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

UPPER CRETACEOUS SYSTEM OR SERIES

NANAIMO SERIES

Principal Features. The rocks of the Nanaimo series^{17, 18, 19} outcrop on the small islands which fringe the northern margin of the San Juan Island group. The rocks are composed of unmetamorphosed conglomerates, grits, arkosic sandstones, and shales. They appear along the north shore of Orcas Island, the outcrops beginning at the base of Buck Mountain and extending westward around Point Doughty and continuing southward as far as Point Kimple. Rocks belonging to the Nanaimo series occur on Stuart Island, Satellite Island, Johns Island, Ripple Island, Cactus Islands, Flattop Island, Gull Rock, White Rocks, Waldron Island, Bare Island, Skipjack Island, Parker Reef, Patos Islands, Sucia Islands, Clements Reef, Matia Islands, and on the Barnes and Clark groups of islands.

---

¹⁷Richardson, James, Report on the Coal Fields of Nanaimo, Comox, Cowichan, Burrard Inlet, and Sooke, British Columbia: Geol. Survey Canada, Report of Progress, 1876-77, pp. 160-192, 1878.

¹⁸Dawson, G. M., The Nanaimo Group: Amer. Jour Sci., vol. 39, pp. 180-183, 1890.

¹⁹Clapp, C. H., Geology of the Nanaimo Map-Area: Geol. Survey Canada, Mem. 51, pp. 1-127, 1914.

---

The outcrops of the upper Cretaceous rocks are usually small and isolated and the geological record is fragmental. These rocks at one time covered the whole map-area with the possible exception of the extreme eastern or southeastern portion. The sediments belonging to the Nanaimo series in this region have not been intruded by any igneous rocks.

On the basis of determinations made on the fossil beds occurring on Sucia Waldron, and Skipjack islands, as well as on Vancouver Island and vicinity, the rocks of the Nanaimo series have been placed in the upper Cretaceous and are essentially equivalent to the Chico Cretaceous of California.

PLATE XV. Above: Upper Cretaceous rocks along the north shore of Orcas Island. Below: Limestone ledge on the shore of East Sound, at the foot of Mount Entrance.

Lithology and Structure. In the type locality the Nanaimo series has been divided into a number of formations mainly on the basis of their lithology^{20, 21} The series is composed entirely of conglomerate, grit, arkosic sandstone, shale, and coal. Though some of the formations are fossiliferous they are noticeably lacking in true limestones.

---

²⁰Clapp, C. H., Geology of the Nanaimo Map-Area: Geol. Survey Canada, Mem. 51, pp. 44-80, 1914.

²¹Clapp, C. H., Sooke and Duncan Map-Areas; Vancouver Island: Geol. Survey Canada, Mem. 96, pp. 224-227, 1917.

---

BARNES AND CLARK ISLANDS

The rocks on the Barnes and Clark group are chiefly coarse conglomerates but they contain interbeds of sandstone and some shale. The pebbles of the conglomerate are composed of andesite, granodiorite, diorite, chert, argillite, graywacke, and specimens of all of the known older formations. The typical matrix is a grayish-brown arkosic sandstone.

The rocks on Barnes Island strike about N 12° E and dip 80° SE. On the north end of Clark Island the rocks strike N 8° W and dip 50° SW.

The southeast end of Clark Island shows a strike of N 30° E, and a dip of 30° SE. The islands and reefs making up the Sisters group, have a similar trend and dip.

Barnes and Clark Islands have been formed by the two limbs of the same syncline and evidently they belong to the same horizon. The north part of Clark Island also forms the limb of an anticline, with the south end and the Sisters group forming the other limb. These folds plunge to the southward at a moderate angle.

Figure 3. Outline map of the Barnes and Clark group of islands.

MATIA ISLANDS

Matia Islands are formed by a fragmental portion of a monoclinal fold which has a persistent strike of N 67° W, and a dip of 68° NE. The islands are composed of three parallel resistant formations separated by two less resistant ones. The latter are formed largely from shale and sandstone. The resistant formations are composed of medium-sized conglomerate and coarse buff-colored arkosic sandstone, with occasional scattered pebbles. In places there are irregular patches of coarse conglomerate. A generalized section across Matia Islands shows:

The sandstones are usually crossbedded and are always arkosic. Occasionally there are fragments of Cretaceous trees which are now turned to coal or partly silicified. The sandstones and conglomerates are evidently delta deposits.

SUCIA ISLANDS

Sucia Islands are formed by the more resistant strata of a plunging syncline, the less resistant ones being covered by sea water. The syncline plunges to the eastward and the individual strata consequently outcrop in the form of a horseshoe, with the open side toward the east.

At the extreme southern edge of Sucia Islands there is a coarse conglomerate with fragments composed almost entirely of the Leech River schists, and fragments of the milky quartz veins that commonly cut these schists. The bluish-gray pulverized schists serve as the matrix of the conglomerate. The larger boulders are composed chiefly of white milky quartz and they stand out in strong contrast with the bluish-colored matrix. Because the conglomerate contains fairly large angular fragments of the fragile schist, and because it contains little besides the fragments of the Leech River schists, the source of the material must have been close at hand. In all probability the conglomerate is the basal member of the Nanaimo series at this locality.

The conglomerate grades upward into a bluish sandy shale composed of pulverized fragments of the schists. This in turn is overlain by light to dark gray sandy shales. The shales are fossiliferous and they contain calcareous and concretionary beds of three inches or so in thickness, at intervals of about 15 feet. The shale appears to be identical with the Haslam formation on Vancouver Island.^{22, 23}

---

²²Clapp, C. H., Geology of the Nanaimo Map-Area: Geol. Survey Canada, Mem. 51, pp. 53-56, 1914.

²³Clapp, C. H., Sooke and Duncan Map-Areas, Vancouver Island: Geol. Survey Canada, Mem. 96, pp. 224-227, 1917.

---

The shale is overlain by a coarse to medium-grained buff-colored sand stone. The sandstone is even-grained and possesses a parting normal to the bedding-plane. For this reason it has been used for the manufacture of paving blocks.

Above the sandstone there is a less resistant formation, presumably a shale, which is entirely covered by soil or by tide-water.

The generalized section as exposed on Sucia Islands, is as follows:

By differential chemical action of the salt water on the sandstones of the Nanaimo series curious erosion surfaces have resulted. Sometimes hollow caverns have been produced, and more commonly the whole surface resembles a honeycomb. (See Plate XIV,B).

The northern limb of the synclinal fold on Sucia Island is also the southern limb of an anticline, with Clements Reef representing the northern dip.

PATOS ISLANDS

Patos Islands are composed entirely of cross-bedded sandstone and conglomerate. The individual strata pinch out rapidly along the strike and no division of the rocks into formations is possible. These cross-bedded sediments were laid down as delta deposits, and excellent examples of top-set, fore-set, and bottom-set beds are now exposed. From the nature of the sediments accurate measurements of the strike and dip are not possible. However, the strike follows parallel to the south shore-line, and the beds always dip to the northward at angles ranging from 45 to 65 degrees. The thickness of the rocks exposed on Patos Islands is about 1450 feet.

PLATE XVI. Above: Point Disney, Waldron Island, showing the immense conglomerate bed overlain by fossiliferous shaly sandstone. Below: The Point Disney conglomerate.

ORCAS ISLAND

The outcrops of the upper Cretaceous rocks occurring along the north and northwest shores of Orcas Island are composed chiefly of thin alternating beds of sandy shale and shaly sandstone. These beds change in lithology rapidly along the trike. The sandstones are generally well cemented, and like all of the rocks of the Nanaimo series in this map-area, they are always arkosic. They contain fragments of volcanic rocks, together with relatively undecomposed fragments of acid plutonic rocks. Quartz, in some instances, is only a subordinate constituent. Silica is the usual cementing material.

The massive conglomerate that forms Point Doughty, besides containing fragments of all of the older rocks exposed on the San Juan Islands, includes boulders of coarse basic plutonic rocks of several varieties not seen in this region. To the southward, and overlying the Point Doughty conglomerate, there are several thinner beds of conglomerate, sandstone, and lignitic shale. The latter are rich in fossil leaf impressions.

Where the beds are not crumpled by thrusting, the rocks of the Nanaimo series on Orcas Island have a persistent strike of N 65° W, and they invariably dip to the southward. It is not probable, however, that the outcrops all belong to a single monoclinal fold, for the section includes several unexposed horizons of great thickness, and the adjoining areas to the west are faulted and broken.

The section, starting from Point Thompson and proceeding south-westward, is as follows:

The lignitic shale containing the fossil plants is crumpled and broken.

Still farther southward the rocks are concealed for a distance of half a mile. At this point a coarse conglomerate bed about 35 feet thick outcrops at the water's edge. The conglomerate bed which forms the greater part of Freeman Island evidently belongs to the same horizon. The sandstone and shale strata on Freeman Island strike N 55° W, dip 65°-75° SW, and overlie the conglomerate. The corresponding strata on Orcas Island are crumpled and broken.

Point Kimple, which is located about three-quarters of a mile south of Freeman Island, is composed of medium-textured conglomerate with thin interbeds of sandstone and shale. There are five horizons of this conglomerate and their general strike is N 80° W. They dip to the southward at angles of 20-30 degrees.

The rocks of the Nanaimo series form a submarine shelf or platform that extends from Orcas Island to Parker Reef. The sandstones and sandy shales which form Parker Reef strike N 65° W and dip to the northward at an angle of 60 degrees. Apparently they represent part of the northern limb of the anticlinal fold, the southern limb of which is exposed on the north shore of Orcas Island.

WALDRON ISLAND

The upper Cretaceous rock exposures on Waldron Island are largely confined to the higher southeast side, and to scattered points along the northern margin. The elevated region extending northeastward from Point Disney is composed of bluish-gray sandstone, coarse conglomerate, and fossiliferous shaly sandstone. The boulders of the conglomerate frequently attain a diameter of several feet. Altered andesite, granodiorite, and chert are the most abundant constituents of the conglomerate boulders, although the older rocks of the region are well represented. In addition, the conglomerate contains many boulders of coarse-textured basic plutonic rocks, and also nephelite and cancrinite syenites, all of which are foreign to this locality.

The rocks composing the southeast side of Waldron Island are folded into a basin-shaped fold. The structure has been complicated by the fact that the formations have slipped on each other with a sort of rotational motion.

Figure 4. Outline map of Waldron and Skipjack Islands.

Scattered outcrops occur along the north shore of Waldron Island, but they cannot be followed inland because of the thick covering of glacial drift. These outcrops are composed of buff-colored sandstone with a minor amount of conglomerate. The sandstones contain abundant remains of fossil Ostrea.

There is an anticlinal fold between Waldron and Bare islands, while between Point Hammond and Fishery Point, there is a synclinal fold. The average strike is about N 65° W. On the east side of the island, immediately north of the elevated region, there appears to be an anticline with an axis that would intersect the opposite side of the island to the south of Fishery Point. Just how the fold was produced in the elevated portion of the island is not clear.

Several years ago a hole was drilled in the east central part of Waldron Island, to a depth of nearly 1500 feet. The writer has not been able to secure the log of the drill-hole, but the greater part of the core is still on the island. The location of the hole was unfortunate, for the drill penetrated through several hundred feet of conglomerate and sandstone the section of which was already well exposed along the shore-line.

BARE ISLAND

Bare Island is composed of alternating beds of conglomerate, grit and buff-colored sandstone. The rocks are cross-bedded, with a strike of N 70°-80° W and dip about 80° NE. Fossil Ostrea are found on this island.

SKIPJACK ISLAND

Skipjack Island is composed of alternating beds of coarse and fine conglomerate, grit, and shaly sandstone. The sandstone is relatively soft, and it is eroded with sufficient rapidity to form embayments with parallel sides between the conglomerate strata. The section on Skipjack Island is about 500 feet thick. The beds strike from N 85° E to nearly east and west, and dip to the northward at an angle of about 70 degrees.

WHITE ROCKS

White Rocks, which are located about a mile to the south of Waldron Island, are composed of grit and conglomerate with some interbeds of coarse sandstone. The beds strike N 30° W and dip 41° NE.

GULL ROCK

Gull Rock is composed of coarse conglomerate with an interbed of less resistant sandstone, the latter being largely eroded away. The beds strike N 65° E. and dip 65° SE.

FLATTOP ISLAND

Flattop Island is composed of about 250 feet of coarse conglomerate, which is underlain by at least 35 feet of thin-bedded dark-gray shale and shaly sandstone. The beds strike N 65°-70° E and dip 25°-26° SE.

RIPPLE ISLAND

The formations exposed on Ripple Island are evidently equivalent to those occurring across the channel on Johns Island. A formation consisting of thick and thin-bedded buff-colored sandstone is overlain by about 125 feet of conglomerate. This in turn is followed by thin-bedded shale and sandstone. The beds strike N 80° W and dip 45° SW.

PLATE XVII. Figs. 1, 2, and 3. Condonella suciensis n.sp. Type specimen. Figs. 4, 5, & 6. Type specimen. Figs. 7 & 8. Cucullaea suciensis n.sp. Type specimen. Fig. 9. Fusulina sp. Enlarged specimen from the limestones of the Leech River group, Orcas Island.

CACTUS ISLANDS

Cactus Islands are composed of conglomerate, cross-bedded sandstone, and shale. The generalised section exposed on East Cactus Island is as follows:

At the east end of Cactus Islands the average strike of the rocks is N 73° W and the dip is 55°-63° SW. At the west end of the group the average strike is about N 65° W and the dip is 60°-66° SW.

JOHNS ISLAND

The generalised section exposed on Johns Island is as follows:

At the east end of Johns Island the beds strike N 65° W and dip about 35° SW. At the west end of the island the beds have an average strike of N 60° W and a dip of 50°-55° SW.

STUART ISLAND

The rocks on Stuart Island have been closely folded into an anticline and a syncline whose general trend is N 70° W (See Fig 4.) About 1500 feet of conglomerate with irregular patches of cross-bedded sandstone are exposed on the north limb of the anticline. Underlying the conglomerate there is a great thickness of alternating layers of dark carbonaceous shale and light gray sandstone. The shale strata usually have a thickness of one to six inches, while the sandstone layers are generally somewhat thicker.

The south limb of the anticline, which is at the same time the north limb of the syncline, is represented most prominently by the conglomerate formation mentioned above. This conglomerate forms a ridge that extends from one end of the island to the other, and it connects the two main parts of the island. The same conglomerate formation expresses itself on the south limb of the syncline, where it forms Tiptop Mountain, the highest elevation on the island. Reid Harbor is located in the axis of an elongated structural basin. Along the shore to the southwest of Tiptop Mountain, the rocks are compressed into chevron folds.

Figure 5. Outline map of Stuart, Satellite, and Johns Island.

SATELLITE ISLAND

Satellite Island is composed of the same formations as those outcropping on Stuart Island. The anticline occurring on Stuart Island extends across Prevost Harbor and embraces the rocks on Satellite Island. The rocks have an average strike of N 80° W.

Age and Correlation. The lignitic shales occurring south of Point Doughty on Orcas Island have been described by Newberry.²⁴ He considered the fossil plants to be identical with those occurring in the sandstones in the vicinity of Bellingham, and all of these formations were referred to the Cretaceous. Some of these lignitic beds contain a large thick-shelled species of Ostrea, which also occurs on Waldron Island in association with known marine upper Cretaceous fossils.

---

²⁴Newberry, J. S., Description of the Fossil Plants Collected by George Gibbs, Geologist to the United States Northwest Boundary Commission under A. Campbell: Jour. Boston Soc. Nat. Hist., vol. 7, pp. 506-525, 1863.

---

The best known fossil beds of this region are those occurring on the Sucia Islands. Species from this locality were described and figured by Meek²⁵ in 1876, by White²⁶ in 1884, and by Whiteaves²⁷ in five volumes, 1876-1903.

---

²⁵Meek, F. B., Descriptions and Illustrations of Fossils from Vancouver and Sucia Islands, and other Northwestern Localities: U. S. Geol. and Geogr. Survey of the Territories, Bull., vol. 2, pp. 351-376, 1876.

²⁶White, C. A., Cretaceous Fossils from Vancouver Island Region: U. S. Geol. Survey, Bull., pp. 33-48, 1884.

²⁷Whiteaves, J. F., Geol. Survey Canada, Mesozoic Fossils, vol. 1-5, 1876, 1903.

---

The fossiliferous formation on the Sucia Islands is 700 feet thick and the fauna contains a great variety of species. The formation, as a whole, may be characterized by the abundance of the following species:

Juoceramus vancouverensis Shumard
Cinula obliqua Gabb
Baculites chicoensis Trask
Crassatellites conradiana Gabb
Trigonia evansana Meek
Margarita ornatissima Gabb
Cyprimeria lens Gabb
Glycimeris suciensis n. sp.

The fossiliferous horizon on Skipjack Island is not more than a foot thick. It is especially characterized by the following:

Perna excavata White
Trigonia evansana Meek
Cinula obliqua Gabb
Glycimeris suciensis n. sp.

At Point Hammond on Waldron Island, a large thick-shelled species of Ostrea occurs in association with Trigonia evansana. The same species of Ostrea occurs near Fishery Point on Waldron Island, on Bare Island, and at various points on Orcas Island. The richest fossil-bearing horizon on Waldron Island is located just above the Point Disney conglomerate. Although a large variety of species is present, it is characterized by Cucullaea ponderosa Whiteaves, Cucullaea truncata Gabb, Glycimeris suciensis n.sp, Cinula obliqua Gabb, and Trigonia evansana Meek.

DESCRIPTION OF NEW GENUS AND NEW SPECIES

GASTROPODA

GENUS CONDONELLA, NEW GENUS

Shell small, discoidal, each whorl being coiled upon the preceding one; umbilicus broadly conical, converging towards the posterior side; anterior side convex; posterior side flat or somewhat concave; each whorl slightly and obliquely emarginate upon the preceding one; aperture sub-ovate to crescent-shaped.

Named in honor of Herbert T. Condon, comptroller of the University of Washington.

CONDONELLA SUCIENSIS n. sp.

Plate XVII. Figs, 1, 2, 3.

Shell consisting of six whorls, increasing rather slowly in size; test thin, sub-nacreous, and crossed obliquely by numerous fine transverse lines.

Dimensions.

Locality. The only specimen known was collected on Sucia Island at a point about 300 feet above the base of the fossil-bearing shales.

Disposal of Type. Paleontological collection of the U. S. National Museum, Washington, D. C.

The specimen was examined by Dr. Stanton and Dr. Dall, who said that it resembled the fresh-water genus, Planorbis, more than any marine form they had ever seen. Since the specimen was found in strata that were rich in strictly marine fossils it cannot be considered as a variety of that genus.

Superfamily ARCACEA Deshayes

GENUS GLYCIMERIS DACOSTA
GLYCIMERIS SUCIENSIS n. sp.

Plate XVII. Figs, 4, 5, and 6.

Shell small, moderately compressed convex, equilateral, and almost round in outline; beaks small, nearly central and incurved, projecting but little above the superior border; outer surface marked by a close, regular net-work of radiating and concentric raised lines.

Dimensions.

Locality. The type specimen was collected on the Sucia Islands where it is fairly abundant. It is also found on Skipjack and Waldron Islands.

Disposal of Type. University of Washington Paleontological Collection.

G. suciensis was classified by Whiteaves as Glycimeris veatchii. The writer examined a large number of specimens from the Sucia Islands, Skipjack Island, and Waldron Island, and none were seen that exceeded the type C. suciensis in size. The type G. veatchii is much higher in proportion to its length, than any of the specimens observed.

GENUS CUCULLAEA LAM.
CUCULLAEA SUCIENSIS n. sp.

Plate XVII. Figs. 7 and 8.

Shell moderately large, ventricose, rounded and equilateral; anterior and posterior ends rounded without any pronounced shoulder; beaks prominent, broad, fairly close together, curved inward and a little forward, placed nearly central; cardinal area moderately large, broad, and marked with well defined, divergent, ligamentary grooves; shell thick, but tapering rapidly at the ventral margin; surface marked by moderately coarse, well defined radiating lines and by irregular and less strongly defined coarse concentric lines.

Dimensions.

Locality. Collected on the Sucia Islands at the south margin of Fossil Bay.

Disposal of Type. University of Washington Paleontological Collection.

C. suciensis is distinguished from C. ponderosa, and from C. fruncata, by its rounded, equilateral shape, and by the character of its surface markings.