STEPPES OF ASIA AND AMERICA 57 



It is the steppes of the more remote parts of the world 

 which now support the vast herds of sheep, horses, and 

 cattle necessary for the wants of civilized communities. 

 Further, as steppe regions do not require to be cleared 

 of trees, and, where the rainfall is sufficient, often pro- 

 duce abundant crops, we find that it is in the steppe 

 regions that the cultivation of cereals is being most 

 vigorously pushed at the present time. The regions of 

 dense population are mostly regions of abundant rain, 

 and therefore were once forest regions. Formerly these 

 watered lands were liable to be periodically flooded by 

 the overflow of the fertility of the steppes. This great 

 tide is now being gradually regulated, and the steady 

 stream of wheat, of wool, of meat, and so forth, which , 

 pours into the civilized world, is the biological equiva- 

 lent of the flocks of rodents and the flights of locusts 

 which the steppe sent out in earlier days, and of the 

 hordes of wandering nomads which came later. 



To this general account we may add a few words on 

 the special conditions, climatic and other, found in the 

 steppes of temperate Asia, the region to which the 

 following description specially refers. Steppe condi- 

 tions reign over that great area of Central Asia which 

 is practically ringed by mountain chains, as well as to 

 the west of it, but the fauna throughout this area is 

 not uniform. The mountain chains themselves have 

 their own characteristic animals, and the plateau of 

 Tibet, with special conditions of climate, has a peculiar 

 fauna of its own. Excluding Tibet and the mountain 

 chains then, we have a great steppe and desert area 

 which extends from the eastern base of the Pamirs to 

 the Khingan Mountains, and is separated from the 

 forest region to the north by the great area of elevated 

 ground in which the Siberian rivers arise, and from the 



