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.
SUBTERRANEAN FORESTS.
In the year 1708, a breach made by the Thames, at an extraordinary high tide, inundated the marshes of Dagenham and Havering, in Essex. Such was the impetuous rush of the water, that a large passage or channel was torn up, three hundred feet in width, and in some parts twenty feet in depth. In this way, a great number of trees, that had been buried there many ages before, were exposed to view. With one exception, that of a large oak, having the greatest part of its bark, and some of its heads and roots in a perfect state, these trees bore a greater resemblance to alder than to any other description of wood. They were black and hard, and their fibers were extremely tough. No doubt was entertained of their having grown on the spot where they lay; and they were so numerous, that in many places they afforded steps to the passengers. They were imbedded in a black oozy soil, on the surface of which they lay prostrate, with a covering of grey mold.
In passing along the channel torn up by the water, vast numbers of the stumps of these subterraneous trees, remaining in the posture in which they grew, were to be seen, some with their roots running down, and others branching and spreading about in the earth, as is observed in growing trees. That they were the ruins, not of the deluge, but of a later age, has been inferred from the existence of a bed of shells, which lies across the highway, on the descent near Stifford bridge, leading to South Okendon. At a perpendicular depth of twenty feet beneath this bed of shells, and at the distance of nearly two hundred feet, in the bottom of the valley, runs a brook which empties itself into the Thames at Purfleet. This brook is known to ebb and flow with the Thames; and, consequently, if the bed of shells, as has been conjectured, was deposited in that place by an inundation of the Thames, it must have been such as to have drowned a vast proportion of the surrounding country, and have overtopped the trees near the river, in West Horrock, Dagenham, and the other marshes, overturning them in its progress. In support of this hypothesis, it should be remarked, that the bed of earth in which the trees grew, was entire and undisturbed, and consisted of a spongy, light, oozy soil, filled with the roots of reeds, of a specific gravity much less than that of the stratum above it.
The levels of Hatfield chase were, in the reign of Charles I., the largest chase of red deer in England. They contained about one hundred and eighty thousand acres of land, about one-half of which was yearly inundated; but being sold to one Vermuiden, a Dutchman, he contrived, at a great labor and expense, to dischase, drain, and reduce these lands to arable and pasture grounds not subject to be overflowed. In every part of the soil, in the bottom of the river Ouse even, and in that of the adventitious soil of all marsh land, together with the skirts of the Lincolnshire wold, vast multitudes of the roots and trunks of trees of different sizes are found. The roots are fixed in the soil, in their natural position, as thick as they could have grown; and near to them lie the trunks. Many of these trees appear to have been burned, and others to have been chopped and squared; and this in such places, and at such depths, as could never have been opened, since the destruction of the forest, until the time of the drainage. That this was the work of the Romans, who were the destroyers of all the woods and forests which are now found underground in the bottoms of moors and bogs, is evidenced by the coins and utensils, belonging to that nation, which have been collected, as well in these levels, as in other parts of Great Britain where these subterraneous forests have been discovered.
MOORS, MOSSES AND BOGS.
It having been reported in Lincolnshire, that a large extent of islets of moor, situated along its coast, and visible only at the lowest ebbs of the tide, was chiefly composed of decayed trees, Dr. de Serra, accompanied by Sir Joseph Banks, proceeded, in the month of September, 1796, to examine their nature and extent. They landed on one of the largest of these islets, when the ebbs were at the lowest, and found its exposed surface to be about ninety feet in length, and seventy-five in width. They were enabled to ascertain, that these islets consist almost entirely of roots, trunks, branches, and leaves of trees and shrubs, intermixed with leaves of aquatic plants. The remains of many of the trees were still standing on their roots; but the trunks of the greater part of them lay scattered on the ground, in every direction. The bark of the trees and roots appeared in general as fresh as when they were growing; in that of the birches particularly, many of which were found, even the thin silvery membranes of the outer skin were discernible. The timber of all kinds, on the contrary, was decomposed and soft, in the greater part of the trees; in some it was firm, especially about the knots. Sound pieces of timber had been often found by the country people. In general, the trunks, branches and roots of the decayed trees were considerably flattened; a phenomenon which has been observed in the surtarbrand, or fossil wood of Iceland, and also in that found near the lake of Thun, in Switzerland. The soil was chiefly composed of rotten leaves; and, on being thrown into water, many of these were taken out in a perfect state.
These islets extended about twelve miles in length, and one in breadth, opposite the shore of Sutton, at which place, on digging a well, a moor of the same nature was found under ground, at the depth of sixteen feet, and, consequently, very nearly on the same level with that which constitutes the islets. On boring in the fields belonging to the Royal Society, in the parish of Mablethorpe, to ascertain the cause of the subterraneous stratum of decayed vegetables, a similar moor was found. The appearance of these decayed vegetables was found exactly to agree with that of the moor which was thrown up in Blankney fen, and in other parts of the east fen of Lincolnshire, in making their embankments; barks, like those of the birch-tree, being there also abundantly found. This moor has been traced as far as Peterborough, sixty miles south of Sutton. On the north side, the moory islets extend as far as Grimsby, on the south of the mouth of the Humber: and it is a remarkable circumstance, that in the large tracts of low land which lie on the south banks of that river, a little above its mouth, there is a subterraneous stratum of decayed trees and shrubs, exactly resembling those observed at Sutton. At Axholme isle, a similar stratum extends over a tract of ten miles in length, by five in breadth. The roots there also stand in the places where they grew; while the trunks lie prostrate, amid the roots of aquatic plants and reeds. Little doubt can be entertained of the moory islets of Sutton being a part of this extensive subterraneous stratum, which, by some inroad of the sea, has been there stripped of its covering of soil. The identity of the levels; that of the species of trees; the roots of these affixed, in both, to the soil where they grew; and, above all, the flattened shape of the trunks, branches, and roots, found in the islets, which can only be accounted for by the heavy pressure of a superinduced stratum, are sufficient reasons for this opinion. Such a wide-spread assemblage of vegetable ruins, lying almost in the same level, and that level generally under the common mark of low water, naturally gives rise to reflections on the epoch of this destruction, and the agency by which it was effected.
The original catastrophe which buried this immense forest must have been of very ancient date; but it is to be suspected, that the inroad of the sea which uncovered the decayed trees of the islets of Sutton, is comparatively recent. The state of the leaves, and the timber, and also the tradition of the country people, concur to strengthen this suspicion. Leaves and other delicate parts of plants, though they may be long preserved in a subterraneous situation, can not remain uninjured when exposed to the action of the waves, and of the air. The inhabitants of Sutton believe that their parish church once stood on the spot where the islets now are, and was submerged by the inroads of the sea; that, at very low water, their ancestors could even discern its ruins; and that their present church was built to supply the place of that which was washed away. So many concomitant (though weak) testimonies, render their report to a certain degree deserving of credit, and lead to a supposition, that some of the stormy inundations of the North sea, which in these last centuries have washed away such large tracts of land on its shores, may have carried away a soil resting on clay, and have finally uncovered the trees of these moory islets.