CAUSES OF GEOGRAPHICAL DISTRIBUTION. 247 



Hence, on both sides of the ocean, north of the very 

 sinuous boundary of the antarctic or southern fauna, 

 we find ourselves still in the midst of the diluvial animal 

 world, which extended itself, by a bridge in the vicinity 

 of the North Pole, from the old continents to the 

 mainland of America, and there for a longer period re- 

 tained its ancient appearance in the mastodons and 

 horses. 



There, as well as here, the present order of things — 

 the cantonment of animals — has been in many ways de- 

 termined and modified by mighty glacifications and pro- 

 longed periods of refrigeration. Hence the accordance 

 of so many plants of the extreme north with Alpine 

 plants after the Eocene vegetation had made its entry 

 from the east. Since that age, the reindeer has been 

 forced back to the north, and the musk ox has been 

 expelled and exterminated from the Old World. The 

 elephants, fleeing before the ice, have not returned; and 

 the mammoth, immigrating with a rhinoceros from the 

 north-east, has been destroyed with his associate. Others 

 of his comrades, such as the primaeval ox, died out only 

 a fevif centuries ago as wild cattle; others, like the buf- 

 falo and the beaver, are nearly extinct as denizens of 

 Europe; and others again, the deer and roe-deer, will 

 perish with the forests and the game-laws. But of al- 

 most all the species of which we search for the extrac- 

 tion. Palaeontology supplies us with the history and de- 

 rivation; and in derivation we find the causes of geo- 

 graphical distribution sketched in vivid outlines. 



-17 



