706 G. C. MARTIN TRIASSIC ROCKS OF ALASKA 



no proof that Middle Triassic rocks are present in British Columbia, 

 except in the Kamloops district (see page 714). 



UPPER TRIASSIC 



General distribution. — Upper Triassic rocks are widely distributed 

 throughout those parts of Alaska occupied by the Pacific, Rocky, and 

 Arctic Mountain systems, which are the three major mountain regions of 

 that territory. The Triassic deposits in each of these regions constitute a 

 section which, in its general stratigraphic and faunal character, is more 

 or less typical of that entire region, but which differs in greater or less 

 degree from the sections in the other regions. These resemblances and 

 differences possibly mean that the present major mountain areas occupy 

 the sites of Triassic basins of deposition. The most complete local repre- 

 sentation of these rocks is in the Chitina Valley, which must now, and 

 probably will always, be regarded as containing the typical and standard 

 section of the Upper Triassic rocks of Alaska, and more especially of the 

 Pacific Mountain region. The Chitina Valley section is typical in all its 

 more essential features, both stratigraphic and faunal, of the Upper Tri- 

 assic deposits of southern Alaska, although several horizons known in 

 other Alaskan districts hare not yet been recognized here. The Upper 

 Triassic rocks of the region south of the Alaska Eange are underlain in 

 most places by volcanic beds that include the Nikolai greenstone of the 

 Chitina Valley and the similar, and probably corresponding lavas, or tuffs 

 and lavas of other districts. Volcanic rocks are not present in this strati- 

 graphic position north of the Alaska Range, where the Upper Triassic 

 rocks rest directly on late Paleozoic limestones. 



Daivsonites zone. — The occurrence in southeastern Alaska of an Upper 

 Triassic limestone that is probably older than any Upper Triassic beds 

 known elsewhere in Alaska is indicated by the presence, on the shores of 

 Hamilton Bay, Kupreanof Island, of float containing fossils related to 

 Spiriferina borealis Whiteaves and Laivsonites canadense Whiteaves. 

 Neither of these species have been found elsewhere in Alaska or at any 

 American localities except in the Triassic rocks of Liard River, in the 

 eastern foothills of the Rocky Mountains of British Columbia. 



The Triassic rocks of Liard River (see figure 1), according to McCon- 

 nell, 34 "consist of dark shales, usually rather coarsely laminated, and pass- 

 ing into calcareous shales interstratified with sandstones and shaly and 

 massive limestones." The fossils, which have been described by Whit- 



34 R. G. McConnell : Report on an exploration in tlie Yukon and Mackenzie basins, 

 Northwest Territory. Annual Report of the Geological and Natural History Survey of 

 Canada, new series, vol. iv, 1890, pp. 19D, 49D. 



