w 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 men 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
thus, while the differences between the living creatures of the time
before the chalk and those of the present day appear startling, if placed
side by side, we are led from one to the other by the most gradual
progress, if we follow the course of Nature through the whole series of