beyond the thirtieth parallel, the Andes serve as a screen
to intercept the moisture brought by the prevailing winds from the
Pacific Ocean: rains are copious on their summits, and in Chili on their
_western_ declivities; but none falls on the plains to the _eastward_,
except occasionally when the wind blows from the Atlantic."[1000]

I have been more particular in explaining these views, because they
appear to place in a true light the dependence of vegetation on climate,
the humidity being increased, and more uniformly diffused throughout the
year, by the gradual spreading of wood.

It has been affirmed, that formerly, when France and England were
covered with wood, Europe was much colder than at present; that the
winters in Italy were longer, and that the Seine, and many other rivers,
froze more regularly every winter than now. M. Arago, in an essay on
this subject, has endeavored to show, by tables of observations on the
congelation of the Rhine, Danube, Rhone, Po, Seine, and other rivers, at
different periods, that there is no reason to believe the cold to have
been in general more intense in ancient times.[1001] He admits, however,
that the climate of Tuscany has been so far modified, by the removal of
wood, as that the winters are less cold; but the summers also, he
contends, are less hot than of old; and the summers, according to him,
were formerly hotter in France than in our own times. His evidence is
derived chiefly from documents showing that wine was made three
centuries ago in the Vivarais and several other provinces, at an earlier
season, at greater elevations, and in higher latitudes, than are now
found suitable to the vine.

There seems little doubt that in the United States of North America the
rapid _clearing_ of the country has rendered the winters less severe and
the summers less hot; in other words, the extreme temperatures of
January and July have been observed from year to year to approach
somewhat nearer to each other. Whether in this case, or in France, the
_mean_ temperature has been raised, seems by no means as yet decided;
but there is no doubt that the climate has become, as Buffon would have
said, "less excessive."

I have before shown, when treating of the excavation of new estuaries in
Holland by inroads of the ocean, as also of the changes on our own
coasts, that although the conversion of sea into land by artificial
labors may be great, yet it must always be in subordination to the