272 THE SURVIVAL OF THE UNLIKE. [xV. 



regions again became warm. The gi-eat fluvial period 

 came in, when arctic lands were lower than at present, 

 when the sea stood five hundred feet above its present 

 level, and when the northern rivers were vastly larger 

 than now. This great expanse of water and low eleva- 

 tion of land caused the warmer climate of the high 

 north. Elephants and rhinoceroses roamed northwards 

 to the very shores of the Arctic Ocean, and lions, elks, 

 horses, buffaloes and mastodons inhabited the high 

 latitudes. In the ice of Siberia the elephants are still 

 found, even with the hair intact, preserved in nature's 

 refrigerator for ages. There is evidence that northwest- 

 ern America and northeastern Asia were more closely 

 connected by land than now. The Siberian elephant 

 roamed from one continent to the other. "I cannot 

 imagine a state of circumstances," writes Gray, "under 

 which the Siberian elephant could migrate and temper- 

 ate plants could not." So the floras of America and 

 Asia again became coterminous. 



Now came another change. The terrace epoch 

 came slowly on. The arctic lands were elevated, the 

 water receded and the temperature fell. The earth 

 approached its present condition. The plants were 

 again driven southwards down Asia and America. 

 The western coast of America, by reason of ocean 

 currents, was warmer than the eastern region or than 

 the Japanese region, and the temperate floras went 

 down or persisted in similar climates, giving our Alle- 

 ghany regions and eastern Asian and Himalayan 

 countries similar floras. Subsequently, only minor 

 distributions have taken place. The eastern Asian 

 flora has shown some tendency to extend westward, 

 and some species have reached Europe. Thus we 



