702 G. C. MARTIN TRIASSIC ROCKS OF ALASKA 



Three more or less distinct faunal zones arc indicated by the fossils 

 from the Triassic rocks near Nation River. The fauna of the lower lime- 

 stone differs strikingly from any of the Triassic faunas recognized in the 

 southern part of Alaska. Its Upper Triassic age is indicated by the. 

 ammonites, doubtfully identified as Monophyllites, Placites, and Trachy- 

 ceras (Protmchy cents) lecontei. The ammonite doubtfully identified as 

 Pdpanoceras (Parapopan.occras) sp. is suggestive of the Middle Triassic, 

 but, since it is an immature specimen, its evidence is inconclusive am! is 

 overbalanced by that of the other fossils. The fauna differs strikingly 

 from that of the Chitistone limestone and supposedly equivalent beds of 

 the southern part of Alaska in the absence of such characteristic fossils 

 as Tropites, Juvtivites, Arcesies, and IJalobia cf. superba, and in the 

 abundance of the brachiopods and nautiloids. Its nearest relations among 

 the knoAvn Alaskan faunas are with a fauna found on Canning River, 

 with which it has several species in common, and possibly with some of 

 the collections from Hamilton Bay on Kupreanof Island. 



The calcareous shales and shaly limestones, with Ilalobia cf. superha,. 

 Phurotomaria (?), and Clionites (?), which overlie the limestone just 

 discussed and make up the greater part of the section exposed at this 

 locality, are to be correlated approximately with the Chitistone limestone, 

 although their fauna also differs from those of southern Alaska and 

 resembles that of Canning River in the absence of the common ammonites 

 of the southern region and in the probable presence of Clionites. 



The beds at the top of the section, containing Pseuclomonotis suhcircu- 

 laris (Gabb), represent the boreal Upper Noric horizon of the McCarthy 

 formation. 



Northeastern Alaska (Firth and Canning valleys). — The Upper- Tri- 

 assic rocks of northeastern Alaska are known in two districts — in the 

 Firth Valley near the Canadian boundary, and in the vicinity of Canning 

 River about 130 miles farther vest. The Triassic rocks of these two 

 districts are much alike, consisting mostly of limestone and shale. In 

 both districts the underlying rocks are Permian (?) limestones, while 

 probably in both places (certainly on Canning Paver) the overlying beds 

 are Lower Jurassic shales. 



The Upper Triassic rocks of Firth Piver 25 include black shales, thin- 

 bedded shaly limestones, and possibly some massive limestone. They 

 occur in two areas, in one of which the rocks contain Ilalobia cf. superha 

 Mojsisovics, indicating a Karnic horizon, and in the other they contain 



- 5 A. G. Maddren : Geologic investigations along the Canada-Alaska boundary. U. S. 

 Geol. Survey Bull.. No. 520, 1912, pp. 300. 312-313. 



