1832.] CLIMATE AND VEGETATION. 47 



reason is apparent ; the rocky mountains afford protected situa- 

 tions, enjoying various kinds of soil ; streamlets of water are 

 common at the bottoms of nearly every valley ; and the clayey 

 nature of the earth seems adapted to retain moisture. It has 

 been inferred with much probability, that the presence of wood- 

 land is generally determined* by the annual amount of moisture ; 

 yet in this province abundant and heavy rain falls during the 

 winter ; and the summer, though dry, is not so in any excessive 

 degree.! We see n?arly the whole of Australia covered by 

 lofty trees, yet that country possesses a far more arid climate. 

 Hence we must look to some other and unknown cause. 



Confining our view to South America, we should certainly be 

 tempted to believe that trees flourished only under a very humid 

 climate ; for the limit of the forest-land follows, in a most re- 

 markable manner, . that of the damp winds. In the southern 

 part of the continent, where the western gales, charged with 

 moisture from the Pacific, prevail, every island on the broken 

 west coast, from lat. 38 to the extreme point of Tierra del 

 Fuego, is densely covered by unpenetrable forests. On the eastern 

 side of the Cordillera, over the same extent of latitude, where a 

 blue sky and a fine climate prove that the atmosphere has been 

 deprived of its moisture by passing over the mountains, the arid 

 plains of Patagonia support a most scanty vegetation. In the 

 more northern parts of the continent, within the limits of the 

 constant south-eastern trade wind, the eastern side is ornamented 

 by magnificent forests ; whilst the western coast, from lat. 4 S. 

 to lat. 32 S., may be described as a desert : on this western 

 coast, northward of lat. 4 S., where the trade-wind loses its 

 regularity, and heavy torrents of rain fall periodically, the shores 

 of the Pacific, so utterly desert in Peru, assume near Cape Blanco 

 tho character of luxuriance so celebrated at Guyaquil and Pa- 

 nama. Hence in the southern and northern parts of the con- 

 tinent, the forest and desert lands occupy reversed positions with 

 respect to the Cordillera, and these positions are apparently de- 

 termined by the direction of the prevalent winds. In the middle 

 of the continent there is a broad intermediate band, including 



* Maclaren, art. ' America,' Encyclop. Britann. 



T Azara-says, " Je crois que la qnantite annuelle des pluies est, dans toutes 

 oes conlrees, plus considerable qu'cn Espagne." Vol. i. p. 36. 



