366 
GEOGEAPHICAL DISTKIBUTION, 
Chap. XI. 
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 Grlacial 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 sub¬ 
stantially 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 sup¬ 
planted 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 
