The fauna also of the glacial epoch in North America is less rich in
species than that now inhabiting the adjacent sea, whether in the Gulf of St.
Lawrence, or off the shores of Maine, or in the Bay of Massachusetts.
The extension on the American continent of the range of erratics during the
Post-pliocene period to lower latitudes than they reached in Europe, agrees well
with the present southward deflection of the isothermal lines, or rather the
lines of equal winter temperature. It seems that formerly, as now, a more
extreme climate and a more abundant supply of ice prevailed on the western side
of the Atlantic. Another resemblance between the distribution of the drift
fossils in Europe and North America has yet to be pointed out. In Canada and the
United States, as in Europe, the marine shells are generally confined to very
moderate elevations above the sea (between 100 and 700 feet), while the erratic
blocks and the grooved and polished surfaces of rock extend to elevations of
several thousand feet.
I have already mentioned that in Europe several quadrupeds of living, as well as
extinct, species were common to pre-glacial and post-glacial times.
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