GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 111 



The Uinta is found in the Green River valley of northeastern 

 Utah and northwestern Colorado, where it lies upon the upper 

 Bridger and is the latest of the important Tertiary formations 

 to be found in the plateau region west of the Rocky Mountains. 

 It is probable that the separation of North America from the 

 Old World still continued, for, as a whole, the Uinta fauna 

 is totally different from that of the upper Eocene of Europe. 

 There were, however, a few doubtful forms, which may prove 

 to be the outposts of a renewed invasion. 



The Eocene climate was decidedly warmer than the present 

 one, and subtropical conditions extended over the whole United 

 States and perhaps far into Canada. On the other hand, 

 signs of increasing aridity in the western part of the continent 

 are not wanting, and that must have resulted in a great shrink- 

 age of the forests and increase of the open plains. The vegeta- 

 tion was essentially the same as in the Paleocene, when it had 

 already attained a modern character, the differences from the 

 present being chiefly in regard to geographical distribution. 

 Large palms were then flourishing in Wyoming and Idaho, 

 and another indication of a warm climate is furnished by the 

 large crocodiles which abounded in all of the Eocene stages. 



So far as North America was concerned, the Eocene epoch 

 was brought to a close by extensive movements of the earth's 

 crust, which more or less affected the entire continent and were 

 registered both on the sea-coasts and in the mountain ranges 

 of the interior. Upheaval added a narrow belt of land along 

 the Atlantic and Gulf coasts and the Mississippi Embayment 

 was nearly closed. On the Pacific side the sea withdrew from 

 the great valley of California and Oregon, and in the interior 

 the plateau region was elevated by a great disturbance, which 

 also increased the height of the western mountains. 



Our knowledge of Eocene land-mammals in North America 

 is almost wholly derived from the formations of the western 

 United States, but it may be inferred from the uniform chmatic 

 conditions that there were no very great geographical dif- 



