mountain chains; and may be found perched up, in some cases, many
thousand feet high upon their flanks. And evidence of equal cogency
demonstrates that, though in Norfolk the forest-bed rests directly
upon the chalk, yet it does so, not because the period at which the
forest grew immediately followed that at which the chalk was formed,
but because an immense lapse of time, represented elsewhere by
thousands of feet of rock, is not indicated at Cromer.

I must ask you to believe that there is no less conclusive proof that
a still more prolonged succession of similar changes occurred before
the chalk was deposited. Nor have we any reason to think that the
first term in the series of these changes is known. The oldest
sea-beds preserved to us are sands, and mud, and pebbles, the wear and
tear of rocks which were formed in still older oceans.

But, great as is the magnitude of these physical changes of the world,
they have been accompanied by a no less striking series of
modifications in its living inhabitants.

All the great classes of animals, beasts of the field, fowls of the
air, creeping things, and things which dwell in the waters, flourished
upon the globe long ages before the chalk was deposited. Very few,
however, if any, of these ancient forms of animal life were identical
with those which now live. Certainly not one of the higher animals was
of the same species as any of those now in existence. The beasts of
the field, in the days before the chalk, were not our beasts of the
field, nor the fowls of the air such as those which the eye of man has
seen flying, unless his antiquity dates infinitely further back than
we at present surmise. If we could be carried back into those times,
we should be as one suddenly set down in Australia before it was
colonized. We should see mammals, birds, reptiles, fishes, insects,
snails, and the like, clearly recognizable as such, and yet not one of
them would be just the same as those with which we are familiar, and
many would be extremely different.

From that time to the present, the population of the world has
undergone slow and gradual, but incessant, changes. There has been no
grand catastrophe--no destroyer has swept away the forms of life of
one period, and replaced them by a totally new creation; but one
species has vanished and another has taken its place; creatures of one
type of structure have diminished, those of another have increased, as
time has passed on. And th