LIFE ON PLAINS 405 



of cattle, and by the aid of irrigation will soon possess 

 great agricultural wealth. 



188. Life on Plains. The life conditions on plains are 

 very different from those in places where the irregularities 

 of the surface are great. The climate of plains is quite 

 uniform and depends to a large extent upon their position 

 on the earth's surface. Movement is as easy in one direc- 

 tion as in another, and the lines of travel tend to be 



A HERD OF CATTLE ON THE GREAT PLAINS. 



straight. There is usually no reason for an accumulation 

 of population in any one place, so the population tends to 

 be uniformly distributed. 



As movement from place to place is easy, it is not dif- 

 ficult for the inhabitants of a plain to mass themselves 

 together at one point. In case of invasion by a superior 

 enemy there is no place for hiding or safe retreat, and sub- 

 jection or extermination are the alternatives, unless the 

 plain is so large that the enemy is unable to spread over 

 it. In the case of animals this has been shown in the 

 practical extermination of the American bison and ante- 

 lope. In the case of men it was shown on the plains of 

 Russia in the thirteenth century when the Tartars con- 

 quered the region and threatened to overrun Europe. 



