of former glacial action, in huge boulders transported far from their
parent source.
We do not know that the Glacial epoch was strictly simultaneous at
these several far distant points on opposite sides of the world. But we
have good evidence in almost every case, that the epoch was included
within
the latest geological period. We have, also, excellent evidence, that
it endured for an enormous time, as measured by years, at each point.
The cold may have come on, or have ceased, earlier at one point of the
globe than at another, but seeing that it endured for long at each, and
that it was contemporaneous in a geological sense, it seems to me
probable that it was, during a part at least of the period, actually
simultaneous throughout the world. Without some distinct evidence to
the contrary, we may at least admit as probable that the glacial action
was simultaneous on the eastern and western sides of North America, in
the Cordillera under the equator and under the warmer temperate zones,
and on both sides of the southern extremity of the continent. If this
be admitted, it is difficult to avoid believing that the temperature of
the whole world was at this period simultaneously cooler. But it would
suffice for my purpose, if the temperature was at the same time lower
along certain broad belts of longitude.
On this view of the whole world, or at least of broad longitudinal
belts, having been simultaneously colder from pole to pole, much light
can be thrown on the present distribution of identical and allied
species. In America, Dr. Hooker has shown that between forty and fifty
of the flowering plants of Tierra del Fuego, forming no inconsiderable
part of its scanty flora, are common to Europe, enormously remote as
these two points are; and there are many closely allied species. On the
lofty mountains of equatorial America a host of peculiar species
belonging to European genera occur. On the highest mountains of Brazil,
some few European genera were found by Gardner, which do not exist in
the wide intervening hot countries. So on the Silla of Caraccas the
illustrious Humboldt long ago found species belonging
to genera characteristic of the Cordillera. On the mountains of
Abyssinia, several European forms and some few representatives of the
peculiar flora of the Cape of Good Hope occur. At the Cape of Good Hope
a very few European species, believed not to have been introduced by
man, and on the mountains, some few representative European forms are
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