ers 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 {367} 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 arctic plants and animals, and these would be nearly
the same with those of Europe; for the present circumpolar inhabitants,
which we suppose to have everywhere travelled southward, are remarkably
uniform round the world. We may suppose that the Glacial period came on a
little earlier or later in North America than in Europe, so will the
southern migration there have been a little earlier or later; but this will
make no difference in the final result.

As the warmth returned, t