Geology. 19 



THICKNESS. From N. end of Shrewsbury Lane increases from 

 one foot to about 8 feet ; over most of the hill-top the thickness 

 appears to be 8 to 10 feet ; toward the Bull the thickness is greater, 

 and going down to the N.W. slope it is at least 20 feet. On this 

 part of the hill the cap is a coarse red clayey sand, very full of 

 pebbles. 



X.W. SLOPE. The thick cap ends pretty sharply a few yards 

 above the well-known medicinal well. In the trench the base of 

 the cap was a yellow clayey sand (no pebbles) 2 or 3 feet thick, 

 which passed into London Clay, light in colour. 



EXPOSURES ON SUMMIT. The numerous pits opened E. of Shrews- 

 bury Lane for sand, house foundations, etc., all show sand and 

 pebbles usually much cleaner (less clayey) than the deposit N.W. 

 of the Bull. 



The pebbles are (1) Rounded flints. (2) Flints with much 

 weathered surfaces ; when split these show very striking zones of 

 alteration due to infiltration and weathering. Mr Leach has a good 

 collection and considers them most interesting : he has not found 

 anything quite like them in any other gravels. (3) Quartz : small 

 pebbles, not common. (4) Chert : ditto. (5) Hard dark red ferrugi- 

 nous sandstone not common. Mr. Leach has a few lumps which look 

 like Lower Greensand material, but are not quite so dense as the iron- 

 stone from the Folkestone Beds. (6) Dark Lydian stone ( ? ) with quartz 

 veinings, not common. No trace of worked flints. Mr. Leach has 

 gone over many tons of the pebbles during the last four years, but 

 has never seen any sign of a flake, except some rough neolithic chips. 

 No trace of shells, bones, or derivative fossils. 



On Swanscombe Hill there is a spread of gravel, but no section. 

 It consists chiefly of flint-debris, but a good deal of Lower 

 Greensand chert is found. Mr. A. S. Kennard has found Flint 

 implements belonging to his Hill Group here (13). 



Those who wish to obtain a wider acquaintance with these High 

 Level Drift Deposits should compare them with those found at high 

 elevations in Southern Essex, e.g., Havering-atte-Bower, Langdon 

 Hills, Rayleigh Hills, etc. 



High Terrace Deposits. 



The scanty character, high elevation, simple nature of the 

 constituent rocks and the apparent connection with a system of 

 drainage lying north or north-east of the present Thames, mark off 

 the High Level Drifts from the Drift deposits now to be described. 



At Dartford Heath, 136 feet above O.D., are found extensive 

 deposits consisting mainly of flint in various forms, but also of a 



(13) Proc. Geol. Assoc., Vol. XIX., p. 76. 



