GEOLOGY a species useful in determining the foreign equivalents of the ' zone,' Exogyra, Trigonia, and many brachiopods and other shells, besides some interesting reptilian bones ; while at Maidstone also they have yielded some fine remains of the Iguanodon, nowr in the British Museum, and other extinct reptiles,* along with fragments of wood and coniferous fruits. In the higher portion of their outcrop west of the Medway the Hythe Beds carry large stretches of woodland and common land, including Westerham Common and Brastead Chart, Whitley Scrubs, Knole Park, Great Comp, Mereworth and East Mailing Woods ; but east of the Medway their surface is generally very fertile and highly cultivated, supporting many of the best hop and fruit gardens of the Maidstone district. Sandgate Beds. — The middle subdivision of the Lower Greensand, the Sandgate Beds, consists of dark shaly pyritous clay and muddy glauconitic silt or fine sand, having a thickness of about 80 feet on the coast between Folkestone and Sandgate, where it attains its maximum development. Westward these beds thin away or lose their distinctive clayey character, so that at Maidstone they are represented by only about 14 feet of strata, and a little farther to the west they cease to be recognizable as an independent division. They are very sparingly fossiliferous except in a nodular phosphatic band at their base, which has yielded many brachiopods and other shells.^ Their narrow outcrop is generally marked by the presence of small springs, where the water percolating through the overlying sands is arrested and thrown out by these clayey beds. The destructive landslip which occurred at Sandgate in 1893 was due to the foundering of these beds along their seaward out- crop during a wet season, owing mainly to the action of percolating water.* Folkestone Beds. — As developed in the coast section, the Folkestone Beds, which constitute the uppermost division of the Lower Greensand, are composed of clean-washed light-coloured sands with irregular layers of sandy limestone and cherty seams ('Folkestone Stone'), and darker clayey sand and sandstone at the base, having a total thickness of about 90 feet. Minute siHceous sponge spicules are still recognizable in some of the stony layers, and their presence explains the origin of the chert. The extinct oyster Exogyra is plentiful in some of the beds, and the remains of echinoderms, etc., and casts of large ammonites in others, but fossils are not abundant except near the base and again in a band of phosphatic nodules which occurs at Folkestone 3 or 4 feet below the top of the division. The characteristic fossil of the last-mentioned band is Ammonites mammillatus, and as this species is found in France in a well-marked zone at the base of the Gault, it has been suggested ' See Summary of Progfess of the Geological Survey for 1897, p. 129. 2 For description of these reptilian and other vertebrate remains from the Hythe Beds, see subse- quent article ' Palasontolog)-,' p. 31. 3 See F. G. H. Price, ' On the Lower Greensand and Gault of Folkestone,' Proc. Geol. Assoc. (1875), iv. 135.
- See W. Topley, ' The Landslip at Sandgate,' ibid. (1893), xiii. 40, and Geographical Journal,
April, 1893. II
