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. (15/5. This is merely
an illustration of the admirable laws, first laid down by Mr.
Lyell, on the geographical distribution of animals, as influenced
by geological changes. The whole reasoning, of course, is founded
on the assumption of the immutability of species; otherwise the
difference in the species in the two regions might be considered as
superinduced during a length of time.)
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.
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