-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, which would be detached by the
smallest jar, often remain in their places. In a word, it is certain that
these animals have lived and died when the place which they now occupy
was the surface of as much of the chalk as had then been deposited; and
that each has been covered up by the layer of _Globigerina_ mud, upon
which the creatures imbedded a litt