GEOLOGY since the top of the Weald Clay, wherever exposed to examination, has proved to be sharp and well defined, and to be directly overlain by deposits containing a marine fauna. ATHERFIELD CLAY In the western part of the county the first sediment of this sea was a brown and greyish clay, somewhat sandy in places, known as the Atherfield Clay, from a locality in the Isle of Wight where it is typically developed. As the chief difference between this marine clay and the underlying Weald Clay is in the character of their respective fossils, which are destroyed by weathering at the surface, and as the two de- posits form ground of similar aspect, it is only in fresh and deeply cut sections that we can discriminate between them. In a railway-cutting near Haslemere, the Atherfield Clay was found to have a thickness of 60 feet, and yielded numerous fossils, including Ammonites, Nautilus and bivalve shells of many genera 1 ; and in a stream-section at East Shalford near Guildford, where upwards of a hundred species of mollusca were obtained from it by Mr. C. J. A. Meyer, its thickness was estimated to be about 64 feet. 2 This marine clay has hitherto been supposed to extend right across the county, but in the newly-exposed railway- cutting between Redhill and Earlswood previously referred to, its place was taken by sandy loams which could not be distinguished from the overlying Hythe Beds. Hence we may conclude that it was only in the quieter and deeper parts of the sea of the period that the Atherfield Clay was laid down. LOWER GREENSAND In our upward progress in the geological scale, or northward pro- gress across the present surface of the county, we now reach the belt of sands and sand-rocks which rise up boldly in a long escarpment over- looking the clayey lowlands of the Weald. These are all of marine origin, and are collectively known as the Lower Greensand. This term is often held to include also the Atherfield Clay at their base ; it has reference to the frequent occurrence of abundantly disseminated grains of glauconite, a green silicate of iron, which however is usually decomposed in the sands at the surface, giving rusty red and yellow tints to weathered exposures. These beds were accumulated in a shallow sea, swept by strong currents (as indicated by the prevalence of ' false ' or ' current '- bedding where the material has been deposited on the slopes of sand- banks), and they represent the steady wasting of a land not far distant. Their threefold division into Hythe, Sandgate and Folkestone Beds is based upon characters which are conspicuous at the places indicated by these names on the coast of Kent but become less marked as the beds 1 ' Geology of the Weald,' p. 115.
- ' On the Lower Greensand of Godalming,' by C. J. A. Meyer, Proc. Geol. Assoc.,
sup. to vol. i., 1868.
