FOSSIL SHELLS.
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.