﻿648 MR. H. BURr ON THE DENUDATION" OP [Nov. I9IO,. 



of the Lenham Beds, finally settled by Mr. Clement lieid (22), is 

 now universally accepted ; elsewhere, however, although there is a 

 general tendency to assign a similar date to the other beds, no 

 definite proof is forthcoming. On Netley Heath, between Guildford 

 and Dorking, is a bed of sand (not included in Prestwich's list) in 

 which Mr. Stebbing (25) has found casts of marine shells exhi- 

 biting a general resemblance to those of Lenham ; but they are 

 too imperfect for accurate determination, and opinion is still 

 divided as to their true position. 



Even, however, if we accept the Pliocene age of all these beds,. 

 they do not prove planation by the sea of the whole Wealden 

 area. Prestwich and others who deny planation admit that the 

 Diestian sea washed the northern fringe of that area, but perceive 

 no reason for supposing that it spread much farther south than the 

 line of the present Downs ; and the absence of similar deposits- 

 from the South Downs, and from all the older Wealden beds, though 

 by no means conclusive, affords some negative support to that 

 position. 



(c) Distribution of chert. — Scattered along the North 

 Downs, sometimes as isolated pebbles or boulders, at other times in 

 connection with the Southern Drift or the supposed Pliocene beds,. 

 are quantities of Lower Greensand chert. On the hypothesis of 

 a marine plain these present no difficulty : but they offer so formid- 

 able an obstacle to Prof. Davis's suggestion of a subaerial peneplain, 

 as to deserve more attention than they have hitherto received. It 

 is only in the region of the Darent, where Prestwich and others 

 have mapped it carefully, that the distribution of this chert is 

 thoroughly known, and even there, as Prestwich's paper and the 

 debate on it show (19), important facts were for some time over- 

 looked. The following list, therefore, of the localities where it is to- 

 be found to the west of Wrotham Hill (the eastern boundary of 

 the Darent region) cannot be regarded as at all complete, although 

 it is sufficient for the purpose of the present argument : — 



1. East of the Darent. — Prestwich found chert all along the Downs 

 from the Darent to Wrotham Hill (19, pi. vi, fig. 3). 



2. From the Darent to the Mole. — Prestwich traced Southern Drift 

 only as far as Morant's Court Hill, but Crawshay (19, p. 162) mentions its 

 occurrence (presumably with chert) on the summit of Botley Hill, about 7 

 miles farther west. So far as I know, no Lower Greensand fragments are to 

 be found near the edge of the escarpment between this hill and the Merstham 

 gap ; but Dr. Hinde (6, p. 224) records chert as common rather below the summit 

 of the Chalk Plateau to the east of that pass : how far east it extends is not 

 clearly stated. I could find none in the supposed Pliocene beds at Alderstead, 

 but it reappears to the west of the pass either in or on (I cannot from personal 

 observation determine which) beds of the same age at Shabden Park. Near 

 Walton-on-tbe-Hill and on Headley Heath it is fairly plentiful. 



3. From the Mole to the Wey. — Lower Greensand fragments are 

 found on Panmore Common, and I obtained a few chert pebbles from a field 

 about a mile west of Effingham Hill Lodge. It is comparatively plentiful on 

 Netley Heath (overlying the sand), at Woodcote Lodge in beds associated by 

 Mr. Monckton (13, p. 33) with the Southern Drift, and at Newland's Corner. 



4. West of the Wey. — There is no Drift at all along the Hog's Pack, but 

 Lower Greensand fragments are found sparingly on the Farnham Plateau y 

 under which name I shall, in this paper, include Csesar's Camp, Hungry Hill, 



