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. 



