TRIASSIC. 545 



The evidence gathered from the study of a few fossils found in the area, while not con- 

 clusive, is in favor of referring at least a portion of the series to the Triassic. 



A group of rocks similar in many respects to the above occurs along the Macmillan River 

 40 or 50 miles to the south, but the black chert beds found in that area are absent in the Stewart 

 River series. 



B 3. CAPE THOMPSON, NORTHWESTERN ALASKA. 



In describing the section of Carboniferous and Triassic strata which lie in a 

 syncline south of Point Hope and Cape Thompson, Kindle ^°°^ says : 



The higher beds of the Cape Thompson section are brought in contact with the beds already 

 described [Carboniferous] in the midst of a zone of rather local but complicated folding and 

 possibly of faulting, which renders it impossible to give even an approximate estimate of their 

 thickness as seen from the top of the southeastern portion of the Cape Thompson cliffs; but 

 between the second and the fourth deep ravines separating the high ridges just southeast of 

 the cape along the coast the exposures are continuous for 2 miles, exposing a section of northerly 

 dipping beds in which the dip decreases from 35° to near the middle of the synclinal. We 

 find in the series of cliffs which face the sea to the southeast of the second ravine below Cape 

 Thompson a section which passes without structural complications from the fossiliferous 

 Carboniferous limestones to the top of the highest beds exposed in this vicinity. This section 

 is as foUows: 



Section 2 miles southeast of Ca'pe Thompson. 



Feet. 



(c) Soft black shales 500+ 



(d) Dark cherts and thin-bedded cherty limestones with some greenish bands 25 



(c) Argillites with bands of black, green, and dull red cherts 600 



(6) Light-gray limestone, weathering buff, with some bands of dark chert; apparently barren 



of fossils 2. 000+ 



(a) Light-gray limestone similar to the above, but with less chert and containing numerous 



fossils in which corals are conspicuous 3, 000+ 



In the upper part of the lowest division of this thick limestone series, a of the section, 

 fossds are fairly abundant. * * * Only a few were collected, however. These are given 

 in the following list by Dr. Girty, whose remarks on the general faunal relations of these faunas 

 have already been given. 



Lot 15 A. — Zaphrentis sp., Spirifer aff. striatus, Composita? sp. 



The close physical resemblance of the second division (&) of the limestone series to the 

 lower leaves little doubt that it is also of Carboniferous age. It may represent the Upper 

 Carboniferous, which has not been recognized anjrwhere on the northwestern coast of Alaska, 

 though known on the Yukon and in southeastern Alaska. 



The lithologic change at the top of this limestone series is abrupt. The beds included in 

 c and d are essentially similar, and represent the same formation, although there is less of the 

 calcareous element in the lower beds. FossUs were found, however, only in the upper beds 

 marked d in the section. They occur in great abundance in certain strata in this portion 

 of the section. About 7 feet near the top are composed almost exclusively of shells which 

 have been largely altered to chert. Dr. T. W. Stanton has furnished the following report 

 on the fossils secured from this horizon: 



"Lot 15d. Mouth of creek 2 miles southeast of Cape Thompson. 



"This collection consists of limestone fragments with numerous specimens of aviculoid 

 shells referable to Psevdomonotis subdrcularis (Gabb) or to a closely related species. No 

 other recognizable species are associated with it. This species occurs in an Upper Triassic 

 horizon in California, and it has been accepted as sufficient evidence for the Triassic age of 

 rocks containing it at Cold Bay and in the Copper River region of Alaska. In my opinion, 

 the horizon which yielded it at Cape Thompson is also Upper Triassic. 



"Among the collections obtained by Mr. Collier in the Cape Lisbume region some years 

 ago there are several small lots consisting mainly of a form that seems to be identical with 

 48011°— 12 35 



