Vol. 51.] THE LOWER GBEEXSAND OP EAST SURREY. 101 



14. The Lower Greensand above the Athereield Ceat of East 



Surrey. By Thomas Leighton, Esq., F.G.S. (Read December 



19th, 1894.) 



Contents. 



Page 



I. Introduction 101 



II. The Chert-beds of Leith Hill 104 



III. The Pebble- and Chert-beds East of Dorking 110 



IV. Comparative Table of Sections 119 



V. Conclusions 119 



I. Introduction. 



The district to which this paper refers extends from Leith Hill in 

 the west to Tilburstow Hill in the east, and the beds more particu- 

 larly discussed are those which have been described by the Geological 

 Survey as the Hythe and Sandgate Beds. I exclude the Atherfield 

 Clay from consideration here because, although rarely exposed in the 

 district, it is so distinct in itself and of such persistent occurrence at 

 the base of the series, that there can be no reason for doubting its 

 position as mapped. Many geologists have treated of this district 

 in the past ; amongst the chief are Mantell, 1 Eitton, 2 T. Webster, 3 

 Murchison, 4 Mr. C. J. A. Meyer, 5 and Mr. F. Drew with Mr. W. 

 Topley. 6 The Weald Memoir of the Geological Survey prepared 

 by Mr. Topley, so far as this district is concerned, chiefly from 

 the notes of the late Mr. Drew, sets forth what may be called the 

 hitherto accepted view of the Lower Greensand succession. That 

 view is, that the northern outcrop of the series (as here limited) in 

 the Weald is divisible into three sets of beds, named respectively 

 the Hythe, Sandgate, and Folkestone Beds, which are mapped more 

 or less continuously from the typical areas after which they are 

 named. This view would no doubt have sufficed, but for the new 

 light thrown on the question in 1885 by Dr. G. J. Hinde's paper 

 ' On Beds of Sponge-remains in the Lower and Upper Greensand of 

 the South of England.' 7 It should be remembered that Mr. Topley's 

 memoir is dated 1875, and is based upon surveys made very much 

 earlier, long before the promulgation of the existing views as to the 

 origin of chert. Great praise, then, is due to the late Mr. Drew, 

 since his work in the district is so well set forth that a geologist 

 who is familiar with the country has only to recognize that the 

 references to sandstones about Leith Hill and Wotton refer to the 

 sandy cherts, and he will find the Survey Memoir correct in all 



1 ' A Sketch of the Geology of the County of Surrey,' Brayley & Britton's 

 ' History of Surrey,' 4to. 1841. 



- Trans. Geol. Soc. ser. 2, vol. iv. pt. ii. (1836) p. 103. 



3 Ibid, ser, 1, vol. v. (1821) p. 353. 



1 Ibid. ser. 2, vol. ii. pt. i. (182H) p. 97. 5 Geol. Mag. 1866, p. 13. 



''■ Mem. Geol. Surv. ' Geology of the Weald,' 1875. 



7 Phi). Trans. Roy. Soc. vol. clxxvi. (1885) p. 403. 



