.

As a proof--some of you may recollect, when the South-Western
Railway was in making, seeing shells--some of them large and
handsome ones--Nautili, taken out of the London clay cutting near
Winchfield.

Nautili similar to them (but not the same) are now only found in the
hottest parts of the Indian seas; and what is more, not one of those
shells is the same as the shells you find in the chalk. Throughout
this great bed of London clay, the shells, the remains of plants and
animals, are altogether a new creation. If you look carefully at
the London clay shells, you will be struck with their general
likeness to fresh East Indian shells; and rightly so. They do
approach our modern live shells in form, far more than any which
preceded them; and indeed, a few of the London clay shells exist
still in foreign seas; in the beds, again, above the clay, you will
meet with still more species which are yet alive; while in the
chalk, and below the chalk, you never meet, I believe, with a single
recent shell. It is for this reason that the London clay is said to
be Eocene, that is, the dawn of the new creation.

The chalk, I told you, seems to have been deposited at the bottom of
a still and deep ocean. But the London clay, we shall find, was
deposited in a comparatively shallow sea, least in depth toward High
Clere on the west, and deepening towards London and the mouth of the
Thames.

For not only is the clay deeper as you travel eastward, but--and
this is a matter to which geologists attach great importance--the
character of the shells differs in different parts of the clay.

You must know that certain sorts of shells live in deep water, and
certain in shallow. You may prove this to yourselves, on a small
scale, whenever you go to the seaside. You will find that the shell
which crawl on the rocks about high-water mark are different from
those which you find at low-tide mark; and those again different
from the shells which are brought up by the oyster-dredgers from the
sea outside. Now, the lower part of the clay, near here, contains
shallow-water shells: but if you went forty miles to the eastward,
you would find in the corresponding lower beds of the clay, deep-
water shells, and far above them, shallow-water shells such as you
find here: a fact which shows plainly that this end of the clay sea
was shallowest, and therefore first filled up.

But again--and this is a very curious fact--between the time of the
P