98 NORTH AMERICA 



and Asiatic steppes, and is due to similar causes. Until 

 recently its substantial buffalo and grama grasses sup- 

 ported large herds of bison and numerous other animals. 

 These are now replaced by half -domesticated cattle, 

 tended by mounted herdsmen known as cow-boys. If, 

 however, the prairies are thus almost exclusively 

 pastoral, irrigation has been the means of rendering 

 available part of their naturally fertile soil for agricul- 

 tural purposes, as the demand for cereals has increased. 

 This is especially the case for the generous lands of 

 Canada bordering on the Great Northern forest, south 

 and west of Winnipeg. There is a striking parallel 

 between the lines of modern development of the great 

 temperate grass areas of the world : the Russian steppe, 

 the Argentine pampa, the African veld, and the American 

 prairie : they are becoming the main granaries of the 

 world. The American prairie, however, enjoys the 

 superiority of greater water-power and easier communi- 

 cations. 



The Western Mountains. The winds from the Pacific 

 are the mainsprings of life in western North America. 

 On their moisture and distribution in relation to the 

 features of the relief depend the manifold changes in 

 the vegetation. Moisture decreases from the coast to 

 the inland mountains, and, on the whole, also from north 

 to south. The windward are moister than the leeward 

 slopes ; again, low-lying areas are drier than the ridges, 

 and moisture increases with altitude up to a belt of 

 greatest rainfall, above which it diminishes rapidly. 

 The plains lying between the mountain ranges are 

 naturally arid as compared with the neighbouring 

 slopes. For all these reasons, western North America 

 may be described broadly as a succession of three parallel 

 wooded chains separated by arid troughs and plateaus. 



