DESCRIPTION OF THE ROCKS 703 



Pseudomonotis _ su~b circular-is (Gabb), indicating the Upper Noric. The 

 local relations of the rocks of these two areas are not known. 



The Upper Triassic rocks of Canning River, according to the unpub- 

 lished observations- 6 of Mr. E. de K. LemngwelL who has kindly per- 

 mitted the use of the following statement, include limestones, shales, and 

 sandstones aggregating about 500 feet in thickness. They are underlain 

 by Permian ( ?) limestone and are overlain by Lower Jurassic beds'. 



The fauna of these rocks is certainly Upper Triassic, as is shown by 

 the presence of Clionites and of Halobia cf. superb a Mojsisovics. The 

 presence of the latter fossil suggests a position in the middle or Karnic 

 stage of the Upper Triassic, corresponding approximately to the horizon 

 of the Chitistone limestone. The association of such genera as Mega- 

 lodon (?) and Avicidipecten, which are not known from rocks younger 

 than the Triassic, with such genera as Gervillia, Gryplicea, Cardium, 

 Natica, and Atractites, which are not known from rocks older than the 

 Triassic, would in itself indicate the Triassic age of this fauna. This 

 fauna, differs from the better known Triassic faunas of the southern part 

 of Alaska in the entire absence of the corals and of such pelecypods as 

 Myopluoria and Pleuromya, and in the practical absence of the ammonites, 

 especially in the absence of such ammonite genera as Tropites, Juvavites, 

 and Arcestes, which are very abundant in most of the Triassic areas of 

 southern Alaska. It differs also from the other known Alaskan Triassic 

 faunas in the preponderance of the braehiopods and in the presence of 

 Gervillia and Megalodon ('?), and differs from most of the others in the 

 presence of Clionites. The Alaskan fauna most closely related to this 

 occurs in the lowest bed of the Triassic limestone near Nation River. 



The presence of Pseudompnoiis subcircularis (Gabb) in talus and float 

 material at several localities in the Canning River district indicates the 

 presence of beds corresponding to those of the McCarthy formation. The 

 Pseudomonotis zone from which this material was derived may occur 

 either in the uppermost part of this formation or in a thin overlying 

 formation that has not been recognized. 



Northivestern Alaslca. — The known Triassic rocks of northwestern 

 Alaska include cherts, shales, and thin-bedded limestones exposed in sev- 

 eral areas near Cape Lisburne and in an area about 55 miles farther south, 

 near. Cape Thompson. The Triassic rocks of these two districts not only 

 are practically identical in lithologic character, but apparently occur in 

 very similar. stratigraphic relations to the associated formations. 



- 8 E. de K. Lefflngwell : The Canning River region, northern Alaska. IT. S. Geol. Sur- 

 vey, Professional Paper Xo. — . (In preparation.! 



