704 G. C. MARTIN TRIASSIC ROCKS OP ALASKA 



The Triassic rocks near Cape Thompson 27 consist of cherts, argillites, 

 and thin-bedded limestones aggregating 625 feet in thickness. They rest 

 with apparent conformity on unfossiliferous limestones which overlie a 

 Mississippian (Lower Carboniferous) limestone and which are supposed 

 to be of Carboniferous age. They are overlain with apparent conformity 

 by shales that are possibly Jurassic or Cretaceous. Pseudomonotis sub- 

 circularis (Gabb) has been obtained near the top of the strata referred 

 to the Triassic. 



The Triassic rocks near Cape Lisburne'- 8 consist of thinly bedded black 

 slates, shales, cherts, and cherty limestones, having a thickness of over 

 1,000 feet and containing Pseudomonotis subcircularis (Gabb). Thev 

 constitute the "Middle formation" of the Carboniferous as described by 

 Collier. Neither base nor top of these beds has been recognized, all 

 the observed contacts being faults. The next older rocks known in the 

 vicinity are the Carboniferous ("Mississippian") beds of the Lisburne 

 limestone, and the next younger are the Middle or Upper Jurassic beds 

 of the Corwin formation. 



The southeastward extension of the Pseudomonotis-bearing beds of 

 Capes Lisburne and Thompson is indicated by the presence of cherty 

 limestone float containing Pseudomonotis subcircularis (Gabb) in the 

 Noatak Valley. 29 



Pseudomonotis subcircularis has been found also in float material on 

 Saint Lawrence Island. This does not, however, prove that Triassic beds 

 outcrop on the island, for the fossiliferous boulders may have been trans- 

 ported by ice from the mainland, possibly from the outcrops on the shore 

 near Cape Lisburne. 



General Character and Correlation 

 middle triassic 



The only known Middle Triassic rocks in Alaska are the slates of 

 Brooks Mountain, Seward Peninsula. It has already been shown that 

 these rocks occur in a region where no other Triassic rocks are known, 

 and that Middle Triassic rocks that can be correlated with them do not 

 occur in other Alaskan regions. 



The fossils from this locality include a species of Daonella (see plate 30, 

 figure 3) that is closely related to, although probably not identical with, 



27 E. M. Kindle : The section at Cape Thompson, Alaska. Am. Jour. Sci., 4th ser., vol. 

 28, 1909, pp. 521-522, 526-528. 



28 A. J. Collier : Geology and coal resources of the Cape Lisburne region, Alaska. U. S. 

 Geol. Survey Bull., No. 287, pp. 16. 18, 19-21. pi. 1. 



29 P. S. Smith : The Noatak-Kobuk region, Alaska. U. S. Geol, Survey Bull., No. 536, 

 1913, pp. 79-80. 



