Fig. 277: Nautilus licatus. Fig. 278: Ancyloceras gigas. Fig. 279: Gervillia anceps. Fig. 280: Trigonia caudata. Atherfield Clay.—We mentioned before that the Folkstone and Hythe series rest on a grey clay. This clay is only of slight thickness in Kent and Surrey, but acquires great dimensions at Atherfield, in the Isle of Wight. The difference, indeed, in mineral character and thickness of the Upper Neocomian formation near Folkestone, and the corresponding beds in the south of the Isle of Wight, about 100 miles distant, is truly remarkable. In the latter place we find no limestone answering to the Kentish Rag, and the entire thickness from the bottom of the Atherfield clay to the top of the Neocomian, instead of being less than 300 feet as in Kent, is given by the late Professor E. Forbes as 843 feet, which he divides into sixty-three strata, forming three groups. The uppermost of these consists of ferruginous sands, the second of sands and clay, and the third or lowest of a brown clay, abounding in fossils. Fig. 281: Terebratula sella. Fig. 282: Diceras Lonsdalii. a. The bivavle shell, b. Cast of one of the valves enlarged. Pebbles of quartzose sandstone, jasper, and flinty slate, together with grains of chlorite and mica, and, as Mr. Godwin-Austen has shown, fragments and water-worn fossils of the oolitic rocks, speak plainly of the nature of the pre-existing formations, by the wearing down of which the Neocomian beds were formed. The land, consisting of such rocks, was doubtless submerged before the origin of the white chalk, a deposit which was formed in a more open sea, and in clearer waters. Fig. 283: Perna mulleti. Among the shells of the Atherfield clay the biggest and most abundant shell is the large _Perna Mulleti,_ of which a reduced figure is given in Fig. 283.