tity of the chalk with modern deep-sea mud. _Globigerinoe_,
coccoliths, and coccospheres are found as the chief constituents of both,
and testify to the general similarity of the conditions under which both
have been formed.[3]

[Footnote 3: I have recently traced out the development of the
"coccoliths" from a diameter of 1/7000th of an inch up to their largest
size (which is about 1/1000th), and no longer doubt that they are
produced by independent organisms, which, like the _Globigerinoe_, live
and die at the bottom of the sea.]

The evidence furnished by the hewing, facing, and superposition of the
stones of the Pyramids, that these structures were built by men, has no
greater weight than the evidence that the chalk was built by
_Globigerinoe_; and the belief that those ancient pyramid-builders were
terrestrial and air-breathing creatures like ourselves, is not better
based than the conviction that the chalk-makers lived in the sea. But as
our belief in the building of the Pyramids by men is not only grounded on
the internal evidence afforded by these structures, but gathers strength
from multitudinous collateral proofs, and is clinched by the total
absence of any reason for a contrary belief; so the evidence drawn from
the _Globigerinoe_ that the chalk is an ancient sea-bottom, is fortified
by innumerable independent lines of evidence; and our belief in the truth
of the conclusion to which all positive testimony tends, receives the
like negative justification from the fact that no other hypothesis has a
shadow of foundation.

It may be worth while briefly to consider a few of these collateral
proofs that the chalk was deposited at the bottom of the sea. The great
mass of the chalk is composed, as we have seen, of the skeletons of
_Globigerinoe_, and other simple organisms, imbedded in granular matter.
Here and there, however, this hardened mud of the ancient sea reveals the
remains of higher animals which have lived and died, and left their hard
parts in the mud, just as the oysters die and leave their shells behind
them, in the mud of the present seas.

There are, at 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 _Polyzoa_; 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