t the present day, certain groups of animals which are never
found in fresh waters, being unable to live anywhere but in the sea.
Such are the corals; those corallines which are called Polycoa; those
creatures which fabricate the lamp-shells, and are called Brachiopoda;
the pearly Nautilus, and all animals allied to it; and all the forms of
sea-urchins and star-fishes.

Not only are all these creatures confined to salt water at the present
day; but, so far as our records of the past go, the conditions of their
existence have been the same: hence, their occurrence in any deposit is
as strong evidence as can be obtained, that that deposit was formed in
the sea. Now the remains of animals of all the kinds which have been
enumerated, occur in the chalk, in greater or less abundance; while not
one of those forms of shell-fish which are characteristic of fresh water
has yet been observed in it.

When we consider that the remains of more than three thousand distinct
species of aquatic animals have been discovered among the fossils of the
chalk, that the great majority of them are of such forms as are now met
with only in the sea, and that there is no reason to believe that any
one of them inhabited fresh water--the collateral evidence that the
chalk represents an ancient sea-bottom acquires as great force as the
proof derived from the nature of the chalk itself. I think you will now
allow that I did not overstate my case when I asserted that we have
as strong grounds for believing that all the vast area of dry land, at
present occupied by the chalk, was once at the bottom of the sea, as we
have for any matter of history whatever; while there is no justification
for any other belief.

No less certain it is that the time during which the countries we now
call south-east England, France, Germany, Poland, Russia, Egypt, Arabia,
Syria, were more or less completely covered by a deep sea, was of
considerable duration.

We have already seen that the chalk is, in places, more than a thousand
feet thick. I think you will agree with me, that it must have taken
some time for the skeletons of animalcules of a hundredth of an inch in
diameter to heap up such a mass as that. I have said that throughout the
thickness of the chalk the remains of other animals are scattered.
These remains are often in the most exquisite state of preservation.
The valves of the shell-fishes are commonly adherent; the long spines
of some of the sea-urchins, w