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 falis during the 
winter; and the summer, though dry, is not so in any excessive 
degree.{_ We see nearly 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. 82° S., may be described as a desert: on this western 
coast, northward of Jat. 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 
the 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. 
+ Azara says, “ Je crois que Ja quantité annuelle des pluies est, dans toutes 
ces contrées, plus considérable qu’en Espagne.”—Vol. i. p. 36. 
