University of Washington Publications in Geology The Geology of the San Juan Islands

SEDIMENTARY ROCKS
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PENNSYLVANIAN-PERMIAN SYSTEMS

LEECH RIVER GROUP

Principal Features. The Leech River group^{11, 12} is well represented in the rocks outcropping on the San Juan Island map-area. It forms the central part of the syncline on San Juan Island, and is well exposed on Lopez Island and other islands in the eastern portion of the map-area. It outcrops in many places on Orcas Island, and forms the south or mountainous half of Lummi Island. On the mainland to the east, the rocks belonging to the Leech River group outcrop at the south end of Chuckanut Drive, on the Pacific Highway.

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¹¹Dawson, G. M., Report on a Reconaissance of Leech River and Vicinity: Geol. Survey Canada, Report of Progress, 1876-77, pp. 95-102, 1878.

¹²Clapp, C. H., Southern Vancouver Island: Geol. Survey Canada, Mem. 13, p. 35, 1912.

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The Leech River group is composed of a great variety of rock types. It contains graywacke, argillite, conglomerate and breccia, grit, schist, phyllite, slate, volcanic tuff, chert, limestone, and coal.

On the southern part of Vancouver Island, Clapp¹³ distinguishes a group of metamorphosed "argillaceous and arenaceous sedimentary rocks," as the Leech River "formation.". Overlying the Leech River sediments and grading into them, he describes a group of tuffaceous rocks which are known as the Malahat volcanics.

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¹³Clapp, C. H., Sooke and Duncan Map-Areas, Vancouver Island: Geol. Survey Canada, Mem. 96, pp. 66-93, 1917.

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On the San Juan Islands it is not possible to make such a sub-division, and on account of the wide range of rock types presented, it has been considered advisable to use the name, Leech River "group." Volcanic tuffs occur interbedded with the purely sedimentary strata at several horizons within the group. So far as lithology is concerned, the Malahat volcanics occurring on Southern Vancouver Island are identical with the tuffaceous graywackes which form the basal member of the Leech River group in the San Juan Island map-area.

Lithology and Structure. The dark colored slaty schists and argillites are perhaps the most abundant rock types occurring in the Leech River group. They range from quartz-mica schists and phyllites to normal slates and argillites. Quartz-biotite and quartz-sericite schists and phyllites are abundant in the eastern part of the map-area. These rocks usually contain considerable amounts of magnetite and graphite. When the percentage of carbonaceous matter is high the rocks are almost black in color when viewed from a distance.

The slates and argillites exhibit several stages of metamorphism and they are often somewhat schistose. They often alternate with massive beds of graywacke which is sometimes tuffaceous. The graywackes range from fine-grained rooks to coarse grits and are usually well cemented. They often contain rounded or nodular mudstone inclusions scattered irregularly through the coarser-grained deposits. Fragments of chert derived from the Orcas group form the most abundant constituent of the rocks of the Leech River group. Both orthoclase and plagioclase (about Ab 70 An30) are usually present in the sediments, but the percentage of quartz is below the typical amount for such rocks. Sericite, chlorite, epidote, serpentine, kaolinite, magnetite, and graphite occur in varying amounts. It is noticeable that the conglomerates are practically free from pebbles of granite, though fragments of granite porphyry and andesite are fairly common. In many localities the sediments of the Leech River group have been cut by dikes and stringers of white milky quartz.

SAN JUAN ISLAND

The lowest member of the Leech River group, as exposed on San Juan Island, is a tuffaceous and cherty graywacke. It overlies the Orcas cherts with approximate conformity. This graywacke is typically fine-grained and occurs in beds of varying thickness. In places it appears as thin beds which differ from each other only in the size of the fragments composing them. Occasionally the graywacke contains scattered layers of chert, and it is possible that the conditions which brought about the deposition of the Orcas cherts continued on, and additional sediments, including tuffaceous material, were added to them. The basal graywackes have a probable maximum thickness of several thousand feet. They have the general composition of a dacite, and their weathered surfaces are almost indistinguishable from that of a weathered andesite in the hand specimen.

The basal graywackes outcrop throughout the elevated region in the vicinity of Point Caution, and on account of their resistance to erosion, the outcrops form a series of elevated ridges. Since the rocks of both the Orcas and Leech River groups are embraced in the broad open synclinal fold which plunges towards the southeast, the individual rook formations outcrop in the form of a horseshoe. The elevated ridges representing the outcrops of the basal graywackes consequently have the shape of a horseshoe. They are seen on Biological Hill, the San Juan Range, Mount Grant, and on Little Mountain. The upper limit of the graywackes is marked by a well defined formation about 100 feet thick, composed of coarse breccia and conglomerate. This formation underlies a portion of the village of Friday Harbor and is encountered at several localities near the southwestern side of San Juan Island.

The breccia formation is followed by several hundred feet of carbonaceous argillite which has no banding or apparent structure of any kind. This is followed by a tremendous thickness of thin-bedded alternating light and dark layers of argillite which often grades into phyllite. Occasionally there are interbeds of graywacke, grit, or conglomerate.

The uppermost strata of the group are composed of thick conglomerate, grit, graywacke, and slate, and it is possible that these formations belong to the early Mesozoic systems. These upper formations occupy the core of the major plunging synclinal fold on Lopez Island and do not outcrop on San Juan Island.

In addition to the igneous intrustions which have almost everywhere penetrated the rooks of the Leech River group, these rocks are frequently cut by stringers and veins of white milky quartz.

BROWN ISLAND

Brown Island is composed of the basal graywackes of the Leech River group. These rocks have been intruded by dikes and sills of the Eagle Cliff porphyrite, and in places the sedimentary rocks have been overturned so that they dip towards the northward.

TURN ISLAND

The tuffaceous graywacke composing Turn Island has been largely destroyed by intrusions of the Eagle Cliff porphyrite. The igneous rooks now make up the greater part of the island.

DINNER ISLAND

Dinner Island is composed of thin-bedded graywacke which trends northwesterly and dips towards the southwest.

GOOSE ISLAND

Goose Island, and also the rocky peninsula to the north of Cattle Point on San Juan Island, are composed largely of graywacke which has been intruded by dikes and sills of the Eagle Cliff porphyrite. The rocks have an average strike of about N 55° W, and they dip towards the northeast at angles varying from 35 to 65 degrees.

LOPEZ ISLAND

A great thickness of alternating beds of light and dark colored argillite occurs along the south margin of Lopez Island. The individual layers of argillite are from one to three inches thick. The dark layers contain notable quantities of graphite and this gives the rocks a dark sooty appearance. In places the argillites grade into mica schists and phyllites, and they sometimes contain interbeds of graywacke, grit, and conglomerate. These sedimentary rocks have been intruded by dikes and sills of the Eagle Cliff porphyrite and they are generally somewhat silicified near the contacts.

In the vicinity of Iceberg Point, the Leech River sediments trend about N 65° W and dip towards the northeast at angles varying between 40 and 70 degrees. Between Davis Bay and the boat-landing at Richardson, the rocks have an average strike of about N 55° W, and they dip towards the northeast at an angle of about 70 degrees.

The rocks occurring in the vicinity of Point Davis are composed of argillite, slate, graywacke, and conglomerate. At Point Davis they strike N 40° W and dip towards the northeast at an angle of 35 degrees. Along the shore of Cattle Point Narrows, about opposite Deadman Island, the rocks have a strike of N 35° W and a dip of 35 degrees towards the northeast. At the most northern of these outcrops, which occur along the shore about a mile to the north of Point Davis, the strike is N 10° E, and the dip is 35 degrees towards the southeast. Still farther northward on Shark Reef the rocks trend about north and south and dip towards the east at angles varying between 15 and 20 degrees. The bend in the strike of the rock formations to the north of Point Davis is quite evident when viewed from the westward.

The outcrops of graywacke and thin-bedded argillite occurring in the vicinity of Fishermans Bay have an average strike of about N 40° E and a dip of about 40 degrees towards the southeast.

The rocky peninsula which extends out from the north end of Lopez Island to form Upright Head is composed largely of conglomerate with minor amounts of graywacke. These rocks strike about N 20°-40° W and dip about 35° NE.

The rocks composing Humphreys Head consist of massive beds of graywacke and grit which contain scattered irregular nodules of black mudstone. These beds strike about N 10°-40° W and the average dip is about 45 degrees towards the northeast.

Near the southeast corner of Hunter Bay an outcrop of thin-bedded slate, argillite, and graywacke shows a strike of N 55° W and a dip of 60° N.E. At the southeast side of Mud Bay some thin-bedded graywackes show a strike of N 52° W and a dip of 42° NE.

In the vicinity of Watmough Bight the Leech River sediments have an average strike of N 55° E and a dip of about 70° NW. At Watmough Head the strike is nearly east and west and the thin-bedded and somewhat schistose rooks dip steeply to the northward.

The rook outcrops occurring in the interior portions of Lopez Island are composed mainly of the Eagle Cliff porphyrites, and the scattered remnants of Leech River sediments are of little value in determining the structure.

DEADMAN ISLAND

The graywacke and grit which compose Deadman Island strike about N 65°-70° W and dip about 60° NE.

WHALE ROCKS

Whale Rocks are composed of fine-grained argillaceous graywacke which has a reddish color. These rocks have little or no banding but their general strike appears to be about N 40°-45° E and the dip is about 30° SE.

MUMMY ROCKS

Mummy Rocks are composed of graywacke and grit with occasional beds or pockets of argillite. In places the rocks are cut by quartz stringers. The beds strike N 60° W and dip 45° NE.

BUCK ISLAND

Buck Island is composed of graywacke which has been badly shattered by intrusions of Eagle Cliff porphyrites.

LONG ISLAND

Long Island is composed of conglomerate, grit, massive graywacke, thin-bedded argillaceous graywacke, and thin-bedded schistose argillites and slates. At the west end of the island the strike is N 40°-45° W and the dip is 35° NE. The central and eastern parts of the island have a strike of N 75° W and a dip of about 65° NE. The small islands to the south of the central part of Long Island, and tied to it by means of low sand bars, are composed chiefly of thin-bedded shaly argillites and graywackes.

CHARLES ISLAND

Charles Island is composed chiefly of thin-bedded alternating light and dark layers of somewhat schistose slates and argillites. The predominating dark color of these rocks is caused by their relatively high content of carbonaceous matter which gives them a dull sooty appearance when viewed from a distance. Interbeds of conglomerate, grit, and graywacke also occur on Charles Island. The strike of the beds varies from N 70° W to N 80° W, and the dip ranges from 60 to 75 degrees towards the northeast. The small rocky islands to the northeast of Charles Island are composed of carbonaceous slaty schists which have similar strikes and dips.

SECAR ROCK

The graywacke composing Secar Rock has been so greatly shattered by igneous intrusions that the structure is not in evidence.

HALL ISLAND

Hall Island is composed of thin-bedded graywacke and argillite which strike N 70° W and dip from 50° to 70° N.E.

ICEBERG ISLAND

The massive graywacke composing Iceberg Island has been intruded and shattered by Eagle Cliff porphyrites.

ALECK ROCKS

The thin-bedded carbonaceous slaty schists composing Aleck Rocks trend about N 75° W and dip steeply towards the northeast.

COLVILLE ISLAND

Colville Island is composed of thin-bedded carbonaceous slaty schists and graywackes with occasional beds of grit and conglomerate. The strata trend about east and west and the average dip is about 55 degrees towards the north.

BOULDER ISLAND

With the exception of a thin remnant of Leech River sediments extending out from its southern margin, Boulder Island is composed entirely of Eagle Cliff porphyrites. The Leech River sediments dip steeply towards the north.

CRAB ROCKS

The Leech River sediments composing Crab Rooks trend northeasterly and dip towards the southeast. At the end of the nearby peninsula on Lopez Island the strike is northwesterly and the rocks dip towards the northeast.

RAM ISLANDS

Although Ram Islands are composed largely of Eagle Cliff porphyrites, a sufficient amount of the host rocks have been left to show that the strike is parallel to the long direction of the islands, and the dip is about 20 degrees towards the southeast.

CENTER ISLAND

The thin-bedded carbonaceous slate, graywacke, and grit composing Center Island have a strike of about N 18° E and a dip of about 25° SE at the southern end of the island. At the northern part of the island the strike is about N 25°-30° W and the dip is about 30°-40° NE.

TRUMP ISLAND

Trump Island is composed chiefly of thin-bedded slate, argillite, and graywacke. In places these rocks weather to a bright red color. The elevated region along the east side of Trump Island is composed of massive graywacke. The rocks on Trump Island have a strike of about N 20° W and a dip of 45° NE.

DECATUR ISLAND

The massive graywacke, grit, and argillite which compose the elevated peninsula to the north of Trump Island strike about N 5° W and dip steeply towards the southwest.

The northern and elevated portion of Decatur Island is composed largely of massive and thin-bedded graywacke together with a considerable amount of conglomerate, grit, and argillite. In places these rocks have been shattered by igneous intrusions. The conglomerates at the northwest corner of the island strike about N 55° E and dip about 70° SE.

The thick and thin-bedded graywacke, grit, slate, and argillite occurring in the vicinity of Fauntleroy Point have a strike of about N 75° E and dip towards the northwest at an angle of 75 degrees.

The rounded and elevated dome which forms Decatur Head is composed of conglomerate with occasional interbeds of argillite, graywacke, and grit. The strike of these rocks is about N 80°-85° E, and the dip is about 45° NW.

An outcrop of carbonaceous thin-bedded argillite occurs on the west side of the elevated peninsula which forms the southern extremity of Decatur Island. The Leech River sediments occur as a narrow belt near the water's edge, while higher on the cliff and throughout the remainder of the peninsula the Leech River rooks have been practically destroyed by intrusions of Eagle Cliff porphyrite. The sediments occupy the crest of an anticlinal fold which plunges towards the east. At the northern end of these curved beds the strike is N 45° W and the dip is 40° N.E.

JAMES ISLAND

James Island is composed of conglomerate, shale, argillite, graywacke, and grit which have been intruded by one or two dikes of igneous material. The structure, as shown in the figure, is very complicated.

Figure 2. Outline map of James Island

Some of the rocks occurring on James Island are much less metamorphosed than the usual Leech River sediments, and it is possible that they should be correlated with the Haro formation.

FLOWER ISLAND

Flower Island is composed of massive graywacke, grit, and conglomerate which have been considerably broken by folding. The strike and dip varies in different parts of the island, but in general the trend is about north and south and the dip averages around 60 degrees towards the west. The dip and strike at different parts of this island show a remarkable discordance with each other.

SHAW ISLAND

The Leech River sediments occurring on Shaw Island consist chiefly of the basal graywacke member. The rocks in this region are badly shattered and broken, and they contain in-folded and in-faulted fragments and blocks of the Orcas chert. Intrusions of igneous material serve to make the problems in structural geology still more complicated. The same type of conditions are en countered on Canoe Island.

ORCAS ISLAND

The Leech River sediments occurring on Orcas Island to the southeast of Mount Woolard are badly shattered by intense folding and faulting. They have been involved in the minor folding or crumpling which embraces the rooks along the southern side of Orcas Island. The Orcas cherts have been faulted in with the rocks belonging to the Leech River group. The basal graywacke forms the chief representative of the Leech River group in this region, but the overlying breccia and argillite are exposed in several places.

The Orcas cherts which outcrop along the west sides of Mount Entrance and Mount Constitution Range are overlain by the graywackes of the Leech River group. On Mount Constitution Range the graywackes trend about N 35°-45° E and dip towards the southeast at moderate angles. These rocks are largely confined to the basal graywacke member though occasionally the over lying argillites may be seen.

Along the northeast shore of Orcas Island, from Point Lawrence to the foot of Buck Mountain, the Leech River sediments trend about N 60° W and dip towards the southwest at an average angle of about 60 degrees. The strata are composed of thin-bedded graywacke, shale, argillite, slate, schist, grit, conglomerate, limestone, and coal. To the north of Mount Pickett these sediments are broken up by igneous intrusions, and sills of igneous material occur occasionally at all parts of the long straight shore-line.

A series of small lens-shaped deposits of limestone occur intermittently from Raccoon Point to Point Lawrence. These limestones contain a considerable amount of carbonaceous matter and their weathered surfaces are usually black in color. They contain micro-fossils of Carboniferous age. The inner bedded graywacke, grit, and conglomerate strata are composed largely of fragments of the spotted Orcas chert together with fragments of andesite and volcanic tuff.

On the accompanying geological map of the San Juan Islands, a large area in the vicinity of Mount Pickett Range is shown in the color denoting the Turtleback complex. It would have been just as logical to have shown this whole area in the color denoting the rocks of the Leech River group. The former color was adopted for two reasons: (1) The Leech River sediments are badly broken up by igneous intrusions of several kinds; (2) The structure of the rocks in this region would not be well indicated if the whole area were shown as one color. Apparently Mount Pickett Range is located on the axis of a synclinal fold. The southern limb of this fold is largely obliterated by igneous intrusions.

The rocks belonging to the Orcas and Leech River groups on Mount Constitution Range are clearly overthrust upon the Leech River sediments to the northward. The strike of the latter is nearly at right angles to that of the former, and the break or fault line between them is clearly evident. On the east side of the range the fault line is occupied by Mountain Lake.

A fault which apparently has a considerable magnitude extends through the island, following the valley connecting the villages of Olga and Doe Bay. To the southeast of this fault line only the uppermost members of the Leech River group are to he seen, and these are free from igneous intrusions. In general these rocks trend northeasterly and dip towards the southeast. In the vicinity of Obstruction Pass the Leech River graywackes, slates, and conglomerates occur in gently undulating folds. Near its southwest entrance Obstruction Pass occupies the axis of a synclinal fold, while farther eastward it follows the axis of an anticlinal fold.

PLATE XIV. Above: Looking northwestward from the slopes of Mount Constitution. East Sound in the center; Canadian islands in the right background. Below: Honyecomb sandstone on the Sucia Islands.

OBSTRUCTION ISLAND

The graywacke, slate and grit found on Obstruction Island occur in gently undulating folds. At the eastern corner of the island an anticlinal fold plunges towards the eastward at a gentle angle. At the southwest corner of Obstruction Island the strike is about N 45°-50° E, and the dip is about 25° SE.

BLAKELEY ISLAND

The only outcrops of Leech River sediments occurring on Blakeley Island are located on the rocky peninsula which forms its northern extremity. This peninsula is composed largely of conglomerate which appears to be identical with that occurring at Upright Head on Lopez Island. The conglomerates and their interbedded graywackes and slates occurring on Blakeley Island strike about N 60° E and dip about 60° SE.

DOE ISLAND

The thick and thin-bedded argillite and graywacke occurring on Doe Island trend about N 70° E and dip towards the southeast at a gentle angle. These rocks are badly broken up by intrusions of the Eagle Cliff porphyrites.

PEAPOD ROCKS

Peapod Rocks are composed of graywacke, grit, conglomerate, and slate which trend northeasterly and dip towards the southeast. The rocks apparently belong to approximately the same horizons as those occurring in the vicinity of Obstruction Island.

STRAWBERRY ISLAND

The Leech River sediments which compose Strawberry Island, consist of thick-and thin-bedded carbonaceous argillite and graywacke. These rocks trend nearly north and south and the dips are almost vertical. The general dip is slightly towards the eastward.

CYPRESS ISLAND

Sedimentary rocks belonging to the Leech River group occur only at the northern extremity of Cypress Island. They consist chiefly of thin-bedded and dark-colored carbonaceous argillites, slates, and graywackes. Along the shore to the northwest of Eagle Cliff the rocks strike N 70° E and dip 30° SE. To the northeast of Eagle Cliff the Leech River sediments strike N 60°-75° W, and the dip varies from 25 to 55 degrees towards the southwest. The rooks have been considerably distorted by intrusions of the Eagle Cliff porphyrites. To the north of Eagle Harbor a remnant of the Leech River sediments shows a strike of N 60° E and a dip of 60° SE.

TOWHEAD ISLAND

Towhead Island is composed chiefly of dark-colored thin-bedded argillites and slates which strike N 70° E and dip 40° SE.

CONE ISLANDS

Cone Islands are composed of dark-colored thin-bedded schistose argillites and slates which have been intruded by Eagle Cliff porphyrites. One of the more northern islands of the Cone group shows a strike of N 70° E and a dip of 35° S.E. Another one of the islands shows a strike of N 55° E and a dip of 65° S.E.

SINCLAIR ISLAND

The conglomerate, grit, graywacke, and slate occurring along the southern margin of Sinclair Island apparently being the same general horizons as those found in the vicinity of Obstruction Island. The rocks occurring on Sinclair Island have a persistent strike of N 70° E, and the dip varies between 35 and 60 degrees towards the southeast.

LUMMI ISLAND

The southeastern and elevated half of Lummi Island is composed of dark-colored and usually thin-bedded argillite, graywacke, slate, grit, and conglomerate belonging to the Leech River group. These rocks have an average strike of N 40° W and an average dip of 40° NE. At Carter Point the rocks strike N 35° W and dip 40° NE. On Lummi Rocks and along the shore of Lummi Island to the eastward, the strike is N 40°-45° W and the dip is 35° NE. At the northern end of the elevated portion of Lummi Island the strike of the rock formations turns towards the westward. The most northernmost crop along the west side of the island has a strike of N 50°-65° W and a dip of 40°-50° N.E.

Along the east or dip-slope side of Lummi Island the dips and strikes are not consistent. This is due to the fact that in places the slaty rocks bay slipped down the dip-slopes. A few scattered dikes of the Eagle Cliff porphyrites may be seen in this region.

VITI ROCKS

The graywacke and grit composing Viti Rocks strike N 55° W and dip 55° SW. An apparent anticlinal fold occurs between Viti Rocks and the south end of Lummi Island.

ELIZA ISLAND

The dark-colored schistose slates and graywackes occurring at the western extremity of Eliza Island strike north and south and dip at an angle of about 50 degrees towards the east. The rocks occurring at the southern extremity of Eliza Island, and also on Eliza Rock, strike about N 10° E and dip about 10°-25° SE.

JACK ISLAND

Jack Island is composed of silvery-gray phyllite, schist, slate, graywacke, and grit. These rocks are out by numerous veins and stringers of white quartz. At the northern end of the island the strike is N 65° W and the dip is 32° SW. At the southern extremity of Jack Island, the strike is N 75° W and the dip is 30° SW.

SAMISH ISLAND

The schistose slates and graywackes occurring near the western extremity of Samish Island are somewhat carbonaceous, though they possess a silver-gray lustre. The most northern of these outcrops has a strike of N 60°-85° E and a dip of 75°-80° SE. At William Point the strike is N 45° W and the dip is 35° SW. All of these rocks are cut by numerous stringers of quartz.

GUEMES ISLAND

Along the south shore of Guemes Island, near the southeast corner, the thin-bedded carbonaceous and somewhat schistose slates and graywackes strike about N 60° W to N 75° E, and dip towards the south at an angle of about 70 degrees. Immediately north of Boat Harbor the strike of the thin-bedded slaty rocks is N 45° W and the dip is about 80° NE.

The sedimentary rocks belonging to the Leech River group on Guemes Island are so greatly shattered and broken up by igneous intrusions of several periods that the structural features shown by the remnants are not very reliable.

FIDALGO ISLAND

The somewhat carbonaceous graywacke, grit, slate, conglomerate, and argillite occurring on Capsante Peninsula and underlying the City of Anacortes strike about N 20° W and dip about 70°-85° SW.

Age and Correlation. The Leech River group is for the most part of fresh or brackish water origin and virtually unfossiliferous. At intervals the marine waters came in for a sufficient length of time to deposit an occasional limestone bed. The weathered surfaces of these limestones are always covered with a layer of black carbonaceous matter apparently derived from the limestones themselves.

The limestones are usually recrystallized but along the shore of Orcas Island, to the north of Mount Constitution Range, some of them contain micro-fossils in abundance. Among these fossils the foraminifer, Fusulina, is perhaps the most abundant. Some of the beds are composed largely of small fragments of corals and other larger fossils, together with scattered specimens of Fusulina.

Fusulina reached its period of maximum development in the Pennsylvanian time. Since the deposition of the Orcas group of sediments continued on into the Mississippian, the sediments belonging to the Leech River group are probably to a large extent of Pennsylvanian age. The fossil-bearing limestones are probably located several thousand feet above the base of the Leech River group, with several distinct types of lithology intervening. It is probable that the lower members of the Leech River group are Mississippian in age, and that the uppermost members are of Permian and possibly Triassic age.

In the Skagit and Hozomeen ranges of Washington the upper part of the Hozomeen series¹⁴ is to be correlated with the Leech River group. The Cache Creek series of central and northern British Columbia, which is apparently equivalent to the San Juan series, is argillaceous in its upper members and also contains Fusulina-bearing limestones scattered through it. At the International boundary between Washington and British Columbia a group of argillites and graywackes known as the Chilliwack series¹⁵ seems to possess the same general characteristics as the rocks of the Leech River group.

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¹⁴Smith, G. O., and Calkins, F. C., A Geological Reconnaissance Across the Cascade Range near the Forty-ninth Parallel: U. S. Geol. Survey Bull. 235, pp. 22-23, 1904.

¹⁵Daly, R. A., Geology of the North American Cordillera at the Forty-ninth Parallel: Geol. Survey Canada, Mem. 38, pp. 508-516, 1912.

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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.

It is possible that some of the argillaceous rocks occurring in the central elevated portion of the Olympic Mountains are to be correlated with the rocks of the Leech River group.