EOCENE 499 



the southwestern part of Colorado. This was followed by the very 

 much larger Wasatch lakes, of which there were several, nearly or 

 quite contemporary. The principal body of water extended from 

 New Mexico, over eastern Utah and western Colorado to the Uinta 

 Mountains, around the eastern end of which it formed a strait, 

 expanding again north of the mountains and covering all south- 

 western Wyoming to the Wind River Mountains. This great lake 

 must have been 450 miles long by 250 miles wide in its broadest 

 part. A second lake filled the Big Horn Basin of northwestern 

 Wyoming, which, then as now, was shut in by mountains. In 

 southern Colorado, east of the main range of the Rocky Moun- 

 tains, were two small lakes believed to be of this age. 



The Bridger lakes, which were much smaller than the Wasatch, 

 were not all contemporaneous, but in part successive. The oldest 

 one ( Wind River substage) occupied the Wind River Basin, north 

 of the mountains of that name. Two later lakes were in the upper 

 Green River valley in Wyoming and a third in the same valley 

 south of the Uinta Mountains. Finally, a small lake of this age 

 occupied the Huerfano Canon in southern Colorado. 



A great mountain-making disturbance drained the Bridger lakes, 

 elevating all the ranges to which the post-Cretaceous revolution 

 had given birth and establishing a new lake basin, the Uinta. 

 This basin lies principally to the south of the Uinta Mountains in 

 northeastern Utah and northwestern Colorado, and occupies part 

 of the basin of the Wasatch and Bridger lakes. The three stages 

 of strata may be seen here, one over the other. 



The rocks which were accumulated in these successive lake 

 basins are principally sands and clays, with an occasional gravel 

 bank. They are indurated but still soft rocks which weather 

 readily and give rise to the characteristic bad-land scenery already 

 described. 



The Eocene epoch was brought to a close by a series of move- 

 ments which added a narrow strip of land along the Atlantic and 

 Gulf coasts, at the same time raising northern Florida into an 

 island. In the interior the plateau region was elevated and 

 drained, and no extensive bodies of water were ever established 



