migrated from one to the other. It is indeed a remarkable fact to see
so many of the same plants living on the snowy regions of the Alps or
Pyrenees, and in the extreme northern parts of Europe; but it is far
more remarkable, that the plants on the White Mountains, in the United
States of America, are all the same with those of Labrador, and nearly
all the same, as we hear from Asa Gray, with those on the loftiest
mountains of Europe. Even as long ago as 1747, such facts led Gmelin to
conclude that the same species must have been independently created at
several distinct points; and we might have remained
in this same belief, had not Agassiz and others called vivid attention
to the Glacial period, which, as we shall immediately see, affords a
simple explanation of these facts. We have evidence of almost every
conceivable kind, organic and inorganic, that within a very recent
geological period, central Europe and North America suffered under an
Arctic climate. The ruins of a house burnt by fire do not tell their
tale more plainly, than do the mountains of Scotland and Wales, with
their scored flanks, polished surfaces, and perched boulders, of the
icy streams with which their valleys were lately filled. So greatly has
the climate of Europe changed, that in Northern Italy, gigantic
moraines, left by old glaciers, are now clothed by the vine and maize.
Throughout a large part of the United States, erratic boulders, and
rocks scored by drifted icebergs and coast-ice, plainly reveal a former
cold period.
The former influence of the glacial climate on the distribution of the
inhabitants of Europe, as explained with remarkable clearness by Edward
Forbes, is substantially as follows. But we shall follow the changes
more readily, by supposing a new glacial period to come slowly on, and
then pass away, as formerly occurred. As the cold came on, and as each
more southern zone became fitted for arctic beings and ill-fitted for
their former more temperate inhabitants, the latter would be supplanted
and arctic productions would take their places. The inhabitants of the
more temperate regions would at the same time travel southward, unless
they were stopped by barriers, in which case they would perish. The
mountains would become covered with snow and ice, and their former
Alpine inhabitants would descend to the plains. By the time that the
cold had reached its maximum, we should have a uniform arctic fauna and
flora, covering the central parts of Europe, as far
south as the Alps and Pyrenees, and even stretching into Spain. The now
temperate regions of the United States would likewise be covered by
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