THE GEOLOGY OF LUMMI AND ELIZA ISLANDS
WHATCOM COUNTY, WASHINGTON
by PARKER EMERSON CALKIN B.S. Tufts University, Medford, Mass.
A Thesis submitted in partial fulfilment of the requirements for the degree of
MASTER OF SCIENCE
in the Department
of GEOLOGY
We accept this thesis as conforming to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
April, 1959 ABSTRACT
Lummi and Eliza Islands form the northeast part of the
San Juan Island group in northwest Washington. Lummi is a long, narrow island characterized by a rocky, mountainous southern half and a low, northern half. Eliza is a small T-shaped island southeast of Lummi Island.
Lummi Island is underlain by igneous, metamorphic, and sedimentary rocks of Paleozoic to Lower Cenozoic age. The oldest rocks are believed to be those of the Lummi Island
Metamorphic and Igneous Complex which form a small, isolated knob in the middle of the island. These are hornblendic rocks, intruded by quartz-albite rocks and cut by numerous aplite and lamprophyric dikes. The age and origin of these rocks is un• known but they may be older "basement" rocks brought to their present position through faulting.
Shale, graywacke and granule conglomerate of the
Carter Point formation (Paleozoic or Mesozoic) underly most of southern Lummi Island. These rocks show all the character• istics of the typical "graywacke suite" such as great thick• ness, clastic character, rhythmic bedding, and graded bedding.
The only fossils found were a few carbonized plant stems im• bedded in fine-grained graywacke. The rocks forming the bed• rock of Eliza Island may be a more metamorphosed equivalent of these.
Overlying the Carter Point formation on the southeast side of Lummi Island and directly underlying the sandstone at the northern end are the Reil Harbor volcanics. Although they occur in five isolated outcrops these rocks are grouped
together on the basis of lithology and outcrop features. In contrast to an earlier intrusive interpretation these occur as submarine (pillow) lavas and interbedded breccia with tuffaceous - argillaceous rocks rather than as dikes or sills.
The lavas of some of the outcrops are spilitic and in most cases are extremely altered. The breccias are dominantly vol•
canic - clastic types which show some reworking. The age of the volcanics and underlying Carter Point formation is unknown; however, interbedded sedimentary rocks contain radiolarian tests suggestive of Mesozoic age.
Northern Lummi Island is underlain by plant-bearing lithic-feldspathic arenites and conglomerates of the Chuckanut formation (Paleocene). These are believed to have a contin• ental fluviatile origin on the basis of: absence of marine fossils; conspicuous amounts of hematite imbedded in the sand• stone; moderate sorting and rounding; apparent large-scale heterogeneity evidenced by internal structures such as prom- inant cross bedding and cut - fill structures, and the domin• ance of sandstone and conglomerate facies.
The Carter Point formation and the overlying volcanics on the southeast side of Lummi Island strike N 40 W and dip
45 degrees NW. Drag folds suggest that southern Lummi Island represents the eastern limb of a northwest plunging anticline. The Chuckanut formation and the underlying Reil Harbor vol- canics at the north end of the island have been folded into three synclines which strike northwest-southeast and plunge gently northwest.
During the Pleistocene, northern Lummi Island was blanketed with glacial drift while the higher knobs here and the rocks of southern Lummi were grooved, polished or eroded by the glaciers. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my
Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Parker E». Galkin
Department of Geology
The University of British Columbia, Vancouver 8\ Canada.
Date 29- A^rll, 1959 CONTENTS
Chapter Page
I. INTRODUCTION 1 Location and access 1 Previous geological work 1 Field Work 4 Acknowledgments . . . . 5
II. GEOGRAPHY 6 Surface Features 6 Lummi Island 6 Eliza Island , 8 Climate 9 Vegetation 9 Culture ' 10 Water supply and drainage 11
III. GEOLOGY 12 General Features 12 Lummi Island Metamorphic and Igneous Complex ... 14 Introduction 14 Description 15 Hornblendic rocks ..... 16 Quartz-albite rocks 19 Dikes 21 Veins and albitization 22 Sequence of events 22 Discussion 23 Carter Point Formation 25 Introduction 25 Previous Work 25 Stratigraphies relations on Lummi Island .... 26 Sedimentary structures 30 Graded-bedding 30 Cross-bedding 31 Slump structures 31 Intraformational breccia 31 Lithology at the coarse fraction 32 Diagenesis and the graywacke problem 37 Lithology of the fine fraction . 39 Veins 40 Origin and conditions of deposition 40 Age and correlation 42 Reil Harbor volcanics 45 General 45 Outcrop features 46 Description 51 Pillow Lavas 51 Amygdules, veins, and vugs 54 Alteration 54 Page
Breccias 56 Origin of the clastic breccias 61 The spilite problem 62 Tuffs 68 Previous geological work 70 Age Relations 72 Chuckanut formation 75 General 75 Previous work 75 General stratigraphy - Lummi Island 77 Lithology 80 Conglomerate 80 Sandstone 82 Diagenesis 90 Sedimentary structures 91 Cross-bedding 91 Graded-bedding 93 Concretions 93 Intraformational breccias 95 Mud balls . 95 Carbonaceous deposits of Lummi Island 96 Origin and conditions of deposition 105 Paleoclimatology 106 Age and correlation 107 Glaeiation 108 Geomorphology 114 Coastlines 114 Lithologic control of weathering 114 Marine cliffs and terraces 115 Fretted surfaces 117 Lummi Point 117 Structure . 119 Regional structure 119 Carter Point formation and Reil Harbor vol• canics of the southern half of Lummi Island 120 Eliza Island 123 Structure of the sedimentary and volcanic rocks a.t the northern half of Lummi Island 123 Cross-island faults 126 Bibliography 128 Appendix 133 ILLUSTRATIONS
Plate Page
1. Geologic map of Lummi and Eliza Islands in pocke4^^p 2. Diagramatic Structural Sections, Lummi Island . . in pe^ekWc^s. 3. Map showing location of water wells on the ( s northern half of Lummi Island in poefce-15) View looking East from Orcas Island showing the southern two-thirds of Lummi Island . . . frontispiece Figure
1. Index Map 3 ''2, Eliza Island looking southeast from Lummi Island . 18 3. Hand specimen of hornblendic rock, Lummi Island Metamorphic and Igneous complex 18 4. Section of the Carter Point formation 28 5. Laminated siltstone and fine-grained graywacke, Carter Point formation 29 6. Photomicrograph of graywacke, Carter Point formation 29 7. Photomicrograph showing graded bedding in laminated siltstone, Carter Point formation . . 33 8. Hand specimen of shale granule breccia, Carter Point formation 33 9. Mineral composition, Carter Point formation, graywackes 35 10. Carbonized plant stems in a specimen of fine• grained graywacke, Carter Point formation ... 47 11. Pillow lavas, Reil Harbor volcanics ... 47 12. Limestone pod interbedded with ribbon chert , Reil Harbor volcanics 50 13. Contorted ribbon chert, Reil Harbor volcanics ... 50 14. Photomicrograph of spilitic lava, Reil Harbor volcanics 57 15. Breccia of the Reil Harbor volcanics 57 16. Photomicrograph of tuffaceous argillite, Reil Harbor volcanics 67 17. Photomicrograph of specimen 5/7/6-2A from the tuff sequence overlying the Reil Harbor volcanics 67 18. View looking SE at Migley Point showing con• glomerate of the Chuckanut formation lying upon the eroded surface of the pillow lavas of the Reil Harbor volcanics 78 19. Short stratigraphic section of the Chuckanut formation at its base on Lummi Island 79 20. View of the Chuckanut formation at Fern Point ... 92 21. Cumulative frequency, curve of a typical sand• stone, Chuckanut formation 84 Figure Page 22. Mineral composition, Chuckanut formation, sandstone 86 23. Petrography of representative samples of the Chuckanut formation,sandstone ... 87 24. View N. showing cross-bedded sandstone, Chuckanut formation 94 25. View SW of spine-like pattern in sandstone, Chuckanut formation 94 26. Hand specimen of black micaceous sandstone lens, Chuckanut formation 97 27. Photomicrograph of the micaceous sandstone shown above (Figure 25) 97 28. Coalified wood fragment interbedded with sand• stone, Chuckanut formation 99 29. Irregular masses of coalified vegetal material with radiating stringers occurring in sandstone,Chuckanut formation 99 30. Photomicrograph of a tangential section from a specimen of coalified wood, Chuckanut formation 102 31. View NE showing a coalified log (A) cutting across beds of the Chuckanut formation 104 32. View SW showing glacial grooves and polished surfaces in Reil Harbor volcanics , 104 33. Folds in stratified outwash deposits (A) formed by thrust of glacier 116 34. Wave-cut cliff and bench in Reil Harbor volcanics . 116 35. (a and b) Fretted surface, formed by differ• ential wave erosion of sandstone, Chuckanut formation 118 36. View NE of Chuckanut formation showing small scale fault 125 TABLES
Page
Table 1. Table of formations 14
Table 2. Comparison of outcrop features of the
Reil Harbor volcanics 48
Table 3. Petrography of the outcrops of the
Reil Harbor volcanics 52 View looking E. from Orcas Island shov; ing the southern two-thirds of Lummi Island and Mt. Baker in the background W.R.Danner, July, 1957. CHAPTER I
INTRODUCTION
LOCATION AND ACCESS
Lummi Island and adjacent Eliza Island are located in western Whatcom County in northwestern Washington (see Figure
1). They form the northeastern part of the San Juan Island group. The area included in the geologic map of this report is that occupying the northern half of the Anacortes Topo• graphic Quadrangle between 122° - 34' and 122° - 44' west longitude, and between 40° - 30' and 48° - 45' north latitude.
The mainland opposite Lummi Island is easily reached by car and is an approximate two hours drive from Vancouver, British
Columbia or a fifteen minute drive from Bellingham. Roads lead from US 99 through Ferndale or via shore road from
Bellingham through the Lummi Indian Reservation to a car ferry at Gooseberry Point. Lummi Island may be reached in ten minutes by this ferry. Eliza Island may be reached only by private boat or plane. Small boats may be rented at Gooseberry
Point or on Lummi Island.
PREVIOUS GEOLOGICAL WORK
The most complete published account of the general 2 geology of the San Juan Islands including Lummi Island was written by R.D.McLellan of the University of Washington as a
Ph.D. thesis. McLellan worked in this area in the spring and summer months of 1922 through 1925 and his report and geologic map at a scale of 1" = 1 mile were published by the University of Washington Press in 1927.
In recent years Dr. W.R. Danner of the University of
British Columbia has been studying the geology of the San
Juan Island area in some detail and his report will be pub• lished by the University of Washington Press as a revision of the McLellan work previously mentioned.
Most of the geological work near Lummi Island has been prompted by the occurrence of coal, building stone, natural gas, and the possible presence of oil in the Chuckanut formation of western Whatcom County. A complete account of the general geology of western Whatcom County was given by
Jenkins (1923) in connection with the coal deposits. Shedd
(1902) reported on the Chuckanut Bay sandstone. Leighton
(1919) reported on the roadbuilding sands and gravels of
Washington and included in this report a sieve analysis of a sample of glacial drift from Lummi Island. In 1935 Glover reported on the oil and gas possibilities of this area and de• scribed the general lithology, structure, and stratigraphy of the Chuckanut formation. The Chuckanut formation has been reported on by numerous other writers including Weaver (1916 3
Figure 1. Index map of northwest Washington and southwest British Columbia showing the location of Lummi and Eliza Islandso 4 and 1937), Culver (1936), and Newcomb, Sceva, and Olaf (1949) in their report of the ground water resources of western
Whatcom County.
FIELD WORK
Fieldwork on Lummi Island by the writer was begun
April 4, 1958, and was continued on a part-time basis through
May 22, 1958. Several additional trips were made in October
1958 and January 1959 to re-examine certain areas in more detail.
The geology was mapped on low-level aerial photo• graphs taken in 1955. These photographs were of particular help in working the inland area of the mountainous southern half of Lummi Island as they show most of the logging roads which are not plotted on the topographic map. The geology was transferred to a topographic map at a scale of 1302 feet to 1 inch enlarged from the U.S. Geological Survey Anacortes
Quadrangle, 15 minute series, topographic sheet. 5
ACKNOWLEDGMENTS
Many persons have contributed to this report and
have aided the writer in this study. Dr. J.V. Ross and Dr.
H.P. Trettin have offered advice and constructive criticism
both in the field and in the laboratory. Dr. W.H.Matthews
and Dr. K.C.McTaggart also aided in the laboratory work. For
helpful suggestions in the study of the coalified plant material and for their identification, the writer wishes to
thank Dr. G.E. Rouse. Assistance was rendered in the field
early in April 1958 by Mr. D. Shipp of Vancouver. Thanks are also due to my wife Joan for her critical reading of the manuscript.
Acknowledgment is due to the officers of the U.S.
Department of Conservation office in Bellingham for their help
in securing aerial photographs of the area. Information on water supply and well records was given by Mr. Livermore of
Ferndale and Mr. R.F.Chatfield of Bellingham.
Many residents of Lummi Island have offered information
on the location of fossils, the vegetation, and the cultural
history of the island.
The writer especially wishes to express his apprec•
iation of the many helpful suggestions in the field and in the
laboratory received from Dr.W.R. Danner, under whose direction
the work was carried out. CHAPTER II
GEOGRAPHY
GENERAL
Lummi and Eliza Islands lie within the Puget Trough
section of the Pacific Border physiographic province. The
Puget Trough section is a long north-south lowland lying just west of the Cascade Mountains and east of the Olympic Mountains.
Locally, Lummi and Eliza Islands lie just to the west of the
Whatcom Basin which consists of a low, glacially-smoothed, upland till plain, drained chiefly by the Nooksack River.
SURFACE FEATURES
Lummi Island
Lummi Island is separated from the mainland to the east by Hale Passage, and from Orcas Island to the west by the strait of Georgia.
It is nine miles long, nearly two miles wide at its maximum, and 8.2 square miles in area.
The most striking characteristic of the island, esp• ecially as seen from a distance, is the sharp change in topo• graphy between the southern and northern half, (see frontis• piece) . The southern half of Lummi Island is very rocky and mountainous; its highest point, Lummi Peak, rises precipitously to an altitude of 1740 feet.
This mountainous topography is dominated by a long 7 ridge which is bounded on the southwest side by steep cliffs and their talus slopes which are all aligned northwesterly, parallel to the strike of the rock formations. On the opposite side of the ridge, the surface slopes more gently toward the northeast and closely follows the dip of the beds.
Some of the talus slopes on the southwest side of the island extend from water level up to 1000 feet. In most cases the actual mantle cover is less than a foot thick on these slopes which are dangerous to cross. It was reported (McLellan
1927) that several people who attempted to climb the slopes met with fatal accidents.
Two small rocky islands rise 25 feet above the high tide mark off the southwest shore, directly west of Lummi Peak.
Called Lummi Rocks, they have a combined area of approximately three acres.
Two bays are cut into the southeastern side of the island. Inati Bay, the northernmost one, provides good shelter for small fishing boats during parts of the stormy winter season. Riel Harbor to the south forms only a shallow inden• tation.
Towards the extreme south the high altitudes of the island quickly decline, and the island becomes narrower, ending in Carter Point.
The abrupt change in topography between the northern and southern parts of Lummi Island occurs across the island in a line with another shallow indentation called Sunrise Covev. 8
North of this point much of the island is covered by glacial drift, and with the exception of a rocky knob near the northern• most tip, its elevations are below 200 feet. This northern• most tip of Lummi Island is called Migley Point. About three hundred feet to the west of this point is a small, rocky island of less than a quarter of an acre in area. Local residents report that it is at times a resting place for seals.
Along the west side of Lummi Island there are four low points extending out to the west. The southernmost of these forms a sheltered bay, now used for small boat landings, and is called Legoe Bay. To the east from Fern Point, the northern• most of these points, rolling, rocky hills reach an altitude of 357 feet. Opposite this height on the east side of Lummi
Island is low, sandy, Lummi Point which projects into Hale
Passage.
Eliza Island
Eliza Island is named after Lieutenant Francisco Eliza, the Spanish explorer who discovered the San Juan Islands in
1791 (McLellan, 1927). It is located about three quarters of a mile to the east of Carter Point, and is 170 acres in area
(see figure 2). Eliza Island is built mainly of glacial drift which stretches out in a direction about N 15 W from a bedrock knob. Two long sand bars extend about a half mile from the west side of this bar to join with another small rock knob.
The highest elevation occurs between the aforementioned sand bars where a swamp and small slough exist. 9 CLIMATE
Lummi Island and the immediate surrounding area has an equable oceanic climate with extreme temperatures uncommon and precipitation moderate. The average rainfall varies between
25 and 30 inches per year and occurs mostly in the winter. The mean average temperature is about 50 degrees Fahrenheit.
Winds are gentle on the average, usually coming from the south• west in the summer and from the southeast in the winter.
VEGETATION
The southern mountainous half of Lummi Island is generally quite heavily wooded despite the thin cover of soil in certain areas. The most extensive of the larger trees is
Douglas Fir (Pseudotsuga taxifolia) which with Grand Fir (Abies grandis). Cedar (Thu.ja plicata?), and Hemlock (Tsuga hetero- phylla) has been cut for lumber and pulp over the past quarter century or more. Many of the areas which have been stripped of large timber are now covered by second growth Maple, Alder,
Willow, Cottonwood, and small Fir trees. On the elevated bed• rock knob south of Inati Bay there is an extensive cover of
Madrona (Arbutus menziesii) trees.
The northern end, where not cleared for farming, is thickly wooded, mainly by deciduous trees such as Alder, Maple,
Oak, Western Birch, Wild Cherry, Willow, and other trees.
Some of the area is poorly drained and supports only shrub growth. Some of the more numerous low floras of Lummi Island 10 include Buckbrush, Wild Rose, Salal, Salmonberry, Thimbleberry,
Hardhack, Blackberry, Oregon Grape, Devil's Club, and Nettles.
Eliza Island at one time was heavily wooded with conifers similar to the assemblage on Lummi Island. Recently, a good deal of this has been cut, and these areas are now covered with low shrubs and some small deciduous second growth trees.
CULTURE
The northern half of Lummi Island is well settled, with most of the land area utilized in farming. Some of this land is cultivated for market crops, but a larger percentage is utilized as grazing land for beef or dairy cattle and sheep.
Some chicken farming is also carried on.
Logging has been important in the past and thus many access roads have been cut over the hilly southern end of the island.
The biggest industry over the years has been fishing in the waters surrounding the Island, both commercial and, more recently, sport fishing. Reef-net fishing for salmon is the most important commercial method on Lummi Island.
The Island is also a summer resort area. Although only one commercial resort is in operation, numerous private summer homes are located along the shores.
At the present time Eliza Island is owned and used as a private estate by a Bellingham family. 11
WATER SUPPLY AND DRAINAGE
The fresh water supply on Lummi Island is generally secured from ground water although a dammed stream above Sun• rise Cove supports nearby homes. In general, ground water is of good quality and hardness. Iron is the most common object• ionable constituent although it is confined chiefly to the recessional outwash and Recent alluvial deposits (Newcomb,
Sceve, and Olaf, 1949). Water from the deeper glacial deposits is sometimes slightly brackish. Sulfur is present in some of the water from the Chuckanut formation on Lummi Island.
Appendix I shows some of the water well records of
Livermore and Sons, Inc., and of the B and C Drilling Company on Lummi Island. Much of the ground water is taken from sand and gravel lenses in the till or beds of outwash. The Ter• tiary sandstones do not always appear to be a reliable source of water as some horizons produce relatively large quantities of water while others are quite poor producers. This is probably due to the fact that locally they are well-cemented, poorly sorted, and often irregularly and discontinuous stratified (Newcomb, Sceve, and Olaf, 1949)
Surface streams on Lummi Island are limited to the south end, and even here there are few which run continuously all year. In general, these few streams follow the dip of the beds toward the northeast. Depressions in the bedrock and in the Quarternary deposits over some parts of the island support small sloughs or swampy areas. CHAPTER III
GEOLOGY
GENERAL FEATURES
Lummi Island is underlain by igneous, metamorphic, and sedimentary rocks of Paleozoic? to Lower Cenozoic age. The oldest rocks, the Lummi Island Metamorphic and Igneous Complex, are exposed in a completely isolated knob near the middle of the island. These are dominantly hornblendic metamorphic rocks which are cut by a leucocratic igneous rock and by aplite and lamprophyric dikes.
The southern, mountainous half of Lummi Island is underlain by the Paleozoic or Mesozoic Carter Point formation.
This formation consists of a thick, essentially unfossiliferous sequence of graywackes and interbedded black shales, siltstones, argillites, and conglomerate-breccias. They resemble rocks of the "graywacke suite" throughout the world. Similar appearing but slightly more metamorphosed rocks crop out on Eliza Island and are correlated to the Carter Point formation. Rocks of the Carter Point formation strike northwest and dip towards the northeast.
Five small, isolated knobs of volcanics, grouped to• gether on the basis of lithology and outcrop characteristics, and here designated as the Reil Harbor volcanics, are found at the margins of the northern low half of Lummi Island and at one locality on the southeast side of the island. These volcanics appear to unconformably overlie the Carter Point for• mation and are probably of Upper Paleozoic or Mesozoic age.
They consist of spilitic and andesitic? pillow lavas of inter• bedded ribbon cherts, breccias and interbedded argillites. At certain places the lavas contain small mostly recrystallized lenses of limestone.
The northern half of the island is dominantly under• lain by the Chuckanut formation of Early Eocene or Paleocene age. At the northern end of Lummi Island it is seen to lie on the eroded surfaces of the Reil Harbor volcanics. It is composed of moderate to poorly sorted, cross-bedded, feld- spathic and lithic arenite, conglomerate, and siltstone.
Interbedded with these rocks are fragments of coalified wood, leaves, and other plant remains.
The rocks of the Chuckanut formation and the under• lying volcanics at the northern end of the island are folded into three synclines which strike northwest - southeast and appear to plunge to the northwest. 14
TABLE I Table of Formations
Era Period-Epoch Name Lithology
Cenozoic Quaternary-Recent Alluvium and beach deposits. Pleistocene Glacial and inter- glacial deposits.
Tertiary-Paleocene Chuckanut Cross-bedded, formation feldspathic aren- ite, conglomerate and siltstone \tfith carbonaceous material.
Mesozoic or Reil Harbor Pillow lavas, Paleozoic volcanics interbedded rib= bon chert, breccia and inter• bedded argill• ites.
Carter Graywacke, int er- Point bedded black Formation shale, siltstone, argillite, and conglomerate- breccia.
Unknown Lummi Hornblendic Island Meta• rocks, cut by morphic and igneous rocks, Igneous aplite and lam• complex prophyric dikes.
LUMMI ISLAND METAMORPHIC AND IGNEOUS COMPLEX
Introduction
The Lummi Island Metamorphic and Igneous Complex is a name here assigned to a small composite mass of metamorphic and intrusive rock cropping out northwest of Sunrise Cove in the middle of Lummi Island. It forms an elevated knob, approx• imately twenty acres in area, which is surrounded on all sides by glacial till and outwash deposits. This outcrop was not shown on McLellan's map (McLellan, 1927) of Lummi Island al• though somewhat similar rocks were found and mapped by him on other of the San Juan Islands. These latter rocks he named the Turtleback Complex.
The great majority of the rocks exposed on this knob are hornblendic rocks with varying amounts and compositions of light-colored minerals, and showing various degrees of contamination. Closely associated with these are leucocratic, quartz-albite intrusive rocks. These are exposed in a few, small, isolated localities around the margin of the knob.
Cutting through the hornblendic rocks are several aplite and lamprophric dikes. It should be emphasized that exposures are poor as the knob is covered by a heavy shrub growth and those rocks bare of shrubs or trees are often covered with moss.
Because of this hindrance, it is thought that there may be other rock types present which were not seen.
Description
The rocks of the Complex are divided, for convenience of description, into three general groups. These are:
(1) hornblendic rocks: (2) leucocratic quartz-albite rocks:
and (3) aplite and lamprophyric dikes. Q 16
Hornblendic Rocks
A number of specimens were taken of the hornblendic rocks from different parts of the knob. Thin-sections were made from some of these and showed considerable variation in composition. Described below are three of the rocks which represent examples of a few of the variations in composition and texture seen.
Specimen 5/5/3-5 was taken from rock which shows good schistose texture in the outcrop, with bands and schlierenrlike lenses of green hornblende. The thin-section consists of small (,20mm) idioblastic, slightly bluish-green, actinolitic hornblende, transformed in part to brown biotite. Porphyro- blasts (1.30mm) and smaller xenoblastic laths of albite (An 3) are present, and are full of inclusions of hornblende and clouds of granular epidote. Small amounts of large, raggedly terminated clinopyroxene are also present. These grains of clinopyroxene appear to have been largely converted to pale- green hornblende. Index oil determinations compared to the curves of Hess (1949) place these in the Endiopside-Diopside category. Available grains were not suitable for 2V deter• minations. Chlorite is insignificant in this section but is as abundant as 3% in other rocks of this type. Cutting this and similar rocks are veins of water-clear albite, sericite, quartz, and sheaflike masses of prehnite.
Specimen 5/5/3-13 differs megascopically from the specimen described above in the lack of alignment of hornblende. 17
In thin-section it resembles it except that it is seen to con• tain fresh andesine (An 33) in irregular, connected clusters in addition to its highly epidotized, more sodic plagioclase.
Many of the rocks seen in the knob contain stringers and contiguous, irregular masses of feldspars and quartz
(Figure 3). Specimen 5/5/3-10 taken from these rocks contains:
50$ andesine (An42); 30% intergranular quartz; 11% bluish-green to green hornblende; 2% brown biotite; and 4% deep-green chlorite associated with 2% partially oxidized magnetite. Many of the andesine laths are weakly and some completely zoned.
These laths are full of granular epidote, and some clay and sericite inclusions. They are generally tabular in shape.
The hornblende, largely anhedral, has been made over in part to brown biotite which in turn has altered to deep green chlor• ite and magnetite. Intergranular quartz is grouped in irregular clusters and in part replaces and deeply embays the epidotized plagioclase. The section is cut by a vein of extremely fine white mica and a vein of prehnite. Specimen 5/5/3-14 is similar to 5/5/3-5 except that is is cut by a 2 inch wide vein of ferroan diopside with prominant parting parallel to 100
(Diallage).
Mineralogically and texturally these are metamorphic or recrystallized rocks which are in an unstable state. They cannot truly be assigned to a metamorphic facies; however many of the rocks most nearly resemble metamorphic rocks of the Figure 2. Eliza Island looking south east from Lummi Island, W.R. Danner July 1957. Infrared film.
rO
Figure 3. Cut surface of hand speci• men of hornblendic rock from the Lummi Island Metamorphic and Ig• neous complex (age unknown) showing irregular masses of quartz and feldspar. 19
"Quartz-Albite-Epidote-Almandine" subfacies of the "Green- schist" facies (Fyfe, Turner, and Verhoogen, 1958, p. 224).
The present mineral assemblage suggests therefore that they are products of relatively low-grade regional metamorphism. Evid• ence in this small outcrop as to the direction of metamorphism exhibited by the assemblage or as to the true parent rock is inconclusive. Uralitization of the pyroxene, production of epidote from originally more calcic feldspars, and patchy development of brown biotite seen in these rocks are found in progressively metamorphosed basic igneous rocks as well as being characteristic of alteration of other types of regionally metamorphosed rocks.
It is believed that these specimens do represent regionally metamorphosed rocks which have been contaminated after formation to various degrees by injection of light
minerals. In the first specimen discussed (5/5/3-5)} the unusual porphyroblasts of feldspar; in the second case (5/5/3-13) the appearance of fresh andesine in a rock already containing highly altered sodic plagioclase; and, finally, in the third case (5/5/3-10), the presence of fresh, clear quartz enclosing porphyroblasts of hornblende and embaying the altered feldspar, all may suggest late, wet contamination with light colored minerals from some nearby body of magma.
Quartz-Albite Rocks
The second group is composed of dense, medium to 20 coarse-grained somewhat granitic-looking rocks. A typical specimen, (5/5/3-D, contains clear quartz (,30mm) in clusters replacing or embaying albite crystals (,45mm). The average percentages appear to be 38$ quartz with 54$ albite. Most of the albite appears to be packed with epidote grains; how• ever those determinable are nearly pure albite. Biotite, somewhat altered to chlorite, is present in amounts usually less than 3%t and occurs as deformed or bent plates between the quartz and the plagioclase crystals. Epidote, amounting to about 5%, fills fractures and shear lines in the rock.
Field relations of these quartz-albite rocks and even thin section examination does not immediately appear to show proof of their origin. In thin section, the albite grains do not always show good tabular form and appear somewhat rounded.
In the field, the contact of the quartz-albite rocks with the metamorphic rocks is sometimes very sharp, and, at other locations, it is seen to be somewhat gradational. In no case were the quartz-albite rocks seen by the writer to clearly cut the metamorphic rocks. It could be suggested on the basis of the rounding of the feldspar, the large amounts of quartz, and the general lack of clear intrusive relationships, that these rocks are recrystallized sedimentary rocks. However, on the basis of the complete zoning seen in many of the feldspars; the apparent homogeneity of the feldspars, the arrangement of the quartz in clusters, and the sporadic and intrusive-like occurrence of the outcrops, and, finally, the implication of 21
nearby magmatic action in the contamination of the hornblendic
rocks, these quartz-albite rocks are interpreted as intrusive,
igneous rocks.
These intrusives have undergone some later recrystall-
ization and stress as shown by parallel strain lines running
through adjacent quartz grains, and by the occurrence of
faulted plagioclase. Some further replacement and solution of
the feldspar may have occurred at this time.
Dikes
Cutting rocks of the first and perhaps of the second
group are aplite and lamprophyric dikes. Aplite dikes show a
sugary, xenomorphic texture of 40$ quarts (.45mm) and 60$
albite (An 10), averaging 1.5mm in diameter. The albite is
mostly altered to epidote; the rock is cut by veins of granular
epidote.
The lamprophyric dikes vary in grain size. Specimen
5/20/2-1 is a fine-grained rock with 5 to'10$ microphenocrysts
of subhedral green hornblende (.09mm long) in a groundmass of
J altered feldspar, biotite, chlorite, and magnetite. Some of
the dikes show foliation of the hornblend phenocrysts.
The source of these dikes is not known. They may,
however, be related to the same magmatic body which was the
source of contamination of the hornblendic rocks. 22
Veins and Albitization
Veins of albite, prehnite, and quartz cut through many of the rocks in this knob. The whole significance of these veins cannot be realized from evidence seen; however, the albite may represent a source of albitizing solutions for transformation of more calcic plagioclase. Prehnite, when found in sheaf-like groups in sodic rocks may indicate meta- somatic transformation of calcic plagioclase by heated mag• matic waters (Harker, 1950). From available evidence, the albite, prehnite, and quartz are interpreted as late hydro- thermal veins which may be related to the aplite and lampro• phyric dikes. These veins may then explain the common occurr• ence of sodic plagioclase in many of the rocks of the Complex.
In addition, it is probable that low-grade metamorphism and saussuritization of the plagioclase have played a role in the formation of the albite.
Sequence of Events
The following theory as to the sequence of events in the formation of this complex is offered:
1. Pre-existing, regionally metamorphosed, hornblendic
rocks.
2. (a) Intrusion of leucocratic, quartz-albite rocks
of group two. 23
(b) Contamination of regionally metamorphosed, horn•
blendic rocks by injection of light minerals, probably
from magma which formed the rocks of group two.
3. (a) Intrusion of aplite and lamprophyric dikes
(b) Introduction of hydrothermal solutions, albitiz-
ation of plagioclase and formation of quartz, pre-
hnite, and albite veins in all of the rocks.
It is suggested that this Complex represents a meta- morphic, hornblendic host rock that has been partially contam• inated and mixed with a leucocratic, quartz-albite rock, and later cut by dikes and veins. Whether this is the true or complete history cannot be proven. Various other rock types and textures are probably present. However, this may at least illustrate the complexity of inter-relations represented in this composite body.
Discussion
As noted previously this knob is surrounded on all sides by till or glacial drift, so contact relations cannot be used in age determination. No rocks are found elsewhere on
Lummi Island which resemble them. Rocks reported to be quite similar"1" occur on other San Juan Islands, and are called the
Turtleback Complex. (McLallen (19275 p. 14-9) described them as, "a confused network", containing the following types:
1 Personal communication, Dr. W.R. Danner 24
"dunites of the Fidalgo formation; Eagle Cliff porphyrites;
Work gabbro-diorites; Colquitz quartz-diorites; scattered off•
shoots of diorite porphyrites; scattered off-shoots of rhyolite
porphyry; a series of granodiorite porphyry off-shoots together with aplites, pegmatites, and igneous quartz veins; a series
of lamprophyric off-shoots, ranging from basic porphyrites to
ultrabasic pyroxenites and hornblendites." Because of the
small amount of rock exposed, such a separation on Lummi Island would be difficult if not impossible, even for one familiar with these formations.
McLellan (1927) considered the igneous rocks of this
Turtleback Complex to be pre-Cretaceous in age due to the fact
that Cretaceous and Eocene sediments of the San Juan Island
region were not cut by igneous rocks. They were thought to
be Mesozoic because they were composed of rock formations which were seen to cut late Paleozoic sedimentary rocks on
some of the San Juan Islands. He related the intrusions to
the late Jurassic batholiths of the Pacific Coast.
The age of the Lummi Island Metamorphic and Igneous
Complex is not known and cannot be determined on the basis
of contact relations. However, if these were recently intruded
or contaminated rocks, it would be likely that there would be
some indication of similar intrusion or contamination in the
arenites, graywackes or volcanic rocks of the island.
The simplest structural solution is that these are
older rocks, possibly pre-Carboniferous, around which the 25 younger rocks now concealed by glacial drift have been de• posited, or that they represent "basement" rocks that have been brought from depth to the surface through faulting.
CARTER POINT FORMATION
Introduction
The name, Carter Point formation, is applied here to a thick, essentially unfossiliferous sequence of graywackes and interbedded black shales and siltstones, argillites, conglom• erates, and breccias, which form the southern and elevated half of Lummi Island. The name is derived from the name of the southernmost projection of Lummi Island.
Previous Work
The sedimentary rocks of the southern half of Lummi
Island were included by McLellan (1927) in the Leech River group of the San Juan Island map area. The Leech River group was considered to be well exposed on other islands in the east• ern part of the map area and to form the central part of the syncline on San Juan Island to the west.
The group was said to be composed of varied rock types including graywacke, argillite, conglomerate and breccia, grit, schist, phyllite, slate, volcanic tuff, chert, limestone and coal. 26
McLellan named the rocks the Leech River group because of their lithologic identity with the argillaceous and arena• ceous sedimentary rocks and overlying tuffaceous volcanics of
Southern Vancouver Island. The latter were known on Vancouver
Island as the Malahat volcanics and the former were distinguished by Clapp (1912) as the Leech River formation.
Stratigraphic Relations on Lummi Island
The Carter Point formation underlies most of the south• ern half of Lummi Island. Stratigraphically, it is exposed from sea level on the west coast to its contact with the over• lying Reil Harbor volcanics on the east coast. This represents a section of approximately 4500 feet. There is some doubt as to whether the Reil Harbor volcanics overlie the total sequence or whether they are interbedded with the graywacke; however, for convenience of description here, the section will be con• sidered to end at the contact with the volcanics.
The sequence is wholly clastic, and it is probably aafe to say that it is domlnantly argillaceous in character. The principal material is shale or silty shale and much thin bedded, highly indurated argillaceous material, here called argillite.
In many localities, especially low down in the section, these argillaceous rocks are regularly interbedded with fine-grained graywacke or siltstone beds varying in thickness from laminae to two or three feet in thickness. These may well be described 27 as rhythmites (Pettijohn, 1957). Figure 4 illustrates a roughly measured section of the Carter Point formation from the southwest side of Lummi Island. In addition to the medium- bedded to laminated rock sequences (figure 5)j there are thick sections of fissile shale, argillite, and shale with a good parting parallel to the bedding. These sequences are found up to 40 feet thick and in several cases, conveniently located beds have been quarried for road mantle.
Despite the predominance of shales and argillites, the most conspicuous rocks are the thick, massive units of coarse graywacke and granule conglomerate which form vertical cliffs along the west side of this southern half of Lummi
Island. It is not uncommon to find these sections up to 150 or 200 feet in thickness. Little macroscopic indication of bedding is shown in these beds except occasional alignment of conglomerate or shale lenses or subparallel arrangement of aand- sized black shale particles (figure 6).
The most noteworthy feature of all of the units of the
Carter Point formation is that they may not be traced laterally along the strike for any great distance. For example one is unable to trace a shale unit for as great a distance as 50 yards along the strike before it interfingers with a coarser litho- logic facies. For this reason, detailed measured sections from different localities can be lithologically correlated with sections measured at other localities, only through general characteristics of the whole section. For example, a zone of 0 TOP 20 708 20 142
61
BOTTOM 167 K^vVv 143
SYMBOLS
Graywacke S.S-
srlty _ 83 shaly
163 interbedded shale 8 75 50 Shale _ 894 Argil li te • 00 O O O O 213 — Siltstone
interbedded 84 shale 69 Cgl. _ Breccia Lens III Sh._ Argillite Lens
282 986 Conglomerate • o • a o • 26 24 1010 1 308 Concealed
667 44 Thick bedded Med._Thin bedded 41 Thin bedded_ Laminae
Figur •e 4. Section of the Carter Point formation measured on the southwest side of Luinmi Island (SE£ sec,26, T. 37 N.j R» I E,), 29
Figure 5. Thin bedded to laminated sequence of siltstone and fine grain• ed graywacke of the Carter Point for• mation (age unknown). View facing E. at the NW corner of the southern mountainous half of Lummi Island. W.R.Danner, 1958.
Figure 6. Photomicrograph of gray• wacke of the Carter Point formation (age unknown) showing alignment of dark shale chips. Ordinary light, X24. 30 massive, coarse graywacke and granule conglomerate in the upper part of the section here can be traced for nearly 1000 yards along the general strike with only small breaks of shale or siltstone. As illustrated in figure 4 it is also common to find conglomerate, shale breccias, or argillite in lenses from
6 inches to several feet in length.
The vertical arrangement of rock units and lenses seem to show little reason or order on a small scale; however, the whole sequence represented on Lummi Island appears to show a general increase of coarse material toward the top.
Sedimentary Structures
Small-scale sedimentary structures are seen in the
Carter Point formation and are generally confined to the silt or argillaceous units. These include: graded-bedding; cross- bedding; and structures due to contemporaneous deformation.
Grade-Bedding
The graded-bedding here is best developed in the rhythmic sequence in single bipartite layers or laminae of silt and silty shale. As defined by Shrock (1949, p. 78), the principle of graded-bedding may be stated as follows: "In a single bipartite layer, the texture grades from coarse in the lower part of the stratum to fine in the upper part, the finer upper part ending abruptly against the coarse base of the next overlying layer." In many cases here, the lower three- fifths of the bipartite unit does not appear to be graded in the field. This lower part is overlain by one-fifth part of actual graded material; for example, black silt grades up to black shale. This is overlain by about one-fifth part of fine material, or black shale in the case of the example above.
The actual graded-bedding is the type attributed to turbidity currents (Pettijohn, 1957) where each successive increment is similar to the preceding except that the former contains one less coarse grade. Much of this grading is best seen in thin- section (figure 7).
Cross-Bedding
Frequently the graded-bedding is interrupted by uni• formly textured beds of sand or silt and these often show cross bedding on a very small scale. Individual cross-bedded units are usually confined to bands less than six inches thick.
Slump Structures
Closely associated with the graded bedding are slump features, or structures due to contemporaneous deformation.
These are variously described as slip bedding, curly bedding, hassock structure, and convolute bedding. They are generally found on a small scale in the finer units.
Intraformational Breccia
Particularly characteristic of the conglomerate are sections of intraformational breccia and evidences of small- scale scour and channeling. Figure 8 illustrates the common appearance of a shale - granule breccia. It is thought that the wedges of shale and siltstone in the coarse rock and the channels of granules in the shale are due to the subaqueous fragmentation and scour of turbidity currents. These breccias are not only found at the base of the conglomerate units but are often scattered throughout the whole section of conglomerate
It is believed that thin beds of mud and silt, deposited with the conglomerate, were broken-up and brecciated when the coarse particles were swept over them.
Lithology of the Coarse Fraction
The conglomerate is a massive, grey rock which weathers to a brownish-red color. It is dominantly a granule conglom• erate with few larger particles. In the outcrop, it is seen to grade into graywacke and, mineralogically, there is little difference. Characteristically, the granules of the conglom• erate are often discoid or wedge shaped and generally subrounded
Sorting varies but in general is fair.
The matrix which may form 1% of the rock is similar to that of the sandstones and will be discussed below. Bedding as previously mentioned is rare; however, lenses of finer rocks and argillite slivers of granule size present in the rocks are normally aligned parallel to the bedding of the associated finer rocks (figure 6).
The graywackes of this formation show considerable Figure 7. Photomicrograph showing graded bedding in laminated siltstone of the Carter Point formation (age unknown). Ordinary light, X26.
Figure 8. Cut surface of hand specimen of shale - granule breccia of the Carter Point formation (age unknown) showing shale lenses in matrix of subrounded granules. Specimen from breccia sequence near the $00 foot level on the SE side of Lummi Island. variance. All are highly indurated and the finer-grained sand•
stones might easily be mistaken for basic igneous rocks. Many
of the coarser grained specimens are typified by preferred
orientation, parallel to the bedding, of minerals and rock
particles, especially thin slivers of shale or argillite
particles. According to Gilbert (Williams, Turner, and Gilbert
1955), this orientation is to be expected in typical graywackes
however, according to Pettijohn (1957) a completely chaotic
arrangement of particles is typical. Lack of bedding or very
thick bedding is the rule for the coarser sandstones; and the
beds become thinner as the grain size is reduced.
Under the microscope the rock is marked by moderate
to poor sorting with angular to subangular particles. These
particles are tightly compressed in a recrystallized matrix of
chlorite, sericite, and clay-sized detrital material. Mineral-
ogically, the rock is polymictic; however, a general dominance
of lava fragments is observed. Figure 9 shows the variation
in mineral composition. The average composition excluding the matrix, of seven representative specimens is approximately:-
Rock fragments 37% Plagioclase 27% Quartz 20$ Biotite, hornblende, pyroxene, and other unstable minerals 9% Chert 8%
The quartz grains, often wedge-shaped, show undulatory
extinction and the grains of several specimens show parallel
alignment of strain lines. Marginal replacement by authogenic micaceous minerals is common. No secondary overgrowth was Figure 9. Mineral composition, Carter Point for•
mat iong graywackes. 36' observed. Some of these quartz grains occur in the typically interlocking aggregates of quartzite. Other aggregates suggest vein derivation. The chert, too, was seen to be undergoing marginal replacement. Apparently, most of these chert par• ticles were full of original impurities before deposition. The feldspar is apparently all plagioclase and most of the grains observed in thin-section were of andesitic composition. If or- thoclase is present, it occurs in insignificant amounts. The feldspars are all highly altered to sericite, chlorite, and epidote. Because this alteration is nearly complete in many cases, it is probable that much of it must have occurred after deposition.
Subrounded rock fragments, mainly altered volcanic fragments, are the dominating constituent of the sandstone. In many of the specimens examined, these volcanic rocks consist of andesites, basalts, microfelsites, and some amygdaloidal and highly vesicular, glassy rocks. Many of the lavas are por- phyritic with large phenocrysts of augite, showing poor, sub- ophitic texture. Other rock fragments contain phenocrysts of both hornblende and augite in a fine-grained groundmass in which occasional plagioclase laths can be distinguished.
Locally, metamorphic-derived, quartz-feldspar and hornblende-biotite-chlorite-feldspar aggregates are numerous.
Sliver-like particles of siltstone, shale, argillite, and slate are common in the coarser rocks. Many of the shale particles are relatively fresh, and judging from the indented borders of many, were in a plastic state at the time of deposition.
Dark minerals of detrital origin are common in many horizons and sometimes amount to as much as 15%. No one mineral is dominant throughout the sequence; however, locally, relatively fresh augite crystals, some as large as 1.7mm in longest dimension, are common. These minerals indicate rapid erosion and deposition without extensive disintegration.
Other minerals commonly found include biotite, muscovite, hornblende, and some epidote fragments.
Diagenesis and the Graywacke Problem
The problem of the definition of a graywacke has been much discussed and many papers have been written describing various classifications. Some writers, including Carozzi
(1952), and Dunbar (1957)9 consider that a graywacke is a sandstone containing at least 33% of easily weathered materials with minor amounts of basic and metamorphic rock fragments.
Twenhofel (1950) considered graywackes as the basic equi• valent of an arkose. Today on the other hand, many students appear to prefer the textural classification of Pettijohn (1957)
Williams, Turner, and Gilbert (1955)> or Krumbein and Sloss
(1956). Krumbein states that a graywacke must contain 20% matrix composed of clay and a paste of chlorite and sericite.
Pettijohn defines a graywacke in part as a sandstone with clay-sized detrital matrix exceeding 15$. Gilbert places the 38 matrix cut-off point at 10%. The writer feels that Gilbert's definition is the most useful of those given above. Gilbert notes that "there is no statistical basis for distinguishing grains and matrix", although he implies that most people con• sider thet matrix composed of particles smaller than 20 microns.
He also points out that when many loosely packed, poorly sorted rocks which may have originally contained 20% or more of clay- sized matrix are put under compression the subsequent result is that their matrix is reduced in bulk to form as little as
10% of the indurated rock.
The Carter Point graywackes have been extremely in• durated and in most cases, the clay-sized matrix appears to compose as little as 5% of the rock with most of the matrix composed of chlorite and sericite and strings of opaque carbon• aceous material. The original detrital outlines of the quartz, plagioclase, and the rock fragments are difficult to distinguish from the matrix, and it is evident that recrystallization of the original matrix and some replacement of the larger par• ticles by the matrix has occurred. It is also probable that before induration occurred, the rock contained up to 15 or even
20$ clay-sized particles; however, compaction forced the clay into thin films around the grains, and subsequent recrystalliz• ation under pressure has formed the present matrix of micaceous mineral flakes, leaving subordinate amounts of clay-sized particles in evidence. It is thought that in many cases alter• ation and subsequent formation of large chlorite flakes around the grains must hide the finer matrix. It is the writer's
opinion that these rocks should be called graywackes despite
the fact that their matrix often contains less than 10$ clay-
sized detrital material.
Lithology of the Fine Fraction
As the rocks become finer-grained they contain a
larger percentage of quartz, and less unstable rock fragments
and minerals. .The sorting is also better as the grain size
decreases and the particles themselves seem to become more
spherical but often less rounded.
The appearance of the siltstones in the hand specimen varies considerably. Some might be mistaken for basic lavas
because of their induration, while others show evidence of
shearing and cleavage in the alignment of folia of sericite
and chlorite. This alignment gives a crude schistosity to the
rock. Under the microscope many of these fine rocks are seen
to be so completely altered and full of carbonaceous matter
that quartz is the only identifiable detrital particle.
Many of the fine, platy rocks which would be called
shale in the outcrop, are seen to be very silty when examined
under a microscope. The clay fraction of these shales appears
as a semi-opaque mass. A large percentage of this is organic matter which is indicative of deposition under non-circulating
or reducing conditions. No pyrite was seen in these rocks.
Some of these with fine bedding plane fissility are hard and 40
apparently highly indurated and might easily be called slate.
Others less fissile would better be described as argillite.
Veins
Although disarrangement of individual units has not been great, the rocks of the Carter Point formation have apparently undergone tremendous stress as evidenced by numerous small scale faults, folds, cleavage, and numerous irregular joints.
Following, and possibly contemporaneous with the deformation, the rocks were invaded by hydrothermal solutions with sub• sequent formation of numerous quartz, calcite, prehnite, and sericite veins. In some instances, calcite is seen to replace the matrix of the graywacke. Much of this calcite may be precipitated from ground waters. Quartz veins are particularly noticeable in the sequence and often give the finer invaded rocks a marblized appearance.
Origin and Conditions of Deposition
McLellan (1927) considered the Leech River group of the
San Juan Islands to be, for the most part, deposited in fresh or brackish water. He thought that at intervals, marine waters invaded the area and deposited the sections of fossiliferous limestone which occur within the group on other islands. The writer helieves that the sequence on Lummi Island, the Carter
Point formation, is typical of flysch fades or of the gray• wacke suites throughout the World and therefore that it is best 41 explained by marine, possibly brackish water deposition in an orogenic environment. The pillow lavas (Reil Harbor volcanics) suggest that this was a eugeosynclinal environment.
The similarities of the Carter Point formation with the typical flysch deposits of the World are numerous and include: the thick, continuous deposition and rhythmic alternation of graywacke and shale; the absence of a carbonate sequence; the occurrence of graded-bedding and associated slump structures; the lack of large-scale cross-bedding; the general appearance of coarse rocks high in the section; the associated pillow lavas (Reil Harbor volcanics); and the absence of faunal re• mains. Even the fe\ir coalified plant remains which are found interbedded with the graywacke are found in many flysch de• posits of marine deposition. These flysch deposits are gener• ally considered to be products of deep water marine deposition in a geosyncline.
In the case of the Carter Point formation the sediments were waste products of high landmasses, in as much as they are texturally and mineralogically very immature. The types of source terranes were dominantly intermediate or basic volcanic rocks but crystalline and metamorphic terranes were also sources. Much of this sediment was rapidly transported to the border of the geosyncline where it formed unstable accumulations and was periodically dislodged by storms, submarine tremors or over inclination. Thrown into suspension in the sea water, the sediments were rapidly transported by turbidity currents 42
down the slope and into deeper water where the fine particles
settled upon the coarser particles. In addition to depositing
sediments, these turbidity currents probably caused minor
erosion and the formation of small-scale cross-beds, and intra-
formational breccias. An irregular bottom surface combined with this erosion effect contributed to the formation of lens•
like bedding in some of the units.
Many of the thin-bedded silts and shales were accum•
ulated slowly in times of relatively calm water. During times
of heavy rain and storms more rapid erosion occurred, and
coarser material was brought to the slope and deposited.
The lack of marine fossils, the highly carbonaceous black
shales and siltstones, and the associated pillow lavas indicate
that the basin of deposition was probably restricted although
probably marine and it was not an area where fauna lived.
Age and Correlation
McLellan (1927) believed that the lower members of the
Leech River group were Mississippian in age and that the upper• most members were of Permian and possibly Triassic age. This was generally based on the occurrence of Fusulina, fragments of
corals, and other larger faunas in the recrystallized lime•
stones of the Leech River group on the north shore of Orcas
Island.
The only fossils which were found in the Carter Point
formation on Lummi Island were small, unidentifiable, coalified 43 plant stems (figure 10). These were found imbedded in medium- grained graywacke in only one locality (see geologic map).
These sedimentary rocks are overlain by pillow lavas and inter• bedded argillites which contain recrystallized radiolarian tests thought to resemble genera common to the Mesozoic.
Locally this sequence of graywacke and shale on Lummi
Island is correlated with the rocks which occur on the western and southernmost projections of Eliza Island. Here are seen rhythmic sequences of graywacke, siltstone and shale similar to those on Lummi Island except that they have been regionally metamorphosed and deformed to a greater degree. Many of the fine-grained graywackes and siltstones have nearly reached the phyllitic grade and show good axial plain cleavage in the outcrop. Since the Reil Harbor volcanics lie between the
Lummi Island and Eliza Island sequences, it might reasonably be assumed that the Reil Harbor volcanics are interbedded in one originally continuous sequence; however, Eliza Island may have been brought to its present position by faulting. The evidence for this is now obscured by the intervening Hale Passage.
Correlation with the Leech River group, on other of the
San Juan Islands, or with the rocks of the type locality of the
Leech River formation on Vancouver Island is uncertain. The type rocks of the Leech River formation contain no fossils and their age is unknown. They are typically composed of phyllite, schist, or very highly indurated graywacke although unmeta- morphosed rocks are assigned to this formation on other parts 44 of Southern Vancouver Island. The rocks of Lummi and Eliza
Islands might be a less metamorphosed equivalent of the Leech
River formation; however, except for the rocks on Samish Is• land and on the mainland to the east, other rocks assigned to the Leech River on the San Juan Islands are of varying ages 2 and of different overall composition. This correlation differs from the earlier correlation of McLellan (1927. p. Ill) who stated that, "the Leech River sediments occurring at the type locality on Southern Vancouver Island are identical in lithology with those found in the San Juan Island map-area."
McLellan (1927) correlated the Leech River group with other series of rocks in the surrounding areas. In the Skagit and Hozomeen ranges of Washington, the upper part of the
Hozomeen series was correlated with the Leech River group.
The Cache Creek series of central and northern British Columbia was considered equivalent to the Paleozoic series of rocks in the San Juan Island area. In its upper members, the Cache
Creek contains limestone, argillite and graywacke sequences similar to those of the Leech River group. The Chilliwack ser• ies cropping out near the 49th parallel in Washington and
British Columbia was also considered to possess the general characteristics of the Leech River group.
To consider the Carter Point formation similar to other
2 Personal communication, W.R. Danner sequences is understandable and easily done; however, to say that it is the same age as these rocks on the basis of general lithologic and textural similarity is dangerous. Graywacke sequences are common in the western Cordillera and may have easily been deposited at different times under similar crustal conditions.
REIL HARBOR VOLCANICS
General
The name, Reil Harbor volcanics, is proposed for a series of sub-marine pillow lavas and interbedded clastic and flow breccias which crop out along the shores of Lummi Island.
These rocks occur in five distinct areas, the largest of which is located adjacent to Reil Harbor on the southeast side of the island and occupies an area of approximately fifty acres.
The rocks here directly overlie the Carter Point formation.
At Sunrise cove two slightly separated outcrops occur, one of which also directly overlies the Carter Point formation. At
Legoe Bay the volcanics crop out and come in contact only with glacial material. Besides the aforementioned outcrops, there is a long outcrop of the volcanics along the shore north of
Lummi Point, and another outcrop at Migley Point which is dir• ectly overlain by the Chuckanut formation. Although the five outcrops are isolated from one another and cannot be proven without doubt to be of the same age, they are all grouped to- 46 gether on the basis of lithology and outcrop features. All of these outcrops with the exception of the one just north of Lummi
Point form conspicuous marine cliffs.
3 Outcrop Features
In contrast to earlier interpretations of McLellan (see p. 70), the Reil Harbor volcanics are observed to occur as a sequence of submarine lava flows and interbedded breccias with tuffaceous sediments rather than as dikes or sills. The pillow lavas which characterize and dominate three of the outcrops are composed of a dark green, aphanitic, sometimes porphyritic rock. The pillows themselves are roughly ellipsoidal (figure
11), and range from a few inches at Legoe Bay to a maximum of four feet at Reil Harbor. As far as determined, the pillows are quite massive although the smaller pillows at Legoe Bay are locally more vesicular than the average. Individual pillows are locally highly sheared and at one outcrop they are outlined by a narrow black zone of fine glassy basalt. This zone was probably formed by rapid chilling of the outer skin of the pillow.
Interbedded with some of the pillow lavas are recry- stallized limestone pods ranging from a few inches to approximate ly three feet in length (figure 12).
3 Table 3 shows a comparison of the outcrop features of the five different outcrops. Figure 10. Carbonized plant stems in specimen of fine-grained graywacke of the Carter Point formation (age unknown) exposed in the south cen• tral part of Lummi Island. Actual size.
Figure 11. Pillow lavas of the Reil Harbor volcanics (age unknown) ex• posed at Sunrise Cove. Taken from the vertical. Dip of pillows is ver• tical and indicates bottom to SW (bottom of photograph) October 1958 Table 2 - Comparison of outcrop features of the Reil Harbor Volcanics
Outcrop Pillow lava Breccias and percent Interbedded Sedimentary Ribbon Chert Jasper Limestone and percent of Outcrop Rocks and percent of and percent of Pods of Outcrop Outcrop Outcrop .i
Reil 95$ None observed 1$ 4$ Harbor -Pillows -Thin beds of argillite -Present in -Occurs -Present poorly at upper contact 10 foot as with ribbon defined -Thin laminae between sequences, veins chert. ribbon chert layers . with pillow- in lava. lavas.
Sunrise 75% 24$ i$ : Cove i -Pillows -Clastic and some -Thin beds of argillite 1 -Trace with rNone -Present quite well flow breccia overlie breccias and 1 sedimentary observed in pillow defined -Frag, are lapelli- some contain recrysta- layers. lava. bomb size. lized Radiolarian -Occur in middle of tests. pillow sequence.
Legoe 50% 40$ 10$ ; Bay -Pillows -Clastic and some -Numerous thin beds ' small and flow breccia. interbedded with -. Occurs only -Plentiful .-None well -Frag, are lapelli- breccia and contain as angular as veins observed defined bomb size. recrystallized blocks in and as -Overlie pillow Radiolarian tests. breccia. inclusions lavas. in breccia.
Lummi 99$ 1$ Point -Pillov/s -None observed -Hone —None .-None poorly -Victric tuff, pro• observed observed observed defined bably not part of pillow lava seque• nce. -Overlies pillow lava.
Migley 60$ 40$ Point -None observed -Pillows -Clastic breccias. -Scattered -Noticeable .-Present in mostly -Frag, are Eapelli to single as veins pillow poorly bomb sized. beds in in lava and lava. defined -Interbedded through• breccia. in breccia. out pillow lava. 49
The ribbon chert which is interbedded with the lavas at Reil Harbor and at Migley Point is also a good indication of submarine extrusion. Generally, these beds are green or black chert and are highly contorted (figure 13). A bedding thickness of three inches for the chert is remarkable per• sistent at Reil Harbor and a thickness of 60 feet of these beds can be measured at this locality. The few specimens examined under the microscope were partially recrystallized and con• tained fine micaceous impurities and some disseminated car• bonate. Chert at other outcrops is limited to small green or black stringers less than a foot long. Ferruginous chert
(jasper) occurs as veins or stringers in the lavas and breccias of Reil Harbor and Migley Point.
The literature on the chert problem is extensive and the amount of chert present in the volcanics does not warrant lengthy description; however, the following observations are offered. In the field the bedded chert appears to be of syn- genetic origin. Since the sections examined were barren of organic remains, the remains were either destroyed by recry- stallization or they were never present and the chert"is a product of non-biological precipitation. Assuming the latter, one possible answer is that the vulcanism supplied the silica and built up the concentration so that flocculation and depos• ition of colloidal silica occurred contemporaneously with the volcanic action. At one locality, a large limestone pod is 50
Figure 13. Contorted ribbon chert in the volcanics (age unknown) at Reil Harbor. View looking northwest. Vv.R.Danner, May 1958. 51 found interbedded with the chert. If, as Correns (1950) points out, conditions necessary for accumulation of precipitated
silica are those at which carbonates are dissolved, it is difficult to explain both the limestone and the chert without a delicate change in the pH ratio. However, Danner (1957) has noted rhythmic precipitation of ribbon chert and limestone in a graywacke-volcanic sequence in the Cascades foothills of
Washington State, and cherts and limestones are observed in the very similar Franciscon formation of California (Tollaferro and Hudson, 1943).
. Description
Pillow Lavas
Due to the extreme alteration of most of the lavas and' the variance between outcrops, a table of representative rock descriptions for each outcrop has been constructed for comparison purposes (table 4).
The freshest specimens examined were from the pillow lavas at Legoe Bay. Here, the rock consists of plagioclase phenocrysts sub-ophitically enclosed by phenocrysts of augite, all included in a felted groundmass of plagioclase microlites.
Many of the feldspars were definitely near pure albite in composition as examined with sodium lamp and immersion methods.
Only a few grains were clean enough to determine the relief without question. It was noted, however, that extinction angles appeared to be below 20 degrees. The clinopyroxene 52
Table 3 - Petrography of the outcrops of the Reil Harbor Volcanics i Locality Veins, Fracture and Rock Type and Mineral Composition Texture j p Specimen Dominant Alteration Vesicle Fillings
i Plagioclase to epidote & sericite Veins: Avg. of Plagioclase (comp. undetermined) -60 Subophitic ; (extreme)3 calcite, chlorite, Altered 5/13/2-2 Clinopyroxene (augite) -25 i and Chlorite * - 5 Clinopyroxene to chlorite quartz, & epidote Andesite- Rei l -10 (low) Quartz veins lined Basalt? Harbo r 5/13/4-1 Semi-opaque groundmass Olivine to chlorite (complete) with actinolite Plagioclase (comp. undetermined) - 1 Extremely fine ; Plagioclase to epidote & sericite Veins: Plagioclase (secondary albite) - 5 grained and ' (moderate) albite, calcite, Keratophyre- 10/24/3- Clinopyroxene -;.'5 glassy ! to albite? and quartz. Spilite? 4 Chlorite -10 Clinopyroxene to chlorite Quartz and albite Calcite -9 Cataclastic < (moderate) veins lined with Cov e Semi-opaque groundmass -70 Calcite & chlorite alt. of ground- actinolite | mass (moderate - extreme) Plagioclase (albite-oligoclase) -30 Plagioclase to epidote & sericite Veins and Vesicle Spilite Clinopyroxene • -50 Bp.hitic (extreme-complete) Fillings: Sunris e /29/1-2 Chlorite -10 4 Clinopyroxene to chlorite rims prehnite, calcite, Semi-opaque groundmass -10 (moderate) chlorite, actinolite and albite Plagioclase (5$ phenocrysts - -67 Plagioclase to epidote & sericite Vesicle Fillings: Avg. of (Albite-An 5 and some Andesine?) Porphyritic- chlorite Spilite 10/25/3 Clinopyroxene (phenocrysts) -15 felted texture. (low) -3 and (Mg - rich Augite) Clinopyroxene to chlorite zeolites 5/6/1-3 Olivine - 1 Subophitic i Orthoclase (phenocrysts) - 3 Quartz - 1
Ba y Magnetite and Semi-opaque groundmass -14
Lego e Plagioclase (comp. undetermined) -50 Porphyritic Plagioclase to epidote & sericite Vesicle Fillings: 5/6/1-4 Clinopyroxene (phenocrysts) -25 (extreme) chlorite Spilite? Chlorite and Semi-opaque Subophitic Pyroxene to chlorite calcite groundmass -25 (low) Calcite replacement (moderate) Plagioclase (5$ phenocrysts) -48 Plagioclase to epidote & sericite Vesicle Fillings: Avg. of (Na Oligoclase - Albite) Microporphyritic. (extreme) chlorite Spilite 10/24/2- Clinopyroxene (Mg-rich augite) -25 Pyroxene to chlorite quartz 1 and Chlorite - 2 Subophitic (low) Magnetite - 5
Lumm i 10/25/1- Poin t 1 Semi-opaque groundmass -20
Plagioclase (comp. undetermined) -50 Plagioclase to epidote, & sericite Veins: 10/25/2- (An 40 -McLellan, 1927) Subophitic and other clay minerals calcite, quartz, 1 Clinopyroxene -20 Clinopyroxene to chlorite and epidote Altered Ande- site-Basalt? Semi-opaque groundmass -30 (moderate) Poin t Migle y
2. 1 Semi-opaque groundmass - composition varies but probably a Albitization has probably occurred in the pillow lavas of Sunrise mixture of secondary iroh oxides, partially devitrified basic Cove, Legoe Bay, and Lummi Point. glass, leucoxene, sphene and clay minerals. 3. Extent of alteration - trace, low, moderate, extreme, and complete, 53 examined by sodium light and immersion methods proved, where determinable, to be augite, very near the endiopside - augite border. Less than 1% olivine is present and possible pseudo- morphs of serpentine after olivine were observed in one thin- section examined from this outcrop. Other minerals, such as magnetite, sphene, and ilmenite, are present in insignificant amounts. The same combination of plagioclase and augite and an aphitic texture is found to characterize the lavas of the other outcrops. One major difference, noticeable in thin- section, is the change in the grain size of the feldspars and pyroxene, in some cases being so fine that the rock was nearly cryptocrystalline. Difficulty in determining the exact com• position of the feldspars was met because of the large number of inclusions and in most cases, the relief of only a few feldspars could be determined. In thin-sections of rocks from
Lummi Point and Sunrise Cove:,., the feldspars appeared to have a relief equal to or less than balsam. At the type locality,
Reil Harbor, and at Migley Point, the feldspars x^ere so com• pletely altered that no determination of relief or composition could be made. It is noteworthy that the feldspars exhibit a poor zoning in many of the thin-sections examined.
The groundmass varies in the specimens from different localities, but it is thought to be generally composed of a semi-opaque mixture of glass-palagonite, chlorite, clay miner• als, sphene, leucoxene, iron oxides and fine particles of feldspar and pyroxene. 54
Amygdules, Veins, and Vugs
Vesicule fillings of chlorite, quartz, calcite, epidote, and zeolites were observed although they are not so numerous as they appear to be in descriptions of pillow lavas by many authors. In the rocks examined, chlorite and calcite were the dominant vesicle filling. Veins of calcite, quartz, chert and
jasper, pennine (chlorite), albite, sericite, actinolite, and prehnite were identified. All combinations were also found of these minerals in the veins; however, the actinolite generally occurs by itself or lines the edges of quartz or albite veins with radiating clusters of green needles. The chlorite is pale to deep green in color, and characteristically shows good aggregate structure in some of the rocks. It should also be noted that the prehnite was only observed in specimens from
Reil Harbor and as rounded inclusions in the breccias at
Sunrise Cove.
Alteration
With the exception of the rocks at Legoe Bay, the rocks are extremely altered. The Tfeldspars have been rendered almost unrecognizable by argillaceous alteration, saussuritization, and by some sericite and chlorite. In some cases the feldspars were completely removed or rendered undistinguishable from the groundmass. Chloritization, and serpentinization of the ground- mass and finer mafic minerals is also considerable, giving a •55 distinct green color to the thin-sections in plain polarized
light. Chlorite typically appears as plates covering a con•
siderable area of the slide and generally shows anomalous inter•
ference colors. Locally, replacement by calcite is important although it is generally restricted to the veins or vesicle
fillings. Silicification also occurs locally although it is not extensive at any locality. Alteration of ilmenite to
leucoxene, argillaceous alteration, and secondary formation of
limonite, hematite, and epidote is indicated in the groundmass although individual grains are distinguished with difficulty.
The albitization previously mentioned has apparently gone on to some extent in most of the lavas and in at least one local•
ity, albite has been disseminated throughout the rock from veins and has crystallized without pseudomorphing the highly altered primary feldspars.
Five characteristics of these rocks are of possible
importance in determining the general conditions and degree of
albitization; they are:
1. The presence of poor zoning in some of the fresher
plagioclase grains.
2. The presence of relatively unaltered pyroxene (figure
14).
3. The unstable assemblage represented.
4. The occurrence of plagioclase with apparent positive
relief and oligoclase or sodic andesine composition.
5. The absence of calcic plagioclase inclusions in albite
or albitized feldspar. 56
It may be suggested from the above points that albit- ization has been slight, in many cases effecting some grains and not others although completely altering the grains attacked.
The lavas generally exhibit the following features which are characteristic of spllitic lavas throughout the world:
1. Basic composition consisting principally of highly
sodic plagioclase.
2. Evidence of hydrothermal activity in the form of
veins and vesicle fillings.
3. The presence of augite.
4. The characteristic pillow lava occurrence.
5. The association of jasper and bedded chert.
6. The low potash content as exhibited by mineral content.
7. The general lack of olivine.
In addition to these points, the ophitic or subophitic texture and the presence of augite as the only significant primary mafic mineral serve to predict the former association with the basaltic rock clan.
Breccias
Extensive sections of breccias of volcanic origin are interbedded with the pillow lavas at Sunrise Cove and Migley
Point, and are found at Legoe Bay overlying the pillow lavas where they form more than $0% of the outcrop (figure 15).
Closely interbedded with these breccias at Sunrise Cove and
Legoe Bay are tuffaceous siltstones and argillites, containing the recrystallized remains of radiolarian tests. Figure 14. Photomicrograph of spilitic lava from the Reil Harbor volcanics (age unknown) cropping out at Legoe Bay. Relatively fresh augite (A) crystals occurring in a groundmass of extremely altered (chloritized) plagioclase (B) laths. Ordinary light, X64,
Figure 15. Breccia of Reil Harbor volcanics (age unknown) exposed Legoe Bay. View SE, October 1958. 58
At Sunrise Cove and at Migley point the size of the
inclusions varies between a few millimeters and six inches.
The general appearance is somewhat deceiving as the inclusions
do not usually weather above the matrix and both matrix and
inclusions are the typical dark green color and aphanitic
texture. With a casual inspection, these might be mistaken
for true flow breccias or even as flows because of the fine nature and homogenous appearance. However, in the thin-sections made, there was revealed a fairly diversified gathering of volcanic rock textures. These inclusions were packed very
tightly in a fine-grained semi-opaque matrix.
One thin-section of a specimen of fine-grained breccia
from 'Sunrise Cove showed recognizable fragments of basalt,
prehnite vein fragments, a large percentage of volcanic rock
fragments containing feldspar phenocrysts, smaller laths of
feldspar enclosed by secondary quartz crystals, water-clear
albite, and sericite. Few pyroxenes were present in any of
the fragments, but there were occasional, deformed, fibrous hornblende crystals. Most of the feldspars of these fragments were extremely altered to epidote, but quite a few were iden•
tified as slightly below balsam in relief, and were probably near albite (An 10) in composition. The fragments and matrix of the rocks are cut by numerous quartz and water-clear albite veins lined with sericite, and also by actual veins of seri•
cite. Vesicules and fractures are also filled with these late minerals. 59
Although original minerals and textures are probably greatly changed, it is likely that late magmatic solutions from overlying flows invaded the partially consolidated breccia.
Some pyroxenes which originally enclosed the feldspars ophit- ically were replaced by quartz and also altered to hornblende.
Soda-bearing liquids were also present and albite was deposited as veins and throughout the rock. Subsequently, much of the calcic andesine or labradorite was albitized, and sericite and localized epidote sheets were probably deposited. Chloriti- zation and formation of epidote from feldspar have probably occurred largely since this hydrothermal invasion.
The inclusions or the fragments of the breccia appear to have been somewhat rounded; however, the general homogeneity of fine glassy matrix and subangularity indicates a fairly rapid deposition.
At Legoe Bay the clastic breccias are coarser, frag• ments varying from three to eighteen inches. These are more obviously considered as clastic breccias at the outcrop rather than flow breccias as often fragments of various colors (red, brown and green) are enclosed in a fine, green and red matrix.
Blocky inclusions of black, dark-green, and red chert (jasper) are noticeably abundant as inclusions along with hematite- stained trap rocks, scorias, and tuffs. These fragments show some rounding or reworking as the fragments did at Sunrise
Cove, and are often tightly packed together. The matrix appears to be fine-grained material composed of rock particles, glass, 60 and fine alteration minerals (epidote, clay and chlorite).
The matrix composes less than 1% of most specimens of the breccia examined. Fine earthy hematite is common in many frag• ments and in the matrix of the breccia.
Specimen 5/22/2-3, taken from the finer breccia at this outcrop (Legoe Bay) was examined in thin-section. It contains numerous scoriaceous rock fragments. These are characterized by faintly outlined feldspar laths in a light- brown, hematite-stained matrix of cryptocrystalline material and partially devitrified basic glass. Amygdules are formed of partially devitrified glass, calcite, and chlorite. A few fragments consist of porphyritic andesite with % andesine crystals larger than 2 mm. These occur in a fine hematitic groundmass of feldspar microlites and glass. One of these fragments were seen to contain nearly 10$ quartz. In general, the particles of this specimen show only slight rounding.
Specimen 5/6/1-6 taken from the same outcrop at another locality contains 75$ rock fragments packed tightly in 2% matrix which is composed of fine felsitic particles, grains of clinopyroxene, and fine micaceous material. Fragments consist of andesite (plagioclase, An 40), dacite, scoraceous and glassy volcanic rocks, vltric and crystal tuff particles, and large, slightly reworked pyroxene crystals. These are all cemented with calcite. The.scoria fragments contain quartz-lined, chlorite-filled vesicles, and a few vesicles containing an aggregate of a mineral resembling talc. Alteration in these last two specimens is moderate in comparison to most of those
at Sunrise Cove.
Specimen 5/6/1-8 was taken from a highly weathered
portion of the breccia sequence at Legoe Bay. It consists of
very fine-grained traprock fragments in a groundmass of even
finer grained aphanitic rock, apparently of the same compos•
ition. This represents a small (six feet thick) section of
flow breccia interbedded with the clastic breccias and sedi• mentary rocks.
The interbedded sedimentary rocks are generally fine,
silty, tuffaceous or argillaceous rocks which weather to a
dull brown color. They occur most generously at Legoe Bay
throughout the breccias, but also occur at Sunrise Cove and
at Reil Harbor. Thin-sections of the argillites at Sunrise
Cove and Legoe Bay reveal innumerable recrystallized radio•
larian tests (Figure 16),
Origin of the Clastic Breccias
The evidence for the origin of the clastic breccia
sequence from this discussion indicates that while pillow
lavas were being extruded at one spot, pyroclastic material
may have been laid down elsewhere. Some of these pyroclastic
and flow rocks were carried to this area where they were de•
posited in water with the lavas and flow breccias. Periods
without volcanic activity were characterized by deposition and
accumulation of clay and silt in water abundant in Radiolaria 62 and probably other protozoans. Evidence is lacking for the mode of transportation of the fragments. Perhaps they are breccia flow deposits or were carried from land and deposited by turbidity currents. Innumerable methods are possible; however, it is only safe to say that transportation was probably not directly by air as some rounding and sorting is indicated.
The Spilite Problem
4/
The origin of the soda. . rich volcanic rocks called spilites has been a problem for geologists for a large number of years and much has been written on this subject. Here it is only possible to give some attention to the problem as it effects the Reil Harbor volcanics.
As the name is used today, a spilite is an extrusive rock characterized by albite or oligoclase feldspars but one that is generally low in silica and has all the other character• istics of a basalt, for example, ophitic texture and augite.
Chemically, it is characterized by a larger than normal amount of sodium oxide.
Without a chemical analysis it is impossible to know exactly how rich the lavas of Lummi Island are in sodarand .; whether they would fit most authors' requirements for a spilite.
It should be noted that most of the rocks show an unstable assemblage, as considerable alteration of the plagioclase to
4 Soda - Na20 epidote has occurred. It would appear that in some of these more altered rocks, the albite may in part be a product of
saussuritlzation or of the removal of calcium from plagioclase
to form epidote with subsequent enrichment of the plagioclase
in soda.:-. Although this process is of some importance in the
production of albite, it would neither explain the albitization
in the rocks of Legoe Bay where the feldspar was relatively
clear of inclusions, nor would it explain or make use of the
occurrence of albite or prehnite veins. Clearly, some of the
rocks are spilitic and suggest that other methods of albitIz•
ation, in addition to residual alteration, have been active.
The first step in explaining these rocks is to decide whether the spilites were derived from a magma of olivine -
basalt or tholeiitic composition, either by differentiation
or contamination of a normal basaltic magma, i.e. primary ^
origin of albite, or by metasomatic introduction of soda into
rocks which first crystallized as "normal" basalts, i.e.
secondary origin of albite.
The following points may lend support to a primary
origin of the albite-oligoclase feldspars in the spilites of
the Reil Harbor pillow lavas:
1. The presence of many, relatively unaltered augite
crystals, enclosing albite crystals.
2. The presence of lateral zoning in a few of the
calcium-deficient feldspars.
3. The lack of partially albitized feldspars or in•
clusions of calcic feldspars in the albitized 64
feldspar crystal.
The following may lend support to the secondary origin
of the feldspars or to the metasomatic theory:
1. The presence of albite in vesicles and as veins in
some of the spilitic rocks.
2. The presence of chlorite, calcite, actinolite, and/
prehnite as veins and vesicle fillings which suggests
redeposition of displaced calcium removed from the
feldspars.
3. The uneven nature of the albitization, with some
feldspars albitized and some apparently not albitized
in the same rock specimen.
4. The general evidence of metasomatic activity itself.
The support of the primary theory given above may be
repudiated fairly easily. The lack of labradorite or andesine
inclusions might well be explained in these rocks by the
tremendous degree of alteration. If there were inclusions or
basic remnants they might well be covered by later alteration
and be indistinguishable. As for the nature of the relatively
fresh feldspars, it may be said that they were left unaltered
in the albitization process. In addition to this, ophitic
textures are always characteristic of calcium plagioclase or
of supposed albitized rocks, and there is as yet no known mechanism by which this texture could be formed from primary
albite or soda rich feldspars. The presence of the zoning, although it is poorly defined, indicates that the degree of albitization varied and was slight in these rocks so that zone outlines were preserved. It is generally regarded that the albite of many and possibly of all spilites is of secondary, i.e. metasomatic, origin (Turner and Verhoogen, 1951).
The following points must be taken into consideration concerning the time of albitization of the volcanics on Lummi
Island:
1. Vesicles and fracture fillings rimmed or entirely
filled with water-clear albite indicate that the
rocks had cooled and crystallized before intro•
duction of the soda liquids.
2. Lack of cross-cutting relations of the albite and
other veins may indicate that most of the veining
went on nearly contemporaneously.
3. The occurrence of keratophyre or quartz keratophyre
fragments in the breccias at Sunrise Cove may
indicate that some of the albitization occurred in
the neck of the volcano prior to the ejection and
deposition of the fragments; however, the evidence
is inconclusive as albite veins cut fragments and
the matrix in this breccia. If the albite vein
represents the source of the albitizing solutions, it
is likely that the albitization occurred after the
breccia was deposited. 66 4r.(2>. The thin-sections of the breccias at Legoe Bay- showed no good indication of any albitization.
Evidence for more than one period of albitization is lacking at any of the outcrops.
The next logical question is: Where did the albitizing solutions come from?
Two main alternative mechanisms have been recognized by most authors. They are:
1. That the spilites are a direct result of the marine
environment and the sodium ions and water necessary
for soda metasomatism may come from the seawater.
2. That chemical alteration of the rocks occurred by
residual fluids derived from the rock's own parent
magma, i.e. autometasomatism. Perhaps as geosynclinal
sinking and vulcanism occurs, crystallization pro•
ceeds, giving rise to sodic, residual solutions
necessary for albitization and related processes (Turner and Verhoogen,195D. It has also been pointed out by Turner and Verhoogen,
(1951) and others that soda might be assimilated into basaltic magma from underlying graywacke or subarkose sequences known to be rich in soda.
Descriptions of the spilitic rocks of the Metchosin volcanics on the Olympic Peninsula (Park, 194-6) indicate that there is some similarity of these rocks with the Reil Harbor volcanics on Lummi Island. Park used the sea water theory Figure 16. Photomicrograph of the Reil Harbor volcanics (age unknown) of tuffaceous argillite containing radiolarian tests (white spots). Note conical tests on right side of photograph and suggestion of minute spines on large test to left. Ordinary light X64.
Figure 17. Photomicrograph of specimen 5/7/6-2A from the tuff sequence over• lying the Reil Harbor volcanics (age unknown) north of Lummi Point. Shows euhedral quartz embayed by glass (A) fresh plagioclase crystal (lower right), and numerous other grains of fresh quartz and feldspar. Crossed nicols, X24. 68 to explain the source of albitization; however, since that
time, this theory has received considerable criticism.
G.C. Amstutz has pointed out in an unpublished manuscript,
three main reasons why this sea water theory is not a good one for the spilites of the Olympic Peninsula. First, the ex• pected gradation of high albite content at the bottom of the sequence to low albite content at the top is not shown. 'Sec• ondly, the rocks are not nearly porous enough for the passage of aqueous solutions and thirdly, that there is not evidence of sea-water deposition, for example gypsum, polyhalites, and halites. Although this criticism may be hasty it serves to illustrate that the problem of albitization is not yet solved in many areas.
Further investigation and more through sampling of the Reil Harbor volcanics on Lummi Island may lead to good
evidence for one of the mechanisms of albitization.
Tuffs
A series of vitric and crystal tuffaceous rocks are
exposed between the Reil Harbor volcanics and the Chuckanut formation on the east coast of Lummi Island just north of
Lummi Point. These tuffs apparently overlie the pillow lavas with no angular unconformity (actual contact slightly sub• merged at low tide). They are deposited as regular beds which
grade within 25 feet with complete angular conformity into arenites of the Chuckanut formation. 69
At extreme low tide, approximately two feet of olive- green, massive, vitric tuff are exposed. Irregular, slightly devitrified glass shards make up more than. 75% of the rock as seen in the thin-section and these shards are held in a glassy, semi-opaque groundmass of fine micaceous material and de• vitrified glass.
Lying upon the vitric tuff are medium bedded, bluish highly silicified, crystal tuffs. Thin-section 5/7/6-3 is typical of these tuffs. It contains 25% clear, subangular quartz, 6% subrounded felsitic fragments, and 1% of fractured plagioclase fragments in a cloudy matrix of silicified, fel• sitic material, glass, iron oxide, and clay. Both this section, and sections of the vitric tuff show cataclastic textures.
Quartz appears fractured and smaller grains show undulatory extinction.
Circulating ground water rich in silica derived from the underling vitric tuff layers have highly silicified this crystal tuff. Some argillaceous alteration has also occurred in the groundmass; however, the rock in thin-section appears unusually fresh compared to the Reil Harbor volcanics. Carls• bad twinned plagioclase crystals appear completely unaltered
(Figure 17).
Specimen 5/7/6-2A was taken from coarse, buff-sand• stone beds lying conformably on the crystal tuff referred to above and was at first when seen in the field believed to be the true arenite of the Chuckanut formation. The thin-section 70 reveals 40$ quartz crystals, 1% andesine (An 30-An 42), and
15$ rock fragments in a matrix composed of partially devitri- fied, weakly birefringent, glass shards. The fresh euhedral quartz, in part deeply embayed by glass, dominates the rock.
The andesine which appears to vary somewhat in composition, is untwinned or only faintly twinned (albite law) but shows ex• ceptionally clear concentric zoning. The rock fragments con• sist of rounded basalt, andesites, devitrified glass, and microfelsitic particles, and occasional fragments of low-grade metamorphic rocks. Except for the glass, which is turbid, barely birefringent and has in some cases formed sphereolites, the rock is extremely fresh appearing. No indication of a depositional environment is indicated, but it may well have been laid down almost directly by explosive volcanic action.
Previous Geological Work
The rocks, here called the Reil Harbor volcanics, were considered by McLellan (1927) to be part of a large series of aphanitic igneous rocks which crop out over much of the San
Juan Island map area. McLellan named these the Eagle Cliff porphyrite. The bodies themselves, he said, occurred as dikes and sills on the basis of exposures on cypress Island, San
Juan Island, and on other of the San Juan Islands. On Cypress
Island he observed "porphyrites" cutting Leech River slates
(probably correlative with the Carter Point formation), and serpentinized dunites of the Fidalgo formation. McLellan ad- mitted that the ellipsoidal nature and the texture of the rocks would ordinarily indicate that they were flow rocks but be• lieved that they were feeders to former flow rocks and thought that they represented the uppermost portions of the dikes.
Except on Orcas Island, these porphyrites were described petrographically as resembling basalts and basic andesites.
On Orcas Island, where they are intruded by rocks of the Turtle- back complex, alteration is considerable. Albitization has taken place with the typical associated alteration suite sim• ilar to that now recognized at Legoe Bay or Sunrise Cove on
Lummi Island. The porphyrites belong, McLellan said, to the more acid type of basalt porphyrite and in places they were thought to grade into diorites or andesite porphyrites. Al• though his examination of the Eagle Cliff Porphyrites on Lummi
Island must have been very rapid, he did examine in detail the outcrop at Migley Point. He described the rock here as having a semi-andesitic texture with a relatively large per• centage of acid or intermediate andesine. As pointed out pre• viously in this report, the specimens of pillow lava collected here by the writer were so altered that feldspar determination could not be made accurately and so these rocks may well be andesitic rather than spilitic as most of the rocks are.
McLellan made no mention of the abundant breccias at Migley
Point in his report. Age Relations
McLellan (1927) assigned the Eagle Cliff Porphyrites
(and therefore the Reil Harbor volcanics) to the late Triassic or early Juriassic period. As noted previously, the Eagle
Cliff porphyrites cut rocks of the Fidalgo formation whichin turn intrude the supposed upper Paleozoic to Mesozoic Leech
River group; however, the Eagle Cliff porphyrite is intruded by off-shoots from the late Jurassic batholith included in the
Turtleback complex by McLellan on Orcas and Blakely islands.
McLellan first supposed that the porphyrites belonged to the
Metchosin volcanics of Eocene age but he noted the contact at
Migley Point where the Chuckanut formation (Paleocene) lies on the eroded surface of the porphyrites. He believed that they were related to the Vancouver volcanics (Vancouver group).
In the past description and discussion, the rocks of the five isolated outcrops of volcanics have been considered together and have been called the Reil Harbor volcanics.
Although the lithology and the outcrop features of the rocks of these outcrops are very similar, it is impossible to prove that the rocks of all five outcrops are of the same age and stratigraphic position. There is some indication that the southern half of Lummi Island is separated from the northern half by a large fault cutting across the island near Sunrise
Cove (see p.126). If this fault is present, there is a possibility that the volcanics at Reil Harbor and possibly of 73 those at Sunrise Cove are not correlative with the volcanic rocks of the other three outcrops to the north on Lummi Island.
The actual lower contact of the volcanics at Reil Harbor, is partially obscured; however, it appears that the pillow lavas here lie upon the Carter Point formation without noticeable angular unconformity. The lower contact of the volcanics at
Sunrise Cove is also obscured but the strike of chert and sedi• mentary rocks in the breccias correspond to those in the adja• cent graywacke and shale of the Carter Point formation. The dips of the outcrops at Reil Harbor and at Sunrise Cove are somewhat steeper than those of the closest outcrop of the
Carter Point formation which may imply that there was some faulting between formation or slight unconformity. The upper contact of the volcanics at Migley Point with the Chuckanut formation shows no significant angular unconformity. The pillows of the lavas here are poor in directional character• istics; however, ribbon chert sequences in the volcanics show dips and strikes very close to those in the Chuckanut for• mation at the contact.
If the tuffaceous sequence north of Lummi Point was considered as part of the Reil Harbor volcanics sequence or of the same age as the volcanics at Lummi Point, it could be said that angular conformity between the overlying Chuckanut formation and the Reil Harbor volcanics was certain. However, the extremely fresh appearance of the vitric and crystal tuffs tiere, and their dissimilarity with other rocks on Lummi Island leads one to believe that they are quite a bit younger than the underlying pillow lavas and may even represent subaerial deposition and volcanic action in the Cretaceous or early
Paleocene just prior to the deposition of the Chuckanut for• mation. The contact between the tuffs and the pillow lavas is submerged here, but the pillows of the Reil Harbor volcanics nearby appear to strike conformably below the Chuckanut and conformable tuffs.
The recrystallized radiolarian tests in the tuffaceous siltstones and argillites of the volcanics (figure 16) were examined by Dr. W.R. Danner. The only information he could give is that there were quite a few cone-shaped tests which are characteristic of some Mesozoic genera.
The evidence presented indicates that the volcanics on
Lummi Island were deposited as flows and breccias on the sea floor, and probably, while pillow lavas were being extruded at one location, limestone was precipitated or breccia deposits were accumulating elsewhere. Some of the volcanics were subsequently albitized and all were highly chloritized and epidotized.
Whether all of the volcanics here or possibly only the volcanics of the southern or of the northern outcrops were brought to the surface by the Eagle Cliff porphyrite dikes
(McLellan, 1927), and should be included with this formation is another question which may possibly be answered by further detailed mapping in the San Juan Island group. Structural re- lations and radiolarian tests on Lummi Island indicate that the rocks are probably Mesozoic in age.
CHUCKANUT FORMATION
General
Arkosic, plant-bearing sandstones and conglomerates of the Chuckanut formation form most of the bedrock of the northern third of Lummi Island. The best exposures are found along the shores, but poor, partially drift-free exposures, dominantly of conglomerate, form the high knolls and ridges of the interior. These rocks are believed to be continental fluviatile origin.
Previous Work
Rocks of this formation, exposed in parts of western
Whatcom and Skagit counties, were first described by White
(1888) as part of the Puget Group of the Eocene of western
Washington. Later work was done by Shedd (1902), Jenkins
(1923), McLellan (1927) Glover (1935), and Weaver (1937).
At the present time geologists and paleobotanists at Western
Washington College of Education in Bellingham are studying the floral assemblage and stratigraphy of the Chuckanut formation.
McLellan (1927) first described these rocks as they 76 occur on Lummi Island and found that their lithology and plant
fossils were identical with those of White's Puget Group which was well exposed along the Chuckanut Drive on the Pacific
Highway. McLellan called them the ehuckanut formation, and subsequent writers have done the same.
Glover (1935) and Weaver (1937) measured stratigraphic sections of this formation along Chuckanut Drive, on the shore of Samish Bay, and along the west side of Lake Whatcom between
South Bay and Lake Louise. Weaver (1937, p. 79) described the 11,272 foot section along Chuckanut drive as the most complete with: "the lower portion of predominantly sandstone containing shaly intercalcations followed above by massive coarse-grained sandstone. About 30$ of the thickness upward from the base consists of sandy shale containing fossil leaves and a considerable quantity of carbonaceous shale. The middle portion is characterized by alternations of medium- and massive grained sandstone with intercalations of subordinate amounts of grayish-brown shale. The upper part contains a thick lens of conglomerate alternating with sandstone." Included in this sequence are thin but economically important beds of coal which are most common in the upper part of the section.
In the area around Bellingham, excluding Lummi Island, the rocks of the Chuckanut formation rest unconformably on pre-Cretaceous, graphitic schists and phyllites. 77
General Stratigraphy - Lummi Island
On Lummi Island the Chuckanut formation disconformably
overlies pillows lavas and breccias of the Reil Harbor vol•
canics, and at one point on the east side of the island, the
sandstones appear to be separated from these volcanics by 30
to 40 feet of volcanic tuffs of uncertain correlation. The
first mentioned relationship is well-exposed at Migley Point
where the Chuckanut formation is seen to lie without noticeable
angular unconformity on the eroded surface of the volcanics
(figure 18). Figure 19 illustrates the short stratigraphic
section measured at this contact seen at the high tide mark.
Although 25 feet of basal conglomerate is represented in
Figure 19. the contact can be traced seaward at low tide where
the conglomerate is observed to lens out, leaving arkosic
sandstone immediately overlying the eroded surface of the Reil
Harbor volcanics. Contrary to what might be expected, very
few pebbles of these volcanics could be identified in the
quartz and chert pebble conglomerate at the base. This would
suggest that the basal section was deposited under relatively
stable conditions and that it was deposited fairly slowly.
The residual volcanic pebbles or cobbles were ground to fine material while deposition was going on, and were relatively
unstable compared to the quartz and chert.
Approximately equal amounts of pebble conglomerate and
sandstone of the Chuckanut formation are found on Lummi Island. Figure 18. View looking SE at Migley Point showing conglomerate of the Chuckanut formation (Lower Tertiary) lying upon the eroded surface of pillow lavas of the Reil Harbor volcanics. Strike and dip of the Chuckanut formation here is N 50 V/ 55SW. The strike and dip of the underlying volcanics appears to be within a few degrees of these values. May 1958 79
10o Sandstone, arkosic, buff; coarse to medium grained.
67 EH 66 9. Sandstone, arkosic, pebbly; subrounded chert pebbles.
8. Sandstone, arkosic, rusty; few pebbles.
7o Sandstone, arkosic, pebbly, gray-buff; calcite cement,
60 Sandstone, arkosic, pebbly; pebbles less than £in.
5o Sandstone, arkosic, grading to pebble conglomerate. 4o Sandstone, arkosic, gray-buff; streaked with 2 biotite. o 3o Sandstone, arkosic, pebbly, buff; pebbles £in. in 39 H 36 < diameter and well rounded.
0- 0
Co o o 2. Sandstone, arkosic, gfayljfcp buff; contains thin
< 25 o e o o o O 3 X O O o o o O O © * 0 |o o O © ° 1. Conglomerater pebble, loosely packed, massive; [ O© o aO ©* * • medium grained sandstone matrix, pebbles well O © • O rounded, dominatly of chert, jasper, and quartz; k •> © o e o break in conglomerate where there is a thin lens of gray siltstone with thin chips of gray shale.
O O o OO o * °
o o O O o
o e o o O © « O A o O O O
A o # *» 0 o> o e d 0 RE IL HARBOR Ok" <7 A 1/VAyVV V OLCAWGS
Figure 19o Short stratigraphic section of the Chuckanut formation at its base on Lummi Island,, Characteristically, the conglomerate forms the resistant layers (figure 20). Neither the beds of conglomerate nor the beds of sandstone can be traced over any distance before they lens out or grade into distinctly coarser or finer litho- facies. Here, the Chuckanut formation also displays an apparent large-scale heterogeneity as it is not uncommon to find the coarse conglomerate in contact with fine sandstone in cut- and fill-structures, cross-bedding, and other types of contact structures. Bedding thickness is also highly variable the average layer being nearly three feet thick.
LITHOLOGY
Conglomerate
Conglomerate units of the Chuckanut formation form almost half of the outcrop of the formation on Lummi Island.
They form most of the hills on the north end of the island and in outcrops along the shore, they occur as resistant lenses and beds of varying width.
The conglomerate is generally massive and some of the units are greater than thirty feet in thickness. The overall color is a rusty brown although the pebbles themselves vary from red to black to white. It is dominantly a pebble con• glomerate; however, the particles vary from large cobbles to granules. The pebbles are subrounded to wellrounded and approach an equidimensional shape. Imbrication is poorly developed and is unreliable as a directional criterion. 81
Rough pebble counts were made in the field, and random collections of pebbles were examined under a binocular micro• scope. An estimate of the relative amounts of each pebble type in the conglomerate at Fern Point shows:
Chert, Quartzite, and Jasper 43$ Volcanics 23$ Granitic rocks and Gneisses 19$ Quartz 5$ Arkose 5$ Graywacke and Siltstone 3$ Argillite, Slate and Phyllite 2$
The compositions or particle types represented vary somewhat between units, but the above percentages would seem to approach the approximate composition of the comglomerates cropping out on Lummi Island.
The black or green chert and the granitic particles form many of the larger pebbles. Pebbles of jasper are abundant locally, as for example at the basal contact at Migley
Point. The volcanics, which are generally quite highly altered, are dark green to grey in color, and appear to be dominantly of andesitic or dacitic composition. One specimen i of conglomerate examined in thin-section-revealed particles of dacites, andesites, and quartz latites. All of these par- tides are highly sericitized or chloritized. A number of particles have been replaced so that the secondary chlorite amounts to greater than 40$ of the particle. Many of the granitic types appear to contain much quartz, and those few examined In thin-section were quartz diorites, quartz monzon- 82 ites, and diorites. Although the number of actual quartz pebbles is not excessive in the conglomerate, most of the other pebbles contain quartz-vein material to a great extent, and the finer conglomerate sizes also show increasing amounts of quartz. Thin-section examination revealed that some of the quartz pebbles are derived from veins, and many show the interlocking boundaries of quartzite. The finer fraction also contains more arkosic sandstone and graywacke particles. Low- grade metamorphic rocks do not appear to be numerous in the outcrops examined. A few pebbles of serpentine were seen in thin-section.
The conglomerate varies from a very dilute, sandy stage to a concentration of about 70$ pebbles and 30$ sand.
The matrix is similar to the finer grained rocks of the
Chuckanut formation. The conglomerates often appear to be well-cemented with calcite, and many of the fractured pebbles are laced with veins of calcite. Occasional traces of autho- genic silica are observed in the matrix. In one-thin-section examined the matrix and pebbles of the conglomerate appeared to be floating in a coarsely crystalline calcite cement, and it is assumed that the cement was precipitated prior to deep burial or compaction.
Sandstone
The finer facies of the Chuckanut formation on Lummi
Island consist of sandstone and siltstone. No shale facies of this formation crops out on Lummi Island. Although there are olive-gray siltstone units here, they are not numerous.
In general, the sandstone is of medium grade, with grains between } 50mm and .25 mm in diameter, and is a rusty brown to grey color. According to the standard rock color chart
(Geological Society of America), the color ranges from dusky yellow (5y6/4) to light olive-gray (5y5/2).
A size analysis of a typical sandstone was made using
U.S. Standard screens #20 through #270, and a cumulative frequency curve was plotted (figure 21). According to Trask
(1932), a coefficient of sorting (So) of less than 2.5 in• dicates a well-sorted sediment. This value appeared to be high as noted by Pettijohn (1949), and also according to
Krunbein and Tisdel (1940, after Leroy 1955) who gave 1.45 as the average. In the sample considered here the figure was
1.36 which indicates that it is certainly moderately well- sorted. A skewness of 0.B6 indicates that coarser sizes pre• dominate in the sample plotted. The sandstones are true arenites according to Williams, Turner, and Gilbert (1955) as they are clean and contain no significant detrital clay-sized matrix. The average particle appears to be subangular shaped, although the chert and rock fragments present are generally more rounded, and the quartz is often more angular than the average. Numerically, the sphericity averages 0.4-0.6 (Petti-
John, 1949).
A number of typical hand specimens and nine represen• tative thin-sections were examined. Although there is con- DIAMETER IN MM
Median — 53
First Quartile- - - - 67
Third Quartile - - —.36
Sorting Coefficient 1.36 Skewness .86
Figure 21. Cumulative - frequency curve of a typical specimen of sand• stone of the Chuckanut formation on Lummi Island,
Tor MDj IQI siderable variation in composition (figure 22), the average specimen contains quartz, quartzite, chert, plagioclase- and potassium-feldspar, volcanic rock fragments, low-grade meta- morphic rock fragments such as argillite, slate, phyllite, and low-grade schists. Granitic rock fragments and occasional particles of siltstone were also present (figure 23).
Many of the quartz particles appear to be chips pro• duced by crushing as they are quite angular and often wedge- shaped. Many quartz grains also show the beginnings of cataclastic breakdown. Undulatory extinction is pronounced in some quartz grains, and the effect of stress is seen in many particles where rows of secondary fluid pores transversed the grains. These effects were apparently produced in the parent rock before its erosion and deposition in its present setting.
Much of the quartz occurs in aggregates with interlocking grain boundaries, and is apparently of vein origin in some cases, and is of metamorphic origin in other cases. Secondary overgrowths of quartz were present but not common. Much of the quartz seen under the binocular microscope was of the clear, transparent variety.
The chert particles present are generally coarser and often better rounded than the rest of the grains in a given specimen. Many are cut by secondary quartz veins and also appear to be partially recrystallized. In at least one speci• men, chalcedony or chert has been precipitated as a cement to a small extent. 36
QUARTZ QUARTZITE CHERT
FELDSPAR ROCK FRAGMENTS MICA
Figure 22. Mineral composition, Chuckanut formation, sandstone. «7
Figure 23. Petrography of representative samples of the Chuckanut formation, sandstone. Slides of the sandstone particles were made and etched with hydrofluoric acid, and then were stained with sodium cobaltinitrite. The plagioclase was seen to outnumber the potassium-feldspar particles in a ratio of three to one in the sections studied. The potassium-feldspar types present are mainly orthoclase with only minor amounts of microcline. The composition of the plagioclase is generally andesine, but oligoclase and some rare albite was also determined. Carlsbad, albite, and pericline twinning are seen in the plagioclase, but it is noted that sometimes as much as one third of the plagioclase is untwinned or only partially twinned, suggesting a possible metamorphic origin. Wormy intergrowths of quartz in the orthoclase and a few particles of replacement-perthite are noted in a number of slides. Being bent and also fractured in many instances, the feldspars and the quartz often show signs of predepositional stress. As a rule, the feldspars show high hydrothermal alteration, being sericitized and saussuritized to such an extent that the individual grains are often difficult to identify as feldspar. Argillaceous alter• ation and decomposition is not common although it was evidenced to the writer by the cloudy nature of some of the feldspar grains.
Often the most common identifiable particles after quartz, chert, and the feldspars are the volcanic-greenstone particles. In almost every case they are highly altered to chlorite, and in some cases more than half of the particle is 89 covered with a single chlorite flake. Generally, the particles are so fine grained and cloudy that determination of rock type is difficult, but those determined by the writer were andesitic.
In some of the slides studied, rounded and elongated particles of slate and phyllite were common. Most of them appeared to be of the pelitic type with muscovite, chlorite, quartz, and in every case, with dusty, opaque graphite or iron flakes. In addition to the slate and phyllite fragments, there are often particles of low-grade schists, probably of the greenschist facies. Minerals shown in these schists are mica, chlorite, calcite, epidote, graphite, feldspar, and quartz. Chlorite pokiolitically enclosing graphite flakes is common. It is likely that some of the particles observed with intergrown feldspar and quartz are of metamorphic origin also.
Particles of granitic and dioritic rocks are not too common but were observed to be present in some of the specimens studied in good quantity. Myrmekite with clear quartz and feldspar was found as a particle in three or four of the sections studied, possibly indicating either a granitic parent rock or a metamorphic rock of high rank.
A number of siltstone particles were also observed but these were not abundant in any of the specimens studied.
In specific units, one of the most important constit• uents of the sandstone are long biotite flakes, often laid out in layers 10 to 20 mm apart, parallel to the bedding. Mus• covite is also present but not nearly so numerous as the biotite. In one locality on the east side of the island,
biotite forms a lens of *jr inch width and 3 feet long. The
adjacent sandstone contains about 13$ biotite.
The particles mentioned above constitute most of the
sandstone. Other minerals such as hornblende, augite, olivine
serpentine, epidote, and microperthite, are present in only
very minor amounts. A magnetic separation, made of several
disintegrated sandstone specimens, revealed in the coarser
sandstone the presence of some transparent pink garnets,
negligible amounts of magnetite, and some limonite. The most
important particles observed in this separation were numerous
rock and mineral grains coated with red hematite, a white
precipitate containing specular hematite flakes, and some
particles composed wholly of earthy hematite.
Diagenesis
The packing and cementation varies between different
units in the sandstones. Many units show a large amount of
compaction with sheared feldspars, quartz, and wavy biotite.
Noted in these tightly packed sandstones was some secondary
overgrowth of quartz, and, to some extent, the apparent occurr
ence of pressure solution at grain contacts in the quartz and
feldspar grains. In other units, the sandstones are extremely
friable with no or negligible cement and little compaction,
resulting in a highly porous and permeable sandstone.
Approximately one quarter of the sandstones and almost all the conglomerates on Lummi Island are quite well-cemented with finely granular calcite. Some sandstones are tightly packed, and in one section, the calcite was seen to have appar• ently wedged its way between thin, wavy biotite sheets. Cal• cite cementation seems to be most common in those areas where biotite or fossil plant material is abundant. Where the sand• stones are very firmly cemented with calcite, the calcite appears to be replacing all of the mineral and rock particles, including quartz which is being replaced along fractures and along the lines of fluid pores.
Sedimentary Structures
Cross-bedding
Cross-bedding is the most obvious internal structure of the Chuckanut formation on Lummi Island. Time did not permit proper statistical determinations as to the scale and inclin- ational-directional variability; however, cross-bedded units appear to vary between one and three feet in thickness. The cross-bedding planes themselves are often well-outlined by biotite-rich layers, by claystone inclusions, or often by thin pebble layers. Rough measurements of the direction of dip showed an apparent extreme variability as dips appeared to change direction several times within a 25 foot long unit.
It is likely that these cross-beds on Lummi Island indicate an unstable current system but the dominant dip is not known.
Figure 24 shows a typical cross-bedded sandstone unit Figure 20. View of the Chuckanut for• mation (lowar Tertiary) exposed at Fern Point showing more resistant beds of conglomerate, and less re• sistant sandstone dipping steeply northeast. View looking SE, . May 1958. 93 on Lummi Island. These beds were often useful in identifying
"tops" in near-vertical beds.
Graded Bedding
Graded bedding is shown in many of the coarser units of the Chuckanut formation on Lummi Island, and is often found in some of the thicker units in which cross-bedding is found.
Generally, the best graded bedding here is shown by units of dilute, sandy conglomerate grading upward to a better sorted, finer conglomerate or to a moderately sorted sandstone.
Pettijohn (1957) points out that graded bedding and current bedding are earmarks of a deep and shallow water sedimentation facies, respectively. If graded bedding does occur with cross-bedding as it does here, it would be normal to expect a grading where the mean size of the particle would decrease up• ward but the sorting would remain constant. This latter type is typical of deposition by waning currents rather than by turbidity currents (PettiJohn, 1957).
Concretions
Differential weathering due to differential resistance by calcite-cemented concretions has produced the spine-like pattern illustrated in Figure 25. Concretions such as these are found throughout the sandstone, and are formed by differ• ential cementation of calcite around carbonaceous detritus.
The bedding is seen to pass straight through some of these Figure 24. View N. showing cross-bedded sandstone of the Chuckanut formation (Lower Tertiary). Fern Point, October 1958.
Figure 25. View SW of spine-like pattern in sandstone of the Chuckanut for• mation produced by resistant calcite concretions. NE side of Lummi Island, 1/2 mile south of Migley Point, May 1958. concretions, thus indicating a post-depositional origin; others are structureless.
Intraformational Breccias
Near the lower contacts of a number of the coarser
sandstone or pebble conglomerate beds are found narrow breccia zones. These consist of thick, lensoid masses of a bluish
silty shale in a coarse matrix of sandstone or conglomerate.
In most cases there is no trace of a shale or similar silt•
stone layer beneath; and it is believed that during periods of
slow stream transportation or damming and lake formation,
clay was deposited. Later, with increased volume or steepen•
ing of the stream gradient, these clays were broken up and
swept away. The more sturdy, plastic pieces of clay remained
and formed the breccia.
Mud Balls
On the east side of Lummi Island, channel structures,
cut- and fill-structures, and large spherical masses of grey
silty shale occur in the coarse sandstone beds. These masses,
some of which are two feet in diameter, are weathering spher•
ically or exfoliating. They are believed to be "mud balls"
(Twenhofel, 1950, p. 593). Here, they are thought to be formed
from wet mud which was dislodged from a cliff and rolled into
a stream channel to be incorporated subsequently with the
stream sediments. At first, the center of the mud ball was impervious to water but, later, water entered after lithi- fication, and expanded, compelling cracking of the outside layers into spherical chips.
Carbonaceous Deposits of Lummi Island
Two very small carbonaceous deposits worthy of differ• entiation and description occur in the Chuckanut formation on
Lummi Island. The first deposit consists of well-rounded coal particles found in a black micaceous lens (figure 26) on the northeast side of the island. The second deposit comprises coalified leaves and woody debris found in great abundance in the sandstones at Fern Point. The latter appear as though they had been predominantly coalified after deposition in this lo• cation.
The black, disc-shaped lenses containing the rounded coal fragments of the first category are one inch thick and approximately two feet in diameter. In addition to the coal, they are composed of: over 65% biotite; lesser but equal amounts of quartz, chert, and sodic plagioclase with minor microcline; quartzite; volcanic and metamorphic rock frag• ments (figure 27). The surrounding cross-bedded sandstone, a feldspathic arenite (Williams, Turner, Gilbert, 1955) con• tains a few scattered particles of coal.
Examined in detail, the coal particles appear to be approximately semibituminous to subanthracite in rank. Some large < cellular particules examined in thin-section resembled Figure 26. Hand specimen of black mi• caceous sandstone lens found in the Chuckanut formation (Lower Tertiary) on the NE side of Lummi Island. Con• tains small particles of coal.
Figure 27. Photomicrograph of the mi• caceous sandstone shown above (fig• ure 25). Coal fragment (A) surr• ounded by wavy flakes of biotite (B) and feldspar (C). Ordinary light, X24. 98 opaque attritus, but several thin spots revealed the uniform red-brown of typical coalified wood, anthrazylon. Other frag• ments were of opaque attritus, consisting of pyrite and fussain, and translucent attritus with leaf fragments, wood, some cuticle tissue, and at least one pollen grain.
There are two possible explanations for the formation of this deposit. First, the fragments could have been derived from the erosion of former coal deposits and redeposited here.
By the second method, plant remains dropped into the water with mica were later metamorphosed to coalify the plant fragments.
The second method is the more probable answer since the coal particles are so friable that even short transportation is un• likely, and also, since most of the other woody material was apparently coalified in place. Probably woody fragments and biotite were carried from a nearby source to a quiet, shallow river pool where the two settled to the bottom and were rapidly buried. As evidenced by the weaving of the biotite around the sand grains, subsequent compaction with deep burial and metamorphism produced this coaly lens as found today.
The more obvious coalified fragments (second category) are found dominantly on Fern Point where they are interbedded with the sandstones and conglomerates. Here are found: numerous small lenses of shiny coal, probably actual coali• fied leaves lying parallel to the bedding; coalified pieces of wood (figure 29) some still showing tree ring structure when
cross-sectioned; a few whole coalified logs, often filled with 99
Figure 28. Coalified wood fragment interbedded with sandstone of the Chuckanut formation (Lower Tertiary), at Fern Point. The fragment is surrounded by a narrow shell of very limy sandstone (white). May, 1958.
Figure 29. Irregular mass of coalified vegetal material with radiating strin• gers, occurring in sandstone of the Chuckanut formation (Lower Tertiary). Fern Point, October 1958. 100
limy siltstone or clay; and also, shapeless masses of coalified vegetal material sending out stringers for three or four feet
in every direction (figure 29). Much of the coalified wood is apparently banded with alternating shiny bands (vitrain) and dull bands (durain). Most of this banding or stratification appears to be intrinsic, and probably iias resulted from differential coalification of annual rings or woodrays. One specimen examined was reported on as follows:'^ "The petrological types represented are
anthraxylon and translucent attritus, approximately 50-50. However, the attritus appears to be a degradation product of woody cells lying between anthraxylon lenses." It is possible that some of the logs had been acted on by bacteria and coal• ified slightly before finally coming to rest in their present setting. Microscopic examination of a few specimens showing flattened tree rings and a general woody make-up revealed opaque strands of coalified material (figure 30). These strands appear to represent intruded humic materials and are not intrinsic in the wood. They probably resulted from infil• tration of and subsequent solidification of organic solutions with fissures and cracks of the wood. All of the coal when tested with cold HCL effervesced to some extent, and one hard specimen observed in thin-section
5 Personal communication, Dr. G.E. Rouse. 101 showed a compressed cell structure in which each cell was filled with finely crystalline calcite. The presence of lime solutions in and around the coal after its deposition appar• ently was general as concretion-like, calcite-cemented knobs of sand and siltstone hold fragments of coalified matter, and many stretched-out, coalified wood fragments are surrounded by calcite-cemented sandstone or limy siltstone (figure 28). The rank of all of this coalified matter appears to be sub-subituminous on the basis of hand specimen character• istics. No evidence of animal or plant microfossils was found with which to date the wood, but examination of sections of one specimen revealed structures, indicating a fairly close relationship to the modern conifer genera Pinus, Larix, or Picea. Because sufficient detail is not present for affiliating the coalified wood to any of these modern genera, it would be more accurate to affiliate the wood taxonomically with either the fossil genera Piceoxylon Gothan or Pithyoxylon Kraus. Most of the wood material was probably deposited inv.a river and carried to this area. As decaying leaves and wood became waterlogged and soft, they sank to the bottom where they were interbedded with sands and gravels or rolled about collecting much coarse sand and then were covered over. One exception to this general case occurs at Fern Point where a coalified log lies at a high angle to the obvious stratifi• cation of the sandstone, (figure 31). The undisturbed nature Figure 30. Photomicrograph of a tangen• tial section from a specimen of coal• ified wood from the Chuckanut for• mation (Lower Tertiary), showing opaque strands of coalified material (A), lenticular wood ray cells (B) and a general compressed cell stru• cture. Specimen from Fern Point. Ordinary light, X64. 103
of the adjacent bedding indicates that the log was apparently-
stuck almost upright in the silt while medium to coarse sand
and some silt layers were waterlain around it. Since the
vertical thickness crossed by the coalified log is nearly six
feet, there is good evidence that deposition in this area was
relatively rapid in order to preserve this log in the sediment.
Upon burial of the wood, coalification processes were probably
intensified with the vertical pressure of the overburden and
the compression of the relatively tight folding. Soft logs
and loose watery material were squeezed out into lenticular
shapes and stringers, and even the sturdy logs were flattened
and stretched. Either at this time or contemporaneously with
deposition, the cellulose was replaced by calcite in many
cases, and concretions were formed.
Coal, in fragments, thin layers, and lenses, is
distributed irregularly throughout the whole thickness of the
Chuckanut formation in western Washington (Glover, 1935).
Beds of considerable thickness, some of which have been of
commercial importance, occur at several places in the series,
but dominantly in the upper part. One of the more important
commercial beds is 14 feet thick, and is in the syncline
underlying the city of Bellingham.
However, all of the coal deposits on Lummi Island are
very small, as mentioned before, and are of no economic im•
portance as sources of coal. Local residents tell of a pros•
pect pit that was dug inshore from these coalified logs in
hopes of finding an economic .source, but no coal was found. Figure 31. View NE, showing a coalif• ied log (A) cutting across beds of the Chuckanut formation (Lower Tertiary) which strike NW (lov/er left to upper right) and dip steeply NE. Fern Point, October, 1958.
»
Figure 32. View SW showing glacial grooves and polished surfaces in the Reil Harbor volcanics (age unknown) at Legoe Bay. Small, shallow grooves in foreground and larger grooves in background. Glacier moved SW (left to right). October 1958. 105
Origin and Conditions of Deposition
Evidence from the Chuckanut formation on Lummi Island
indicates that the formation is continental in origin, and
that it was deposited by swiftly-moving streams moving toward
the southwest. The following evidence is tabulated in support
of a continental and fluviatile origin:
1. The absence of marine fossils and the abundance of
plant remains.
2. The large amount of hematite imbedded in the sandstone
and conglomerate.
3. The apparent large-scale heterogeneity; for example,
the conglomerate lenses in contact with fine sand•
stone in cut- and fill-structures.
4. The presence of large-scale cross-bedding.
5. The moderate sorting but rapid deposition evidenced
in some locations.
6. The presence of dominant sandstone and conglomerate
without limestone or significant shale deposits.
Previous reports by White (1888), Glover (1935) and
Weaver (1937) have described the Chuckanut formation in general
as being laid down on broad valley floors, probably in the
form of wide alluvial fans. Local ponding of water in the
valleys permitted the accumulation of stratified sands and
clays, and the development of large swamps whose vegetal
matter formed the present coal beds. Subsidence during the
time of deposition allowed accumulation of great thicknesses of
sediments. 106
On Lummi Island no real swamp phase is recorded and the sedimentary rocks present indicate relatively continuous transportation and reworking.
The exact source of the sediments themselves is not known; however, due to their moderate sorting and the subrounded nature of the grains, a lengthy transportation might be in• ferred. It is believed that the material came from the erosion of nearby lavas, and metamorphic rocks and granites of a mountain chain which had newly risen to the east. The lith- ology on Lummi Island suggests that the lavas v/ere probably the closest source.
Paleoclimatology
A luxuriant vegetation is indicated at the time of deposition by the presence of numerous fossil plant remains including: palm leaves, (prevalent in the lower sequence only); well-preserved ferns; deciduous, angiosperm leaves; and numerous coniferous tree remains found in the sandstone, conglomerate, and shales. Some leaves and pieces of wood are found at Fern Point and on the east side of Lummi Island but the large assemblages have been found at various localities on the mainland, especially along the Chuckanut Drive.
The palm leaves suggest that at the beginning of deposition of the Chuckanut formation, the climate was some• what dryer and warmer than the present. This dry, warm climate was apparently followed by a gradual lowering of tem• perature and an increase in rainfall. Barton (1916) in 107
studying arkose deposits indicates that continental deposits
of the type here described are typical of moist temperate
conditions.
Age and Correlation
Early attempts at age determinations and correlation
of what is now named the Chuckanut formation were made by
Lesquereux (1859) and Newberry (1863). Newberry correlated
fossil plants from the Chuckanut Drive area with those of the
Upper Cretaceous rocks to the south of Point Doughty on Orcas
Island. The latter, known as part of the Nanaimo series,
contain interbedded marine fossils. Although this correlation was later discarded on the basis of the interbedded marine
fossils and by later comparisons of plant fossils (McLellan
1927), the rocks are quite similar in lithology. In fact,
the materials composing their boulders and pebbles are iden•
tical (McLellan, 1927).
Dr; Knowlton of the U.S. Geological Survey studied
fossil leaves from the strata in question (Chuckanut formation)
and in 1901, in a report by Landes on the coal deposits of
Washington, he noted that the strata containing these leaves were temporarily correlated with the Eocene coal measure of
the Puget Group in King and Pierce counties 100 miles to the
south. McLellan (1927, p. 136-137) states that: "recent work
on the fossil plants by Dr. Knowlton has placed the Chuckanut
formation in the vicinity in the lower Eocene," but he also
stated (p. 138) that "the beds do not represent the lowermost 108 portion of the Eocene." McLellan further remarked (p. 138) that: "the Chuckanut flora is very different from the middle and upper Eocene flora occurring in the vicinity of Seattle."
Weaver (1935, p. 90) apparently disregards this last statement as he states that: "the Chuckanut formation may represent a time interval beginning in the late Cretaceous and continuing into the middle or possible later Eocene." This means it is probably in part contemporaneous with the continental Eocene beds of the Puget Group to the south and probably represents the time interval in Eastern Washington during which the
Swauk and Roslyn formations accumulated. Misch (1952) noted that the Chuckanut formations are now generally considered
Paleocene in age, however, he believes that at least part of these rocks were formed during the late Cretaceous.
In summary, the writer agrees with Weaver (1935, p.
90) in his reasoning that a definite correlation of the
Chuckanut formation cannot be made until a complete monographic study has been made of the entire assemblage of flora from the base to the top. The results of such a study have not yet been published.
GLACIATION
The glacial history of the Puget Sound area was first described in detail by Willis (1898). He proposed a sequence of two glaciations, Admiralty and Vashon, with a single inter- glacial interval called the Puyallup. Bretz (1913), follow• ing Willis1 general three part sequence, gave a detailed account of the glaeiation in the Puget Sound region which attempted to cover all phases of the glaeiation. Local de• tails of the sequence in the area have been contributed by- different writers since that time. Recent work by Crandell,
Mullineaux, and Waldron (1958) in the southeastern part of the Puget Sound lowland of Washington is noteworthy. They have replaced Willis1 sequence by four glaciations separated by nonglacial intervals during which the climate approached or attained conditions like those of the present. Their se• quence includes: the Orting glaeiation which may be early
Pleistocene in age; the Alderton nonglacial interval; the
Stuck glaeiation of early to middle Pleistocene; the Puyallup nonglacial interval; the Salmon Springs glaeiation of middle to late Pleistocene age, an unnamed erosion interval (non• glacial interval); and the most recent Vashon glaeiation.
The Vashon glaeiation is correlated with the (Tazewell) max• imum of the Wisconsin stage in the United States, and radio• carbon dates from peat in the lowland suggest that the glacier uncovered the lowland south of Seattle at some time prior to
14,000 years ago.
It is believed that mountain glaciers from the Cascade
Range contributed little to the continental glaciers which appear to have originated in British Columbia. 110
Evidence of glaclatlon in the San Juan Islands is plentiful as the glaciers performed a large amount of erosion in the general region (McLellan, 1927). The direction follow• ed by the upper portions of the glacial ice in this region was not controlled by the underlying topography, but the course of the deepest glacial erosion was partly determined by the presence of fault or fracture zones or by previously existing channels.
The extent to which glaciation has modified the topo• graphy of Lummi Island is not completely known but glaciers apparently overrode the whole island. Rocks at the higher elevations of the northern half and many outcrops on the high southern half of the island have been polished and grooved by glacial action (figure 32). While glacial erosion and polish• ing went on at the higher elevations, a thick blanket of drift was deposited over most of the low northern half of Lummi
Island.
In the northern half, glacial striations, grooves and stoss and lee slopes indicate that the ice moved southwestward
(geologic map). Similar glacial markings on the higher southern half indicate a south to southeasterly movement. This apparent sharp change in direction might suggest some local control of the deep ice and a general southerly or southeasterly movement of the main body as the ice overrode the islands.
The bedrock surface was very uneven and therefore the thickness of the drift cover varies, the original depressions Ill holding the thicknest deposits and the hills being only lightly covered. The thickest deposits on Lummi Island ex• ceed 160 feet. The drift cover consists of both unconsolidated, stratified or unstratified washed drift or outwash, and un- sorted till and clay. Gravel and sand occur in lenses and beds interspaced with gravelly and pebbly clays, soft clays, and hard clayey gravels and sand, called hardpan by local residents (A The deposits of clay which occur up to 50 feet in thickness are generally blue or slightly greenish in color when fresh but they appear to contain considerable amounts of iron in places and weathered sections show a rusty-brown color. Stratified outwash and poor to unstratified washed gravel and sand deposits up to 80 feet in thickness occur on Lummi Island. Often these deposits are tightly packed and at a distance some might easily be confused with the Chuckanut 112 formation. In general these outwash deposits are quite clean and fairly well sorted. A sieve analysis made in 1919 of a sample of the outwash from a deposit near Village Point appears to bear out this situation. Retained on Sieves 10-Mesh 28.2 Remarks: "sand from this 20-Mesh 49.8 place is well graded, com- 30-Mesh 70.4 posed of hard materials, and 40-Mesh 80.4 showed a tensile strength in 50-Mesh 90.2 7-day briquets 138.9 per 80-Mesh 97.5 cent as great as the Standard 100-Mesh 98.2 Ottawa sand, and in the 28- 200-Mesh 99.8 day briquets 162.8 per cent Passing 200-Mesh 0.2 as great. No organic con• tent was detected by the colorimetric test." Sieve Analysis and Remarks on a Sample of Sand Taken from a Glacial Outwash Deposit Near Village Point on Lummi Island (after Leighton, 1919: The Road Building Sands and Gravels of Washington). On the east side of Eliza Island a cliff of till and outwash up to 50 feet thick occurs. Here are seen regular alternating layers of well stratified drift and unsorted till. At one location stratified layers have been folded by the over• riding glacier, and these folds are unconformably overlain by a thin deposit of unsorted, clayey drift (figure 33). These unconsolidated sediments of glacial origin were partly, if not wholly laid down in marine water and contain shells and shell fragments. In parts of Whatcom County these shells are very abundant in the till and the outwash. On Lummi Island, marine shells have been found in the stratified drift and some have reportedly been found in the till. At a locality just a few hundred feet south of the knob of Lummi 113 Island Metamorphic and Igneous Complex, a marine shell was found resting on the till surface below six feet of well sorted, clean gravel deposits. This shell occurred at an altitude close to 200 feet. Former sea levels as high as 290 feet have been recorded on Orcas Island (McLellan, 1927). Large erratic boulders up to 6 feet in diameter are commonly found scattered over Lummi Island in the till, or resting on exposed bedrock surfaces. They are generally quite well rounded and most consist of quartzo-feldspathic gneiss, diorite, quartz diorite, granodiorite, or granite. Most of these are believed to have been derived from the Coast In• trusions of British Columbia. On the beach just west of the Baker farm on the west side of Lummi Island are found boulders of a very fine, dense, black sandstone containing large numbers of valves of the Pelecypod Bucia. These boulders are believed to have been transported from Harrison Lake north of 6 the Fraser Valley in southwestern British Columbia. It is not possible to separate distinct glacial in• vasions from the material exposed on Lummi or Eliza Islands as has been done to the south. McLellan (1927) believed that the great bulk of the sediments in the San Juan Island area were deposited during the Puyallup interglacial epoch. Exam• ination of well records (Appendix 1) and cliff exposures of the glacial drift show various sequences, some sections 6 Personal communication, W.R. Danner 114 apparently showing as many as three separate layers of till or pure clay between gravel or sandy layers. These sequences may only indicate minor retreats and readvances of the ice. GEOMORPHOLOGY In addition to glaciation, certain other geomorpho- logical processes, their controls, and the features produced by them on Lummi Island are of interest and are briefly dis• cussed here. Coastlines It is apparent when looking at a map of Lummi Island that the southwest coastline of Lummi Island is quite regular and straight and probably represents a state of maturity, while the southeastern coastline is sinuous and uneven. It is believed that the relatively open waters of Georgia Strait washing and beating against the cliff on the east side has tended to even-out many of the irregularities which might be formed due to lithology. On the east side the currents of Hale Passage were not as important as the lithology of the rocks attacked in determining the form of the coastline. Lithologic Control of Weathering As previously mentioned, lithology of the bedrock has apparently been an important factor in erosion of the south- east coast of Lummi Island. Here, Inati Bay and Reil Harbor have been carved into relatively nonresistent shale and argillite sequences while the Reil Harbor volcanics have re• sisted erosion and now stand out as a knob which projects out into Hale Passage. Similar resistant knobs are formed by the outcrops of the Reil Harbor volcanics at other locations. Lummi Peak is another example of high elevation probably due to lithologic control. The rocks at the peak are composed of highly indurated fine-grained graywacke which resemble fine-grained igneous rock in general appearance. In the northern part of Lummi Island the conglomerate of the Chuckanut formation stands high above the sandstone. The higher portions of this northern part are formed by con• glomerate and it is apparent when the geologic outcrop map is examined that lithology is an important control in the erosion here. Marine Cliffs and Terraces Wave-cut cliffs and terraces are conspicuous at many places along the coastline of Lummi Island. In most cases the terraces are characterized by the development of beaches which increase the distance from the marine cliff to deep water and decrease the effects of wave action. At Migley Point such a profile of equilibrium or maturity has not been reached and a noticeable marine cliff and wave-cut bench nearly bare of fine sediments, occurs on the Reil Harbor volcanics. Figure 33. Folds in stratified outwash deposits (A) formed by thrust of glacier. Folds overlain by unsorted till (B) which is in turn overlain by stratified sand and gravel (C). View SW, glacier moved SE (jrefl Lu right-). &I9k* f° East side Eliza Island, W.R.Danner, May, 1958. Figure 34. Wave-cut cliff and bench in Reil Harbor volcanics (age unknown) at Migley Point. View NW at low tide. October 1958. 117 Most of this bench is apparently above the wave base and is exposed at the low tide level (figure 34). Fretted Surfaces Figure 35a and b show the fretted surfaces developed in the sandstone of the Chuckanut formation cropping out a few feet above the high tide mark on the northwest shore of Lummi Island. No discernable lithologic difference causing differential resistance to erosion can be seen in the sand• stones themselves. It is believed that during times of storms and rough water, high waves break high and lick-away at the sandstone producing the groove-like pattern (a). The cat's paw pattern (b) is produced by the erosion effect of splashing water particles on the sandstone as the waves break against the shore. Lummi Point A cuspate beach or spit, called Lummi Point projects into Hale Passage from the northeast side of Lummi Island. A submerged sandy ridge extends northeastward from Lummi Point and except for a small break in the middle of the passage, it extends to the mouth of Lummi River on the Mainland. It is thought that the spit has been formed by the encroachment of the Lummi River Delta from the mainland in combination with the action of longshore currents in eroding and moving sand and pebbles from the Chuckanut formation north and south of the spit. Figure 35. Fretted surfaces formed by- differential wave erosion of sand• stone of the Chucaknut formation (Lower Tertiary) at Fern Point. View taken NE, May 1958. 119 STRUCTURE Regional Structure To quote McLellan (1927) and more recently W.R. Danner (personal communication), the detailed structure of the San Juan Island map-area is extremely complicated. The Paleozoic rocks have been subjected to many periods of folding and faulting and have been intruded at various times by igneous rocks. Many of the islands are separated by wide channels and thus continuity of structure is often broken. These channels also probably serve to hide faults or unconformities which might give a key to the comprehensive structural picture of the region. McLellan built much of his large-scale structural interpretation around a nucleus of three large islands; Orcas, San Juan, and Lopez. He believed that these islands displayed a broad open syncline plunging 35 degrees SE. He also thought it likely that a fault of considerable magnitude occupied each of the major channels. Exactly where Lummi Island fits into his structural picture is not altogether clear. He believed that the Leech River sedimentary rocks (Carter Point formation) on Lummi Island were structurally related to those on the north shore of Orcas Island as both have approximately the same strike. Both McLellan and Weaver (1935) recognized that the 120 Chuckanut formation on Lummi Island is not only structurally related to corresponding rocks of the formation on the mainland, but that it is also probably structurally related to the rocks of the Nanaimo series on Matia Island approximately five miles to the northwest. These two rock units strike into one another and were evidently folded during the same periods of folding. Carter Point Formation and Reil Harbor Volcanics of the Southern Half of Lummi Island The structure of the Carter Point formation and of the volcanic rocks of the southern half of Lummi Island appears to be quite straightforward; however, the scarcity of horizon markers, and the thick timber and brush cover at some locations may inject some note of uncertainty in the interpretation. The whole southern half of this island appears to represent the eastern limb of a northwesterly plunging anti• cline. The overall strike of the rocks varies between N 20 ¥ and I 60 W and the beds dip towards the northeast at angles near 45 degrees. The dips and strikes along the east or dip- slope side of the southern half are not consistent. This may be due to the fact that in many places the shale or argillite has slipped down the dip slope. Small scale graded-bedding and cross-bedding indicates that the beds are not overturned. The general outline as well as the topography of the southern half of the island clearly follows the structure. At Carter Point, the strike is N 40 W and north from here the rocks curve westward to strike N 60 W. About a mile and a quarter north of Carter Point, the rocks turn northward again and continue on a strike of approximately N 40 W to the contact with the glacial drift at the northernmost outcrop on the west side of the Island. Another noticeable variance with the general average N 40 W trend is found in the northern end of the southern half of the island near Sunrise Cove. Here, the rocks strike approximately east-west and dip 50 to 80 degrees northward. These two conspicuous changes in the strike occurring at opposite ends of the Paleozoic - Mesozoic out• crops may represent two large-scale drag folds on the eastern limb of a northwestward plunging anticline. Small-scale folds in these rocks are not common, but a few small drag folds observed in the argillite and in the ribbon chert of the vol• canics at Reil Harbor tend to corroborate the above structure. Both jointing and cleavage are well developed in the Carter Point formation but they are not clearly defined in most locations. Where cleavage was measured, it showed a dip greater than that of the bedding. The joints and cleavage planes served as channelways for mineral depositing solutions and as previously mentioned, the Carter Point formation is cut by an extremely large number of quartz veins. Jointing is also well developed in the Reil Harbor volcanics. A small cove cut in the volcanics just north of Reil Harbor is appar• ently caused by wave erosion of rock, weakened by a fault, and numerous joints which trend northwest/southeast and dip to the northeast, parallel to the chert beds. 122 The extent of faulting in the Carter Point formation is not completely known because of the thick brush cover in many places and the lack of horizon markers. Numerous small faults with displacements less than 15 feet are seen along the shoreline at the northwest corner of the southern half of the island. Many of these have a vertical dip and trend NW-SE. These probably represent but a few of many similar faults which occur throughout the rocks here. Two well defined zones of shearing possibly related to faults of unknown displacement cut through the pillow lavas at Reil Harbor. These appear to be vertical and strike NW-SE, nearly parallel to the strike of the chert beds. Whether there is a fault between this knob of pillow lava and the sedimentary rocks of the Carter Point formation to the west is not certain. The contact is obscured from view by sediments and brush. The chert at the base of the volcanics in this area is brecciated however and this, with the fact that the basal chert beds dip more steeply than the nearest rocks of the sedimentary sequence, might suggest that this large block of volcanics has been faulted downward in relation to the sedimentary rocks. At Sunrise Cove the contact between the volcanics and the sedimentary rocks is also obscured and the relation between the most southerly outcrop of the volcanics here and adjacent graywackes is not completely understood as no indication of bedding has been observed in this outcrop of the volcanics. 123 Eliza Island The graywacke and argillite on Eliza Island appear to have been metamorphosed to a greater degree than those rocks on Lummi Island and many outcrops show a well defined axial plain cleavage. On the westernmost bedrock knob, the rocks appear to form a small synclinal bowl plunging gently toward the northeast. The rocks of the southern bedrock knob form another syncline which appears to plunge toward the southeast. Cleav• age on the east side of this knob strikes N 20 E and dips 35 degrees SE. Structure of the Sedimentary and Volcanic Rocks at the Northern Half of Lummi Island Just as the rocks of the Carter Point formation and the Reil Harbor volcanics on the southern half of Lummi Island appear to have been folded as a unit, the Reil Harbor volcanics at the northern end appear to have been folded as a close knit unit with the Chuckanut formation. The rocks here have been folded into a series of synclines and anticlines which strike approximately N 50 W and plunge gently to the northwest. This structure is nearly identical to that on the mainland to the southeast where rocks of the Chuckanut formation are folded into broad, open folds that also trend gently NW-SE and plunge northwestward. From Migley Point where the conglomerate overlies the 124 volcanics, to the volcanics at Legoe Bay, the rocks are folded into a series of three synclines and two complete anticlines. At Migley Point the rocks strike N 50 W and dip 55 SW into a syncline which trends nearly E/W and plunges to the northeast. The two southerly synclines strike about N 60 W. The most southerly expression of this fold structure is reflected in the interbedded argillites of the volcanics at Legoe Bay, and in the sedimentary rocks of the Chuckanut formation on strike to the northwest. These rocks strike N 40 W and dip steeply (80-85°) into the syncline to the northeast. In general, the southwest limbs of the synclines appear to be steeper than the northeast limbs. Faulting does not appear to be an important factor in the structure of the Chuckanut formation and the only clearly visible faults are small-scale features with displacements less than a few feet which occur along the coastline of the northern half of the island (figure 36). Extreme shearing, fracturing, and some faulting has apparently gone on within the volcanics underlying the Chuckanut formation. At Migley Point the deformation is most evident with quartz-rich fracture zones and a large number of narrow fault or shear breccias, rich in secondary epidote and often filled with jasper stringers. 125 Figure 36. View NE of Chuckanut for• mation (Lower Tertiary) showing small scale fault (2 ft. displacement). Fern Point, October 1958. Cross-Island Faults McLellan (1927) believed that the southern part of Lummi Island was the up-thrown side of a fault which cuts sharply across the island. The writer agrees with this inter• pretation. It is also believed that there may also be another large cross-island fault which separates the Lummi Island Metamorphic and Igneous complex from the Chuckanut formation and Reil Harbor volcanics outcrops to the north. However, no actual physical evidence can be seen in the rocks for either of these large faults. Age of Deformations Since the exact age of the Carter Point formation and the Reil Harbor volcanics is not known, it is difficult to ascribe an age to the deformation; however, it is probable that the major folding occurred at some time between the Lower Jurassic and the Upper Cretaceous period. This period of de• formation, called the Coast Range orogeny in Canada by White (1959)j is said to be the most complex tectonic event in the history of the Canadian Cordillera. The number of periods of deformation during this orogenic period is not known, but cleavage and jointing in the Carter Point formation may suggest more than one period of orogeny. McLellan (1927) noted that these rocks may have been folded to some extent during the Late Paleozoic. 127 The next major period of folding, succeeding that of the Coast Range began in the Upper Cretaceous and continues to the Recent time. It is called the Puget orogeny by White (1959). The ancestral Cascade Mountains were developed in the late Miocene or early Pliocene deformation (Newcomb, Sceva, and Olaf, 1949) and it is believed that at this time NW-SE trending folds were developed in the Chuckanut formation and in the underlying Reil Harbor volcanics at the northern end of Lummi Island. Although the largest part of the folding seen today in these rocks probably went on at this time (Newcomb, Sceva, and Olaf, 1949) deformation occurred again near the close of the Pliocene Epoch. This deformation re• sulted in a regional uplift of the Cascade Range and a general structural upwarp which extended through the San Juan Islands and into Vancouver Island. The reason why rocks of the Carter Point formation apparently do not reflect this Tertiary fold• ing to any great extent is not completely known. It may be that the Miocene folding was surfacial in nature and the rocks at the south end of Lummi Island were elevated by faulting after this folding. It is also possible that this up-thrown southern block of sedimentary rocks for some unknown reason was able to resist the stresses of the Tertiary orogeny. The whole region has been uplifted since the last glac• ial period. This is evidenced by the marine shells found in the drift above 150 feet on Lummi Island and at 290 feet on Orcas Island. Elevated, gravelly beaches seen on Eliza Island suggest that there has been a recent uplift of 10 to 20 feet in the area. 128 BIBLIOGRAPHY Arnold, R. and Hannibal, . H., 1913, Stratigraphy of the North Pacific Coast of America: Proc. Am. Phil. Soc, v. 52, p. 566-571. Barton, D.C., The geologic significance and genetic classi• fication of arkose deposits; J. Geol., v. 24, p. 416- 449.(1916) Bretz, H.J., 1913, Glaeiation of the Puget Sound region: Wash. Geol. Survey Bull., no. 13. 1920, The Juan de Fuca Lobe of the Cordilleran Ice Sheet: Jour. Geol., v. 28, p. 333-339. Brown, R., 1870, Glacial scratches near Bellingham Bay, Washington: Am. Jour. 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Parberry property (NE^NE^ sec. 16, T.37 N,,R.I. 35.) Soil 2 2 Clay, sand, and gravel fine 4 6 Sand, fine and gravel 1 7 Clay, brown 9 16 Sand, coarse, and gravel - little clay 17 33 Sand, fine, gravel, clay, blue 5 38 Clay, blue and sand, fine 2 40 Sand, coarse and gravel 3 43 Sand, fine and clay, brown 3 46 Sand, coarse and clay, brown - little clay 8 54 Clay, very sandy, brown 14 68 Clay, sandy, blue 5 73 Sand and gravel, coarse and clay, blue 6 79 Sand, fine (water) 7 86 7 See well location map in pocket (Plate 3) 134 4. Well on Flockenhagen property (SE|SE£ sec. 9, T. 37 N., R.l.E.) Soil 1 1 Hardpan, gravelly - boulder 7 8 Clay, gravelly, blue 52 60 Boulder clay 41 101 Clay, hard, gravelly, blue 8 109 Sand (water) 5 114 5. Well on J. Granger property (NW^SW^ sec. 10, T. 37 K., R.ltE.) Fill 1 1 Soil 1 2 Clay, hard, black 4 6 Hardpan 7 13 Clay, soft, blue - some gravel 27 40 Conglomerate 6 46 Rock, very hard, green 124 170 (water at 105-159 ft. 1/2 G.P.M.) 6. Well on Haven property (SE^NE^ sec. 9, T.37 N.,R.l.E.) Soil 1 1 Sand, coarse and gravel 12 13 Clay, gravelly, blue-boulder 11 24 Sand, blue and gravel 6 30 Sand, coarse and gravel 40 70 Sand and gravel 38 108 Sand, gravel, and clay, blue 10 118 Sand and gravel 20 138 Sandstone, coarse (water, 400 G.PiH.) 5 143 7. Well on CE. Castle property (SE^NW^ sec. 9, T.37 Nn R.l.E.) Soil 4 4 Sand and gravel 4 8 Clay, blue 6 14 Sandstone, coarse and conglomerate 16 30 Sandstone, coarse - conglomerate 52 82 Sandstone, coarse (some water) 33 H5 135 8. 'Well on M. Tuttle property (NE^NW^ sec. 9, T. 37 N.,R.l.E.) Soil 1 1 Hardpan, very gravelly 4 5 Hardpan 5 10 Clay, very sandy, blue 24 34 Clay, gravelly, blue 13 47 Gravel (water) 4 51 9. Well on K. Gardner property (NW^NW^ sec. 9, T. 37 N.-,R.l.E.) Gravel, coarse 3 3 Gravel, coarse - some clay 8 11 Gravel, coarse - some clay - salt 7 18 Gravel, fine 9 27 Sand, black 6 33 Clay, black and green 2 35 Clay, blue 20 55 Sand, fine (water) 7 62 10. Well on Walker property (NW^NW£ sec. 9, T. 37 N,,R.l.E.) Gravel, coarse 3 3 Gravel, coarse - some clay 9 12 Gravel, coarse - salt 14 26 Clay, black and green and sand 4 30 Clay, blue 5 35 Clay, gravelly, blue 24 59 Sand, coarse - blue clay (water) 3 - 62 11. Well on G. Johnson property (NW^NW^ sec. 9, T. 37 N«,R.3..E.) Gravel, loose 5 5 Gravel - some blue clay (salt water in lower gravel) 25 30 Clay, soft, sandy, blue 24 54 Gravel, coarse, sandy (water) 4 58 12. Well on J. Brown property (NW£NW£ sec. 9, T. 37 N.„ R.l.E.) Gravel, coarse 18 18 Gravel, coarse - salt 5 23 Gravel (water) 3 26 Sand, black 4 30 Clay, soft, sandy, blue - large rocks 55 85 Sand, fine - some clay 7 92 Sand, fine and gravel (water) 3 95 136 13 Well on Chambers property (NE|-NE| sec. 8, T. 37 N.,R.1.E.) Gravel, coarse 18 18 Gravel, coarse - some salt 15 33 Clay, soft, green to blue 44 77 Sand, fine (water, 9 G.P.M.) 8 85 Clay, blue 14. Well on J. Miller property NE^NE^ sec. 8, T. 37 N.,R.1.E.) Gravel, coarse 13 13 Gravel, coarse and clay 4 17 Gravel, coarse, sandy (salt water) 21 38 Sand, fine 4 42 Clay, soft, sandy, greenish 8 50 Clay, hard, sandy and gravel 4 54 Clay, sandy, blue 27 81 Sand, fine (water) 3 84 15. Well on F. Granger property (SW|- sec 4, T.37 N,,R.X.E.) Soil 11 Gravel 6 7 Sand, fine 8 15 Clay, soft, blue and gravel 19 34 Sand, coarse and gravel 25 59 Clay, sandy, blue 7 66 Sand and gravel, very hard 17 83 Sand, fine, turning blue (water) 20 103 Clay and sand 4 107 Sand (water) 9 116 16. Well on F. Granger property ( (NE^SW^ sec. 5, T.37 N,,R.I.E.) Gravel, coarse 7 7 Gravel, coarse and clay, blue 13 20 Clay, soft, sandy, blue 32 52 Sandstone 29 81 Shale, blue 9 90 Conglomerate 13 103 Sandstone 38 141 Shale, deep blue 4 145 Sandstone, fine 155 300 17. Well on J. Melcher property (NE^NW| sec. 5, T. 37 N,, R.l.E.) Sand, dry Clay, yellow Sandstone, coarse, gray (water) 18. Well on Griesing property (NE^SW|- sec. 32, T. 38 N,,R.l.E.) Gravel, dry and boulder Sand, muddy, brown Sand, muddy, blue Shale, blue Sandstone, dark (water) 19. Well on Austin property (SW^-SE^ sec. 29, T. 38 N.,R.2..E.) Soil Clay, gravelly Clay, hard, gray Sandstone, soft, reddish Sandstone, gray 20. Well on A. Granger property (NE^Ejjf sec. 32, T. 38 NMR.1-E.) Soil, clay and gravel Sandstone and conglomerate Sandstone, fine 21. Well on Langdon property (SW^NE^ sec. 4, T. 37 N,,R.l.E.) Soil Hardpan, gravelly Sandstone, soft Sandstone, gray Sandstone, gray (water, 1000 G.P.H. with sulphur) 22. Well on As'tell property (SW^NE^ sec. 4, T. 37 1'«,R-l*E-) Soil and hardpan, gravelly Sandstone, brown Sandstone, gray (water) 23. Well on M. Heath property (SE£NE£ sec. 4 T. 37 MC,R.I.E.) Soil Gravel Gravel, hardpan - boulder Gravel and clay, blue Sandstone, gray Sandstone (water at 90 ft. 3 G.P.M.) 24. Well on J. Christenson property (NE£ see. 4, T. 37 K.,R.I.E.) Dirt and gravel Clay, soft, blue Sandstone Sandstone (water),(50 G.P.H.) Sandstone, Hard 25. Well on Brown property (WE4-SE| sec. 4, T. 37 N.,R.I.E.) Soil Gravel Hardpan, gravelly S and stone, b r own Sandstone, gray (water at 89 ft. 500 G.P.H. with sulfur) Sandstone, gray 26. Well on J. Anderson property (NE4-SE4- sec. 4, T. 37 N„,R.I.E.) Soil Gravel, dry Hardpan, gravelly Sandstone (water at 65 ft) 27. Well on O'Rouke property (SW£SW£ sec. 3, T. 37 N,,R.I.E.) Hardpan, gravelly Sandstone, gray (water seepage: 40-45 ft. 1 G.P.M. 93-95 ft. 1 G.P.M. 153-155 ft. 1 G.P.M. Chert, hard ?? 139 28. Well on L. Luke property (SE|-NE^ sec. 15. T. 37 1,j R.l.E.) Clay, soft, blue 35 35 Shale, soft, gray 3 38 Shale, hard, gray 37 75 Shale, hard, black 6 81 Shale, gray 9 90 Shale, dark gray with purple cast 13 103 Rock, black, with quartz 31 134 Sandstone 16 150 29. Well on Nolte property (SE^NE| sec. 15, T. 37 R. ilE.) Clay 37 37 Clay, blue and gravel 15 52 Sand ?? 66 118