700 G. C. MARTIN TRIASSIC ROCKS OF ALASKA 



circularis (Gabb) (see plate 29, figure 1), underlain by contorted cherts 

 in which no fossils have been obtained. The cherts are underlain by basic 

 igneous rocks, while the Pseudomonotis-bearing beds are overlain by 

 shales that may be either Triassic or Jurassic. 



Similar contorted cherts, underlain by ellipsoidal lavas beneath which 

 are slates and graywackes, occur near Uyak, on the northwest coast of 

 Kodiak Island. No fossils have been obtained. 



An Upper Triassic limestone occurring on Iliamna Lake 20 has yielded 

 a fauna, composed chiefly of corals, which has not been recognized with 

 certainty elsewhere in Alaska and which, according to Prof. J. P. Smith, 21 

 is of Lower Noric age. No other Triassic rocks are known at this locality. 



Southeastern Alaska. — Upper Triassic rocks occur at several widely 

 distributed localities in southeastern Alaska, where they consist chiefly of 

 limestones having a thickness of apparently only a few hundred feet. A 

 basal conglomerate has been recognized at several localities. The under- 

 lying rocks are Permian (?), except on Gravina Island, where they are 

 Devonian. On Kupreanof Island the Triassic limestone is underlain by 

 ellipsoidal lavas which bear a close resemblance to the lavas that under- 

 lie the Upper Triassic limestones at many other Alaskan localities. These 

 lavas probably overlie a Permian ( ?) limestone. It is possible that much 

 of the greenstone of southeastern Alaska belongs in this position. 



The Triassic limestones of southeastern Alaska are in general charac- 

 terized by faunas containing Ilalobia cf. superba Mojsisovics and conse- 

 quently seem to correspond, at least approximately, in position to the 

 Chitistone limestone, although these faunas contain elements not known 

 in the fauna of the Chitistone limestone and which may indicate either a 

 slightly different horizon or another facies of deposits of the same age. 

 For example, the fossils from Hamilton Bay, Kupreanof Island, include 

 species related to Spiriferina borealis Whiteaves and Trachyceras (Daw- 

 sonites) canadense Whiteaves, which are elsewhere known only in the 

 Triassic rocks of Liard River, British Columbia, and of Bear Island, be- 

 tween Norway and Spitzbergen. 



The Triassic rocks of Gravina Island, 22 which contain only a small pro- 

 portion of limestone, consisting chiefly of conglomerate and shale, contain 

 a. fauna that, although including a species of Ilalobia resembling Ilalo- 

 bia superba Mojsisovics, is of a somewhat different type from the other 



20 G. C. Martin and F. J. Katz : A geologic reconnaissance of the Iliamna region, 

 Alaska. U. S. Geol. Survey Bull., No. 485, 1912, pp. 41-47. 



- 1 James Perrin Smith : The occurrence of coral reefs in the Triassic of North America. 

 Am. Jour. Sci.. 4th ser., vol. 33, 1912, pp. 92-96. 



22 P. S. Smith : Notes on the geology of Gravina Island, Alaska. TJ. S. Geol. Survey, 

 Prof. Paper 95, 1915, pp. 100-104. 



