ersa', and the more the natural
habits of animal and vegetable species are examined, the more do they
seem, on the whole, limited to particular provinces. But when we look
into the facts established by the study of the geographical distribution
of animals and plants it seems utterly hopeless to attempt to understand
the strange and apparently capricious relations which they exhibit.
One would be inclined to suppose 'a priori' that every country must be
naturally peopled by those animals that are fittest to live and thrive
in it. And yet how, on this hypothesis, are we to account for the
absence of cattle in the Pampas of South America, when those parts
of the New World were discovered? It is not that they were unfit for
cattle, for millions of cattle now run wild there; and the like holds
good of Australia and New Zealand. It is a curious circumstance, in
fact, that the animals and plants of the Northern Hemisphere are not
only as well adapted to live in the Southern Hemisphere as its own
autochthones, but are in many cases absolutely better adapted, and so
overrun and extirpate the aborigines. Clearly, therefore, the species
which naturally inhabit a country are not necessarily the best adapted
to its climate and other conditions. The inhabitants of islands are
often distinct from any other known species of animal or plants (witness
our recent examples from the work of Sir Emerson Tennent, on Ceylon),
and yet they have almost always a sort of general family resemblance to
the animals and plants of the nearest mainland. On the other hand, there
is hardly a species of fish, shell, or crab common to the opposite sides
of the narrow isthmus of Panama. Wherever we look, then, living nature
offers us riddles of difficult solution, if we suppose that what we see
is all that can be known of it.

But our knowledge of life is not confined to the existing world.
Whatever their minor differences, geologists are agreed as to the vast
thickness of the accumulated strata which compose the visible part of
our earth, and the inconceivable immensity of the time of whose
lapse they are the imperfect, but the only accessible witnesses. Now,
throughout the greater part of this long series of stratified rocks are
scattered, sometimes very abundantly, multitudes of organic remains, the
fossilized exuviae of animals and plants which lived and died while the
mud of which the rocks are formed was yet soft ooze, and could receive
and bury them.