e t .  Swinomish Slough, on Southern F i d a l g o  quartz West o f  Island, i n fine-grained  graywacke, i n t e n s e s i l i c i f i c a t i o n occur^s i n the form of numerous, c l o s e l y spaced q u a r t z v e i n l e t s p a r a l l e l to s h e a r i n g .  Although  c a l c i t e i s common i n these r o c k s , limestone and c a l c a r e o u s nodules appear to he Deformation  absent. i s everywhere i n t e n s e as i n d i c a t e d by  i s o c l i n a l f o l d s , cleavage and f o l d e d cleavage Structure).  Because of the well-developed cleavage  present which obscures be made.  (See s e c t i o n  on  normally  c o n t a c t s , c o r r e l a t i o n o f u n i t s c o u l d not  Where cleavage i s l e s s pronounced i n d i v i d u a l rock  u n i t s p i n c h out or i n t e r t o n g u e l a t e r a l l y with other u n i t s over short l a t e r a l d i s t a n c e s . F i n e - G r a i n e d Rocks In t h i n - s e c t i o n , p h y l l i t e shows the e f f e c t s o f s t r o n g s h e a r i n g w i t h most of the s i l t - s i z e q u a r t z g r a i n s broken or f r a c t u r e d and i n v a r i a b l y s t r a i n e d .  F i n e - g r a i n e d q u a r t z fragments  are i n p l a c e s drawn i n t o t h i n l a y e r s p a r a l l e l to shear.  Cal-  cite,  largely  the o n l y other important  secondary,  c o n s t i t u e n t appears  the r e s u l t of m a t r i x a l t e r a t i o n .  to be  A few small g r a i n s  of a w a t e r - c l e a r , n e g a t i v e r e l i e f , v e r y low b i r e f r i n g e n t m i n e r a l occurs w i t h the quartz and i s probably secondary  albite.  matrix, making up probably 9 0 per cent o f the rock i s an aceous, c l a y - l i k e mass appearing brown to opaque i n plane  The argilllight.  T h i s " c l a y " m a t r i x has been s t r o n g l y sheared and i s wrapped around the l a r g e r g r a i n s .  26  Figure 7. Folded graywacke on Skagit Island  Figure 6. Faulting i n sheared gray wacke. Northeast s t r i k i n g fault offset by northwest s t r i k i n g f a u l t . Southeast Fidalgo Island  27 Medium-Grained Rocks Medium-grained p o r t i o n s of the graywacke sequence are c h a r a c t e r i z e d by q u a r t z , f e l d s p a r and/or rock fragments s e t i n an i n d u r a t e d a r g i l l a c e o u s m a t r i x .  Shearing i s normally v e r y  evident. Quartz commonly c o n s t i t u t e s 40 per cent o f the rock, o c c u r r i n g mainly as angular, f r a c t u r e d g r a i n s , up to 1 mm i n maximum dimension.  I n d i s t i n c t quartz g r a i n boundaries  which  grade i n t o the matrix are the r u l e , and are p a r t i a l l y the r e s u l t of s m a l l v e r m i c u l a r growths o f c h l o r i t e and q u a r t z . the quartz appears  Commonly  to " f e a t h e r " out i n t o the m a t r i x .  Secondary  growths o f q u a r t z , as rims on g r a i n s , were not observed. Sodic p l a g i o c l a s e , r a n g i n g from a l b i t e to o l i g o c l a s e , makes up from 1 to 10 per cent o f these r o c k s .  Plagioclase  g r a i n s a r e h i g h l y corroded and a l t e r e d to c a l c i t e , s e r i c i t e and/or e p i d o t e . conspicuous  chlorite,  Orthoclase, i f present, i s very i n -  and unimportant.  Chert i s a common c o n s t i t u e n t and i s present i n most specimens though i n v a r y i n g amounts, and i n p l a c e s i s as h i g h as 10 per c e n t .  I t i n v a r i a b l y occurs as rounded, elongated  g r a i n s with the same marginal a l t e r a t i o n as the q u a r t z . Rock fragments,  f o r the most p a r t a l t e r e d b a s i c v o l c a n i c s ,  are common i n p a r t s o f the sequence.  Where p r e s e n t , they are  u s u a l l y elongated, sometimes s t r o n g l y so, i n a plane to cleavage.  parallel  Where rock fragments are predominant a d i m i n u t i o n  of f e l d s p a r i s n o t i c e a b l e .  28 Coarse c l a s t i c fragments are set i n a tough, indurated, predominately a r g i l l a c e o u s matrix containing small fragments of quartz and f e l d s p a r . Authigenesis has r e s u l t e d i n the formation l o c a l l y of b i o t i t e , s e r i c i t e , c h l o r i t e , and c a l c i t e . epidote i s r a r e l y present.  Detrital  P y r i t e i s present as small euhedral  c r y s t a l s d i s t r i b u t e d randomly throughout  the matrix.  Coarse-Grained Rocks The conglomeratic p o r t i o n of the sequence i s s i m i l a r i n a l l respects to the sand s i z e graywacke except f o r the s i z e of fragments.  Considerable v a r i a t i o n i s present i n pebble dimen-  sions with 3 mm r e p r e s e n t i n g an average diameter.  Pebbles are  u s u a l l y sub-rounded to rounded and i f shearing has occurred they are elongated i n plane of shearing.  Q u a r t z i t e s and  p h y l l i t e s are the most abundant pebble m a t e r i a l though greenstone pebbles are not uncommon.  The o r i g i n a l q u a r t z i t e was im-  pure as i n d i c a t e d by secondary s e r i c i t e , formed from i n t e r granular, clay-size d e t r i t a l material. On southeast Fidalgo I s l a n d a number o f sub-rounded boulders (up to 25 cm) of greenstone are conspicuous.  These  tend to be i s o l a t e d and associated only with pebble conglomerates.  The matrix appears to be l a r g e l y a mass o f v a r y i n g s i z e  quartz and p l a g i o c l a s e grains set i n a consolidated a r g i l l a c e o u s base s i m i l a r to that p r e v i o u s l y described. E s t i m a t i n g the r a t i o of matrix to larger g r a i n s seems f u t i l e because of the apparent gradation i n g r a i n s i z e from  F i g u r e 9. Photomicrograph of P a l e o z o i c C ? ) sheared graywacke. P l a n e l i g h t , x 10.  F i g u r e 10. Photomicrography of sheared P a l e o z o i c pebble conglomerate. Pebbles o f q u a r t z i t e , p h y l l i t e and g r e e n stone. P l a n e l i g h t , x 10  sub-microscopic to pebbles 3 or 4 mm i n diameter.  Greenstone  boulders are notably l a r g e r than the average pebble o f the conglomerate.  MESOZOICC?) - LA CONNER FORMATION Rocks considered Mesozoic u n d e r l i e Skagit and KiMet I s l a n d , the h i l l s i n and around La Conner and the h i l l s west of Pleasant Ridge.  These rocks markedly resemble a rock sequence  cropdng out on the south side o f Lopez Island i n the San Juan I s l a n d Archipelago which McLellan (1927) considered C a r b o n i f e r ous and c o r r e l a t a b l e with the Leech R i v e r Group of southern Vancouver  Island.  Subsequently Danner (personal communication)  has found Cretaceous f o r a m i n i f e r a a s s o c i a t e d w i t h interbedded pillow lavas. However the Mesozoic(?) of Skagit Bay can not be conf i d e n t s i l y c o r r e l a t e d rocks of Lopez I s l a n d hence a l o c a l format i o n a l name i s a p p l i e d .  Because the best Mesozoic(?) exposures  occur i n road cuts at e i t h e r end of the new bridge across Swinomish Slough, immediately west o f LaConner, the w r i t e r has c a l l e d the u n i t the L a Conner Formation. The predominant  color of t h i s group of rocks i s dark  gray or b l a c k ; the greenish hues of the P a l e o z o i c ( ? ) sequence are nowhere present.  Although a few pebble l a y e r s were observed  the t h i c k pebble conglomerates and l a r g e boulders noted i n the P a l e o z o i c ( ? ) rocks were not found. Deformation o f the Mesozoic(?) group has been strong as  31 evidenced by recumbent f o l d i n g . spread  nor  so wide-  so s t r o n g l y developed as i n the P a l e o z o i c ( ? )  A r g i l l a c e o u s limestone and Kik.et I s l a n d . but  Rock cleavage i s not  nodules are present  on  rocks.  Skagit  Quartz and c a l c i t e v e i n l e t s are l o c a l l y common  c a l c i t e seems a much l e s s abundant c o n s t i t u e n t of the  matrix  itself.  sequence o f  No v o l c a n i c s were found a s s o c i a t e d with  rock  this  rocks.  In c o n t r a s t to the r a t h e r thin-bedded nature o f  the  P a l e o z o i c ( ? ) sequence, the Mesozoic(?) r o c k s are more massive and b l o c k y ,  f r e q u e n t l y with no  evidence o f bedding.  Even where  bedding i s v i s i b l e l a t e r a l c o r r e l a t i o n i s not p o s s i b l e .  Abrupt  l a t e r a l l i t h o l o g i c changes are c h a r a c t e r i s t i c and beds l e n s with amazing frequency. The  graywacke i s made up of q u a r t z , p l a g i o c l a s e , rock  fragments and matrix and  with  secondary m i n e r a l s .  small or minor amounts of Quartz g r a i n s are angular,  i n maximum dimension, and  i n v a r i a b l y show resorbed  accessories up  up  to 0 . 5  mm  borders,  where replacement by c h l o r i t e and matrix m a t e r i a l has A l b i t e and  to 3  taken p l a c e .  o l i g o c l a s e appear i n sub-rounded g r a i n s , or i n l a t h s mm  i n length.  They show c o n s i d e r a b l e  resorptions  i n v a r i a b l y are a l t e r e d i n v a r y i n g degrees to s e r i c i t e , and/or c a l c i t e .  In one  t h i n - s e c t i o n a few  and  chlorite  very small hornblende  g r a i n s were observed. Chert mm  i s not  i n l e n g t h , and  abundant, o c c u r s  i s generally f a i r l y  r a r e l y i n g r a i n s over well-rounded.  0.5  Rock f r a g -  32 ments, l a r g e l y s l a t e c h i p s , with an average maximum dimension of 2 to 4 cm, are very conspicuous. An indurated a r g i l l a c e o u s matrix i s always present, but i s not dominant, as i s the case i n P a l e o z o i c rocks.  Ten to  20 per cent i s a common average while i t may be i n excess o f 50 per cent i n older r o c k s . Limestone nodules may be up to two feet i n thickness and perhaps twice that i n long dimensions.  They are composed of  a f i n e - g r a i n e d , homogeneous, a r g i l l a c e o u s limestone.  Pyrite  cubes are randomly and sparsely d i s t r i b u t e d and are u s u a l l y bordered by secondary f i b r o u s chalcedony.  Occasional concentra-  t i o n s of p y r i t e were observed at i n t e r s e c t i o n s of microscopic veinlets.  I n one t h i n - s e c t i o n , c i r c u l a r areas, up to 1 mm i n  diameter, composed o f somewhat purer carbonate suggest r e s i d u a l remains of f o r a m i n i f e r a . c r i n o i d stem,  Another t h i n - s e c t i o n shows a p o s s i b l e  ^ r e s e r v a t i o n i s so poor i n both cases that  d e f i n i t e i d e n t i f i c a t i o n cannot be made. Primary Structures Graded Beds  are sedimentation u n i t s c h a r a c t e r i z e d by  a g r a d a t i o n i n g r a i n s i z e from coarse to f i n e , upward from the base o f the u n i t .  These are comparatively common i n the  Mesozoic sequence and are t y p i c a l l y marked by a l i g h t - c o l o r e d s i l t that grades upward i n t o a f i n e - g r a i n e d , dark-colored argillite.  Graded beds observed i n the graywacke of the map  area range i n thickness from 1 to 20 cm.  33 They are g e n e r a l l y considered  to be the end product of  m a t e r i a l s e t t l i n g through quiet bottom water which allows the coarse m a t e r i a l to s e t t l e f i r s t followed by the f i n e c o n s t i t uents.  Consequently they are considered  to be among the best  c r i t e r i a for establishing vertical stratigraphic orientation. Penecontemporaneous Slump Structure i s defined as small scale deformation such as f o l d i n g , f a u l t i n g and b r e c c i a t i o n which commonly occurs i n f i n e - g r a i n e d sediments at or immediately below the land surface or sea bottom. In s e v e r a l l o c a l i t i e s small scale f o l d i n g and f a u l t i n g occurs" i n t h i n shale beds l e s s than 3 mm t h i c k .  These micro-  s t r u c t u r e s are seldom found w e l l developed and are deformed to varying degrees by movements f o l l o w i n g compaction. Channeling occurs l o c a l l y and on a very small s c a l e . Channels are u s u a l l y f i l l e d with f i n e sand i n an a r g i l l i t e p o r t i o n o f the sequence, though o c c a s i o n a l l y channels and enc l o s i n g rock are somewhat more  coarse-grained.  SUMMARY OP PRE-TERTIARY  STRATIGRAPHY  Danner (i960) d i v i d e d the graywackes of the P a c i f i c eugeosyncline i n t o two general s u i t e s as f o l l o w s : "The f i r s t ' s u i t e ' includes rocks of the Devonian through e a r l y J u r a s s i c Age. I t i s c h a r a c t e r i s e d by marine basic v o l c a n i c s , b r e c c i a s , black graywacke", s i l t s t o n e , ribbon cherts and lenses of limestone. With few exceptions the limestones are the only f o s s i l i f e r o u s rocks and provide the sole means of e s t a b l i s h i n g the s t r a t i g r a p h i c sequence.  34  • S3  >.  \  <>.  F i g u r e 1 1 . Graywacke c u t by multitude of ramifying quartz veinlets. South side of Kiket Island.  F i g u r e 12. Photomicrograph of MesozoicC?) a r g i l l a c e o u s limestone nodule. Possible c r i n o i d columnal at lower r i g h t . Plane l i g h t , x 10  35  A second e u g e o s y n c l i n a l ' s u i t e ' i n c l u d e s marine rocks o f J u r a s s i c to Oligocene age and i s c h a r a c t e r i z e d by t h i c k sequences o f marine graywacke, s l a t e , c h i p b r e c c i a s , b a s i c v o l c a n i c r o c k s , graywacke s i l t s t o n e , and a r g i l l i t e s . Ribbon c h e r t forms a very minor p a r t o f the sequence and l i m e stone i s r a r e . F o s s i l s are scarce i n these r o c k s and many formations o f unknown age probably b e l o n g to t h i s ' s u i t e ' " . A summary o f the d i f f e r e n c e s between the P a l e o z o i c ( ? ) and Mesozoic(?) sedimentary rocks o f the S k a g i t Bay area are t a b u l a t e d below:  Characteristic  Group 1, Goat I s l a n d Formation ( P a l e o z o i c ? )  Color  Shades of green to gray Dark gray tbvblack F r e q u e n t l y coarse, D e f i c i e n t i n conconglomeratic glomerate Very i n t e n s e Less i n t e n s e None Calcareous nodules Some present Absent Volcanic, a r g i l l i t e , U s u a l l y s l a t e but minor p a r t o f rock quartzite Commonly major p a r t o f ' Commonly minor p a r t of rock ~o f rock Common Common but g e n e r a l l y l e s s abundant than in Paleozoic(?) Thin-bedded Thick-bedded  Grain  Size  Deformation Limestone Volcanics Rock fragments Matrix  Group 2, L a Conner Formation (Mesozoic?)  <  Calcite Bedding  Rocks here c o n s i d e r e d Mesozoic a r e s i m i l a r i n outcrop appearance and t h i n - s e c t i o n to the C a r t e r P o i n t Formation o f southern Lummi I s l a n d ( C a l k i n s , 1959).  C a l k i n s c o n s i d e r e d the  C a r t e r P o i n t Formation to be Mesozoic i n age on the b a s i s o f s i m i l a r i t y i n l i t h o l o g y to the Nooksack Group of the Cascade Mountain F o o t h i l l s . for  Since C a l k i n ' s work, support  was given  a Mesozoic age by the f i n d i n g o f a Mesozoic ammonite on  36 . an outcrop o f C a r t e r P o i n t .  P o s i t i v e i d e n t i f i c a t i o n o f the  specimen has not yet been made (Danner, p e r s o n a l  communication).  Limestone, c h a r a c t e r i s t i c a l l y interbedded with P a l e o z o i c graywackes, commonly c o n t a i n s f o s s i l s g i v i n g evidence The  of  age.  group here c o n s i d e r e d P a l e o z o i c c o n t a i n s no limestone  t h i s may  but  be an a c c i d e n t of poor exposure. I n the w r i t e r ' s o p i n i o n the g r o s s c h a r a c t e r i s t i c s of  rocks i n the r e p o r t a r e a can be b r o a d l y a p p l i e d to s u b d i v i d e the pre-Tertia.ry i n t o two  groups.  F u r t h e r these two  be g e n e r a l l y equated with the two  groups can  ' s u i t e s ' of Danner.  Consequent-  l y the w r i t e r t e n t a t i v e l y r e f e r s h i s Mesozoic group to the first  ' s u i t e ' o f Danner and h i s Mesozoic to the second  'suite'.  I t can be f o r c i b l y and l o g i c a l l y argued that a l i t h o l o g i c c o r r e l a t i o n o f t h i s nature has l i t t l e v a l i d i t y .  The  area  i s s m a l l , outcrops are a d m i t t e d l y sparce and commonly h i g h l y weathered.  V a r y i n g degrees of deformation  i n the f i e l d may Sampling and  not r e a d i l y  g i v e the same r o c k s d i f f e r e n t  t h i n - s e c t i o n d i s t r i b u t i o n may  apparent  aspects.  not be  t r u l y repres-  entative . To these and other arguments the w r i t e r can but agree.  only  However the l i t h o l o g i c c h a r a c t e r i s t i c s are the only  c r i t e r i a a v a i l a b l e , and i n the absence o f b e t t e r evidence  the  proposed t w o - f o l d s u b d i v i s i o n i s presented as most p r o b a b l e .  Figure 13. Photomicrograph of Mesozoic sheared graywacke. Composed l a r g e l y o f quartz and a r g i l l i t e fragments. Plane l i g h t , x 10  F i g u r e 14. Photomicrograph of Mesozoic f e l d s p a t h i c graywacke, Plane l i g h t , x 10  38 ORIGIN  The f i r s t recorded use of the term graywacke was i n 1789 when L a s u i s working i n the Harz Mountains described a graywacke as a "sandstone made up of fragmental g r a n i t e d e b r i s " . By 1808 Jameson was emphasizing the importance of a " c l a y slate" matrix.  The end o f the 19th century saw B a i l e y (1898)  d e f i n i n g graywacke as a sandstone " c o n t a i n i n g grains o f many d i f f e r e n t minerals and small fragments of r o c k s , u n i t e d by a cement of the composition o f many s l a t e s " . Twenhofel (1926) suggested that graywacke be considered the ferromagnesian widely accepted.  equivalent of arkose but t h i s has not been P e t t i John (1943) considered a graywacke to be  a m i c r o b r e c c i a with the f o l l o w i n g c h a r a c t e r i s t i c s : ( l ) l a r g e , angular d e t r i t a l quartz and feldspar g r a i n s , (2) a clay matrix, (3) a dark c o l o r , (4) tough and v/ell indurated, (5) presence o f rock fragments, (6) presence o f macroscopic  s t r u c t u r e , and (7)  c h a r a c t e r i s t i c rock a s s o c i a t i o n s . In t h i s paper the w r i t e r e l e c t s to use the c l a s s i f i c a t i o n of sedimentary rocks proposed by P e t t i J o h n (1957).  In t h i s  c l a s s i f i c a t i o n a graywacke i s defined as a c l a s t i c rock with a v a r i a b l e angular quartz g r a i n content, u s u a l l y l e s s than 75 per cent and v a r y i n g q u a n t i t i e s o f f e l d s p a r and/or rock f r a g ments.  The coarse-grained fragments are set i n a d e t r i t a l ,  a r g i l l a c e o u s matrix composing at l e a s t 15 per cent of the indurated rock.  I f the matrix i s l e s s than 15 per cent o f the t o t a l  the rock becomes a subgraywacke.  The p r e f i x  "feldspathic"  i n d i c a t e s a graywacke with more f e l d s p a r than rock i n d i c a t e s the converse.  fragments  and  the p r e f i x " l i t h i c "  Accessory miner  als  may be p r e s e n t and v a r y i n g degrees o f a l t e r a t i o n are i n -  v a r i a b l y present. Graywackes are thought  to be formed p r i n c i p a l l y i n deep  water while the c l a s t i c m a t e r i a l i t s e l f i s the product o f i n complete  s o r t i n g and weathering.  G e n e t i c a l l y , graywackes  i n d i c a t e the f o l l o w i n g : (l)  nature o f the source rock, ( 2 ) a t e c t o n i c a l l y a c t i v e a r e a ,  (3)  a source a r e a o f c o n s i d e r a b l e r e l i e f ,  (4) rapid  trans-  p o r t a t i o n o f c l a s t i c m a t e r i a l and ( 5 ) d e p o s i t i o n i n deep water. The  thin-bedded and graded nature o f graywacke suggest  a p u l s a t i n g and i n t e r m i t t e n t sediment  supply.  Sand and s i l t  are d e p o s i t e d on a d e l t a f r o n t or on the c o n t i n e n t a l  margin.  These d e p o s i t s may become u n s t a b l e and i f d i s l o d g e d w i l l down s l o p e as a t u r b i d i t y c u r r e n t .  travel  As t h i s mass o f water and  suspended m a t e r i a l l e v e l s out on the sea f l o o r  the speed de-  c r e a s e s and d e p o s i t i o n commences, l a r g e c o n s t i t u e n t s f i r s t f o l l o w e d by p r o g r e s s i v e l y s m a l l e r g r a i n s . common occurrence o f graded bedding  Consequently the  i n a graywacke sequence i s  t y p i c a l and to be expected. The  " t r i g g e r " necessary to s t a r t a t u r b i d i t y c u r r e n t  may be e i t h e r t e c t o n i c , as i n an earthquake  shock, or c l i m a t i c  i n the way o f storm waves and sea t u r b u l a n c e . Source a r e a o f graywacke i n the S k a g i t D e l t a country i s  40 unknown but presumably volcanic terrain.  i t was  a predominately metamorphic and  The l a c k of f o s s i l s ,  the graded bedding, the  l a c k of r i p p l e marks and c r o s s - b e d d i n g , and the  carbonaceous  nature o f the rocks suggest a r e s t r i c t e d marine b a s i n o f accumul a t i o n which was to  too deep and too t o x i c to permit marine l i f e  survive.  VOLCANIC ROCKS  OCCURRENCE  V o l c a n i c rocks are q u a n t i t a t i v e l y unimportant the map  area.  Small outcrops occur at 5 d i f f e r e n t  locations.  A l l v o l c a n i c exposures are h i g h l y weathered,, making cation d i f f i c u l t  within  classifi-  and l e n d i n g themselves o n l y to the f i e l d  term  greenstone. Greenstone  crops out on the southeast end of Hope  I s l a n d , on Deadman and L i t t l e of  Deadman I s l a n d s , a l o n g a s t r e t c h  s h o r e l i n e west of the entrance to Swinomish Channel,  on  s e v e r a l h i l l s south of La Conner and at a very small outcrop of unknown extent on the n o r t h e a s t s i d e o f Goat I s l a n d . with both l a r g e r fragments ial,  A breccia,  and m a t r i x composed of v o l c a n i c mater-  immediately u n d e r l i e s the T e r t i a r y - p r e - T e r t i a r y unconform-  i t y at the northwest  end o f Ika I s l a n d .  The v o l c a n i c rocks are r e s i s t a n t to e r o s i o n , forming prominent  c l i f f s where exposed  promentories.  to wave a c t i o n , or as s m a l l  41  Field  Description In outcrop the occurrences o f greenstone have many  similar features. though i n places r e s u l t of  Generally  they weather to a d u l l green c o l o r  they are b u f f to r u s t y brown, probably as a  o x i d a t i o n of i r o n .  a p h a n i t i c t e x t u r e and West o f the  F r e s h l y broken s u r f a c e s  show an  a r e , t y p i c a l l y a d u l l , dask green c o l o r .  entrance to Swinomish Channel the greenstones are  s l i c k e n s i d e d w i t h a p o l i s h e d smear o f r e d d i s h h e m a t i t e ( ? ) on polished  surfaces. The  which was quartz  the  only m i n e r a l  identifiable  i n hand specimen i s p y r i t e ,  observed as small cubes i n a few  v e i n i n g i s common l o c a l l y .  v e i n i n g i s present  and  specimens.  To a l e s s e r degree  Secondary calcite  i s occasionally associated with  quartz  veins. P i l l o w l a v a s were noted at one  l o c a t i o n west o f  entrance to Swinomish Channel (southeast The  p i l l o w s are p o o r l y developed, but  about r*jr f e e t i n diameter. was  end o f F i d a l g o  the Island).  show a c o n s i s t e n t s i z e o f  No v e s i c u l a r or amygdaloidal s t r u c t u r e  observed. Two  I s l a n d and  o f the greenstone exposures, namely those on Hope southeast F i d a l g o I s l a n d , are  ultrabasic intrusions. by v e i n l e t s o f quartz an interbedded sively folded  Fractures  are abundant, i n p l a c e s  and/or c a l c i t e .  sedimentary u n i t i s now phyllite.  i n f a u l t contact  with healed  West of Swinomish Channel a h i g h l y sheared, i n t e n -  42 V o l c a n i c rocks on Deadman and L i t t l e Deadman I s l a n d s , as w e l l as those south o f La Conner have experienced mechanical  less  deformation, are more homogeneous i n t e x t u r e and  are somewhat l e s s f r a c t u r e d , and are l e s s i n t e n s e l y  color,  slicken-  s i d e d than those a s s o c i a t e d w i t h u l t r a b a s i c r o c k s . V o l c a n i c and  sedimentary  rocks were not observed i n  d i r e c t c o n t a c t although i n places they crop out w i t h i n 10 15 and  f e e t o f each o t h e r .  to  P o s s i b l y the v o l c a n i c s o f Hope I s l a n d  the a r e a west o f Swinomish Channel are f a u l t e d i n t o contact  w i t h sediments but i t i s a l s o p o s s i b l e the two are the t r u e r e l a t i o n s h i p being obscured  f i r s t l y by r e g i o n a l  f o r m a t i o n and low grade metamorphism, and brought  intercalated;  about by u l t r a b a s i c i n t r u s i o n .  secondly by  de-  deformation  V o l c a n i c rocks o f Deadman  and L i t t l e Deadman I s l a n d s are i s o l a t e d by the waters o f S k a g i t Bay  so contact r e l a t i o n s w i t h other rocks i s obscured.  v o l c a n i c rocks s i t u a t e d south o f La Conner appear to be bedded i n the graywacke sequence.  Although  u n c e r t a i n , a l t e r n a t e outcrops o f greenstone suggest an interbedded  However, inter-  exact r e l a t i o n s are and graywacke s t r o n g l y  relationship.  PETROGRAPHY  A l l the v o l c a n i c rocks are i n t e n s e l y a l t e r e d as  indi-  cated by a b r i e f p e t r o g r a p h i c d e s c r i p t i o n o f some t y p i c a l specimens from d i f f e r e n t  locations.  F i g u r e 15. S p i l i t e v o l c a n i c rocks d i p p i n g s t e e p l y toward the o b s e r v e r . S o u t h e a s t end o f F i d a l g o I s l a n d .  44 L i t t l e Deadman The  Island  volcanic  fine-grained  r o c k f r o m L i t t l e Dead Man I s l a n d  and e x h i b i t s a f e l t y t e x t u r e .  Radial  i s very-  growths o f  highly altered plagioclase microlites display a v a r i o l i t i c texture.  E x t i n c t i o n a n g l e s and l o w n e g a t i v e r e l i e f o f p l a g i o -  c l a s e m i c r o l i t e s i n d i c a t e an a l b i t i c i s l a r g e l y replaced cleavage surfaces  composition.  Plagioclase  by c h l o r i t e and o t h e r c l a y m i n e r a l s  and b o r d e r s .  along  Locally c a l c i t e replaces  plagio-  c l a s e but the o v e r a l l pervading a l t e r a t i o n , c r e a t i n g a gray matte e f f e c t , i s s a u s s u r i t i z a t i o n . replaced  Pyroxene i s almost e n t i r e l y  by c h l o r i t e , a c t i n o l i t e and c a l c i t e .  o c c u r s as d i s c r e t e , pale  yellow-green grains.  Chlorite  also  In addition to  d i r e c t l y r e p l a c i n g p l a g i o c l a s e , c a l c i t e occurs i n small  vein-  lets  amounts,  transecting the rock.  generally Volcanic  as d i s c r e t e g r a i n s  Epidote i s present i n minor o f very small  size.  r o c k s S o u t h o f La Conner I n a g r e e n s t o n e o u t c r o p s o u t h o f L a Conner t h e a l t e r -  ation i s s i m i l a r to that man I s l a n d s .  described  f o r Deadman and L i t t l e  S a u s s u r i t i z a t i o n i s very intense,  Dead-  and c h l o r i t e i s  now a n e x c e p t i o n a l l y p r o m i n e n t p a r t  of the section.  is albite,  a l o n g c l e a v a g e p l a n e s and  and i s commonly r e p l a c e d  b o r d e r s by c h l o r i t e . into the matrix  when e x a m i n e d u n d e r h i g h power.  pyroxenes a r e t o t a l l y replaced  Many o f t h e p l a g i o c l a s e s  by a p a l e  Plagioclase  appear t o grade The o r i g i n a l  u n i d e n t i f i a b l e as t h e y have been l a r g e l y  green, weakly pleochroic  actinolite.  Calcite  i s not p a r t i c u l a r l y prominent but l o c a l l y occurs w i t h f e l d s p a r as a decomposition  product.  A m i n e r a l , not present i n most o f  the v o l c a n i c rocks i s p y r i t e which i s disseminated i n r a t h e r l a r g e amounts through some o f the specimens.  The g r a i n s are f o r  the most p a r t idiomorphic but some show v a r y i n g degrees o f rounding  due to c o r r o s i o n .  S e v e r a l very s m a l l g r a i n s (0.1 mm)  o f a watery c l e a r m i n e r a l w i t h pronounced n e g a t i v e r e l i e f and low f i r s t order c o l o r s were seen i n t h i n - s e c t i o n .  Possibly this  i s a l b i t e or a z e o l i t e . The o u t s t a n d i n g m i c r o s c o p i c c h a r a c t e r i s t i c o f v o l c a n i c rocks not a s s o c i a t e d w i t h u l t r a b a s i c rocks i s the h i g h degree o f alteration;  e s p e c i a l l y s a u s s u r i t i z a t i o n , c h l o r i t i z a t i o n and  to a l e s s e r extent, c a r b o n a t i z a t i o n and u r a l i t i z a t i o n o f pyroxene. V o l c a n i c Rocks from Hope I s l a n d A specimen from the southeast end o f Hope I s l a n d e x h i b i t s s i m i l a r p r o p e r t i e s as those p r e v i o u s l y d i s c u s s e d but has a c a t a c l a s t i c t e x t u r e , presumably the r e s u l t o f p h y s i c a l breakage w i t h i n a f a u l t zone.  Plagioclase m i c r o l i t e s are s l i g h t l y  altered.  m i c r o l i t e e x t i n c t i o n curve i n d i c a t e s  Use o f the  less they  are no more than Abc^An^ and a r e probably a l b i t e or s o d i c oligoclase.  Pyroxenes are almost  t o t a l l y r e p l a c e d by a p a l e  green, weakly p l e o c h r o i c amphibole, probably S t r o n g l y p l e o c h r o i c , reddish-brown  actinolite.  b i o t i t e , occurs i n a s s o c i a t i o n  w i t h c h l o r i t e , mainly i n t e r s t i t i a l to but p a r t l y pseudomorphic  F i g u r e 1 7 . Photomicrograph of s p i l i t e showing h i g h degree o f s a u s s u r i t i z a t i o n . Numerous quartz v e i n l e t s are c h a r a c t e r istic. Cross-nicols, xlO.  F i g u r e 18. Photomicrograph o f m i c r o p o r p h y r i t i c s p i l i t e from flow b r e c c i a on Ika I s l a n d . Cross n i c o l s , x 10  after  pyroxene.  Epidote  i s rare.  minerals not  Chlorite  appears  complete.  Possibly  i s moderately  of b i o t i t e  n  p r o c e s s f o r some a c t i n o l i t e  i s widespread i f  grains are  S p e c i m e n s f r o m west o f S w i n o m i s h C h a n n e l  altered  and  Pyroxenes not o n l y clases  appear  are strongly  from a l b i t e  uralitized.  i n v e r m i c u l a r growths  but a l s o as f l a t  Calcite  bent.  are s i m i l a r  Plagioclases are l a t h - l i k e ,  to range  plates  to soda  Chlorite  oligoclase.  i s very  abundant,  t h r o u g h o u t most o f t h e up  t o 0.2  mm  The  chlorite  a l t e r a t i o n p r o d u c t as i t i s i n v a d i n g and i n the v e i n l e t s .  plagio-  i n maximum  appears  t o be  corroding  Sericite  to  highly  seems t o o c c u r m o s t l y i n s e c o n d a r y v e i n l e t s ,  associated with quartz.  the  Island  c  t h o s e o f Hope I s l a n d .  latest  deformation occurred following  _l ,^ A .Jgqcksi_from Southern Fidalgo c  common.  t o be one o f t h e  t o f o r m as i t s r e p l a c e m e n t  alteration  V o  Magnetite-illmenite  of  the q u a r t z found  in  s m a l l amounts, commonly a s s o c i a t e d w i t h c a l c i t e  dimension.  often the  the  final margins  i s l o c a l l y present i n the  veinlets. Principal  alteration  i n these l a t t e r  chloritization,  u r a l i t i z a t i o n , minor  minor  sericitization.  and  local  rocks appears  carbonitization,  and  to  be  very  Summary o f G r e e n s t o n e P e t r o l o g y A l t e r a t i o n of volcanic associated  with ultrabasic  rocks b o t h independent  intrusion  rocks not a s s o c i a t e d w i t h u l t r a b a s i c s  i s similar.  from  and  However, i n  saussuritization  i s quite  48 i n t e n s e w h i l e i n the o t h e r s i t i s much l e s s prominent.  It  must be borne i n mind that t h i s d i v i s i o n o f v o l c a n i c rocks those a s s o c i a t e d w i t h i n t r u s i o n s and those independent b a s i c i n t r u s i o n s may be more apparent p o s s i b l y has no s i g n i f i c a n c e .  into  of ultra-  than r e a l , and q u i t e  Outcrops  are not adequate to  properly evaluate t h i s . In  summary the o u t s t a n d i n g a l t e r a t i o n these v o l c a n i c  rocks have undergone i s " p r o p y l i t i z a t i o n " , which i s g e n e r a l l y regarded as the r eplacement o f p r e - e x i s t i n g m i n e r a l s by carbona t e s , e p i d o t e , secondary  quartz and c a l c i t e .  Other m i n e r a l s that  may be formed though u s u a l l y o f l e s s importance  are p y r i t e ,  z e o l i t e , a l b i t e and s e r i c i t e . Volcanic Breccia A v o l c a n i c b r e c c i a crops out at the northwest Ika I s l a n d .  I t i s a buff-weathering b r e c c i a , extending to near  the c r e s t o f the n o r t h e r n h i l l of  end o f  and composed o f angular  v o l c a n i c rock up to 3 cm i n maximum dimension.  range downward to m i c r o s c o p i c s i z e d p a r t i c l e s .  fragments  Fragments  F r e s h l y broken  s u r f a c e s a r e a dark yellow-green, somewhat l i g h t e r i n c o l o r the greenstones  described previously.  P l a g i o c l a s e i s a l b i t e i n the form o f l a t h - l i k e lites  micro-  s e t i n a f e l t y m a t r i x o f f i n e r - g r a i n e d f e l d s p a r and u r a l i t -  i z e d pyroxene w i t h minor c h l o r i t e and c a l c i t e . l a t h s , up to 1 . 5 texture. flat  than  mm  A few l a r g e r  i n l e n g t h give the rock a m i c r o p o r p y r i t i c  C h l o r i t e i s very common, both as wormlike growths and  plates.  S e r i c i t e i s present i n s m a l l amounts as a r e -  49  placement o f p l a g i o c l a s e . sheath o f l i m o n i t e . g r a i n s and  P y r i t e i s p r e s e n t , enclosed i n a  Limonite i s f u r t h e r d i s t r i b u t e d i n d i s c r e t e  s m a l l i r r e g u l a r masses throughout  the rock.  The  m a t r i x i s formed o f the same v o l c a n i c m a t e r i a l as the l a r g e r fragments although l o c a l l y , s m a l l i r r e g u l a r blebs of quartz have formed between In  secondary  fragments.  a l l e s s e n t i a l f e a t u r e s the v o l c a n i c rock  comprising  t h i s b r e c c i a i s comparable to those d e s c r i b e d p r e v i o u s l y . strong a n g u l a r i t y o f fragments, and the tendency boundaries  the l a c k of a d i s t i n c t i v e  matrix  f o r fragments to weld together making the  obscure  layed b r e c c i a .  The  i n t h i n s e c t i o n suggests  i t i s not a water  Probably i t s o r i g i n can be e x p l a i n e d i n one  of  the f o l l o w i n g ways. (1)  Flow b r e c c i a formed by the fragmentation o f the  s u r f a c e o f a s t i l l moving but s o l i d i f y i n g l a v a flow.  Because  the hardened s u r f a c e i s i n c a p a b l e o f y i e l d i n g p l a s t i c a l l y the s t i l l  fluid  i n t e r i o r i t tends to break up i n t o  with  angular  fragments which are c a r r i e d along u n t i l flow motion  finally  comes to a h a l t . (2)  A u t o b r e c c i a caused  gas s i m u l t a n e o u s l y throughout  by escape o f s m a l l q u a n t i t i e s o f  the flow which i s u s u a l l y  by r e l i e f o f c o n f i n i n g pressure w i t h r e s u l t a n t r a p i d ion  and  s p a l l i n g along f r a c t u r e s .  caused  vesiculat-  T h i s u s u a l l y r e s u l t s i n a rock  showing a v e s i c u l a r p o r o s i t y o f 10 to 15 per cent. Because t h i s specimen shows no v e s i c u l a t i o n , no of  water t r a n s p o r t , sharp unworn fragmental edges and an  evidence apparent  50 f u s i o n o f fragments,  i t i s suggested  t h i s i s a v o l c a n i c flow  breccia.  ORIGIN  The A.G.I. G l o s s a r y o f Geology d e f i n e s a s p i l i t e as a b a s a l t i c rock w i t h a l b i t i c  feldspars.  Albite i s usually  accompanied by autometamorphic m i n e r a l s , or m i n e r a l s c h a r a c t e r i s t i c o f low grade metamorphosed greenstones, such as  chlorite,  c a l c i t e , e p i d o t e , c h a l c e d o n i c s i l i c a or q u a r t z , a c t i n o l i t e , and o t h e r s . T h i n s e c t i o n study of the v o l c a n i c rocks o f the S k a g i t D e l t a a r e a suggest  they f u l f i l l  the d e f i n i t i o n given above.  However the m i n e r a l assemblage does not n e c e s s a r i l y i n d i c a t e an autometamorphic o r i g i n as the above d e f i n i t i o n would Spilitic or  suggest.  rock*, r e g a r d l e s s o f t h e i r g e o g r a p h i c a l occurrence  t h e i r g e o l o g i c a l age have c e r t a i n c h a r a c t e r i s t i c s  and  a s s o c i a t i o n s i n common (Park, Waters and o t h e r s ) : (1)  V i r t u a l l y always a s s o c i a t e d w i t h marine r o c k s .  (2)  V i r t u a l l y always occur i n the e u g e o s y n c l i n a l phase of  (3)  an o r o g e n i c  belt.  Commonly show p i l l o w s t r u c t u r e (though t h i s i s not a b s o l u t e l y necessary nor are a l l p i l l o w l a v a s spilitic).  (4)  Commonly a s s o c i a t e d w i t h graywackes and bedded c h e r t s .  (5)  Commonly a s s o c i a t e d t h e r e may  be no  w i t h u l t r a b a s i c i n t r u s i o n s though  common genetic  relation.  The  t r u s i o n s are u s u a l l y a l a t e r phase than the though some over l a p p i n g o f the two (6)  A g e n e r a l l a c k of o l i v i n e .  (7)  Compared to b a s a l t a l l s p i l i t e s  may  2  and  F i e l d and o f the map  MgO,  and v e r y low  in  spilites,  occur.  are h i g h i n Na20,  moderately h i g h i n T i 0 , somewhat low CaO  in-  in  A^O^,  K^O.  p e t r o g r a p h i c study i n d i c a t e s the v o l c a n i c  a r e a have p r o p e r t i e s six criteria.  No  and  o f the  first  so the  chemical composition i s not  rocks  associations characteristic  chemical analyses are known.  available  However, the  pre-  dominance o f a l b i t e i n d i c a t e s h i g h soda content, the absence o f orthoclase and  and  of b a s i c p l a g i o c l a s e s  l i m e , w h i l e the presence o f minor amounts o f  indicates  the presence o f TiCV).  greenstones o f S k a g i t The  problem and theories  Bay  o r i g i n of s p i l i t e s is s t i l l  ilmenite  Consequently, on the  m i n e r a l assemblage, a s s o c i a t i o n and the  i n d i c a t e s a l a c k o f potash  may has  basis  of  chemistry, i t appears that  be  considered  spilites.  long been a c o n t r o v e r s i a l  f a r from s e t t l e d .  The  two  most s a t i s f a c t o r y  are:  (1)  O r i g i n from a primary s p i l i t i c magma and  (2)  O r i g i n by subsequent metasomatism and plagioclases basalt.  i n an o r i g i n a l o l i v i n e or  a l t e r a t i o n of tholeiitic  52 The f i r s t If  theory i s s u b s t a n t i a t e d by t e x t u r a l  studies,  igneous rock t e x t u r e s have any g e n e t i c meaning a t a l l , some  s p i l i t e s a r e d e f i n i t e l y primary and form as the r e s u l t o f c r y s t a l l i z a t i o n from a s p i l i t i c magma. A second theory presumes that the o r i g i n a l l a v a was a t h o l e i i t i c b a s a l t , as suggested by the almost e x c l u s i v e a s s o c i a t i o n with o l i v i n e d e f i c i e n t rocks.  S e v e r a l d i f f e r e n t mechanisms  may be i n v o l v e d i n the f o r m a t i o n o f s p i l i t e s from basalts.  Perhaps sea water and water  tholeiitic  logged sediments  associated  w i t h the v o l c a n i c rocks a r e the sources o f Na+ ions and water necessary f o r a l b i t i z a t i o n and a s s o c i a t e d a l t e r a t i o n .  Water  streaming upward from e u g e o s y n c l i n a l sediments undergoing comp a c t i o n i s envisaged as p e r c o l a t i n g up through the c o o l i n g  sub-  marine l a v a causing a l t e r a t i o n . A l t e r n a t i v e l y , autometamorphism o r a l t e r a t i o n by r e s i d u a l aqueous f l u i d s d e r i v e d from the o r i g i n a l magma might be i n v o l v e d . L i t t l e p h y s i c a l o r p e t r o g r a p h i c evidence i s a v a i l a b l e i n any area to s u b s t a n t i a t e or r e j e c t such a mode o f o r i g i n . Another s u g g e s t i o n (Waters, 1955) i s that s p i l i t e s a r e the  r e s u l t o f low-grade  r e g i o n a l metasomatism o f a v o l c a n i c  sequence.  A c c o r d i n g to t h i s scheme the Eocene  spilites of  Washington  were formed from t h o l e i i t i c b a s a l t s by sodium  rich  s o l u t i o n s d e r i v e d from low grade metamorphism o f e u g e o s y n c l i n a l d e p o s i t s a t depth. The s p i l i t e s o f S k a g i t Bay would somatic o r i g i n .  appear to be o f meta-  The i n t e n s e degree o f a l t e r a t i o n and secondary  m i n e r a l i z a t i o n i n d i c a t e s the rock i s c h e m i c a l l y d i f f e r e n t i t s c h a r a c t e r at the time of f o r m a t i o n . secondary  from  The occurrence o f  a l b i t e , g e n e r a l l y as water c l e a r g r a i n s , e s p e c i a l l y  w i t h i n v e i n l e t s , i n d i c a t e s at l e a s t some o f the a l b i t e i s secondary.  Secondary c h l o r i t e , c a l c i t e , s e r i c i t e and quartz w i t h  minor epidote i s evidence o f breakdown o f c a l c i u m s i l i c a t e s , e s p e c i a l l y f e l d s p a r s and pyroxenes. i s a l s o r e l e a s e d which may  During a l t e r a t i o n  r e - p r e c i p i t a t e i n t e r s t i t i a l l y and i n  v e i n l e t s , e i t h e r as quartz or j a s p e r . are moderately  silica  abundant i n the s p i l i t e s  Secondary quartz v e i n l e t s examined.  F u r t h e r evidence i s provided by a few f e l d s p a r g r a i n s which appear to have p o s i t i v e r e l i e f i n d i c a t i n g a h i g h e r normal c a l c i u m content. g r a i n s not a l b i t i z e d .  than  Probably these r e p r e s e n t o r i g i n a l Although the w r i t e r f e e l s the  evidence  p r o v i n g a metasomatic o r i g i n i s c o n c l u s i v e , no evidence i s a v a i l able to i n d i c a t e what s o r t of metasomatic process i s r e s p o n s i b l e .  AGE  P e t r o g r a p h i c a l l y the s p i l i t e s o f S k a g i t Bay  are s i m i l a r  to those d e s c r i b e d by C a l k i n i n the MesozoicC?) rocks o f Lummie ^ 7  I s l a n d , by M c L e l l a n i n the San Juan I s l a n d s , and by Park i n the Eocene rocks o f the Olympic Mountains. earlier, spilites  throughout  However as p o i n t e d out  the world have very  c h a r a c t e r i s t i c s and a s s o c i a t i o n s . s p i l l i t e s are present throughout  similar  W i t h i n the P a c i f i c g e o s y n c l i n e the s t r a t i g r a p h i c column.  Un-  54 l e s s the v o l c a n i c rocks are a s s o c i a t e d w i t h f o s s i l s , or can be "walked o u t " i n o u t c r o p , they can not be equated  i n time.  In the S k a g i t Bay area no f o s s i l s were found, w i t h e i t h e r the v o l c a n i c rocks or a s s o c i a t e d graywackes. Because these s p i l i t e s are found i n t i m a t e l y a s s o c i a t e d w i t h , and presumably interbedded w i t h sediments which a r e t e n t a t i v e l y c o n s i d e r e d to be P a l e o z o i c , the l a v a s a l s o are o f probable P a l e o z o i c age.  LATE CRETACEOUS-EARLY TERTIARY SEDIMENTS  OCCURRENCE  P l a n t - b e a r i n g , a r k o s i c conglomerates  and  sandstones  crop out at s p o r a d i c i n t e r v a l s along the south-edge o f the map area and are e s p e c i a l l y prominent where they form low h i l l s along the N o r t h Fork o f the S k a g i t R i v e r .  A number o f s m a l l ,  i s o l a t e d outcrops occur south o f the r i v e r and are c o l l e c t i v e l y known as " D e l t a Rocks". almost  Ika I s l a n d , to the west, i s composed  e n t i r e l y o f o l d e r T e r t i a r y sediments and i s the o n l y  i s l a n d w i t h i n the map a r e a not formed o f pre-Late p l u t o n i c , or v o l c a n i c r o c k s .  Cretaceous,  As e x p l a i n e d i n the s e c t i o n  dis-  c u s s i n g " S t r u c t u r e " , the T e r t i a r y rocks are preserved i n a l a r g e east-west  syncline.  55 STRATIGRAPHY  S t r a t i g r a p h i c a l l y the T e r t i a r y rocks a r e a conglomera t i c sequence w i t h sandstone, s i l t s t o n e and limy mudstone i n t e r beds.  The conglomerate i s w e l l i n d u r a t e d and t o p o g r a p h i c a l l y  resistant.  F i n e - g r a i n e d p o r t i o n s a r e much l e s s r e s i s t a n t to  erosion. Two u n i t s , which appear p a r a l l e l and concordant, make up the T e r t i a r y o f the map a r e a .  As w i l l be d i s c u s s e d  later,  a s l i g h t l y d i s c o r d a n t c o n t a c t , not v i s i b l e i n the f i e l d i s thought to be present.  Because d e f i n i t e c o r r e l a t i o n can not be  made w i t h d e s c r i b e d u n i t s elsewhere, new f o r m a t i o n a l names a r e a p p l i e d to t h i s sequence.  The o l d e r o f the two u n i t s w i l l be  r e f e r r e d to as the D e l t a Rocks Formation and i s best seen i n a 270  f o o t exposure on the south s i d e o f Ika I s l a n d .  The younger  i s termed the Ika Formation from the e x c e l l e n t exposures on the west and n o r t h s i d e s o f Ika I s l a n d .  As w i l l be brought out i n  l a t e r d i s c u s s i o n the author f e e l s these u n i t s might be c o r r e l a t a b l e to the Chuckanut Formation. D e l t a Rocks Formation The two  D e l t a Rocks Formation i s exposed at D e l t a Rocks, an  s m a l l outcrops  southeast  east s i d e o f Ika I s l a n d .  o f Pleasant  Ridge, and on the south-  A maximum exposed s t r a t i g r a p h i c t h i c k -  ness o f 270 f e e t was measured on Ika I s l a n d .  The contact between  t h i s and o v e r l y i n g Ika Formation i s exposed only on the south s i d e o f Ika I s l a n d , but at no p l a c e i s a contact between the  56 D e l t a Rock Formation and older rocks exposed. In outcrop t h i s cobble conglomerate appears dark greeni s h gray w h i l e f r e s h l y exposed surfaces are a d i s t i n c t l y paler shade o f green to gray.  Maximum observed cobhle s i z e i s about  20 cm w i t h the great m a j o r i t y between 3 to 7 cm.  Gradation from  smallest to l a r g e s t c l a s t i c fragments appears to be the r u l e . Fragments l a r g e r than 2 cm are generally sub- to w e l l rounded and those l e s s than 2 cm are l a r g e l y angular.  Pebbles  and cobbles are u s u a l l y of low s p h e r i c i t y and may appear to have been f r a c t u r e d .  The matrix i s e s s e n t i a l l y compacted sand  and s i l t though r a r e l y c a l c i t e cement i s present. Cobbles and pebbles are composed of many rock types, e s p e c i a l l y q u a r t z i t e and chert w i t h l e s s e r amounts of greenstone v o l c a n i c s , indurated sandstone, and a r g i l l i t e .  A pebble of  sandstone as seen i n t h i n - s e c t i o n was made up p r i n c i p a l l y of angular quartz w i t h l e s s e r amounts o f p l a g i o c l a s e and minor q u a n t i t i e s of o r t h o c l a s e , b i o t i t e , p y r i t e , epidote, hornblende, muscovite and c h l o r i t e .  The matrix i s very minor and seems to  be l a r g e l y composed of very small c l a s t i c fragments.  Possibly  t h i s i s a pebble of Cretaceous Soleduc derived from the area of the present Olympic Mountains.  More l i k e l y these pebbles came  from Soleduc-appearing rocks to the southeast i n the S u l t a n S t i l l a n % u a m i s h area (Danner, personal communication). The conglomerate matrix i s l a r g e l y composed of s t r a i n e d quartz w i t h l e s s e r amounts of p l a g i o c l a s e and m i c r o c l i n e . q u a n t i t i e s of garnet, b i o t i t e and epidote are present.  Minor  Most of  F i g u r e 19. Photomicrograph of conglomerate from D e l t a Rocks F o r m a t i o n . Rounded q u a r t z i t e p e b b l e t o r i g h t . P o o r s o r t i n g and h i g h a n g u l a r i t y o f q u a r t z and f e l d s p a r g r a i n s c h a r a c t e r istic. Cross-nicols, xlO.  F i g u r e 20. P h o t o m i c r o g r a p h o f conglome r a t e m a t r i x , D e l t a Rocks F o r m a t i o n , showing h i g h g r a i n a n g u l a r i t y . Cross-nicols, xlO.  57 the g r a i n s are angular and broken and have undergone v a r y i n g i n t e n s i t i e s of saussuritization. present.  Some s i l t  s i z e fragments are  An a r g i l l a c e o u s m a t r i x or chemical cement i s l a r g e l y  lacking. An interbedded s i l t s t o n e at D e l t a Rocks i s composed p r i n c i p a l l y o f angular s t r a i n e d q u a r t z .  C a l c i c o l i g o c l a s e , high-  l y corroded and p a r t i a l l y r e p l a c e d by s e r i c i t e and s a u s s u r i t e i s the next most abundant m i n e r a l .  Hornblende and epidote are  present i n t r a c e amounts while s e r i c i t e and c h l o r i t e are abundant secondary m i n e r a l s .  A m a t r i x comprises  the rock and appears  to be l a r g e l y  a t l e a s t 10 per cent o f  argillaceous.  A metamorphic source t e r r a i n seems i n d i c a t e d by the m i n e r a l and pebble  assemblage.  No f o s s i l s were found  i n t h i s sequence but i n s e v e r a l  p l a c e s s m a l l carbonized wood fragments were found a s s o c i a t e d w i t h the conglomerate.  A sample o f s i l t s t o n e was macerated i n  the s e a r c h f o r p l a n t m i c r o f o s s i l s but w i t h negative Ika  results.  Formation L i k e the D e l t a Rocks Formation,  Formation  the rocks o f the Ika  a r e e s s e n t i a l l y a conglomeratic  beds o f f i n e r m a t e r i a l .  sequence w i t h  The maximum exposed s t r a t i g r a p h i c  i o n crops out on Ika I s l a n d where 430 f e e t are exposed. 80 per cent i s conglomerate sandstone  and s i l t s t o n e .  o f the conglomerate,  inter-  w h i l e the remaining  Shale appears  sect-  About  20 per cent i s  to be absent.  The c o l o r  both on f r e s h and weathered s u r f a c e s , ranges  58 from b u f f to p a l e r e d to dark r e d , w h i l e f i n e r - g r a i n p o r t i o n s may be b u f f to p a l e o l i v e Maximum observed  gray. boulder s i z e was 30 cm w i t h a g r a d a t i o n  downward to an a r g i l l a c e o u s sandy m a t r i x .  The l a r g e r  pebbles  and cobbles are sub-rounded to rounded and s m a l l e r s i z e s appear more a n g u l a r .  A low s p h e r i c i t y c h a r a c t e r i z e s the m a j o r i t y o f  c l a s t i c grains. Pebbles and  and cobbles are composed o f v e i n q u a r t z , c h e r t  q u a r t z i t e w i t h a v a r i e t y o f other rocks o c c u r r i n g l o c a l l y .  Sandstone, a r g i l l i t e , s l a t e , d a c i t e , v o l c a n i c rocks and undetermined  g r a n i t i c pebbles  o f "Soleduc-appearing" Formation  c h a r a c t e r i z e the l a t t e r .  Pebbles  rocks which are common i n the D e l t a Rocks  do not appear to be present i n t h i s sequence.  The  m a t r i x i s l a r g e l y formed o f p o o r l y s o r t e d angular quartz and feldspar sand-size grains.  Although many o f the pebbles and  boulders a r e r e d , most o f them are b l a c k to green; the o v e r a l l red c o l o r o f the u n i t i s caused  by a r e d m a t r i x .  Carbonaceous m a t e r i a l i s randomly d i s t r i b u t e d the conglomerate  through  u s u a l l y i n the form o f wood t r a s h and fragments.  Two c o a l i f i e d logs were observed, both about 4 f e e t i n l e n g t h and a f o o t i n compressed  diameter.  Interbedded w i t h the conglomerate d i s c o n t i n u o u s beds o f sandstone, stone.  Shale appears  a r e t h i n l e n s e s and  s i l t s t o n e and c a l c a r e o u s mud-  to be t o t a l l y  absent.  Sandstone occurs as lenses o r cross-bedded the conglomerate.  units within  These beds may reach 5 to 6 f e e t i n t h i c k n e s s  Figure 21. T y p i c a l conglomerate of Ika Formation, i n h i l l s near mouth of North Fork of the Skagit R i v e r .  Figure 22. T y p i c a l conglomerate of Ika Formation, i n h i l l s near mouth o f North Fork o f the Skagit R i v e r . Notice poor s o r t i n g and subrounded nature of l a r g e r constituents.  but can be traced only short distances along the s t r i k e .  In  hand specimen these sands appear remarkably uniform but poorly sorted. Shale or s l a t e fragments up to 5 mm i n diameter are common, and randomly d i s t r i b u t e d through the sand.  Color i s  l i g h t gray to b u f f , grains are angular, and porosity and perm e a b i l i t y appear to be very poor.  The matrix appears to be  l a r g e l y a r g i l l a c e o u s though l o c a l l y c a l c i t e i s present. In t h i n - s e c t i o n the sands are seen to be made up of angular quartz g r a i n s , up to 3 mm i n s i z e .  Undulatory e x t i n c t i o n  i s uncommon. Borders o f grains are corroded and grade into the matrix.  Chert and p l a g i o c l a s e are present i n subordinate amounts.  Chert pebbles show the same marginal c o r r o s i o n as do the quartz grains and appear to be sub-rounded, probably i n d i c a t i n g t h i s i s at l e a s t a second sedimentary cycle.  Plagioclase i s usually  s a u s s u r i t i z e d and the composition i s d i f f i c u l t to determine.  On  the basis o f s e v e r a l u n s a t i s f a c t o r y determinations, and because of t h e i r apparent p o s i t i v e r e l i e f , the w r i t e r f e e l s they are probably andesine.  Trace amounts of K-feldspar are present.  Minor secondary c h l o r i t e occurs, l a r g e l y as an a l t e r a t i o n product of matrix or p l a g i o c l a s e .  M a t r i x i s minor and a r g i l l a c e o u s .  Carbonaceous m a t e r i a l i s randomly disseminated through the rocks as small f l e c k s , and plant m i c r o f o s s i l s were extracted from this material. True s i l t s t o n e i s also present, and except f o r smaller grain s i z e i s s i m i l a r to the sandstone.  Carbonaceous m a t e r i a l  and l i m o n i t e are common, the l a t t e r o c c u r r i n g l a r g e l y along  MEASURED SECTION of  61  p o r t i o n of the IKA F O R M A T I O N  Below New B r i d g e across North Fork of S k a g i t  River  1" = 20 142  Conglomerate, becomes p r o g r e s s i v e l y c o a r s e r upward. Boulders to 30 cr i n diameter. o •'<>"• •'°.:-'o-.-'°:. :o a  Sandstone, pebbly, of c h e r t - q u a r t z i t e . Conglomerate, few t h i n sandy beds, considerable black f l i n t .  119 o o; o.'.oo."o'o"o o'. < ;  111  91 84  O O -•  Sandstone, medium to coarse g r a i n , f a i r s o r t i n g , "abundant carbonaceous m a t e r i a l , i n c l u d i n g c o a l i f i e d . tree trunk. :  •p.'<a;o.:c>:b;o:o o.o-  ••o.:OoV".6.;9oo,--.•°.o .':'dq.Q'.Q <  76  Sandstone and conglomerate i n t e r b e d d e d , sone shale and s l a t e fra.grents, r a r e , small limy nodules, abundant carbonaceous m a t e r i a l .  :p:6P.-Q.yo:?a.Po.?o-  3  Bald. •o.o:q'-/d d.<j  70  Sandstone, f i n e to medium g r a i n , f a i r s o r t i n g , l o c a l c r o s s - b e d d i n g , minor pebble l e n s e s , some p l a t y sl-ate fragments, abundant carbonaceous material.  50  ..'. •o. ' o . O o  o o a o o ' a J>]  oo", «* , o _  (? o  o o ^  Sandstone, medium to coarse g r a i n , subgraywacke, c o n t a i n s many pebbles to 3 cm i n diameter, o c c a s i o n a l interbedded. pebble l a y e r s .  30  O.c' J  O  •o'  o  "C  o-.o.o P 0  •P. :°''?-°:P:r-tOCoO.Q-.0  0 PLATE  3  Conglomerate, massive, b o u l d e r s to 26 cm i n diameter, subrounded to rounded, formed of c h e r t , q u a r t z i t e , sandstone, r a r e g r a n i t i c rocks.  62 minor f r a c t u r e s and  c o a t i n g g r a i n s near these f r a c t u r e s .  i s minor but occurs  i n microscopic  Calcite  veinlets.  Immediately above the pre-Upper Cretaceous unconformity on Ika I s l a n d , where the D e l t a Rocks Formation i s absent, i s a s e r i e s of discontinuous a r g i l l a c e o u s limestone  limy beds which might be considered or limy mudstone.  p l a c e s reach a s i z e o f 0 . 5 argillaceous material. rock  mm  present  C a l c i t e grains i n  i n diameter, and are surrounded by  T h i s may  w i t h abundant disseminated  g r a i n s are s p a r s e l y and  either  grade i n t o a very a r g i l l a c e o u s calcite.  randomly present  i n c o n s i d e r a b l e amounts.  Coarse quartz and  sand  limonite i s l o c a l l y  A s s o c i a t e d w i t h t h i s limy  mud  are t h i n zones made up l a r g e l y o f l i m o n i t e and s c a t t e r e d l i m o n i t e oolites.  O o l i t e s are s l i g h t l y deformed but  c e n t r i c development and,  show s t r o n g con-  locally, radial structure.  Plant micro-  f o s s i l s were found i n t h i n s i l t y beds a s s o c i a t e d w i t h the mud.  The  s t r a t i g r a p h i c p o s i t i o n and  g e n e r a l appearance o f  limy the  sequence suggests l o c a l d e p o s i t i o n i n a f r e s h water p o o l . Sedimentary S t r u c t u r e s Cross-bedding i s the most conspicuous primary s t r u c t u r e w i t h i n the sandstone u n i t s . . Time was  not a v a i l a b l e f o r a  t i c a l study o f t h e i r o r i e n t a t i o n , but  they range i n t h i c k n e s s  from s e v e r a l inches up to 2*j? f e e t . marked by b i o t i t e f l a k e s , and grains.  Bedding planes  i n at l e a s t one  statis-  are commonly  case by magnetite  63  F i g u r e 23. C o n g l o m e r a t e o f t h e D e l t a Rocks F o r m a t i o n , d i p p i n g n o r t h ( r i g h t ) S o u t h s i d e o f I k a I s l a n d , Goat I s l a n d i n background.  F i g u r e 24. P h o t o m i c r o g r a p h o f s a n d y s i l t s t o n e of the Ika Formation. Plant m i c r o f o s s i l s were e x t r a c t e d f r o m t h i s material. P l a n e l i g h t x 10.  64 T o r r e n t bedding  was  observed  i n one  2 inch thick  which i n d i c a t e s that at l e a s t t h i s t h i n b i t o f sequence  bed was  formed by d e p o s i t i o n i n q u i e t , standing water.  AGE  AND  CORRELATION  Many lithologic*.. s i m i l a r i t i e s designated  Ika Formation  i n the S k a g i t Bay a r e a and  designated Chuckanut Formation (1959) on Lummi I s l a n d .  e x i s t between the rocks  by M c L e l l a n  those  (1927) and C a l k i n s  These i n c l u d e s i m i l a r i t i e s o f com-  p o s i t i o n , t e x t u r e , d e p o s i t i o n a l s t r u c t u r e s , and presence  of  abundant carbonaceous m a t e r i a l .  criteria  U n f o r t u n a t e l y no f o s s i l  are yet a v a i l a b l e which w i l l d e f i n i t e l y e s t a b l i s h or d i s p r o v e c o r r e l a t i o n o f these two  units.  However, the l i t h o l o g i c  a r i t y and a s i m i l a r i t y o f ages i n d i c a t e d by t h e i r f l o r a s that the Ika Formation  of S k a g i t Bay may  similsuggests  be an i s o l a t e d remnant  o f Chuckanut Formation.' White (1888) f i r s t  d e s c r i b e d the Chuckanut Formation  in  western Whatcom County, and assigned i t to the Eocene Puget Group o f western Washington. Jenkins  Work was  continued by Shedd (1902),  ( 1 9 2 3 ) , M c C l e l l a n (1927), Glover (1935) and Weaver (1937).  The n e a r e s t exposures are immediately  south o f Bellingham where  a 10,000 f o o t s e c t i o n i s exposed along the c o a s t . A c c o r d i n g to Glover  (1935) the Chuckanut i s made up o f a  great t h i c k n e s s of conglomerates, conformably  sandstones and  o v e r l i e the " s c h i s t o f the r e g i o n " .  s h a l e s which unCoal i s  F i g u r e 25. S m a l l f a u l t i n Ika F o r m a t i o n on I k a I s l a n d . Notice small s t r i n g e r s of coaly m a t e r i a l to l e f t and below p e n c i l .  Figure 26. C o a l i f i e d l o g i n sandstone of the Ika Formation. Log i s i n plane of bedding. In road cut just n o r t h of North Fork of the Skagit River.  66 d i s t r i b u t e d throughout the s e c t i o n but reaches i t s g r e a t e s t abundance near the top.  No limestone i s p r e s e n t .  A known  t h i c k n e s s o f 1 0 , 0 0 0 f e e t o f Chuckanut i s present w h i l e i n f e r e n c e s drawn on d r i l l hole d a t a i n d i c a t e s a p o s s i b l e t h i c k n e s s o f 1 6 , 0 0 0 feet. N e i t h e r i n v e r t e b r a t e nor v e r t e b r a t e remains a r e known but there i s a r i c h f l o r a l assemblage which i s c u r r e n t l y under  study  by Miss Marie Pabst at Western Washington C o l l e g e , Bellingham. At the  the present time there i s c o n s i d e r a b l e q u e s t i o n about  exact age o f the Chuckanut.  of work done by Knowlton,  M c L e l l a n (1927), on the b a s i s  o f the U . S . G e o l o g i c a l Survey, c o n s i d e r Weaver ( 1 9 3 5 ) thought an  ed the Chuckanut to be Lower Eocene.  age o f Late Cretaceous to Middle Eocene as most l i k e l y .  Misch  ( 1 9 5 2 ) suggested that the Chuckanut i s Paleocene w i t h perhaps d e p o s i t i o n commencing i n the l a t e s t  Cretaceous.  A possibility  e x i s t s that what i s mapped as Chuckanut i n northwestern Washington may be a c t u a l l y two f o r m a t i o n s , w i t h an as y e t undetected unconformity s e p a r a t i n g them (Danner, p e r s o n a l  communication).  D e t a i l e d p l a n t m i c r o f o s s i l s t u d i e s have not been made of  the Chuckanut so comparisons w i t h those o f the S k a g i t Bay  area a r e not p o s s i b l e .  In a d d i t i o n , p l a n t m a c r o f o s s i l s were not  found i n the l a t t e r area so comparison  i s i m p o s s i b l e w i t h the  r i c h m a c r o f o s s i l assemblage o f the Chuckanut to the n o r t h .  Faunal  remains a r e absent i n both u n i t s . A study was made o f spores and p o l l e n e x t r a c t e d from the  67 Ika Formatiom but a d e f i n i t e age  cannot be assigned to the  Formation on the b a s i s o f m i c r o f l o r a so f a r s t u d i e d . a strong s u g g e s t i o n  o f a Lower T e r t i a r y  Ika  However,  (Paleocene-Eocene) age  i s provided by the f o l l o w i n g f a c t s : (1)  The  presence o f C i c a t r i o c o s i s p o r i t e s , s e v e r a l s p e c i e s  o f which f l o u r i s h e d i n t h i s a r e a d u r i n g the Late and  e a r l y T e r t i a r y , but which disappeared  Cretaceous  d u r i n g the  Middle  Eocene: (2) found  The  presence of F o v e a s p o r i s , a genus which has  i n Germany to extend  only to the Middle Eocene.  most abundant d u r i n g the Late Cretaceous,  been  It  was  and much l e s s common  i n the Eocene; (3)  S a b a l p o l l e n i n d i c a t e s the presence o f Palm t r e e s .  These suggest  a s u b - t r o p i c a l c l i m a t e which c h a r a c t e r i z e d the  Upper Cretaceous 204)  states:  and T e r t i a r y o f the a r e a .  "By Upper Oligocene  the l a t i t u d e o f Oregon had  times  Andrews (1961, p.  the t r o p i c a l elements i n  l a r g e l y disappeared,  f o r the  Bridge  Creek f l o r a of the John Day B a s i n i n the e a s t e r n part of  the  S t a t e presents a d i s t i n c t l y c o o l e r c l i m a t i c assemblage". cause warmer c l i m a t e s were m i g r a t i n g  southward d u r i n g  Be-  the  T e r t i a r y , the l o s s o f s u b - t r o p i c a l elements i n Oregon must have been contemporaneous w i t h or s l i g h t l y l a t e r than a s i m i l a r change i n Washington. the  map-area allowed  Perhaps the near-sea  l e v e l p o s i t i o n of  a s u b - t r o p i c a l f l o r a to e x i s t  slightly  longer than i n the somewhat e a s t e r l y p o s i t i o n o f the Oregon locality.  At any  r a t e , the palm p o l l e n i n d i c a t e s a s u b - t r o p i c a l  68  environment which probably disappeared w i t h i n the map area by Middle to Late Oligocene. A f u r t h e r suggestion of early T e r t i a r y age i s provided by the d o u b t f u l occurrence of G l e i c h e n i a.  This t r o p i c a l f e r n  appears to be l i m i t e d i n t h i s region to the Upper Cretaceous (Rouse, Personal communication). Negative evidence e x i s t s to suggest that the I k a Formation i s not Upper Cretaceous.  Pro to eacid_it es p o l l e n has been found  i n a l l the m i c r o f l o r a s i n v e s t i g a t e d to date from Upper Cretaceous rocks of the Northwest, but has not been found i n T e r t i a r y rocks (Rouse, personal communication).  P r o t o e a c i d i t e s was not ob-  served i n any o f the studied samples. The i n d i c a t i o n s o f Lower T e r t i a r y age presented by these f l o r a s and the l i t h o l o g i c s i m i l a r i t i e s between the conglomerates of Skagit Bay w i t h those of the Chuckanut Formation on Lummi Island suggests the p o s s i b i l i t y of equivalency.  However as the  exact age and exact s t r a t i g r a p h i c r e l a t i o n s of the Chuckanut are i n doubt, and the p r e c i s e age of the I k a Formation i s not known, i t appears best to apply new names to the conglomeratic rocks of the Skagit Bay area.  ORIGIN  D e l t a _ Rocks Formation As pointed out by Twenhofel  (1947) a conglomerate has  l e s s environmental meaning than any other sediment.  The competency  NORTH-SOUTH  C R O S S - SECTION SCALE  THROUGH  HORIZONTAL • VERTICAL  PRE- UPPER  IKA  I" = 3 0 0 ' l" = 300'  CRETACEOUS  ISLAND  70  of the transport medium was adequate to bring the constituents to t h e i r present l o c a t i o n and secondly the source could not be far distant.  Other conclusions can be derived only from more  d e t a i l e d study of the s p e c i f i c formations. On the basis of inadequate exposures the w r i t e r has prepared a c r o s s - s e c t i o n of Ika Island to shoxv- an e r o s i o n a l cuto f f of D e l t a Rocks Formation.  Because o f the low angular d i s -  cordance between the two u n i t s and t h e i r coarse-grained nature, t h i s angular unconformity i s not o b v i o u s l y v i s i b l e i n the f i e l d . On the south side of Ika Island approximately 270 s t r a t i g r a p h i c feet of D e l t a Rocks Formation crop out and d i p rather steeply northward.  This i s o v e r l a i n by Ika Formation  also d i p p i n g northward, but presumably at a s l i g h t l y steeper angle.  On n o r t h Ika Island the unconformity at the top o f the  Go&t Island Formation i n t e r s e c t s the surface but i s o v e r l a i n d i r e c t l y by Ika Formation. Somewhere i n t h i s one-third m i l e , 270 feet of conglomerate has disappeared.  Whether t h i s i s a case of non-deposition seems  u n l i k e l y as i t would require tremendous southward  thickening  which even i n a conglomerate seems excessive. Furthermore i t would presuppose a source to the n o r t h which seems u n l i k e l y when c o n s i d e r a t i o n i s given to the probable source o f Ika Formation c o n s t i t u e n t s . Probably the source l a y to the south w i t h thickening of the conglomerate northward.  The absence of marine f o s s i l s and  the presence of o c c a s i o n a l woody fragments, the poor s o r t i n g ,  71  and the o c c a s i o n a l cut and f i l l s t r u c t u r e suggest to the w r i t e r a continental o r i g i n .  Contained pebbles of "Soleduc-appearing"  rocks suggest the p o s s i b i l i t y part of the source area l a y to the southwest or southeast.  In the Late Cretaceous the Olympics  were u p l i f t e d w i t h consequent  e r o s i o n . Transport agencies may  have c a r r i e d pebbles to the northeast as f a r as the Skagit Bay region. During or immediately a f t e r d e p o s i t i o n of the D e l t a Rocks Formation, u p l i f t occurred to the south or southeast, which i n i t i a t e d erosion and removal of much of t h i s u n i t .  However t h i s  was soon followed by a f l o o d of e l a s t i c s , now known as the Ika Formation. A d e f i n i t e age can not be assigned to the D e l t a Rocks Formation.  I t i s not h i g h l y deformed and l i k e the Ika  appears to be affected only by Miocene f o l d i n g .  Formation  Consequently i t  i s l a t e r than the two periods of deformation which a f f e c t e d s t i l l older rocks. Ika Formation The Ika Formation of Skagit Bay appears to be c o n t i n e n t a l as suggested by the l a c k of marine f o s s i l s and the abundance of plant remains.  The predominant  red color i s due to earthy  hematite i n the matrix and hematite s t a i n i n g of c o n s t i t u e n t grains. This "ocherous hematite i s produced by i r o n bearing minerals i n the r e g o l i t h " ( P e t t i j o h n , 1949).  Hematite s t a i n i n g i s l a r g e l y  72  r e s t r i c t e d to t e r r e s t r i a l rocks, and i s caused by o x i d a t i o n induced by a l t e r n a t e wetting and drying during d e p o s i t i o n . Such appears to be the case i n t h i s sequence. Cut and f i l l s t r u c t u r e s , e s p e c i a l l y of conglomerates i n sandstone suggest a c o n t i n e n t a l o r i g i n . given by the abundance of conglomerate  Supporting evidence i s and sandstone w i t h an  absence of limestone or shale. The w r i t e r envisages these conglomerates  as wedge-shaped  masses t h i c k e n i n g toward the north, p o s s i b l y representing a l a t e r a l equivalent of the Chuckanut exposed to the south of Bellingham.  Conceivably they are a coarser, near source equiva-  l e n t of f i n e r - g r a i n e d sedimentary rocks l y i n g to the northward. A v a i l a b l e data i s not adequate to i n d i c a t e a source but presumably i t l a y to the southeast or east.  The g r a n i t i c rocks  must have been derived by unroofing of pre-Late Cretaceous intrusions.  acidic  Dacite boulders appear i d e n t i c a l to d a c i t e i n t r u -  sions o c c u r r i n g i n small plugs i n the Cascade f o o t h i l l s to the east (Danner, personal communication).  Quartzite and chert  pebbles, being sub- to well-rounded probably represent at l e a s t a second sedimentary  cycle.  Piedmont d e p o s i t i o n most l i k e l y accounts f o r these deposits.  Turbulent, north flowing waters, d r a i n i n g from adjacent  highlands and l a r g e l y unconfined by channels would carry boulders, pebbles and cobbles.  These would be i n d i s c r i m i n a n t l y deposited  by changes i n drainage routes.  The l a r g e cobbles and boulders  would be r a p i d l y rounded, even by short transport.  Smaller  c l a s t i c p a r t i c l e s would remain angular to subangular and such i s the case i n these rocks.  Cross-bedded sandstones would form where  water courses discharged i n ephemeral lakes.  That abundant  vegetation was c a r r i e d to the d e p o s i t i o n a l environments i s i n d i c a t e d by the now c o a l i f i e d logs and the abundant carbonaceous remains. A l t e r n a t e wetting and drying of the sediments i s f a c i l i tated by the postulated frequent changes i n the drainage pattern.  This would r e s u l t i n the p a r t i a l o x i d a t i o n of i r o n -  r i c h minerals to hematite, imparting the c h a r a c t e r i s t i c red color of the matrix.  PALEOBOTANY  GENERAL  During f i e l d mapping of the T e r t i a r y conglomeratic sequences, several t h i n s i l t s t o n e and very fine-grained sandstone u n i t s were observed.  I n v a r i a b l y these contained carbonac-  eous m a t e r i a l , generally as carbonized twigs or small fragments of wood. observed.  No leaves or other i d e n t i f i a b l e macrofossils were I t was thought that these f i n e - g r a i n e d sediments  might contain plant m i c r o - f o s s i l s and w i t h t h i s i n mind s e v e r a l large specimens were c o l l e c t e d .  S t r a t i g r a p h i c r e l a t i o n s between  74  one l o c a l i t y and another are l a r g e l y unknown, but because of the l i m i t e d thickness and nature of the Ika Formation,  the  specimens are thought to be e s s e n t i a l l y contemporaneous.  ANALYTICAL PROCEDURE  S i x samples of Ika Formation and one sample of Delta Rocks Formation were macerated.  A l l the Ika specimens y i e l d e d  plant m i c r o f o s s i l s , but the D e l t a Rocks specimen contained none. Treatment of a l l specimens was i d e n t i c a l .  Aproximately  f i f t y grams of disaggregated m a t e r i a l was covered w i t h hydroc h l o r i c acid to remove any carbonate present.  After rinsing i n  clear water, the specimens were immersed i n h y d r o f l u o r i c for periods ranging from 24 to 100 hours.  acid  A f t e r decanting the  acid and r i n s i n g i n c l e a r water a residue of m i c r o f o s s i l s , carbonaceous fragments, and i n s o l u b l e mineral matter remained. This residue was  immersed i n n i t r i c acid f o r 3 to 24 hours, which  was followed by a f i n a l treatment of potassium carbonate to free the m i c r o f o s s i l s from t h e i r carbonaceous coat.  Several  washings i n clear water followed and the residue was  concentrated  i n a centrifuge.  Where considerable i n s o l u b l e mineral matter  remained, a heavy l i q u i d separation was made using a z i n c c h l o r i d e s o l u t i o n of s p e c i f i c g r a v i t y 2. added to s t a i n the f o s s i l s .  Safranine dye  was  F i n a l l y the m i c r o f o s s i l residue  75 was d i v i d e d among 5 to 7 s l i d e s and immersed i n a p l a s t i c medium d i s s o l v e d i n benzene. A f t e r p r e p a r a t i o n , the s l i d e s were studied under a Z e i s s binocular microscope w i t h adjustable micrometer stage. Photographs were made through the microscope using a L e i c a 35 mm camera.  Adox Dukopan f i l m was used and a green f i l t e r i n -  serted i n the l i g h t source to increase contrast. F i n a l p r i n t i n g was on high contrast Kodak photographic of p r i n t s was 500 diameters.  paper.  The m a g n i f i c a t i o n  F o s s i l i d e n t i f i c a t i o n was made  w i t h photographs and by d i r e c t examination  through the micro-  scope.  IDENTIFICATION  On the whole, the spores and p o l l e n f o r the samples i n v e s t i g a t e d are poorly preserved.  They show signs of consider-  able abrasion and many were broken.  Diagnostic f e a t u r e s , such as  ornamentation and pores, were l a r g e l y obscured, making i d e n t i fication difficult. The w r i t e r made t e n t a t i v e i d e n t i f i c a t i o n s o f some forms using l a r g e l y the group c l a s s i f i c a t i o n o f Krutzsch (1957).  More  s p e c i f i c generic i d e n t i f i c a t i o n s were made by comparisons w i t h Burrard (Eocene) m i c r o f o s s i l s (Rouse, manuscript i n press). Dr. G.Rouse made p o s i t i v e i d e n t i f i c a t i o n o f a l l spores and p o l l e n which could be determined.  The w r i t e r g r a t e f u l l y  76 acknowledges the considerable help rendered by Dr. Rouse i n this  connection. The f o l l o w i n g were i d e n t i f i e d :  A l t e r n o s e p t i t e s sp.  alga  Phragmothyrites eocaenicus Edwards  fungus  C i c a t r i o c o s i s p o r i t e s i n t e r s e c t u s Rouse  fern  ?Gleichenia sp.  fern  Foveasporis Krutzsch  cf. fern  Pinus sp.  pine  Taxodium h i a t i p i t e s Wodehouse  bald cypress  Sabal ^ r a n o p o l l e n i t e s Rouse  palm  Juglans sp.  walnut  Carya j u x t a p o r i p i t e s (Wodehouse) Rouse  hickory  P l a t y c a r y a sp.  hickory  T i l i a sp.  basswood (linden)  Corylus t r i p o l l e n i t e s Rouse  hazel  Alnus.-'-sp.  alder  Other forms were present i n the specimens studied but could not be r e a d i l y i d e n t i f i e d .  G l e i c h e n i a , a diagnostic t r o p i c a l  f e r n , was  The paucity of specimens com-  doubtfully i d e n t i f i e d .  bined w i t h the poor s t a t e of preservation made absolute t i f i c a t i o n impossible.  iden-  Gleichenia became e x t i n c t t h i s f a r north  i n the e a r l i e s t T e r t i a r y , so a d e f i n i t e i d e n t i f i c a t i o n would have considerable age s i g n i f i c a n c e . Many of the forms l i s t e d above are c h a r a c t e r i s t i c of the Burrard Formation of Eocene age. (Rouse, personal communication).  77  B r i e f examination by the w r i t e r o f m i c r o f o s s i l s from the Sooke Formation (probably Lower Miocene) indicated  little  s i m i l a r i t y between the Sooke and the T e r t i a r y rocks of the Skagit Bay area.  Using the broad c l a s s i f i c a t i o n groups of  Krutzsch ( 1 9 5 7 ) » plant m i c r o f o s s i l s i n d i c a t e a Middle to Late T e r t i a r y age for the Sooke f l o r a . Two preparations o f Chuckanut m i c r o f o s s i l s were also b r i e f l y examined and these showed s i m i l a r i t i e s w i t h those o f the Skagit Bay area.  E s p e c i a l l y important was the presence of  Foveasporis Krutzsch, also found i n the Ika Formation o f the Skagit Bay area, which i s r e s t r i c t e d to the Middle Eocene i n Germany.  ENVIRONMENTAL SIGNIFICANCE  Two of the Lower T e r t i a r y genera.; Taxodium and Sabal, :  are warm-temperate to s u b - t r o p i c a l .  Gleichenia, i f t r u l y  present i s also i n d i c a t i v e o f a s u b t r o p i c a l climate.  The r e -  maining forms are i n d i c a t i v e o f a moist but somewhat cooler environment. The r e l a t i v e percentage of genera i n the o r i g i n a l f l o r a oi the distances spores and p o l l e n may have t r a v e l l e d to the s i t e of d e p o s i t i o n , are not known.  Probably the mixture of sub-  t r o p i c a l forms w i t h those c h a r a c t e r i s t i c of cool temperate c l i m ates i s i n d i c a t i v e o f mingling o f d i s t i n c t f l o r a l zones.  Perhaps  the palms, cypress and t r o p i c a l ferns were a c h a r a c t e r i s t i c part of a lowland f l o r a .  The more temperate forms may have come from  h i l l s and mountains to the south or east. Durham (1950, p. 1244) s t a t e s :  "... the Lower Eocene  faunas of the Crescent Formation i n the State of Washington (at about 40°N l a t . ) include reef c o r a l s , large f o r a m i n i f e r a , brachiopods, and t r o p i c a l molluscan genera, c l e a r l y i n d i c a t i n g that t h i s fauna too,  l i v e d i n a t r o p i c a l environment".  The  t r o p i c a l element i n the S k a g i t Bay f l o r a i s compatible w i t h the Eocene environment as known by other evidence. As pointed out e a r l i e r , under the s e c t i o n "Upper Cretaceous—Lower T e r t i a r y Sediments", the t h i c k wedge of conglomerates s t r o n g l y suggests a high mountain source.  These high and  cooler areas might e a s i l y have supported a temperate vegetation which i s represented by spores and p o l l e n i n the Skagit Bay rocks. The w r i t e r has observed a modern day e q u i v a l e n t , bordering Lingayen Gulf on the west side of Luzon I s l a n d , the l a r g e s t i n the P h i l i p p i n e I s l a n d Group.  A sea l e v e l c o a s t a l p l a i n supp-  o r t s a t h i c k t r o p i c a l f l o r a i n c l u d i n g f e r n s , palms, hananas, etc. One-half mile to one m i l e i n l a n d , mountains r i s e a b r u p t l y , culminating i n peaks up to 6500 feet i n e l e v a t i o n .  A steady  v e r t i c a l change i n f l o r a occurs w i t h various c o n i f e r s and other cool temperate forms making an appearance at the higher e l e v a t i o n s . I t seems conceivable that a mixture of t r o p i c a l and temperate f l o r a l elements could occur i n lowland areas of d e p o s i t i o n , such as represented by the Skagit D e l t a .  I t i s also i n t e r e s t i n g to note that at the foot of the mountains, on t h i s t r o p i c a l c o a s t a l p l a i n of Luzon, extensive wedges of c o n t i n e n t a l conglomerates are being deposited.  During  much of the year these are l a r g e l y exposed to the drying e f f e c t s of heat and sun, but during the monsoon season, l a r g e q u a n t i t i e s of coarse conglomeratic m a t e r i a l are brought down by turbulent streams.  Interbedded shales and s i l t s probably contain t r o p i c a l  to s u b - t r o p i c a l to cool temperate f l o r a l remains, as do those of the S k a g i t Bay T e r t i a r y sediments.  The w r i t e r envisages the  Ika Formation as being deposited under c l i m a t i c conditions and w i t h a d e p o s i t i o n a l environment s i m i l a r to those now prevailing along the west coast of Luzon.  MARINE PLEISTOCENE  F o s s i l i f e r o u s marine P l e i s t o c e n e beds are exposed i n a pocket 10 to 15 feet above sea l e v e l at the west end of Hope Island.  The deposit i s small and r e s t s unconformably upon  serpentinite.  The b a s a l p o r t i o n of the unit i s a p o l y m i c t i c ,  unsorted conglomerate composed of angular to rounded boulders up to 2 feet i n maximum dimension.  Upward through the exposed  to 14 f e e t , the average p a r t i c l e s i z e decreases.  Present are  t h i n interbeds of pebbly sand enclosed i n subrounded conglomerates.  12  cobble  The e n t i r e deposit i s very poorly s o r t e d , w i t h  pronounced and abrupt v e r t i c a l changes i n grain s i z e .  In o v e r a l l  80 appearance,  the beds resemble  a sedimentary  r a p i d l y moving, t u r b u l e n t water which was forming new  u n i t d e p o s i t e d by  r a p i d l y agrading and  channels.  The u n i t appears  to be d i p p i n g east at about  2 2 ° , but  because there i s no evidence elsewhere o f p o s t - P l e i s t o c e n e deformation t h i s i s probably a primary d i p . Interbedded w i t h the conglomerates e x h i b i t i n g two  types of f a u n a l remains.  are pebbly  The  first  sands,  are sandy  l a y e r s c o n t a i n i n g an e x c e p t i o n a l l y h i g h percentage o f pelecypod s h e l l fragments,  u s u a l l y l e s s than o n e - h a l f i n c h i n s i z e .  L o c a l l y the s h e l l c o n c e n t r a t i o n i s so h i g h the bed might p r o p e r l y be c a l l e d a coquina.  Another  sandy bed near the top o f the  u n i t c o n t a i n s r e l a t i v e l y undamaged marine i n v e r t e b r a t e remains. Lack o f any  s u b s t a n t i a l t r a n s p o r t or a b r a s i o n i s i n d i c a t e d  the presence o f numerous, f r a g i l e , t h i n - w a l l e d mussel showing n e g l i g i b l e damage.  by  shells  B a r n a c l e s are l e s s commonly present  and are attached to pebbles i n growth p o s i t i o n w i t h no evident abrasion. Faunal forms c o l l e c t e d from the P l e i s t o c e n e a r e : S c h i z o t h a e r u s sp. - (horseclam), a l a r g e ,  thick-shelled  pelecypod. Saxidomus sp. - ( b u t t e r clam), a t h i c k - s h e l l e d Pecten sp, - ( s c a l l o p ) M y t i l u s sp. - (blue Balanus  mussle),  sp. - a s m a l l b a r n a c l e  S e r p u l a sp. - worm tubes  thin-shelled  pelecypod  Figure 2 7 . Invertebrate-bearing, marine Pleistocene conglomerate at east end of Hope I s l a n d . Hammer r e s t i n g on "coquina" zone.  Figure 2 8 . G l a c i a l s t r i a t i o n s and grooving, i n d i c a t i n g i c e movement toward observer. South side of Kiket I s l a n d .  82  These genera are s t i l l found i n h a b i t i n g parts o f Puget Sound, S t r a i t s of Georgia and bays o f the open coast (Dehnel, personal communication). The w r i t e r believes t h i s unit was deposited i n marine waters near the toe of the r e t r e a t i n g Vashon i c e sheet.  Outwash  gravels and sand f l a t s were formed immediately to the south o f the i c e , much of i t being l a i d down under water.  Marine organ-  isms such as Balanus and M y t i l u s established themselves on rocks, while the Schizothaerus, Saxidomus, and worms occupied the f i n e r f g r a i n e d sediments. Occasional channel s h i f t i n g of the high v e l o c i t y , turbul e n t streams d r a i n i n g the i c e margin r e s u l t e d i n e r o s i o n , conc e n t r a t i o n , and b u r i a l of these faunal forms. The c o q u i n a - l i k e beds, which contain a sand or pebbly sand m a t r i x , suggest s t r a n d l i n e concentrations.  Wave a c t i o n  broke up and concentrated pelecypod s h e l l s which are preserved as d i s t i n c t u n i t s .  INTRUSIVE ROCKS  OCCURRENCE  With the exception of the extreme southeast end, the e n t i r e mass of Hope Island i s composed o f u l t r a b a s i c i n t r u s i v e rocks.  To the east, across a narrow channel, these same rocks,  are exposed both at Hunot and T o s i P o i n t s .  Other outcrops occur  83  near the v i l l a g e of Snee-oosh Beach and along the main highway immediately east of town. The south side of Hope Island i s d e l i m i t e d by a westsouthwest trending f a u l t of unknown displacement which has brought v o l c a n i c rocks into contact w i t h s e r p e n t i n i t e .  The  v o l c a n i c rocks occupy a very small area at the extreme southeast t i p of the i s l a n d .  On both sides of the f a u l t the v o l c a n i c rocks  and s e r p e n t i n i t e are i n t e n s e l y sheared and s l i c k e n s i d e d . Another u l t r a b a s i c i n t r u s i o n occurs at the southeast end of Fidalgo I s l a n d associated w i t h a v e i n of strontium minerals and c a l c i t e .  Although t h i s i s also a s e r p e n t i n i t e i t s character  and nature of occurrence are somewhat d i f f e r e n t from the serpent i n i t e s of the Hope I s l a n d - T o s i Point-Hunot P o i n t s area and i s discussed i n the s e c t i o n on Economic Geology. McLellan (1927) assigned the name Fidalgo Formation to i n t r u s i v e masses of s e r p e n t i n i z e d dunites which occur i n the San Juan I s l a n d s .  He recognized three d i s t i n c t rock types: (1) masses  of very coarse-grained d u n i t e , (2) veins of f i n e - g r a i n e d dunite i n j e c t e d i n t o f r a c t u r e s of the coarse v a r i e t y and (3) s t r i n g e r s of s e r p e n t i n i z e d pyroxenite.  Most of the dunites have been  serpentinized. On the basis of L i t h o l o g y and a s s o c i a t i o n , the u l t r a b a s i c rocks of the Skagit Bay area are considered to be part of McL e l l a n s Fidalgo Formation. 1  F i g u r e 29. Jointed serpentinite on n o r t h shore o f Hope I s l a n d .  F i g u r e 30. View west along south shore o f Hope I s l a n d . Cliffs formed o f s e r p e n t i n i t e .  85  PETROLOGY  General The term " u l t r a b a s i c " i s a p p l i e d to those i n t r u s i v e rocks high i n i r o n and magnesium.  T y p i c a l l y they are made up o f  varying q u a n t i t i e s of o l i v i n e and pyroxene w i t h l i t t l e or no p l a g i o c l a s e , amphibole or b i o t i t e .  Dunite i s defined  (Leech,  1953) as a rock containing 95 per cent or more o l i v i n e , w i t h or without minor pyroxene.  With more than 95 per cent pyroxene the  rocks are c a l l e d "pyroxenites".  The intermediate phases are  named on the basis o f t h e i r orthorhombic-monoclinic ratio.  pyroxene  " P e r i d o t i t e " i s an o l i v i n e r i c h , non-feldspathic rock,  which therefore includes dunite and intermediate phases but not pyroxenite.  The v a r i e t i e s of p e r i d o t i t e of i n t e r e s t i n t h i s  area are dunite and h a r z b u r g i t e , the l a t t e r being an o l i v i n e orthopyroxene  rock.  Serpentine i s a c o l l e c t i v e term f o r a  group o f hydrous magnesium s i l i c a t e m i n e r a l s , and s e r p e n t i n i t e i s a name applied to a rock composed of serpentine minerals. The u l t r a b a s i c s o f Skagit Bay are s e r p e n t i n i t e s composed e s s e n t i a l l y of serphophite, a n t i g o r i t e ; minor c h r y s o t i l e , t a l c , chromite and magnetite w i t h r a r e r e s i d u a l s of o l i v i n e and enJKstatite. Field Description In weathered outcrop t h i s rock appears dark gray to dark green though a f r e s h surface i s always a d u l l dark green.  The  86  t y p i c a l brownish-weathering s e r p e n t i n i t e  i s not abundantly  p r e s e n t , probably due to the low i r o n content. graphically  I t i s a topo-  r e s i s t a n t , commonly j o i n t e d rock, which i s i n v a r -  iably a cliff-former.  F r a c t u r e s and j o i n t s are commonly  w i t h smears o f carbonate.  filled  When these s u r f a c e s are exposed by  weathering or e r o s i o n the carbonate gives the rock a s p l o t c h y , gray-white appearance. Thin-Section The evidently  Pescription mineralogy, as seen i n t h i n s e c t i o n  homogeneous over the e n t i r e a r e a .  serpentinite  consists  i s simple, and  T e x t u r a l l y the  o f a mesh o f a n t i g o r i t e v e i n l e t s  enclosing  cores o f serphophite and more l o c a l l y r e l i c s o f o l i v i n e . T y p i c a l l y the i n t e r s t i c e s are zoned, c o n s i s t i n g  o f a marginal  zone o f f i b e r s growing a t r i g h t angles to the g r a i n margins and a c e n t r a l zone i n which the f i b e r s are at r i g h t angles to the first  two zones. Enstatite  formerly constituted  about 5 per cent o f the  rock, but where o r i g i n a l l y present i t has commonly been r e p l a c e d by  serphophite and a n t i g o r i t e to form b a s t i t e .  r a r e occurs as small f i b e r s i n t i m a t e l y antigorite.  In at l e a s t one s e c t i o n  Chrysotile  associated  though  w i t h the  i n c i p i e n t s t e a t i z a t i o n was  seen w i t h t a l c having s l i g h t l y r e p l a c e d the a n t i g o r i t e . Very small f l e c k s o f chromite are s p a r i n g l y hand specimen w i t h a hand l e n s . to be s c a t t e r e d  In t h i n - s e c t i o n  visible in  they are seen  randomly throughout the rock, d i s p l a y i n g  a  87  v a r i a t i o n i n s i z e w i t h a maximum up to about 0.2 mm. i s mainly anhedral, though some euhedral forms e x i s t .  Chromite Magnetite  i s r a r e , appearing as d u s t l i k e p a r t i c l e s d i s t r i b u t e d mostly i n i n t e r g r a n u l a r spaces.  The small amount o f magnetite s t r o n g l y  suggests the o r i g i n a l o l i v i n e was i r o n poor. During the a l t e r n a t i o n o f o l i v i n e to serpentine the replacement  appears to have progressed uniformly from g r a i n  boundaries, and replacement  i s complete i n s e v e r a l specimens.  As mentioned, the e n s t a t i t e , where present, has been pseudom o r p h i c a l l y replaced so an i n d i c a t i o n o f o r i g i n a l m i n e r a l o g i c a l composition i s p o s s i b l e . On t h i s basis the o r i g i n a l rock i s i n t e r p r e t e d as a dunite or very o l i v i n e r i c h h a r z b u r g i t e .  ORIGIN  S e r p e n t i n i t e i s i n contact w i t h only two other l i t h o l o g i c types.  The f i r s t i s the e a r l i e r mentioned f a u l t contact  w i t h v o l c a n i c rocks and the second i s an unconformable contact w i t h o v e r l y i n g g l a c i a l outwash and t i l l .  Neither of these i s o f  m a t e r i a l assistance i n a genetic i n t e r p r e t a t i o n except to suggest that e i t h e r the v o l c a n i c s or the serpentines are exposed because o f f a u l t i n g .  The f o l l o w i n g d i s c u s s i o n i s based p r i n c i p a l l y  on ideas o f Hess ( 1 9 3 3 , 1 9 3 8 , 1 9 5 5 ) , Leech ( 1 9 5 3 ) and Turner and Verhoogen (I960). The s e r p e n t i n i t e s o f the Skagit D e l t a area are of the "Alpine type" which t y p i c a l l y occur i n f o l d e d eugeosynclinal  88  sediments and orogenic b e l t s . lenticular  They most commonly occur as  sheets and t a b u l a r bodies  the deformed sediments,  f r e q u e n t l y concordant  with  however many massive c r o s s - c u t t i n g i n -  t r u s i o n s a r e known. Much c o n t r o v e r s y has a r i s e n , and s t i l l the o r i g i n o f " A l p i n e type" u l t r a b a s i c r o c k s .  continues,  over  The d i s c u s s i o n  has f i n a l l y r e s o l v e d i t s e l f i n t o two a l t e r n a t i v e e x p l a n a t i o n s : (1)  I n t r u s i o n o f a p e r i d o t i t e magma, perhaps o f s e r p e n t i n e  composition (2)  as has been most f o r c e f u l l y presented  by Hess.  I n t r u s i o n by s o l i d flow o f u l t r a b a s i c rock, perhaps  l a r g e l y formed o f c r y s t a l l i z e d o l i v i n e and some pyroxene, the whole l u b r i c a t e d and given m o b i l i t y by i n t e r g r a n u l a r f l u i d s . Bowen and chemical  Tuttle  (1949) have placed t h i s concept  on a s o l i d  foundation. Hess, i n h i s support o f a t r u e hydrous magnesian melt,  has agreed  t h a t many u l t r a b a s i c i n t r u s i o n s were s e m i - s o l i d at  time o f i n t r u s i o n , but does not b e l i e v e t h i s to be a " g e n e r a l " explanation.  He p o i n t s to low d i p , and concordant  s e r p e n t i n i t e which are comparatively  t h i n ; the frequent l a c k of  flow s t r u c t u r e ; and the l a c k o f evidence should r e s u l t  s i l l s of  f o r e r u p t i o n which  from r e l e a s e o f pressure on i n t e r g r a n u l a r f l u i d s .  Because shallow i n t r u s i o n s would l o s e water, s e r p e n t i n i z a t i o n should i n c r e a s e w i t h depth.  The r e v e r s e i s a c t u a l l y t r u e , Hess  m a i n t a i n s , w i t h v i r t u a l l y a l l shallow u l t r a b a s i c being s e r p e n t i n i z e d .  intrusions  Because Hess c o n s i d e r s s e r p e n t i n i z a t i o n to  Figure 31. Photomicrograph of serpentinized dunite w i t h c h a r a c t e r i s t i c mesh texture. Specimen from Hope I s l a n d . C r o s s - n i c o l s , xlO.  90  be a d e u t e r i c process, he suggests the necessary v o l a t i l e s to be d e r i v e d from the magma i t s e l f , w i t h a l e s s e r amount coming from the country rock. Bowen and T u t t l e (1949), l a r g e l y on the basis o f laboratory experiment, have presented evidence to support the concept of " s o l i d i n t r u s i o n s or a magma composed e s s e n t i a l l y o f c r y s t a l l i n e o l i v i n e and pyroxene supported and surrounded by an i n t e r granular magmatic f l u i d .  A f t e r considerable experimentation  Bowen and T u t t l e concluded that there i s "no l i k e l i h o o d that any magma can e x i s t that can be c a l l e d a serpentine magma, and c e r t a i n l y no p o s s i b i l i t y o f i t s existence below 1000°C." In t h i s connection they emphasize the l a c k o f contact e f f e c t s on intruded country rock, hence probable low temperature.  Further-  more o l i v i n e might be expected to flow under s t r e s s , perhaps more e a s i l y than any other s i l i c a t e .  While passing through  sedimentary rocks the magma might p i c k up v o l a t i l e s from the w a t e r - r i c h g e o s y n c l i n a l rocks r e s u l t i n g i n s e r p e n t i n i z a t i o n and consequently s t i l l easier flowage. Both the hypotheses of u l t r a b a s i c emplacement t e n t a t i v e l y accept the concept o f o r i g i n a l source m a t e r i a l i n a p e r i d o t i t e substratum. Recent l a b o r a t o r y and f i e l d evidence i n c r e a s i n g l y suggests the Bowen and T u t t l e hypothesis as most acceptable f o r "Alpine type" u l t r a b a s i c i n t r u s i o n s .  In t h i s connection Turner and  Verhoogen (I960, p.32l) summarize:  91 "We are now able to accept as a s a t i s f a c t o r y working hypothesis the dual concept of i n t r u s i o n of p e r i d o t i t e "magma" i n a l a r g e l y c r y s t a l l i n e cond i t i o n , w i t h simultaneous or subsequent s e r p e n t i n i z a t i o n of i t s c o n s t i t u e n t minerals ( o l i v i n e and ens t a t i t e ) through the a c t i v i t y of aqueous s o l u t i o n s or vapors derived f o r the most part from the surrounding g e o s y n c l i n a l sediments or from i n t r u s i v e bodies of g r a n i t i c magmas. But t h i s , l i k e any other hypothesis, i s subject to f u t u r e m o d i f i c a t i o n or r e j e c t i o n should i t prove incompatable w i t h f a c t s yet to be discovered".  SERPENTINIZATION  There are two p r i n c i p a l theories to e x p l a i n the serpent i n i z a t i o n of u l t r a b a s i c rocks; (1)  Deuteric a l t e r a t i o n w i t h s e r p e n t i n i z i n g f l u i d s coming  from the c o o l i n g u l t r a b a s i c body and (2)  Hydrothermal a l t e r a t i o n brought about by s o l u t i o n s  coming from outside the u l t r a b a s i c mass, perhaps from younger i n t r u s i v e rocks. The f i r s t concept, supported p r i n c i p a l l y by Hess, c a l l s for  a p r e l i m i n a r y c r y s t a l l i z a t i o n of o l i v i n e , then a r e a c t i o n  between the o l i v i n e and water to produce serpentine. for  Support  t h i s theory i s o f f e r e d by l a r g e , more or l e s s uniformly  s e r p e n t i n i z e d bodies which show no r e l a t i o n to sediments, s t r u c t u r e or other i n t r u s i v e bodies. The second theory i s favored by Bowen s 1  work.  experimental  This explanation, l i k e the f i r s t , requires a d d i t i o n of  tremendous volumes of water which presumably come l a r g e l y from water charged eugeosynclinal sediments.  O l i v i n e i s replaced  92  by an equal volume of serpentine w i t h excess MgO removed i n s o l u t i o n .  and SiC>2 being  Although l o c a l l y s i l i c i f i c a t i o n  and  magnesia metasomatism of adjacent rocks does occur, i t i s not common, hence what happens to the magnesia and s i l i c a i n these cases?  Unfortunately the s e r p e n t i n i t e s of the map area give  l i t t l e help i n making a genetic i n t e r p r e t a t i o n ,  STEATIZATION  L o c a l l y t a l c i s present i n very small amounts r e p l a c i n g antigorite.  The process of t a l c formation i n an u l t r a b a s i c  rock i s termed " s t e a t i z a t i o n " (Hess, 1 9 3 3 )  v  I t i s a hydro-  thermal r e a c t i o n , g e n e r a l l y unrelated t o , and l a t e r than serpentinization. A few examples are reported where the only source of a c t i v e s o l u t i o n s i s the u l t r a b a s i c body i t s e l f .  In these cases  i t would seem that t a l c formation i s an aftermath of serpentinization.  The two are r e l a t e d , i n that s t e a t i z a t i o n s o l u t i o n s  would be s i m i l a r t o , but of a lower temperature than those causing s e r p e n t i n i z a t i o n . Talc formation i s very minor and very l o c a l i n the Skagit Bay r e g i o n which would suggest that i t was a l a t e and low temperature a l t e r a t i o n brought about by the f i n a l c o o l i n g of s e r pentinizing solutions.  93  AGE  McLellan  (1927) d e s c r i b e s u l t r a b a s i c rocks o f the  San  Juan I s l a n d s , i n t r u d i n g the Upper P a l e o z o i c Leech R i v e r Eroup. These u l t r a b a s i c s were, i n one  l o c a l i t y , i n t r u d e d by  rocks which he considered Late T r i a s s i c or E a r l y He concluded  that the F i d a l g o Formation  acidic  Jurassic.  i s of T r i a s s i c  age.  As p o i n t e d out e a r l i e r no f i e l d or p e t r o g r a p h i c i o n s are present  i n the map  a r e a to give evidence as to age  type" u l t r a b a s i c s o f the orogenic b e l t s are Intruded the e a r l i e s t phases o f deformation. rocks o f the S k a g i t Bay  it  of  Hess (1955) i n d i c a t e s that " A l p i n e  ultrabasic intrusions.  T e r t i a r y age  relat-  during  Because the e u g e o s y n c l i n a l  a r e a are known to be o n l y o f p r e -  and because s e v e r a l p e r i o d s o f deformation  i s o n l y p o s s i b l e to  s t a t e that the s e r p e n t i n i t e s are  are known, pro-  bably p r e - T e r t i a r y . Leech (1953) d e s c r i b e d s i m i l a r occurrences o f a l p i n e type u l t r a b a s i c rocks from the Shulaps B r i t i s h Columbia.  He found  Upper T r i a s s i c rocks and  Range o f  southwestern  that the main u l t r a b a s i c mass cuts  f u r t h e r that chromite, presumably from  the u l t r a b a s i c i n t r u s i o n s , was  found  i n rocks c o n t a i n i n g pro-  bably Lower J u r a s s i c f o s s i l s .  Hence these i n t r u s i o n s are pro-  bably Upper T r i a s s i c . In the Cascade Mountain f o o t h i l l s , about 33 m i l e s n o r t h east o f La Conner, and  j u s t southwest o f Mt. Baker i s a l a r g e  94 intrusive dunite.  Contained w i t h i n i t are l a y e r s and l e n s e s  o f chromite, some o f which has been u l t r a b a s i c rock,  mined commercially.  This  c a l l e d the Twin S i s t e r s d u n i t e , i s considered  T e r t i a r y i n age, but the b a s i s f o r t h i s age assignment i s unp u b l i s h e d and unknown to the w r i t e r . Hess ( 1 9 5 5 , p.396) presents a map B e l t s o f N o r t h America".  entitled  "Serpentine  An arcuate band o f u l t r a b a s i c s ,  con-  cave westward, and i n c l u d i n g the u l t r a b a s i c i n t r u s i o n s o f the map  a r e a , are shown to be Late T r i a s s i c i n age.  Other  ultra-  b a s i c i n t r u s i o n s o f c e n t r a l and n o r t h e r n B r i t i s h Columbia are thought  to be a l s o Upper T r i a s s i c . Using the p o s t u l a t e d ages f o r s i m i l a r rocks i n adjacent  areas the w r i t e r t e n t a t i v e l y suggests an Upper T r i a s s i c a&e f o r t h e s e r p e n t i n i t e o f the S k a g i t D e l t a a r e a .  STRUCTURE  Regional Although  the o l d e s t rocks are h i g h l y deformed, the  e a r l i e s t o r o g e n i c a c t i v i t y that can be i n t e r p r e t e d w i t h degree o f accuracy o c c u r r e d during the Late Miocene. time the whole coast of North America was gone v a r y i n g degrees intense  thought  any  At that  to have under-  o f u p l i f t , w i t h l o c a l areas undergoing  more  deformation. One  such l o c a l a r e a was  t r e n d i n g upwarp that extended  a broad,  northwest-southeast  from southern Vancouver I s l a n d ,  through the San Juan I s l a n d s , through western S k a g i t County and southeast through the s i t e o f the present c e n t r a l Cascade Mountains.  The Chuckanut Formation, near Bellingham, l i e s  the n o r t h e a s t f l a n k o f t h i s u p l i f t .  The map  on  a r e a i s on the  c r e s t o f t h i s Late Miocene u p l i f t , and i n consequence e r o s i o n has removed most o f the T e r t i a r y cover, exposing the more i n t e n s e l y deformed p r e - T e r t i a r y sedimentary  rocks.  Again i n Late P l i o c e n e and E a r l y P l e i s t o c e n e times, the whole r e g i o n was  a f f e c t e d by n o r t h - s o u t h u p l i f t s and downwarps  that c r e a t e d the present day Cascade and Olympic Mountains and the Puget Sound Trough.  T e r t i a r y rocks of the western S k a g i t  D e l t a p r e s e r v e evidence o f Late Miocene,  northwest-southeast  deformation, but do not show s i g n s o f the n o r t h - s o u t h P l i o c e n e uplift.  P l i o c e n e - P l e i s t o c e n e deformation i n the S k a g i t D e l t a  a,rea was  probably simple t i l t i n g w i t h l i t t l e  compression.  Local Deformation  i s very i n t e n s e i n the map  a r e a and  detailed  s t r u c t u r a l a n a l y s i s o f p r e - T e r t i a r y rocks i s s e v e r e l y h a n d i capped f o r the f o l l o w i n g  reasons:  (1)  P a u c i t y o f outcrops  (2)  H i g h l y weathered and decomposed nature o f many outcrops  (3)  Lack o f any f o s s i l or s t r a t i g r a p h i c  control.  W i t h i n l i m i t s set by time and the author's  ability,  measurements of bedding, cleavage and l i n e a t i o n s were made. Because o f the almost omnipresent  flow and f r a c t u r e cleavage,  NORTH  P A L E O Z O I C ( ? ) GOAT ISLAND FORMATION from • x  0  southern Fidalgo Island and G o a t I s l a n d .  Poles  to cleavage  (20 p o i n t s )  L i n e a t i o n (7 p o i n t s ) P o l e t o average g r e a t c i r c l e through poles t o cleavage.  Plotted  on l o w e r h e m i s p h e r e o f equal area n e t .  NORTH  DELTA ROCKS AND IKA FORMATIONS p o l e s t o b e d d i n g p l o t t e d on lower hemisphere o f equal area n e t . Pole  to average g r e a t c i r c l e poles to bedding. 15  Points  through  98 bedding was  seldom observed, e s p e c i a l l y i n P a l e o z o i c  Consequently a n a l y s i s was  rocks.  made almost e n t i r e l y on the b a s i s  of  cleavage and l i n e a t i o n . At l e a s t two An  stages o f p r e - T e r t i a r y deformation  e a r l i e r cleavage i s marked by elongated pebbles which are  o r i e n t e d w i t h the long axes e s s e n t i a l l y h o r i z o n t a l and east-west. and  occurred.  trending  A l a t e r deformation i n t e n s e l y f o l d e d t h i s cleavage  l o c a l l y f o l d e d the e a r l i e r formed elongate pebbles.  l a t t e r f o l d i n g may  be r e s p o n s i b l e  f o l d s which are incompletely o f the new  La Conner  f o r the recumbent  This  isoclinal  exposed i n road cuts on  either  side  bridge.  Stereographic a n a l y s i s , u t i l i z i n g a l l a v a i l a b l e data, i n d i c a t e s the p r e - T e r t i a r y rocks are f o l d e d along an a x i s w i t h a plunge o f 0°  to 5°  east-west  easterly.  T e r t i a r y rocks are s p o r a d i c a l l y exposed at the edge o f the map The  contact  area i n a broad, g e n e r a l l y  between T e r t i a r y and  only at the northwest end i s evident  An  angular unconformity  s y n c l i n e o v e r l a i n by u n i f o r m l y  south  rocks.  cleavage or l i n e a t i o n s were observed i n the T e r t i a r y  sequence and  there was  to bedding.  w r i t e r has  p r e - T e r t i a r y rocks i s v i s i b l e  o f Ika I s l a n d .  d i p p i n g T e r t i a r y sedimentary  poles  syncline.  i n the f i e l d , w i t h a flow b r e c c i a f o l d e d i n t o a  roughly east-west t r e n d i n g  No  east-west  south  considerable  s c a t t e r i n g on the net  However a p a t t e r n o f p o i n t s  concluded t h a t the T e r t i a r y d e p o s i t s  a s y n c l i n e whose a x i s plunges 17°  to the N 75°  i s evident  of and  the  were f o l d e d i n t o W.  The  anomalous  99 p o i n t s a r e most probably e x p l a i n e d as readings taken on c r o s s bedding  or channel  sands.  Consequently,  w i t h i n the map a r e a , a t l e a s t t h r e e d i s t -  i n c t stages o f deformation have o c c u r r e d .  The f i r s t  two were  d e f i n i t e l y p r e - T e r t i a r y , as T e r t i a r y rocks a r e not a f f e c t e d . The  t h i r d was post-Eocene,  presumably l a t e Miocene, and assoc-  i a t e d w i t h a broad northwest-southeast  upwarp.  The most i n t e r e s t i n g o b s e r v a t i o n i s the s t r i k i n g s i s t e n c e o f east-west  s t r u c t u r a l trends.  are deformed e s s e n t i a l l y along east-west although  per-  P r e - T e r t i a r y rocks axes.  Tertiary  folding,  l e s s i n t e n s e , has a l s o been a l i g n e d east-west. Furthermore  as w i l l be p o i n t e d out i n the s e c t i o n on  Economic Geology, a l l major s t r u c t u r a l f e a t u r e s o f t h e a r e a , i n c l u d i n g f a u l t s , s e r p e n t i n i z e d u l t r a b a s i c i n t r u s i o n s , and a s t r o n t i u m v e i n , have a g e n e r a l east-west  trend.  More d e t a i l e d s t r u c t u r a l analyses o f t h i s and surrounding areas might shed much l i g h t on the s t r u c t u r a l e v o l u t i o n o f the p r e - T e r t i a r y rocks o f the n o r t h e r n Puget Sound  Region.  ECONOMIC GEOLOGY  STRONTIUM  Occurrence The  La Conner c e l e s t i t e - s t r o n t i a n i t e d e p o s i t i s l o c a t e d  about one m i l e southwest o f the town o f La Conner, at the south-  100 east end o f Fidalgo I s l a n d . Conner.  Access i s e a s i e s t by boat from La  To the west, road extends to w i t h i n three-fourths o f a  mile from the mine, but access to the mine i s l i m i t e d to times of low t i d e . The deposit, discovered sometime p r i o r to the f i r s t World War, was mined during both wars but has l a r g e l y remained i d l e at other times. L o c a l Geology U n t i l 1 9 2 9 the geology o f the deposit had never been i n v e s t i g a t e d i n d e t a i l though H i l l (1915> 1916) made reference to i t .  Landis ( 1 9 2 9 ) published r e s u l t s of v i s i t s to the area  i n 1921 and 1 9 2 8 . In 1950 C a l d w e l l and Waterman published a b r i e f a r t i c l e , e s s e n t i a l l y r e c a p i t u l a t i n g the g e o l o g i c a l f i n d i n g s o f Landis.  The present w r i t e r v i s i t e d the deposit  s e v e r a l times during the f a l l of 1961, c o l l e c t e d specimens, made sections and prepared a sketch map o f the area.  This report i s  based l a r g e l y on the l a t t e r work and to a l e s s e r degree on the f i n d i n g s o f Landis. A s e a - c l i f f running west-northwest—east-southeast about 90 feet high provides f a i r l y good rock exposure.  and North-  east from the brow o f the h i l l an o l d surface cut exposes the v e i n on s t r i k e f o r about 125 f e e t .  G l a c i a l d r i f t and f o r e s t  vegetation obscure any f u r t h e r outcrop. to the v e i n from the b l u f f face.  Three a d i t s penetrate  Generally u n s a t i s f a c t o r y  c o n d i t i o n o f the t u n n e l s , and the abundance o f caved m a t e r i a l , hinders geologic i n t e r p r e t a t i o n .  SKETCH N  MAP  102 The  d e p o s i t c o n s i s t s of a c e l e s t i t e - s t r o n t i a n i t e v e i n  s t r i k i n g N60°-70°E and d i p p i n g 4 5 ° the v e i n i s a sheared  to the northwest.  i n t r u s i v e mass o f almost  s e r p e n t i n i z e d d u n i t e , now  Enclosing  completely  l a r g e l y carbonatized.  To the  east,  the s e r p e n t i n i t e i s i n f a u l t contact w i t h h i g h l y a l t e r e d , s p i l i t i c volcanics.  To the west a f a u l t (?) contact places s e r p e n t i n i t e  a g a i n s t p r e - T e r t i a r y graywacke. Vein M i n e r a l i z a t i o n The inches  v e i n i s a s e r i e s o f pod and  lens-shaped  to 3 0 inches i n t h i c k n e s s , a l l l y i n g along the same  horizon.  In the f i e l d  half celestite  the v e i n m a t e r i a l appears to be about  (SrS04) and  amounts o f c a l c i t e .  half strontianite  D e t a i l e d analyses  (SrCO^) w i t h minor  o f run o f mine m a t e r i a l  i n d i c a t e s c e l e s t i t e makes up 37 per c e n t , s t r o n t i a n i t e and  c a l c i u m carbonate and  per cent.  Specimen  cent pure and up  6  bodies  50 per  s e r p e n t i n i t e make up the remaining  p i e c e s o f c e l e s t i t e are almost 100  cent 13  per  s t r o n t i a n i t e 95 per cent pure w i t h c a l c i t e making  the 5 per cent i m p u r i t y  ( C a l d w e l l and Waterman, 1 9 5 0 ) .  C h a r a c t e r i s t i c a l l y the c e l e s t i t e has a b l u i s h to very pale gray t i n g e . even m i l k y w h i t e .  R a r e l y i t i s c o l o r l e s s and  It i s considerably coarser-grained  the s t r o n t i a n i t e and has  t r a n s l u c e n t or  shows good b a s a l cleavage.  commonly r e p l a c e d c e l e s t i t e along cleavage  coats e x t e r n a l cleavage The  than  Strontianite planes  and  also  faces.  s t r o n t i a n i t e , except where c o l o r e d by  limonite, i s  a m i l k y w h i t e , f i n e l y c r y s t a l l i n e , powdery substance.  On  103  Figure 32. Two of the three a d i t s driven to c e l e s t i t e - s t r o n t i a n i t e v e i n . Southeast Fidalgo I s l a n d .  Figure 33. S e r p e n t i n i t e c l i f f s above a d i t s shown i n Figure 32.  104 s u r f a c e s o f vugs and outcrops  i t g e n e r a l l y shows a mammilary o r  b o t r y o i d a l form, whereas f r e s h l y broken s u r f a c e s are r e t i c u l a t e d with a box-like outline.  Evidently a slight reduction of  volume took place d u r i n g replacement as evidenced other i r r e g u l a r openings i n the s t r o n t i a n i t e . conspicuous i n the primary  by vugs and  These are not  celestite.  E v i d e n t l y the s t r o n t i a n i t e replacement i s the r e s u l t o f c i r c u l a t i n g ground waters above the water t a b l e . 1916)  (1915,  observed t h a t carbonate waters w i l l d i s s o l v e s t r o n t i u m  s u l f a t e and r e p l a c e i t w i t h w a t e r - i n s o l u b l e The  Hill  strontium  carbonate.  s t r o n t i a n i t e - c e l e s t i t e r a t i o i s s a i d to i n c r e a s e upward i n  the v e i n , toward the outcrop  (Landis,  1929).  C a l c i t e i s c o l o r l e s s , m i l k y to t r a n s p a r e n t , o c c u r r i n g in  s m a l l v e i n l e t s up to an i n c h i n t h i c k n e s s .  These v e i n l e t s  f r e q u e n t l y show comb s t r u c t u r e , i n d i c a t i v e o f open space f i l l i n g . Limonite imparting  i s l o c a l l y present w i t h i n the v e i n , f r e q u e n t l y  a pale brownish s t a i n to the s t r o n t i a n i t e .  Wot observed by the w r i t e r , but r e p o r t e d by Banner ( p e r s o n a l communication) are s m a l l q u a n t i t i e s o f orpiment and realgar. Bare s m a l l , subangular to subrounded fragments o f c a r b o n a t i t i z e d s e r p e n t i n i t e are found w i t h i n the v e i n , e s p e c i a l l y near the margins.  These i n c l u s i o n s may be the r e s u l t o f some  d i f f e r e n t i a l movement o f the v e i n w a l l s during d e p o s i t i o n o f the v e i n m i n e r a l s .  105 Serpentinite The S e r p e n t i n i t e host rock i s about 180  feet t h i c k with  the s t r o n t i u m v e i n l y i n g about 60 f e e t from the top.  Contacts o f  s e r p e n t i n i t e w i t h adjacent rocks are nowhere exposed but can  be  i n f e r r e d w i t h i n f a i r l y c l o s e l i m i t s , and s t r i k e about W65°E, d i p p i n g about 45°  northwest.  The  suggestion i s t h a t , i n t h i s r e -  s t r i c t e d o u t c r o p , the s e r p e n t i n i t e i s a t a b u l a r body d i p p i n g n o r t h w e s t e r l y w i t h an i n c l u d e d v e i n of s t r o n t i u m m i n e r a l s  also  d i p p i n g at about the same a t t i t u d e . Of s t r u c t u r a l s i g n i f i c a n c e i s the presence o f west—east-northeast  west-south-  s t r u c t u r a l trend i n rocks exposed west o f  the entrance to Swinomish Channel,  e s p e c i a l l y west o f the mine.  At l e a s t one major and s e v e r a l smaller f a u l t s are present i n the p r e - T e r t i a r y sediments west o f the mine, a l l s t r i k i n g i m a t e l y N70°E to E a s t . a t t i t u d e s though dip may the lower  approx-  Much o f the rock cleavage shows s i m i l a r be s t e e p l y n o r t h to south.  As mentioned,  (eastern) contact o f the s e r p e n t i n i t e a g a i n s t v o l c a n i c  rocks i s b r e c c i a t e d and g r a d a t i o n a l through a zone at l e a s t f e e t wide.  Fragments o f v o l c a n i c rocks and a r g i l l i t e , up to 2  inches i n diameter grades  25  are set i n a sheared  upward i n t o a sheared  s e r p e n t i n e m a t r i x that  s e r p e n t i n i t e without  clastic  fragments. The  upper (western)  contact o f s e r p e n t i n i t e a g a i n s t p r e -  T e r t i a r y graywacke i s o f a d i f f e r e n t  sort.  Through a zone aver-  aging 10 f e e t i n t h i c k n e s s , quartz l a y e r s are  conspicuous.  106 Commonly these l a y e r s a r e 1 to 3 inches i n t h i c k n e s s , massive, and vuggy, the vugs c o n t a i n i n g white to l i g h t and l o c a l l y s m a l l cubes o f p y r i t e .  gray quartz  Other quartz bands o f com-  p a r a b l e t h i c k n e s s show a w e l l pronounced  comb s t r u c t u r e and  numerous w e l l developed, s m a l l , s i n g l y terminated, quartz c r y stals.  L o c a l l y , near the top o f the c l i f f , the quartz i s con-  s p i c u o u s l y r e d , as the r e s u l t o f i r o n s t a i n i n g d e r i v e d from leached o v e r l y i n g g l a c i a l t i l l . for  open-space  A v a i l a b l e evidence i s strong  filling.  There i s no evidence o f s i g n i f i c a n t a l t e r a t i o n i n graywacke adjacent to s e r p e n t i n i t e except f o r minor However, s i l i c i f i c a t i o n  silicification.  i s no more i n t e n s e than that seen  else-  where i n graywacke not a f f i l i a t e d w i t h i n t r u s i o n s . A p p a r e n t l y the s e r p e n t i n i t e o c c u p i e s a p o r t i o n o f a f a u l t zone w i t h a number o f p a r a l l e l o r i e n t e d s l i c e s .  Key  beds a r e absent and s l i c k e n s i d e s are a t random angles so the d i r e c t i o n o f movement remains  unknown.  s i n g l e plane o f movement was probably  Displacement  along any  slight.  A v a r i a t i o n i n mineralogy i s conspicuous, both i n hand specimen of  and t h i n s e c t i o n from the v e i n towards e i t h e r  the i n t r u s i o n .  border  Near the v e i n the s e r p e n t i n i t e i s h i g h l y  c a r b o n i t i z e d and the amount o f s e r p e n t i n e low.  Away from the  v e i n the rock i s almost e n t i r e l y s e r p e n t i n e and no r e s i d u a l o l i v i n e was observed. Chalcedony  and o p a l are both extremely common i n the  v i c i n i t y o f the v e i n .  The chalcedony i s h i g h l y f i b r o u s and  locally spherulitic. form which,  Opal i s a dark green, semi-transparent  l i k e the chalcedony, has formed  minute f r a c t u r e s .  Both appear  i n open spaces and  to be l a t e m i n e r a l s i n the  p a r a g e n e t i c sequence because o f t h e i r t endency to surround and d i s s o l v e c a l c i t e , e s p e c i a l l y along the c a l c i t e margins  which  are l o c a l l y s t r o n g l y corroded. C a l c i t e i s an u b i q u i t o u s m i n e r a l , present throughout the rock, but i n g r e a t e s t q u a n t i t y near the v e i n .  Near the v e i n i t  forms a mosaic w i t h i n d i v i d u a l g r a i n s up to 2 mm i n l e n g t h , and i n the s e r p e n t i n i t e i t forms a p l e t h o r a o f r a m i f y i n g and i n t e r secting  veinlets. Of s p e c i a l i n t e r e s t  i s the occurrance o f p i c t o t i t e  (chromium-rich s p i n e l ) throughout magnetite  the s e r p e n t i n i t e .  surrounds most g r a i n s o f p i c t o t i t e .  Both  A rim of magnetite  and p i c o t i t e a l s o occur as dusty, i r r e g u l a r aggregates, as s m a l l d i s c r e t e g r a i n s and as l a r g e euhedral masses up to 0.8 mm i n maximum dimension.  C o n s i d e r a t i o n o f these m i n e r a l s makes two  facts clear: (1)  ,  The presence o f a chromium s p i n e l i n d i c a t e s the a  o r i g i n a l rock was an ultrabasic i n t r u s i o n and not simply a s e r p e n t i n i z e d v o l c a n i c rock. Mat  (2)  The magnetite  been f a i r l y  iron rich.  i n d i c a t e s t h e o r i g i n a l o l i v i n e must have A  T h i s i s i n d i s t i n c t i o n to the s e r p e n -  t i n i t e o f Hope I s l a n d , i n the northwestern part o f the map a r e a , which has o n l y t r a c e q u a n t i t i e s o f magnetite, and consequently was  formed  o f iron-poor, magnesia-rich o l i v i n e .  Perhaps  this  f a c t i n d i c a t e s two fundamentally d i f f e r e n t u l t r a b a s i c magmas  F i g u r e 34. P h o t o m i c r o g r a p h o f s e r p e n t i n i t e enclosing celestite-strontianite vein. In a d d i t i o n t o a n t i g o r i t e , c h r o m i t e and magne t i t e are abundant. The w h o l e is c u t by numerous r a m i f y i n g c a l c i t e v e i n l e t s . Cross-nicols, xlO.  F i g u r e 35. P h o t o m i c r o g r a p h o f s e r p e n t i n i t e a d j a c e n t to c e l e s t i t e - s t r o n t i a n i t e v e i n . A n t i g o r i t e (A), c a l c i t e ( C ) , chalcedony(Ch) and c h r o m i t e a r e abundant. Cross-nicols xlO.  109 were o p e r a t i n g at d i f f e r e n t times.  Probably time o f i n t r u s i o n  was  the same but some s o r t o f chemical s e g r e g a t i o n r e s u l t e d i n  two  s l i g h t l y d i f f e r e n t bodies forming.  Evidence i s l a c k i n g to  s o l v e t h i s problem. P y r i t e i s s p a r s e l y present i n the s e r p e n t i n i t e , as i t i s i n the quartz v e i n l e t s .  However where present i t i s con-  c e n t r a t e d i n d i s t i n c t i v e , commonly sinuous undoubtedly  stringers.  It i s  associated with s i l i c i f i c a t i o n .  A s i m i l a r though much s m a l l e r s e r p e n t i n i t e mass l i e s at the extreme southeast t i p o f F i d a l g o I s l a n d , at the western trance to the s h i p channel.  T h i s s m a l l outcrop i s i n t e n s e l y  deformed w i t h the s e r p e n t i n e cleavage h i g h l y deformed.  Quartz  and c a l c i t e v e i n l e t s are uncommon, nor i s there any other of m i n e r a l i z a t i o n .  en-  sign  Whether t h i s i s a f a u l t e d p o r t i o n o f the  s e r p e n t i n i t e exposed to the west, or a separate p a r a l l e l body i s not know. O r i g i n o f the D e p o s i t :  Serpentinite  A s u g g e s t i o n has been made that the s e r p e n t i n i t e l i e s i n a f a u l t zone.  Evidence f o r such an i n t e r p r e t a t i o n i s summarized  below: (1)  P a r a l l e l to s u b - p a r a l l e l f a u l t s i n a w e s t - s o u t h w e s t —  e a s t - n o r t h e a s t d i r e c t i o n through southeast F i d a l g o I s l a n d .  A  s i m i l a r l y o r i e n t e d f a u l t borders the south s i d e o f Hope I s l a n d . (25 Abundant rock cleavage w i t h a g e n e r a l east  orientation.  southwest—north-  110 (3)  Evidence o f b r e c c i a t i o n at the base o f the s e r p e n t -  inite. (4)  S h e a r i n g i n the s e r p e n t i n i t e i n a w e s t - s o u t h w e s t —  east-northeast (5)  direction.  Celestite-strontianite vein striking  east-northeast  west-southwest—  direction.  (6)  Dips o f a l l the above f e a t u r e s are g e n e r a l l y northwest.  (7)  The a r e a l i e s athwart  a large  northwest-southeast  t r e n d i n g d i s t u r b e d zone, which i s a c t u a l l y near the c r e s t o f a Miocene u p l i f t ,  extending from Vancouver I s l a n d southeast  through  the s i t e o f the present c e n t r a l Cascade Mountains. O r i g i n of Deposit:  Strontium Vein  C e l e s t i t e i s commonly c o n s i d e r e d to be a m i n e r a l and  sedimentary  indeed i s u s u a l l y a s s o c i a t e d w i t h sedimentary  e s p e c i a l l y limestone and dolomite.  I t can occur i n  rocks,  sedimentary  rocks and become concentrated by the a c t i o n o f ground waters or it  has been known to p r e c i p i t a t e out as an e v a p o r i t i c d e p o s i t .  However i n the case o f the La Conner d e p o s i t i t i s thought be hydrothermal (1)  f o r the f o l l o w i n g reasons:  Occurrence  consequently (2)  to  o f the Strontium m i n e r a l s i n a v e i n ,  i t i s necessarily epigenetic.  Complete absence o f any a s s o c i a t e d limestone or  dolomite. (3)  Occurrence  (4)  Presence  o f the v e i n i n an u l t r a b a s i c .rock.  o f p y r i t e - b e a r i n g quartz v e i n s .  On the b a s i s o f the above c r i t e r i a  the w r i t e r  proposes  Ill the f o l l o w i n g sequence o f events to e x p l a i n the genesis o f t h i s deposit: (1)  Deep f a u l t i n g occurred  unknown date ( T r i a s s i c ? ) .  Associated  o f u l t r a b a s i c s , probably d u n i t e . upward i t was g r a d u a l l y carbon d i o x i d e  along a d i s t u r b e d  (2) allowing movement.  w i t h f a u l t i n g was i n t r u s i o n  As the i n t r u s i o n moved  serpentinized  slowly  by water, s i l i c a and  streaming up the same f r a c t u r e d zone.  some o r much o f the water was d e r i v e d synclinal  zone at an  Perhaps  from the surrounding eugeo-  rocks. A f t e r the s e r p e n t i n i t e was emplaced, f r a c t u r e s formed the hydrothermal s o l u t i o n s to continue t h e i r upward Quartz v e i n l e t s and p y r i t e f i r s t  formed, p r i n c i p a l l y  on the upper margin o f the i n t r u s i o n . (3)  As the hydrothermal s o l u t i o n s continued to c o o l ,  c e l e s t i t e and c a l c i t e were p r e c i p i t a t e d i n a c e n t r a l l e n t i c u l a r shaped v e i n .  Some movement o c c u r r e d ,  perhaps by l o c a l f a u l t i n g ,  which f r a c t u r e d the v e i n w a l l s , a l l o w i n g  some m i n e r a l i z a t i o n around  s e r p e n t i n i t e fragments. (4)  At very low temperature chalcedony and o p a l  remaining spaces and l o c a l l y corroded e a r l i e r (5)  filled  calcite.  In the l a s t s t e p , probably a f t e r u p l i f t and e r o s i o n to  near the present l e v e l , ground waters s t a r t e d d i s s o l v i n g SrSO^.  and r e p r e c i p i t a t i n g SrC03.  112 General In common w i t h other s t r o n t i u m d e p o s i t s , the La Conner deposit i s small. 1950)  suggest  Recent estimates  reserves of 1 0 , 0 0 0  which c o u l d , i f necessary  ( C a l d w e l l and Waterman,  tons o f ore above sea  level  supply the worlds needs f o r e i g h t  months. S t r o n t i u m i s not a v i t a l metal and i s low.  The  consequently  i t s value  United S t a t e s uses over o n e - h a l f the world's  total  annual p r o d u c t i o n o f approximately  1 4 , 0 0 0 short t o n s .  s t r o n t i u m i s imported  and Mexico at b a l l a s t r a t e s ,  from England  This  and at lower t o t a l cost than s t r o n t i u m m i n e r a l s c o u l d be duced d o m e s t i c a l l y .  During war  pro-  p e r i o d s when the use o f s t r o n t i u m  compounds rose s h a r p l y , domestic  sources became important;  the  La Conner d e p o s i t has been o f d e f i n i t e v a l u e during both World Wars. The  principal interest  i n t h i s d e p o s i t i s i t s hydro-  thermal o r i g i n and a s s o c i a t i o n w i t h u l t r a b a s i c r o c k s .  GRAVEL AND  CRUSHED ROCK  Three rock q u a r r i e s are l o c a t e d i n the r e g i o n . southeast  o f Pleasant Ridge ( F i g u r e 36)  erates o f the D e l t a Rocks Formation;  One  quarry,  i s opened i n conglom-  a second to the west o f  P l e a s a n t Ridge i s i n graywackes o f the La Conner Formation; the t h i r d  quarry i s on n o r t h e r n McGinn I s l a n d i n Goat I s l a n d  Formation  graywackes.  and  Rocks i n a l l three q u a r r i e s are tough and  113  F i g u r e 36. Quarry i n conglomerate o f the D e l t a Rocks F o r m a t i o n . L o c a t e d n e a r s o u t h e a s t end o f Pleasant Ridge.  114 well indurated. The  A l l q u a r r i e s are operated  by S k a g i t County.  rock i s used i n the crude s t a t e p r i n c i p a l l y f o r r i p - r a p along  the S k a g i t R i v e r and i n dikes around La Conner and other  parts  o f the S k a g i t D e l t a .  roads.  A l i m i t e d amount i s used on county  A s m a l l g r a v e l p i t , i n g l a c i a l outwash at the south end o f P l e a s a n t Ridge i s p r i v a t e l y owned and i s i n t e r m i t t e n t l y used as a source o f concrete  aggregate.  GLACIATION  GLACIATION IN THE PUGET SOUND TROUGH  The  o r i g i n a l P l e i s t o c e n e s t u d i e s i n the Puget Sound  Lowland were by W i l l i s  (1898) and W i l l i s and Smith ( 1 8 9 8 ) .  s t r a t i g r a p h i c s u c c e s s i o n presented  i n these papers has remained  e s s e n t i a l l y unchanged though e l a b o r a t e d on and m o d i f i e d recent work.  The  i n more  W i l l i s e s t a b l i s h e d an o l d e r p e r i o d o f g l a c i a t i o n  which he termed the A d m i r a l t y interglacial, called  g l a c i a t i o n , a long  post-Admiralty  the P u y a l l u p , f o l l o w e d by the e x t e n s i v e and  most recent Vashon g l a c i a t i o n . Bretz  (1913)  i n h i s c l a s s i c paper e n t i t l e d  the Puget Sound Region" continued  this  "Glaciation of  classification.  r e c o g n i z i n g the presence o f m u l t i p l e g l a c i a t i o n s , B r e t z f i a b l y avoided  Although justi-  c o r r e l a t i o n problems by d e f i n i n g the A d m i r a l t y as  c o n t a i n i n g a l l the pre-Vashon d e p o s i t s o f the lowland.  Again i n  115 1920  he  employed t h i s c l a s s i f i c a t i o n i n a d i s c u s s i o n o f  the  "Juan de Fuca Lobe o f the C o r d i l l e r a n Ice Sheet". Considerably  l a t e r , i n 1949,  marriage of geomorphology and l o c a l l y , several Pleistocene  Hansen and Mackin, by a  palynology  e s t a b l i s h e d , at l e a s t  stages.  C r a n d e l l , M u l l i n e a u x , and Waldron (1958), working i n the  southeastern  to s u b d i v i d e three  p o r t i o n of the Puget Sound Lowland were a b l e  the Admiralty  g l a c i a l and  two  o f W i l l i s and B r e t z  i n t e r g l a c i a l periods.  terminology which they introduced  i s as  i n t o at l e a s t  The  Pleistocene  follows:  Vashon G l a c i a t i o n Erosional interval  (non-glacial interval)  Salmon S p r i n g s g l a c i a t i o n Puyallup  non-glacial  interval  Stuck g l a c i a t i o n Alderton non-glacial  interval  Orting g l a c i a t i o n (oldest) Except f o r the Vashon, which seems to c o r r e l a t e to Tazwell  (maximum Wisconsin stage of the c e n t r a l United  the ages o f the three preceeding g l a c i a t i o n s are P o s s i b l y the Salmon Springs  g l a c i a t i o n i s even more p r o b l e m a t i c a l o l d e s t known P l e i s t o c e n e  The  The  and  age o f the  the  Orting  but because i t i s the  deposit, i t i s considered,  proven, E a r l y P l e i s t o c e n e .  States),  uncertain.  i s o f pre-Wisconsin age,  Stuck i s E a r l y to Middle P l e i s t o c e n e .  the  but  c l i m a t i c conditions of  not the  i n t e r g l a c i a l periods were not markedly d i f f e r e n t than those  116 o f the p r e s e n t . Modern day topographic f e a t u r e s are almost r e s u l t o f e f f e c t s f o l l o w i n g the Salmon S p r i n g s Consequently  e n t i r e l y the  glaciation.  pre-Unnamed i n t e r g l a c i a l d e p o s i t s w i l l not be  con-  sidered. F o l l o w i n g the Salmon S p r i n g s g l a c i a l i n t e r v a l e x t e n s i v e stream a g g r a d a t i o n o c c u r r e d i n the Puget Sound Lowland.  Probably  a great p l a i n o f t e r r e s t r i a l d e p o s i t s , c o n t a i n i n g some c o a l and marine fauna near the base, was  d e p o s i t e d at the f r o n t o f the  r e t r e a t i n g Salmon S p r i n g s I c e .  L a t e r u p l i f t , perhaps  f e e t , r e s u l t e d i n a long p e r i o d o f atmospheric  of  erosion.  1000 Because  o f the u n c o n s o l i d a t e d nature o f the m a t e r i a l the area became deeply i n c i s e d by trunk v a l l e y s and t r i b u t a r y streams, arranged  largely  i n a north-south d i r e c t i o n . L a t e r , w h i l e the streams were presumably i n a s t a t e o f  submaturity, the Vashon i c e moved south from the i c e f i e l d s o f B r i t i s h Columbia.  Tremendous q u a n t i t i e s o f outwash were spread  at the southern terminus o f the i c e , but to the n o r t h o n l y a t h i n mantle o f ground moraine and t i l l o v e r l i e s the topography.  L o c a l l y , g r e a t e r t h i c k n e s s e s o f Vashon ground  Moraine obscured  the  i n t e r g l a c i a l , streamformed  C o n t i n u a l i c e r e t r e a t r e s u l t e d i n a complex and changing  interglacial  topography. continually  pattern of lakes i n ice-blocked v a l l e y s .  A l l these  g l a c i a l l a k e s were u l t i m a t e l y d r a i n e d when the Vashon i c e melted back beyond the S t r a i t o f Juan de Fuca, p e r m i t t i n g drainage to the ocean.  At the time of t h i s r e t r e a t the r e g i o n stood at about  117 its  present  as evidenced  elevation.  by marine i n v e r t e b r a t e f o s s i l s found  l y i n g Vashon t i l l , level.  S h o r t l y t h e r e a f t e r , subsidence  i n situ,  over-  up to a maximum o f 2 8 0 f e e t above present sea  Because s t r a n d l i n e s , where p r e s e n t , above 1 0 0 feet a r e  p o o r l y developed  t h i s submergence must have been f o r a very  b r i e f p e r i o d o f time.  Below 100 f e e l w e l l developed  are i d e n t i f i e d which are u s u a l l y c o r r e l a t a b l e . of  occurred  strand l i n e s  S i n c e the r e t r e a t  Vashon i c e then, and a maximum submergence o f -280 f e e t , there  has been a g r a d u a l , though not steady r i s e i n the Puget Sound area to the present  time.  E f f e c t s o f t h i s land r i s e i n the map  area w i l l be d i s c u s s e d i n a s e c t i o n c o v e r i n g geomorphology.  GLACIAL EFFECTS IN THE MAP AREA  S u b d i v i s i o n o f g l a c i a l d e p o s i t s n o r t h o f the Puget Sound Lowland i s d i f f i c u l t  due to the great t h i c k n e s s o f Vashon  which mantles and obscures  older deposits.  till  A l l Pleistocene  d e p o s i t s exposed w i t h i n the map a r e a a r e b e l i e v e d r e l a t e d to the Vashon g l a c i a l stage and the pre-Vashon e r o s i o n a l i n t e r v a l . S t u d i e s i n the Cascades, on Vancouver I s l a n d and the San Juan I s l a n d s i n d i c a t e that a t the maximum extent o f the Vashon g l a c i a t i o n the i c e would be between 2000 to 3000 f e e t t h i c k i n t h i s area ( B r e t z , 1 9 2 0 ) .  Consequently  even the h i g h e s t  h i l l s w i t h i n the map a r e a should have a t one time been capped by c l o s e to o n e - h a l f m i l e o f southward moving i c e .  118 It  would be expected that g l a c i a l e r o s i o n and d e p o s i t i o n  w i t h i n the a r e a would be i n t e n s e , and such seems to be the case. Except on P l e a s a n t Ridge, compacted t i l l outwash i s present thick. Closed  i s uncommon.  Glacial  and on F i d a l g o I s l a n d appears to be very  G l a c i a l s t r i a t i o n s were seen o n l y at one l o c a l i t y . d e p r e s s i o n s , o c c u r r i n g w i t h i n S k a g i t Bay a r e probably the  r e s u l t o f g l a c i a l scour, and w i l l be d i s c u s s e d under "Geomorphology". G l a c i a l outwash mantles the s u r f a c e o f F i d a l g o I s l a n d , though d e p o s i t s are very t h i n at the southeast  end. Because o f  dense f o r e s t growth exposures are few except on the west shore o f the I s l a n d .  Here b l u f f s 25 to 50 f e e t i n height are composed  e s s e n t i a l l y o f g l a c i a l outwash, probably  the r e s u l t o f melt  water a c t i v i t y at the f r o n t o f the r e t r e a t i n g Vashon i c e .  The  outwash c o n s i s t s l a r g e l y o f sands and pebbly sands, g e n e r a l l y cross-bedded and c o n t a i n i n g t h i n l i g n i t i c Unconsolidated  lenses.  outwash d e p o s i t s are a l s o present  on the c r e s t o f a s m a l l h i l l  locally  along the n o r t h shore o f the S k a g i t  R i v e r where a g r a v e l p i t i s l o c a t e d .  Here the outwash i s t h i n l y  bedded sands and pebbly sand, c o n t a i n i n g pebbles up to 50 mm i n maximum dimension. and  a r e composed o f many rock Pleasant  is  Pebbles and g r a i n s a r e subrounded to rounded  an elongated  types.  Ridge, the o n l y e x t e n s i v e area o f g l a c i a l hill,  about two miles l o n g , t r e n d i n g  northwest—south-southeast. e l e v a t i o n , i s at the n o r t h e r n  till,  north-  I t s h i g h e s t p o i n t o f about 110 f e e t end, and the s u r f a c e s l o p e s  gently  119 to s e a l e v e l a t t h e s o u t h e r n end. stricted  t o t h e n o r t h e r n and w e s t e r n edges where o u t c r o p s a r e  exclusively of  E x p o s u r e s a r e poor and r e -  glacial t i l l .  the ridge  penetrated  A w a t e r w e l l d r i l l e d on t h e west  50 f e e t o f c o m p a c t e d t i l l  60 f e e t o f u n d i f f e r e n t i a t e d P l e i s t o c e n e 1950).  Evidently  posited  during  erosion  and canyon c u t t i n g l e f t  underlain  s a n d s and s h a l e s  t h e r o c k s composing P l e a s a n t Ridge were de-  one o f t h e " a d m i r a l t y "  glaciations.  Pre-Vashon  a portion of this material  r e s i d u a l i n t h e same way a s p r e , - T e r t i a r y  were l e f t .  D u r i n g Vashon g l a c i a t i o n a t h i c k l a y e r o f t i l l  its  on t h e i n t e r g l a c i a l h i l l ,  was  modifying  Island  on t h e s o u t h s i d e o f  on a rounded expanse o f p o l i s h e d  sea-level.  graywacke,  cuts  Nl8°E. 2 feet  these.  transects  The b e a r i n g o f t h e s e c o n d a r y s l i c k e n s i d e s i s  P r e s e n t a l s o a r e r o c k g o u g e d t r o u g h s up t o 20 f e e t a c r o s s and 4 i n c h e s deep.  marks a r e l o c a l l y  long,  They h a v e a b e a r i n g o f N52°E  accompany t h e p r i m a r y s t r i a t i o n s .  The  close  The p r i n c i p a l d i r e c t i o n o f s l i c k e n s i d i n g i s  N58°E t h o u g h a s e c o n d , more w e a k l y d e v e l o p e d g r o o v i n g  so  units  shape.  Kiket  and  as an  rock  probably strongly  G l a c i a l s t r i a t i o n s were seen o n l y  to  by  (Sceva,  interstream  plastered  side  Small triangular  chatter  present i n the trough bottoms.  early grooving i s e s s e n t i a l l y p a r a l l e l  to the long  a x i s o f t h e i s l a n d and s u g g e s t s f o r m a t i o n a t an e a r l y s t a g e o f g l a c i a t i o n where t h e t o p o g r a p h y i s y e t e x e r c i s i n g influence are  o n d i r e c t i o n o f i c e movement.  some  local  The w e a k e r s t r i a t i o n s  a l a t e r p h a s e , f o r m e d when t h e i c e was t h i c k e r a n d m o v i n g  bodily  southward over topographic  obstructions.  120 GEOMORPHOLOGY  SKAGIT DELTA  The S k a g i t D e l t a i s a conspicuous and major f e a t u r e o f northwestern Washington. area o f approximately  I t i s a low,  1 2 0 square m i l e s .  physiographic  subtriangular  The g r a d i e n t , s l o p i n g  westward, i s 2 to 4 f e e t per m i l e , and i s so low that problems are common p l a c e .  The d e l t a i t s e l f f i l l s  v a l l e y cut i n t o unconsolidated deposited  drainage  a former  P l e i s t o c e n e sediments t h a t were  i n a b a s i n u n d e r l a i n by T e r t i a r y or o l d e r uncon-  s o l i d a t e d rocks River i t s e l f  (Sceva, 1 9 5 0 ) .  The westward  1  flowing Skagit  i s the p r i n c i p a l c o n s t r u c t i v e agent, b u i l d i n g the d e l -  t a westward i n t o S k a g i t , P a d i l l a and Samish Bays.  The modern  R i v e r drainage  i s i n t o S k a g i t Bay where i t s westward margin  i s encroaching  upon, surrounding  and e v e n t u a l l y t y i n g to the  mainland the i s l a n d s o f S k a g i t Bay. The Samish R i v e r  drains  h i l l s t o the n o r t h o f the d e l t a and i s c u r r e n t l y expanding the d e l t a i n t o Samish Bay. Growth o f the d e l t a i s r a p i d because o f the h i g h sediment load o f the S k a g i t R i v e r and the p r o t e c t i o n o f i t s margins from sea e r o s i o n o f f e r e d by F i d a l g o and Whidby I s l a n d s . A f e a t u r e o f some i n t e r e s t i s the i n c i s i o n o f the S k a g i t River.  Exact measurements o f i n c i s i o n a r e not a v a i l a b l e but  e l e v a t i o n s taken from the U.S.Geological  Survey topographic maps  show the r i v e r s u r f a c e v a r y i n g from 0 f e e t below land l e v e l a t the mouth o f the S k a g i t R i v e r , to perhaps 15 f e e t n o r t h o f Mt.  121  Vernon. to 15  T h i s suggests recent u p l i f t , perhaps on the order o f  feet.  discussed  Other evidence  bearing on recent u p l i f t w i l l  The  ISLANDS  contact between the d e l t a and  i s gradational.  swamps and mudflats the bay.  be  i n the f o l l o w i n g s e c t i o n s .  SHORE LINES OF MAINLAND AND  Bay  10  The  the waters o f S k a g i t  A f l u c t u a t i n g , i r r e g u l a r zone o f s a l t water separates  the dry land from the waters o f  shore l i n e , i n p l a c e s , appears more abrupt  due  to man-made dikes which have reclaimed p a r t s of the swamp border, and  turned  them i n t o r i c h a g r i c u l t u r a l  land.  Where the shore i s the r e s u l t o f a c t i v e e r o s i o n r a t h e r than a g g r a d a t i o n ,  as i t i s on the d e l t a margin, the  e f f e c t s are c o n s i d e r a b l y d i f f e r e n t . incomplete  and narrow rock-cut  L o c a l l y they may  show n o t c h i n g  topographic  Most o f the i s l a n d s show  t e r r a c e s w i t h accompanying  cliffs.  at the base o f the c l i f f .  The  widths o f wave-cut t e r r a c e s are v a r i a b l e and nowhere e x a c t l y known.  I t appears, however, to be broader on the south shore o f  i s l a n d s , presumably due  to i n c r e a s e d wave a c t i v i t y , which i n t u r n  i s caused by the p r e v a i l i n g southwesterly  winds.  A s i m i l a r s i t u a t i o n p r e v a i l s on the west shore o f F i d a l g o I s l a n d as shown w i t h i n the map between t h i s shore and  area.  The  only r e a l d i f f e r e n c e  that o f the i s l a n d s l i e s i n the  o f m a t e r i a l s being a t t a c k e d  by wave e r o s i o n .  are composed of r e s i s t a n t rocks  character  Whereas the i s l a n d s  such as s e r p e n t i n i t e and  indurated  122  graywacke with a consequent slow rate of erosion, the west coast of Fidalgo Island i s formed of r e l a t i v e l y unconsolidated and outwash.  The unconsolidated  till  deposits erode rapidly with the  formation of a wide wave-cut and wave-built  terrace.  The  bay  bottom within several hundred feet of shore i s composed of sand and s i l t with included pebbles, cobbles and boulders rived from g l a c i a l  de-  till.  Between Snee-oosh Beach and Tosi Point serpentinite crops out at sea l e v e l r e s u l t i n g i n a reduced rate of erosion and a narrow wave-cut terrace. On the whole, the water immediately to the north of islands appears to be the s i t e of deposition.  This i s probably  a "leeward effects with water moving northward under wind and current influence, eddying i n the lee of the islands, r e s u l t i n g in  deposition of i t s coarse c l a s t i c load. Physiographic  is  non-existant  evidence of any but the most recent  i n the islands.  uplift  The isolated and poorly devel-  oped strand l i n e s , found i n the northern Puget Sound Lowlands and in  the San Juan Islands, lying between 100 and 280 feet above  sea l e v e l , are missing.  Also absent are any evidence of the more  highly developed shorelines lying between sea l e v e l  and 100 feet.  Perhaps these are absent only because of l a t e r erosion around the margins of islands and the removal of e a r l i e r , incipient wavecut terraces. Around several of the islands, especially Goat and Hope, and also on the rocky headland of southeast  Fidalgo Island,  123 t h e r e i s a suggestion o f an i n c i p i e n t n o t c h i n g at an e l e v a t i o n of  about t e n f e e t above mean sea l e v e l .  T h i s n o t c h i n g i s very  weak, being u s u a l l y nothing more than a s l i g h t l y rounded dep r e s s i o n i n the c l i f f f a c e , but they are a l l c o n s i s t e n t i n having the same e l e v a t i o n .  O h v i o u s l y , wherever a rock-cut t e r r a c e i s  present at modern sea l e v e l , i n c i p i e n t n o t c h i n g probably present.  Probably  common.  i s not  t h i s i s why n o t c h i n g i s not conspicuous o r  While not proof i n i t s own r i g h t , t h i s n o t c h i n g  c o r r o b o r a t i v e evidence  offers  that u p l i f t on the order o f 10 f e e t  o c c u r r e d i n the r e c e n t p a s t .  COVES SEA CLIFFS AND CAVES  Except  f o r the f a c t they are surrounded  by a l l u v i u m  r a t h e r than water, the h i l l s o f western S k a g i t D e l t a a r e s i m i l a r to and  the i s l a n d s o f S k a g i t Bay.  P l e a s a n t Ridge i s composed o f t i l l  u n c o n s o l i d a t e d sediments r a t h e r than i n d u r a t e d p r e - P l e i s t o -  cene rocks but t o p o g r a p h i c a l l y i t seems to have r e a c t e d to e r o s i o n i n the same way as i t s o l d e r c o u n t e r p a r t s . E s p e c i a l l y along the S k a g i t R i v e r , but a l s o along McGinn Islands n o r t h s i d e , the h i l l s promentories the h i l l .  are c h a r a c t e r i z e d by rocky  e n c l o s i n g a s e m i - c i r c u l a r lowland, open away from  These enclosed areas are f l a t - f l o o r e d , u s u a l l y o f  the same e l e v a t i o n as the surrounding  a l l u v i a l p l a i n , and bounded  by v e r t i c a l to near v e r t i c a l c l i f f s o f 2 to 20 f e e t i n h e i g h t . They a r e , i n g e n e r a l appearance, shaped l i k e a d i m i n u t i v e c i r q u e .  124  The  f l o o r s of these coves are always swampy and  t h i c k growth o f r e e d s , h o r s e t a i l s and A very  s i m i l a r cove i s now  west s i d e o f Ika I s l a n d . c i r c u l a r shape,  other  The  vegetation. on  the  I t i s c h a r a c t e r i z e d by a roughly  by steep w a l l s , a f l a t  of t i d e s .  swamp  i n the process of formation  f l o o r and  swamp growth which i s yet open to the bay vagaries  covered w i t h a  and  a  semi-  prolific  subject  to  hollow on Ika I s l a n d i s q u i t e  the  obviously  the r e s u l t of marine e r o s i o n , i n t h i s case p a r a l l e l to  the  s t r i k e o f the rocks  A similar  o r i g i n i s postulated the d e l t a .  along  the a x i s o f a s y n c l i n e .  f o r the hollows now  In other words the g e n e t i c  erosion, s i l t i n g uplift  and  existing in h i l l s  sequence was:  of the cove w i t h a l l u v i u m ,  i s o l a t i n g the cove from the  and  of  marine  later,  gradual  sea.  A f e a t u r e c h a r a c t e r i s t i c of p r a c t i c a l l y a l l the h i l l s i s steep c l i f f s , e s p e c i a l l y on the western and T h i s i s the the i s l a n d s .  same s i t u a t i o n now  southwestern s i d e s .  d i s p l a y e d on the rocky c l i f f s o f  An o r i g i n o f marine e r o s i o n i s a s c r i b e d to both.  Another f e a t u r e o f i n t e r e s t , though not sea caves at the base o f many c l i f f s . and  These are u s u a l l y shallow  elongated i n a h o r i z o n t a l d i r e c t i o n .  w h i l e l o o k i n g at a h i l l  from a d i s t a n c e  conspicuous, are  I f they could be  they might be  as l e n s - l i k e , w i t h a long a x i s p a r a l l e l to the ground.  seen  described Caves  are r e s t r i c t e d to the south s i d e o f h i l l s , composed o f T e r t i a r y Sedimentary r o c k s , exposed along River.  the North Fork o f the  Skagit  T h e i r e l e v a t i o n i s always the same, perhaps 10 to 12 f e e t  above sea l e v e l .  T h e i r form and  shape seems to be l a r g e l y  125 determined by bedding which i n these areas d i p toward the sea cliffs,  and p e r m i t t e d e x c a v a t i o n o f e n t i r e bedded b l o c k s .  A  s t r i k e p a r a l l e l to the c l i f f m a t e r i a l l y aided the agents o f e r o s i o n , and indeed, caves are e n t i r e l y absent on c l i f f where the f o r m a t i o n s t r i k e i s at a l a r g e angle to the  faces cliff.  The l a r g e s t cave occurs i n a conglomerate-sandstone sequence on the n o r t h s i d e o f the N o r t h Fork o f the S k a g i t R i v e r i n the l o c a t i o n marked on map  "cave".  T h i s cave i s about  35 f e e t wide by 5 f e e t h i g h at the entrance and extends back perhaps 25  feet.  A f e a t u r e of i n t e r e s t of  i n t h i s cave i s the r o o f c o a t i n g  amorphous white c a l c i t e , sometimes almost mammilary i n form.  No s t a l a c t i t e s are p r e s e n t .  The c l i f f  above the cave i s about  30  f e e t h i g h w h i l e on top a heavy f o r e s t v e g e t a t i o n grows to the cliff  edge.  The w r i t e r a s c r i b e s the f o l l o w i n g o r i g i n to t h i s  c a l c i t e coating:  r a i n water, p e r c o l a t i n g through the f o r e s t  tends to become s l i g h t l y a c i d i c .  soil  As t h i s a c i d i c water continues  downward i t d i s s o l v e s c a l c i u m carbonate from the i n t e r s t i c e s o f the  conglomerate.  When the water p e r c o l a t e s out through the cave  r o o f i t evaporates w i t h r e s u l t a n t p r e c i p i t a t i o n o f c a l c i u m c a r bonate.  E v i d e n t l y s t a l a c t i t e s are not formed because the water  i s not f o l l o w i n g s p e c i f i c channels, but i s p e r c o l a t i n g almost i n d i s c r i m i n a t e l y through the conglomerate and seeping out over the  e n t i r e cave r o o f .  126 Blocks excavated during cave formation are t o t a l l y absent except for those that have recently f a l l e n .  The only possible  genetic explanation i s that these are sea caves, carved by the waves of Skagit Bay prior to a recent, s l i g h t l o c a l u p l i f t .  "DEEPS" IN SKAGIT BAY  The term "deeps" i s here used to characterize closed depressions on the f l o o r of Skagit Bay. two such deeps occur:  Within the map  area  one southeast of Hope Island and the  second west of Seal Rocks. The f i r s t i s roughly c i r c u l a r , has a closure i n excess of 60 feet and covers an area, below the 60 foot contour, of 130 acres.  The second i s of l i n e a r shape and p a r a l l e l to the long  axis of Skagit Bay.  It also has a closure of about 60 feet and  covers an area of 270 acres. Bretz (1913) discusses the drainage surface developed  on  the u p l i f t e d "Admiralty" deposits during the i n t e r g l a c i a l prior to the readvance of Vashon i c e .  He concludes that most of the  main Puget Sound channels are g l a c i a l l y modified r i v e r valleys formed on this Admiralty P l a i n . south, supports t h i s concept.  Skagit Bay, from Hope Island Moving south down Skagit Bay  into  Saratoga Passage and through Possession Sound to Admiralty S t r a i t s the waters become progressively deeper and the bathymetric contours display a form very reminiscent of t e r r e s t r i a l r i v e r canyons.  127 N o r t h of Hope I s l a n d the bathymetric p i c t u r e i s confused though the o v e r a l l p a t t e r n o f a channel i s s t i l l  present!  South o f Hope I s l a n d drainage was o b v i o u s l y south w h i l e to the n o r t h the s i t u a t i o n i s not so c l e a r .  D i d drainage go west  here, through Deception Pass or southward i n t o the main At the present time Deception Pass have served as a channel.  from  channel?  i s e n t i r e l y too shallow to  However, perhaps  Vashon d r i f t or t i l l  has p a r t i a l l y blocked the channel, o r perhaps  s l i d e and t a l u s  m a t e r i a l from the h i g h b o r d e r i n g c l i f f s has reduced However that may be, i t appears  i t s depth.  drainage from the area  southeast o f Hope I s l a n d was n o r t h , between Hope and F i d a l g o I s l a n d s , thence e i t h e r west through Deception Pass, or around Hope I s l a n d and south down the main channel.  This l a t t e r  course  a d m i t t e d l y r e s u l t s i n a p e c u l i a r stream p a t t e r n f o r drainage which i s thought  to be  consequent.  A number o f cases o f southward drainage swinging west and i n t e r s e c t i n g northward m i r a l t y sedimentary  f l o w i n g r i v e r s are recorded on the Ad-  plain.  T h i s seems to be the case i n the  S k a g i t Bay - Saratoga Passage and at the present time  defies  explanation. The  "deeps" of S k a g i t Bay l i e i n these o l d channels but  are not d i r e c t l y r e l a t e d to them.  An e x p l a n a t i o n can be made  o n l y by i n t e r p r e t a t i o n o f bathymetric contours and the known h i s t o r y o f the a r e a . possible  Consequently  the w r i t e r suggests two  origins: m  (1)  a darning o f the channel by moranic  (2)  g l a c i a l gougKing by Vashon i c e .  or t i l l m a t e r i a l or  128 Adequate evidence  i s not available to select between  these two a l t e r n a t i v e explanations.  SUMMARY OF POST VASHON HISTORY AS INDICATED BY PHYSIOGRAPHY  As pointed out e a r l i e r , evidence  shows that at the time  of Vashon g l a c i a t i o n sea l e v e l lay s l i g h t l y higher than i t does now.  In the immediate area Bretz (1913) says the following: "In the b l u f f overlooking the c i t y of Mt. Vernon, in the same latitude as Cattle Point (San Juan Island), Vashon outwash gravel shows stream bedding to the base of the exposure, a l t i t u d e 40 feet. Though d e l t a bedding i s present, i t occurs only i n i n d i v i d u a l horizontal beds i n which the gravel i s forget. This section thus indicates that the sea was below 40 feet above tide when the Vashon Ice retreated across the region". In work on the Qualicum Delta, underlying Northern  Bellingham, Bretz goes on to show that sea l e v e l l a y between 30 and 75 feet above  present mean tide during the retreat of  Vashon i c e . Work i n the San Juan Islands and farther south i n dicates sea l e v e l was some 40 feet higher during Vashon retreat than now. Within the map area the only indicator of sea l e v e l i s the occurrence of marine invertebrates i n g l a c i a l outwash on the east end of Hope Island.  The lower l i m i t of f o s s i l  occurrence  i s now about 12 feet above sea l e v e l indicating only that the water was above t h i s l e v e l . Evidence from other areas as mentioned i n the section on glaciology shows that the region sank after retreat of the Vashon  129 ice,  and  than  that  of  has  subsequently  possessed  t h i s was  the best ideas  glaciation,  harmony w i t h t h e  i n the  movement  Great  feet  as  lesser  include lifted  this  to a r i s e  remains,  certain  coves  island  rebound.  by  uplifted  Latest up  and  down  i s seen  in hills  uplift  of  per-  r o c k - c u t t e r r a c e s and  farther  south i n the  Seattle-  evidence of recent u p l i f t , a r e a has  accompanying caves;  cliffs.  in  communication).  Confirming  and  evidence  upward, i s n o t  an o s c i l l a t i n g  i n c i s i o n o f the S k a g i t R i v e r i n t o sea c l i f f s  Wo  c r u s t a l movement,  theory of e u s t a t i c  i n t e n s i t y , w i t h i n t h e map  marine eroded of  prior  that  d i a s t r o p h i c movement, a s l i g h t  indicated  Bremerton areas.  somewhat g r e a t e r  area.  Lakes a r e a i n d i c a t e  latest  marine m o l l u s c a n  of  here  (Danner, p e r s o n a l The  haps 20  w i t h i n t h e map  c o u l d p o i n t out  downward a f t e r  t o an a l t i t u d e  d u r i n g the Vashon d e - g l a c i a t i o n .  observed  One  risen  o f the d e l t a  been c i t e d .  though These  the D e l t a s u r f a c e ; isolated, and  up-  swampy,  incipient  notching  130 BIBLIOGRAPHY American G e o l o g i c a l I n s t i t u t e , I960, Glossary of geology and r e l a t e d sciences with supplement, 2nd ed. Andrews, H.N., 1961, Studies i n paleobotany: New York, John Wiley and Sons, Inc. 488 p. Arnold, G.A., 1947, An i n t r o d u c t i o n to paleobotany: New York, McGraw-Hill Book Co., 433 p. B a i l e y , E.B., 1930, New L i g h t on sedimentation and t e c t o n i c s : Geol. Mag., v. 67, p. 77-92. 1936, Sedimentation i n r e l a t i o n to t e c t o n i c s : Geol. Soc. America B u l l . , v.47, p. 1716-1718. 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