We know that the extreme regions of North America many degrees
beyond the limit where the ground at the depth of a few feet
remains perpetually congealed, are covered by forests of large and
tall trees. (5/9. See "Zoological Remarks to Captain Back's
Expedition" by Dr. Richardson. He says, "The subsoil north of
latitude 56 degrees is perpetually frozen, the thaw on the coast
not penetrating above three feet, and at Bear Lake, in latitude 64
degrees, not more than twenty inches. The frozen substratum does
not of itself destroy vegetation, for forests flourish on the
surface, at a distance from the coast.") In a like manner, in
Siberia, we have woods of birch, fir, aspen, and larch, growing in
a latitude (64 degrees) where the mean temperature of the air falls
below the freezing point, and where the earth is so completely
frozen, that the carcass of an animal embedded in it is perfectly
preserved. (5/10. See Humboldt "Fragmens Asiatiques" page 386:
Barton's "Geography of Plants"; and Malte Brun. In the latter work
it is said that the limit of the growth of trees in Siberia may be
drawn under the parallel of 70 degrees.) With these facts we must
grant, as far as QUANTITY ALONE of vegetation is concerned, that
the great quadrupeds of the later tertiary epochs might, in most
parts of Northern Europe and Asia, have lived on the spots where
their remains are now found.
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