690 G. C. MARTIN TEIASSIC ROCKS OF ALASKA 



MIDDLE TRIASSIC ROCKS 



The only Middle Triassic rocks known in Alaska are some black slates 

 occurring in the York Mountains, in the western part of Seward Penin- 

 sula. The geology at this locality is complex and obscure and has not 

 been studied in detail. It is consequently impossible to describe the 

 stratigraphic relations. All that is known 5 concerning the occurrence of 

 Triassic rocks at this place is that some fossils which were given to E. M. 

 Kindle, and which are said to have been obtained from black slates on 

 Brooks Mountain that were previously considered as probably early Paleo- 

 zoic, include Daonella cf. lommeli Wissman and an undetermined species 

 of Ceratiies ( Gymnotoceras) . 



UPPER TRIASSIC ROCKS 



Chitina Valley (W rang ell Mountains). — The most complete section of 

 Upper Triassic rocks in Alaska which is now known is in the Chitina 

 Valley (see plate 26), where there are several thousand feet of marine 

 Upper Triassic strata, mostly limestones and shales, resting with appar- 

 ent conformity on a thick series of lavas, whose precise age has not been 

 determined, but which are probably either Triassic or late Paleozoic (Per- 

 mian ?). The sequence of Upper Triassic rocks in the eastern and west- 

 ern parts of the Chitina Valley is shown in the following sections: 



General Section of Triassic Rocks in the Nisina Valley 



Upper Triassic: Feet 



McCarthy formation (black shale, with a few thin beds of 

 limestone and with much thin-bedded black chert at the 

 base. Contains Pseudomonotis subcircularis) 1,500=5,500 



(Conformity ?) 



Nizina limestone (thin-bedded limestone, becoming shaly to- 

 ward the top) . No fossils yet found. 1,000-1,200 



( Conformity. ) 



Chitistone limestone (massive bluish gray limestone, with 

 HaloMa cf. superba, Terebratula, Spiriferina, Tropites, Juva- 

 vites ( ?) , Arcestes, and Atractites) l,S00-2,000 



(Conformity ?) 

 Triassic or Permian : 



Nikolai greenstone (basaltic lava flows) 4,000-5,000 



(Basal contact and underlying rocks not exposed.) 



General Section of Triassic Rocks in the Kotsina and Kuskulana Valleys 



Upper Triassic : Feet 



McCarthy formation (black shales, with a few thin beds of 



limestone.. Contains Pseudomonotis subcircularis) 2,000? 



5 E. M. Kindle : The faunal succession in the Tort Clarence limestone, Alaska. Am. 

 Jour. Sci., 4th ser., vol. 32, 1911, p. 329. 



