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 scored rocks plainly reveal a former cold period.
The former influence of the glacial climate on the distribution of the
inhabitants of Europe, as explained by Edward Forbes, is substantially as
follows. But we shall follow the changes more readily, by supposing a new
glacial period slowly to come on, and then pass away, as formerly occurred.
As the cold came on, and as each more southern zone became fitted for the
inhabitants of the north, these would take the places of the former
inhabitants of the temperate regions. The latter, at the same time would
travel further and further 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.
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