At whatever elevations these shells may have been found, and however
remote from the parts of the globe now occupied by water, it is certain
that they were once generated in the sea, by which they were deposited.
The Altain chain of primitive mountains in Siberia is flanked on each
side by a chain of hills inclosing marine shells. On a comparison of the
forms, contexture and composition of these shells, as they have been
found imbedded in rocks, not the slightest difference can be detected
between several varieties of them and those which still inhabit the sea.
At Touraine, in France, a hundred miles from the ocean, and about nine
feet beneath the surface, a bed of fossil shells has been found nine
leagues in length, and about twenty feet in thickness. Such beds are
known to exist in every part of Europe; and in South America, according
to Ulloa, they are very frequent.
Great Britain abounds in these fossil productions. In the cliffs of the
isle of Sheppey, bordering on the Thames, several varieties of the crab,
and lobsters nearly whole, have been found in a petrified state. Within
the elevated lands in the vicinity of Reading, in Berkshire, an
abundance of oyster-shells has been found, many of them entire, and
having both their valves united. At Broughton, in Lincolnshire, there
are two quarries abounding in fresh-water shells, which are found in a
blue stone, supposed to have been formerly clay, and to have been
gradually indurated. A bed of shells, twelve feet thick, and lying in a
greenish sand, has been found about a mile from Reculver, in Kent. At
Harwich, at the entrance of the river, a sandy cliff, fifty feet in
hight, contains shells, of which there are no less than twenty-eight
varieties. On digging a moorish pasture, in Northamptonshire, many
snails and river shells were found; and these were the more abundant in
proportion as the workmen proceeded to a greater depth. And, lastly, the
petrifactions known by the name of _belemnites_, have been found in
chalk pits, in different parts of the kingdom: they are usually
cylindrical, or conical, and sometimes contain a hollow nucleus. They
are supposed to constitute a species of nautilus, and very frequently
occur in the coarser kinds of marble.