u] FEATURES OF ENVIRONMENT 31 



degrees of deserts, unmitigated deserts, periodical 

 deserts shading into rather arid stretches, semi- 

 deserts, and lastly steppes, pampas or prairies which 

 are subject to prolonged drought, periodical or un- 

 certain. As a rule bad deserts are surrounded by 

 a belt of half-deserts, and these pass into fair pasture 

 land. The French word prairie, the Russian steppe 

 and the South American pampa practically mean the 

 same, namely grassy plain. 



We mostly associate with the idea of a desert a 

 boundless extent of sand without any vegetation, 

 but this is not necessarily the case. There are huge 

 deserts, which are stony, or rocky tablelands, or full 

 of chains of mountains, and again there are sandy 

 deserts with even tree-like growth on them, and 

 certainly with grass, which however may be so scanty 

 that one appreciates it only if he lies down upon 

 the ground and then observes the grey-green shim- 

 mer. 



There are, broadly speaking, five such arid com- 

 plexes in the world. 



1. The largest extends from the coast of North- 

 West Africa through the Sahara and thence with 

 many interruptions through Arabia and Persia into 

 North- West India ; the neighbourhood of Lakes Caspi 

 and Aral, Turkestan, great portions of Tibet and of 

 Mongolia, there as the so-called Gobi or Shamo, i.e. 

 sea of sand. 



