THE COLONIZA TION OF NE W ENGLAND. 271 



narrow tenure of the land. Drawn into the cur- 

 rents of air that sweep the mountain's side they 

 are forced downward, to be parched in the valleys 

 below. Yet they maintain themselves. They are 

 fighting it out on that line." 



That the great bulk of our fauna, however, is 

 composed of southern types is evident, and may 

 be explained by the direction of the mountain 

 chains, which form no barrier to the northward 

 march of animals ; while our poverty, as com- 

 pared with Europe, may be due to the form of the 

 continents themselves, the tropical lands of 

 America being scattered about among islands, or 

 connected with the northern temperate zone by 

 a very narrow isthmus ; while Europe, on the 

 other hand, has easy connection with all parts of 

 the Old World. 



