446 THE TRIASSIC PERIOD 



On each side of that island were the waters of the shallow in- 

 land sea that extended westward across the site of the Wasatch 

 Mountains to the eastern shore of the Great Basin land, which 

 was upheaved at the close of the Carboniferous or Permian ; east- 

 ward the sea extended to an unknown distance. Western Texas, 

 northwestern New Mexico, and the adjoining part of Arizona were 

 covered by these waters, while nearly all of Mexico was land, 

 except an apparently isolated body of water in Sonora. The 

 Mexican land, joined to the Great Basin land, enclosed the sea on 

 the south and west ; northward its waters ended a little beyond 

 the forty-ninth parallel of latitude, and did not extend so far west 

 as the Selkirk and Gold ranges of British Columbia. In some 

 places this inland sea was established by transgression over ancient 

 lands ; in Wyoming, for example, Triassic beds rest upon pre- 

 Cambrian crystalline rocks. 



Over this great area were deposited a series of rocks, chiefly 

 sandstones, containing much gypsum and some salt, an evidence 

 of salt-lake conditions ; but in southwestern Colorado, northwest- 

 ern New Mexico, and western Texas fresh-water conditions pre- 

 vailed, at least toward the end of the period. The thickness of 

 the strata varies from 600 to_ 2000 feet. In this inland Trias very 

 few fossils of any sort have been found, and none of them are 

 marine. In many places the reference of these beds must be 

 made upon purely stratigraphical grounds. 



On the western shore of the Great Basin land we find an en- 

 tirely different state of things from that which obtained on the 

 Atlantic border or in the interior region. The part of the Great 

 Basin area which had been land during the Palaeozoic went down, 

 allowing the ocean to extend across the site of the Sierra and to 

 cover western Nevada, and in British Columbia it submerged the 

 land eastward across the mountains. The Pacific coast-line was 

 thus considerably to the east of its present position, and from it 

 a gulf extended into southeastern Idaho. Marine Trias also re- 

 curs on the shores of Alaska. The Pacific coast Trias has a maxi- 

 mum thickness of 4800 feet, and contains representatives of nearly 

 all the series which make up the system. Its successive faunas 



