DESCRIPTION OF THE ROCKS 701 



recognized Alaskan Triassic faunas. The abundant corals in some of the 

 limestone beds on Gravina Island suggest that they may represent the 

 LoAver ISToric coral fauna of Iliamna Lake. 



It is only at Hamilton Bay, 23 on Kupreanof Island, that Pseudomonotis 

 sub circular is (Gabb), indicative of the boreal Upper Noric, has been 

 found. At this place the Pseudomonotis zone (the strata being over- 

 turned) is separated from the ITalobia zone by a conglomerate which 

 suggests an unconformity corresponding to the one for which the writer 

 believes there is strong evidence at the base of the Pseudomonotis zone in 

 the western part of the Chitina Valley and at Skolai Pass. 



On Admiralty Island there are contorted cherts, somewhat similar to 

 the Upper Triassic cherts of Cook Inlet, apparently overlying the Triassic 

 limestone, but they have yielded no fossils and may not be Triassic. 



The top of the Triassic beds of southeastern Alaska has not been recog- 

 nized, but it is probably marked by a great unconformity, for the next 

 younger sedimentary rocks known in this region are Lower Cretaceous 

 or possibly Upper Jurassic. 



Yukon River.— -The only known Triassic rocks in the Yukon Valley 

 are near the mouth of Nation River, 24 not far below the Canadian bound- 

 ary. They consist of thin-bedded limestones and calcareous shales, at 

 least 400 feet thick, resting probably with unconformity, though without 

 marked discordance of bedding, on a lower Permian ? (Artinskian) lime- 

 stone. The top of the Triassic rocks has not been observed, but since the 

 next younger rocks known in this region are Lower Cretaceous, the upper 

 contact of the Triassic rocks is probably marked by a profound uncon- 

 formity. 



Section of Upper Triassic strata on south bank of Yukon River, 1 mile above 



Nation River 



Feet 



Calcareous shale and shaly limestone with Pseudomonotis subcircularis 

 (Gabb) , Rhynehonella ? sp., and Terebratula sp 20+ 



Calcareous shale and shaly limestone with Halobia cf. superba Mojsiso- 

 yics, Plcurotomaria ? sp., and Glionites ? sp 320 



Limestone with Rliynclwnella sp., Terebratula sp., Spiriferina sp., Halo- 

 bia sp., Aviculipecten sp., Pecten sp., Pleurophorus f sp., Natica ? sp., 

 Orthoceras sp.. Nautilus sp., Popanoceras {Parapopanoceras) ? sp., 

 Monophyllites ? sp., Placites ? sp., and Trachyceras (Protrachyceras) ? 

 cf . lecoutei Hyatt and Smith 60 



(Underlain unconformably ? by lower Permian (?) limestone with an 

 Artinskian fauna.) 



2s w. w. Atwood : Some Triassic fossils from southeastern Alaska. Jour. Geology, 

 vol. 20, 1912, pp. 653-655. 



21 Alfred H. Brooks and E. M. Kindle : Paleozoic and associated rocks on the upper 

 Yukon, Alaska. Bull. Geol. Soc. Am., vol. 19, 1908, pp. 262, 297, 304-305, 313. 



