It has been inferred, with much probability, that
the presence of woodland is generally determined by the annual
amount of moisture (3/2. Maclaren, article "America" "Encyclopedia
Brittannica."); yet in this province abundant and heavy rain falls
during the winter; and the summer, though dry, is not so in any
excessive degree. (3/3. Azara says "Je crois que la quantit?
annuelle des pluies est, dans toutes ces contr?es, plus
consid?rable qu'en Espagne."--Volume 1 page 36.) 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 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.
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