WEALDEN FORMATION, a series of fresh-water strata belonging to the lower creta ceous epoch. Having been originally studied in the parts of Kent, Surrey, and Sussex called the Weald, this local name was given to the formation. It has been divided into two series, which do not differ very materially from each other, viz., Weald clay, 560 ft.; Hastings sand, 740; total 13_00. The Weald clay consists of blue and brown clay and shale with thin beds of sandstone and shelly limestone. These strata were probably lake or estuary deposits, and contain the remains of the land flora and fauna, often in great abundance. The beds of limestone called Sussex marble, are almost entirely com posed of a species of paludina, not very different from the common P. oiripara of Eng lish rivers. The clays are often laminated by thin layers, consisting of immense num bers of the shells of minute cyprides. But the most remarkable animal remains are those of the huge reptiles which lived on the land, tenanted the air, or abounded in the sea, such as the iguanodon (q.v.), hyleosaurus (q.v.), pterodactyl (q.v.), and the numerous species of turtles which have been described from these strata. The vegetable fossils belong chiefly to ferns, and to the gymnospermatous orders of conifers and cycads; the fruits of several species of both orders have been found; and in some places the rolled'trunks of endogenites and clathraria, belonging to cycads, and of different species of coniferous wood, occur in enormous quantities, as at Brook Point, in the Isle of Wight. where the shore at low water is strewn with them.
The Hastings beds contain more sandstone and less clay than those of the upper Weald clays. The picturesque scenery of the High Rocks and other places iu the of Tunbridge, is weathered out of the beds of white sandstone belonging to this period. The remains of the huge Wealden reptiles abound in the sandstones of this division. The Tilgate forest-beds, where Dr. Mantel] first found the iguanodon, and the rocks in the neighborhood of Hastings, are the best-known repositories of those remarkable fossils.
The deposition of the Wealden beds was followed by a gradual depression of the land when these fresh-water deposits were covered by the estuary beds of the newer green sand, The depression continued until the fresh-water and estuary strata formed the bottom of a deep sea, on which were deposited the immense beds of chalk and allied strata which form the bulk of the cretaceous series. In the process of elevation, these beds have suffered denudation, so that districts which were covered with cretaceous beds have been cleared of them, and immense valleys have been furrowed through the chalk, greensand, and Wealden.