I was much struck with the marked difference between the vegetation of
these eastern valleys and those on the Chilian side: yet the climate,
as well as the kind of soil, is nearly the same, and the difference of
longitude very trifling. The same remark holds good with the
quadrupeds, and in a lesser degree with the birds and insects. I may
instance the mice, of which I obtained thirteen species on the shores
of the Atlantic, and five on the Pacific, and not one of them is
identical. We must except all those species, which habitually or
occasionally frequent elevated mountains; and certain birds, which
range as far south as the Strait of Magellan. This fact is in perfect
accordance with the geological history of the Andes; for these
mountains have existed as a great barrier since the present races of
animals have appeared; and therefore, unless we suppose the same
species to have been created in two different places, we ought not to
expect any closer similarity between the organic beings on the opposite
sides of the Andes than on the opposite shores of the ocean. In both
cases, we must leave out of the question those kinds which have been
able to cross the barrier, whether of solid rock or salt-water. [5]
A great number of the plants and animals were absolutely the same as,
or most closely allied to, those of Patagonia. We here have the agouti,
bizcacha, three species of armadillo, the ostrich, certain kinds of
partridges and other birds, none of which are ever seen in Chile, but
are the characteristic animals of the desert plains of Patagonia. We
have likewise many of the same (to the eyes of a person who is not a
botanist) thorny stunted bushes, withered grass, and dwarf plants. Even
the black slowly crawling beetles are closely similar, and some, I
believe, on rigorous examination, absolutely identical. It had always
been to me a subject of regret, that we were unavoidably compelled to
give up the ascent of the S. Cruz river before reaching the mountains:
I always had a latent hope of meeting with some great change in the
features of the country; but I now feel sure, that it would only have
been following the plains of Patagonia up a mountainous ascent.
March 24th.--Early in the morning I climbed up a mountain on one side
of the valley, and enjoyed a far extended view over the Pampas. This
was a spectacle to which I had always looked forward with interest, but
I was disappointed: at the first glance it much resembled a distant
view of the ocean, but in the northern parts many irregularities were
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