The Iguanodon, first discovered by Dr. Mantell, was an herbivorous reptile, of which the teeth, though bearing a great analogy, in their general form and crenated edges (see Figs. 289 _a_ and _b_), to the modern Iguanas which now frequent the tropical woods of America and the West Indies, exhibit many important differences. It appears that they have often been worn by the process of mastication; whereas the existing herbivorous reptiles clip and gnaw off the vegetable productions on which they feed, but do not chew them. Their teeth frequently present an appearance of having been chipped off, but never, like the fossil teeth of the Iguanodon, have a flat ground surface (see Fig. 290, _b_) resembling the grinders of herbivorous mammalia. Dr. Mantell computes that the teeth and bones of this species which passed under his examination during twenty years must have belonged to no less than seventy-one distinct individuals, varying in age and magnitude from the reptile just burst from the egg, to one of which the femur measured twenty-four inches in circumference. Yet, notwithstanding that the teeth were more numerous than any other bones, it is remarkable that it was not until the relics of all these individuals had been found, that a solitary example of part of a jaw-bone was obtained. Soon afterwards remains both of the upper and lower jaw were met with in the Hastings beds in Tilgate Forest, near Cuckfield. In the same sands at Hastings, Mr. Beckles found large tridactyle impressions which it is conjectured were made by the hind feet of this animal, on which it is ascertained that there were only three well-developed toes. Fig. 289 a, b: Tooth of Iguanodon Mantelli. Fig. 290: a. Partially worn tooth of young individual of the same; <i>b.</i> Crown of tooth in adult worn down. Fig. 291: Cypris spinigera. Occasionally bands of limestone, called Sussex Marble, occur in the Weald Clay, almost entirely composed of a species of _ Paludina,_ closely resembling the common _P. vivipara_ of English rivers. Shells of the _Cypris,_ a genus of Crustaceans mentioned (p. 57) as abounding in lakes and ponds, are also plentifully scattered through the clays of the Wealden, sometimes producing, like plates of mica, a thin lamination (see Fig. 292). Fig. 292: Weald clay with Cyprides. Hastings Sands.—This lower division of the Wealden consists of sand, sandstone, calciferous grit, clay, and shale; the argillaceous strata, notwithstanding the name, predominating somewhat over the arenaceous, as will be seen by reference to the following table, drawn up by Messrs. Drew and Foster, of the Geological Survey of Great Britain: Names of Subordinate Formations. Mineral Composition of the Strata. Thickness in feet. Hastings Sand Tunbridge Wells Sand Sandstone and loam 150 Wadhurst Clay Blue and brown shale and clay, with a little calc-grit 100 Ashdown Sand Hard sand, with some beds of calc-grit 160 Ashburnham Beds Mottled white and red clay, with some sandstone 330