our
mountain-chains, the courses of our rivers, and the soundings
of our oceans, are not things primordially arranged in the
construction of our globe, but results of successive and complex
actions on a former state of things; _that_, again, of similar
actions on another still more remote; and so on, till the original
and really permanent state is pushed altogether out of sight
and beyond the reach even of imagination; while on the other
hand, a similar, and, as far as we can see, interminable vista
is opened out for the future, by which the habitability of our
planet is secured amid the total abolition on it of the present
theatres of terrestrial life."

Geology, then, teaches us that the physical features which now
distinguish the earth's surface have been produced as the ultimate
result of an almost endless succession of precedent changes.
Palaeontology teaches us, though not yet in such assured accents,
the same lesson. Our present animals and plants have not been
produced, in their innumerable forms, each as we now know it,
as the sudden, collective, and simultaneous birth of a renovated
world. On the contrary, we have the clearest evidence that some
of our existing animals and plants made their appearance upon the
earth at a much earlier period than others. In the confederation
of animated nature some races can boast of an immemorial antiquity,
whilst others are comparative _parvenus_. We have also the clearest
evidence that the animals and plants which now inhabit the globe
have been preceded, over and over again, by other different
assemblages of animals and plants, which have flourished in
successive periods of the earth's history, have reached their
culmination, and then have given way to a fresh series of living
beings. We have, finally, the clearest evidence that these successive
groups of animals and plants (faunae and florae) are to a greater
or less extent directly connected with one another. Each group
is, to a greater or less extent, the lineal descendant of the
group which immediately preceded it in point of time, and is
more or less fully concerned with giving origin to the group
which immediately follows it. That this law of "evolution" has
prevailed to a great extent is quite certain; but it does not
meet all the exigencies of the case, and it is probable that
its action has been supplemented by some still unknown law of
a different character.

We shall have to consider the question of geologi