g trees, as Humboldt says the Orinoco alligators are; might be
early colonists. It is manifest, too, that reptiles of other kinds would
be among the first vertebrata to people the new continent. If we
consider what will occur on one of those natural rafts of trees, soil,
and matted vegetable matter, sometimes swept out to sea by such currents
as the Mississippi, with a miscellaneous living cargo; we shall see that
while the active, hot-blooded, highly-organized creatures will soon die
of starvation and exposure, the inert, cold-blooded ones, which can go
long without food, will live perhaps for weeks; and so, out of the
chances from time to time occurring during long periods, reptiles will
be the first to get safely landed on foreign shores: as indeed they are
even now known sometimes to be. The transport of mammalia being
comparatively precarious, must, in the order of probability, be longer
postponed; and would, indeed, be unlikely to occur until by the
enlargement of the new continent, the distances of its shores from
adjacent lands had been greatly diminished, or the formation of
intervening islands had increased the chances of survival. Assuming,
however, that the facilities for immigration had become adequate; which
would be the first mammals to arrive and live? Not large herbivores; for
they would be soon drowned if by any accident carried out to sea. Not
the carnivora; for these would lack appropriate food, even if they
outlived the voyage. Small quadrupeds frequenting trees, and feeding on
insects, would be those most likely both to be drifted away from their
native lands and to find fit food in a new one. Insectivorous mammals,
like in size to those found in the Trias and the Stonesfield slate,
might naturally be looked for as the pioneers of the higher vertebrata.
And if we suppose the facilities of communication to be again increased,
either by a further shallowing of the intervening sea and a consequent
multiplication of islands, or by an actual junction of the new continent
with an old one, through continued upheavals; we should finally have an
influx of the larger and more perfect mammals.

Now rude as is this sketch of a process that would be extremely
elaborate and involved, and open as some of its propositions are to
criticisms which there is no space here to meet; no one will deny that
it represents something like the biologic history of the supposed new
continent. Details apart, it is manifest that si