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 remarkable 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 latitude 38 degrees to the extreme point of Tierra del Fuego, is densely covered by impenetrable 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 latitude 4 degrees South to latitude 32 degrees South, may be described as a desert; on this western coast, northward of latitude 4 degrees South, 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 Guayaquil and Panama.

Hence in the southern and northern parts of the continent, the forest and desert lands occupy reversed positions with respect to the Cordillera, and these positions are apparently determined by the direction of the prevalent winds.