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. 



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