2 VERTEBEATA OF THE TERTIARY. 



the west side of the range was a broad continent, composed of mostly- 

 marine Mesozoic rocks, whose boundaries are not yet well ascertained. 

 Towards the close of the Laramie the bed of the grreat eastern sea begran to 

 emerge from the watere, and the continent of the western side of the great 

 range descended. The relations of the two regions were changed ; the 

 east became the continent and the west became the sea. The latter, receiv- 

 ing the drainage of the surrounding lands, was a body of fresh water, whose 

 connection with the ocean permitted the entrance of a few marine fishes 

 only. This was the great AVasatch Lake, whose deposits extend from the 

 headwaters of the Yellowstone far south into New Mexico and Arizona, 

 between the Eocky Mountains on the east and the Wasatch range on the 

 west. Its absence from the east side of the former range indicates the con- 

 tinental condition of that area at the time. The only locality where the 

 Wasatch deposits ai-e extensively deposited on the Laramie, is in the region 

 intermediate between the two di.stiicts in Wyoming and New Mexico. Here 

 the sediments of the former are seen to have succeeded those of the latter, 

 and to have been coincident with an entire cessation of brackish conditions. 

 Elevations of the continent northward and southward conti'acted the area 

 of the gi-eat Wasatch sea, and perhaps deepened it, for at this time were 

 deposited the fine limestones and silico-calcareous shales of the Green River 

 epoch. There is no evidence that these beds had a greater eastern exten- 

 sion than that of the parent Wasatch Lake. King has given distinct 

 names to these ancient lakes. I think it better to pursue the usual course 

 of using for them the names already given to their deposits, as involving 

 less strain on the memor}- ; the more as the number of these lakes will be 

 probably enlarged by future discoveries. The only known region covered 

 by this lake west of the Wasatch range, is represented to-day by the 

 calcareous strata in Central Utah, which I have called the Manti beds. The 

 exact equivalency of these is, however, not quite certain. Fiu-ther con- 

 traction reduced this area to perhaps two lake basins, whose deposits now 

 form two isolated tracts in Southern Wyoming, and are known as the 

 Bridger formation. Continued elevation and di-ainage caused the desicca- 

 tion of these basins also, leaving only, so far as present knowledge extends, 

 a body of water on the south of the Uinta Mountains, in Northeastern 



