But this is no valid argument against what would be effected by occasional
means of transport, during the long lapse of geological time, whilst the
island was being upheaved, and before it had become fully stocked with
inhabitants. On almost bare land, with few or no destructive insects or
birds living there, nearly every seed which chanced to arrive, if fitted
for the climate, would germinate and survive.
DISPERSAL DURING THE GLACIAL PERIOD.
The identity of many plants and animals, on mountain-summits, separated
from each other by hundreds of miles of lowlands, where Alpine species
could not possibly exist, is one of the most striking cases known of the
same species living at distant points, without the apparent possibility of
their having migrated from one point to the other. It is indeed a
remarkable fact to see so many plants of the same species 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 many 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.
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