, during the long lapse of
geological time, whilst an island was being upheaved and formed, 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, would be sure to 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 the 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 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 o