Classification of marine and fresh-water Strata. — Upper Neocomian. — Folkestone and Hythe Beds. — Atherfield Clay. — Similarity of Conditions causing Reappearance of Species after short Intervals. — Upper Speeton Clay. — Middle Neocomian. — Tealby Series. — Middle Speeton Clay. — Lower Neocomian. — Lower Speeton Clay. — Wealden Formation. — Fresh-water Character of the Wealden. — Weald Clay. — Hastings Sands. — Punfield Beds of Purbeck, Dorsetshire. — Fossil Shells and Fish of the Wealden. — Area of the Wealden. — Flora of the Wealden. We now come to the Lower Cretaceous Formation which was formerly called Lower Greensand, and for which it will be useful for reasons before explained (p. 282) to use the term “Neocomian.” LOWER CRETACEOUS OR NEOCOMIAN GROUP. Marine Fresh-water Upper Neocomian—Greensand of Folkestone, Sandgate, and Hythe, Atherfield clay, upper part of Speeton clay. Middle Neocomian—Punfield Marine bed, Tealby beds, middle part of Speeton clay. Lower Neocomian—Lower part of Speeton clay. Part of Wealden beds of Kent, Surrey, Sussex, Hants, and Dorset. In Western France, the Alps, the Carpathians, Northern Italy, and the Apennines, an extensive series of rocks has been described by Continental geologists under the name of Tithonian. These beds, which are without any marine equivalent in this country, appear completely to bridge over the interval between the Neocomian and the Oolites. They may, perhaps, as suggested by Mr. Judd, be of the same age as part of the Wealden series. UPPER NEOCOMIAN. Folkstone and Hythe Beds.—The sands which crop out beneath the Gault in Wiltshire, Surrey, and Sussex are sometimes in the uppermost part pure white, at others of a yellow and ferruginous colour, and some of the beds contain much green matter. At Folkestone they contain layers of calcareous matter and chert, and at Hythe, in the neighbourhood, as also at Maidstone and other parts of Kent, the limestone called Kentish Rag is intercalated. This somewhat clayey and calcareous stone forms strata two feet thick, alternating with quartzose sand. The total thickness of these Folkestone and Hythe beds is less than 300 feet, and they are seen to rest immediately on a grey clay, to which we shall presently allude as the Atherfield clay. Among the fossils of the Folkestone and Hythe beds we may mention _Nautilus plicatus_ (Fig. 277), _ Ancyloceras (Scaphites) gigas_ (Fig. 278), which has been aptly described as an Ammonite more or less uncoiled; _Trigonia caudata_ (Fig. 280), _Gervillia anceps_ (Fig. 279), a bivalve genus allied to Avicula, and _Terebratula sella_ (Fig. 281). In ferruginous beds of the same age in Wiltshire is found a remarkable shell called _Diceras Lonsdalii_ (Fig. 282), which abounds in the Upper and Middle Neocomian of Southern Europe. This genus is closely allied to Chama, and the cast of the interior has been compared to the horns of a goat.