We have
found it reaching, by its contiguous islands, within one hundred and
fifty miles of the coast of Europe on the one side, and almost touching
the West India Islands on the other, while, by its connecting ridges, it
bound together Brazil and Africa.
But it may be said these animals and plants may have passed from Asia to
America across the Pacific by the continent of Lemuria; or there may
have been continuous land communication at one time at Behring's Strait.
True; but an examination of the flora of the Pacific States shows that
very many of the trees and plants common to Europe and the Atlantic
States are not to be seen west of the Rocky Mountains. The magnificent
magnolias, the tulip-trees, the plane-trees, etc., which were found
existing in the Miocene Age in Switzerland, and are found at the present
day in the United States, are altogether lacking on the Pacific coast.
The sources of supply of that region seem to have been far inferior to
the sources of supply of the Atlantic States. Professor Asa Gray tells
us that, out of sixty-six genera and one hundred and fifty-five species
found in the forests cast of the Rocky Mountains, only thirty-one genera
and seventy-eight species are found west of the mountains.
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