CENOZOIC ERA: AGE OF MAMMALS 635 



two epochs were not unlike. In the early Eocene (Fort Union), a cool 

 to mild temperate climate, with a much greater rainfall than now, pre- 

 vailed over the Dakotas, Wyoming, Montana, and as far north as 

 the Mackenzie River in Canada, as is shown by the remains of the 

 walnut, hickory, viburnum, grape, elm, poplar, sequoia, and yew, 

 and by the presence of numerous, often thick, beds of lignite. In 

 the earliest Eocene the vegetation of Greenland, Iceland, and Spitz- 

 bergen included alders, magnolias, lindens, poplars, and birches, 

 indicating a climate similar to that of south temperate France and 

 California at the present time. In the later Eocene palms flourished 

 in southern England ; and the waters were tenanted by crocodiles 

 and giant sea snakes, indicating a climate like that of tropical America 

 to-day, and warmer than in the western interior of North America. 



Oligocene. — The climate of the Oligocene in Europe appears to 

 have been slightly cooler than during the Eocene. The occurrence of 

 palms in the Baltic region, however, indicates a temperature such as 

 now prevails in Spain and Italy. Nothing is known of the grasses, 

 and the development of the teeth of the mammals does not afford a 

 positive proof of their presence. The presence of crocodiles in the 

 Oligocene deposits of South Dakota implies a climate such as is now 

 found in Florida. 



Miocene. — Although the vegetation is similar to that of the 

 Oligocene, there is evidence of a gradual lowering of the temperature 

 in the Miocene ; palms ceased to exist north of the Alps ; and towards 

 the end of the epoch there was a lowering of the temperature in the 

 Arctics. In Colorado Miocene deposits no palms have been found, 

 but the presence of figs, which now do not grow north of the coast 

 of the southern states, and of two genera of trees which are now con- 

 fined to the tropics (Weinmania) indicates that the climate of this 

 mountainous region was more equable, moister, and somewhat warmer 

 than now, although it is probable that on the Great Plains arid con- 

 ditions prevailed. A layer of fan-palm leaves a foot in thickness in a 

 formation of this epoch in northern Washington points to almost 

 tropical conditions in that region. The occurrence of breadfruit 

 trees associated with temperate region trees in the Middle Miocene 

 of Oregon indicates a somewhat warmer climate there than now. 



Pliocene. — The gradual cooling of the climate of Europe con- 

 tinued in the Pliocene, during which epoch there was a slow south- 

 ward movement of the northern forest trees and a disappearance 

 of delicate tropical types. Towards the very end of the Pliocene there 



