32 THE WANDERINGS OF ANIMALS [CH. 



2. The greater portion of Middle and Western 

 Australia. 



3. South- West Africa, from the coast of Damara- 

 land inwards, including the so-called Kalahari, which 

 however seems to be more like a steppe. 



4. Parts of the South-West of the United States, 

 e.g. Salt- Lake desert, Californian desert, Colorado and 

 Mojave desert of Arizona. This complex stretches far 

 into Northern Mexico. 



5. Parts of Patagonia and Argentina, and a 

 narrow strip along the west coast of Chile. 



As examples of the smallest average annual 

 amount of rainfall the following places may be men- 

 tioned : Copiapo in Chile, less than J inch ; Mojave 

 (Arizona), Suez and Amu Daria (Turkestan) 2^ inches. 

 For comparison, Cambridge with 23 inches. 



It is a common error that such deserts are the 

 beds of former seas. This is true of some, but by far 

 the greater part are not of marine origin ; moreover 

 an old sea-bed need not be barren. The factors 

 which cause deserts have nothing to do with the sea. 

 Most of those areas of land which have no river- 

 drainage into the sea are in time converted into 

 deserts. Witness the Salt Lake of Utah, the Caspi, 

 Aral and the Dead Sea ; they all are centres of sandy 

 deserts, because their rivers cannot carry away the 

 sand out of the country. Sand is, by the way, nothing 

 but the comminuted debris of rocks, of mountains. 



