﻿Yol. 66.~\ THE WESTEKN END OP THE WEALD. 663 



hardly uncovered at Hindhead, and his lead has been followed by 

 other writers; but this leaves the question of size untouched, 

 while suggesting, perhaps, rather more difference of age between 

 the two drifts than is quite compatible with the differences in level. 

 "Without denying, therefore, that Prestwich's explanation may be the 

 true one, I am inclined to look about for other causes as well, and 

 the following suggestion seems worth taking into consideration. 



When the plain was first upheaved it was covered with a thin 

 layer of Drift, containing a small quantity of chert ; but as this 

 material would be quickly worn away in a marine gravel, it is 

 unlikely that its pebbles would be either large or numerous at any 

 distance from their source. The earliest consequent streams 

 caused a downward wash of this marine drift over almos*t the whole 

 plain, but very soon a few of them obtained such a superiority over 

 their neighbours that for the future they formed practically the 

 whole of the consequent drainage-system. One of these success- 

 ful rivers was the Blackwater, while another, as we shall presently 

 see, flowed immediately to the west of the Earnham Plateau ; and 

 the scarcity of chert on the latter is due, not so much to the Hythe 

 Beds being still covered up (except so far as they were concealed 

 under the marine drift) as to the situation of the plateau between 

 two successful consequent streams, instead of on a main line of 

 drainage. Its chert in fact is, on this view, mainly, if not wholly, 

 derived from a marine source. The great depth of the gravel may 

 be due to some local warping of the plain ; it lies immediately north 

 of an important longitudinal anticline, and although the latter was 

 probably formed, for the most part, at an earlier date, yet it is possible 

 that during the upheaval of the plain a second slight movement 

 occurred here, and that the Plateau Drift is a mass of ' aggraded ' 

 material at the foot of the slope so formed (see § II, p. 658). 



A wide belt of gravel (fig. 4, F, p. 664), practically identical in 

 composition with that of the plateau, and continuous with it,, 

 extends down the southern slope of the hill, reaching the 500-foot 

 contour at Upper Old Park, 1 and descending almost to the 400-foot 

 line at Upper Hale. It is no part of my present purpose to discuss 

 the origin of this drift, and I am content to treat it (provisionally) 

 as merely a part of the Plateau Gravel that has slipped down the 

 hillside. There are, however, some outliers of similar gravel at a 

 lower level which merit careful attention. The first of these is not 

 marked on the Geological Survey map, but is described by Monckton 

 & Mangles (14, p. 81) as lying half a mile west of Farnham 

 Castle, and as being probably derived from the Plateau Drift. With 

 the help of Mr. Monckton's notes, which he kindly sent me, I have 

 entered this gravel in fig. 4 (A), in what appears to be its correct 

 position, but I have no accurate information as to its extent. 

 It lies just above the 400-foot level, about at the junction of the 

 Chalk with the Eocene, and contains practically no chert. The 



1 The • Upper Old Park' of the map used by the Geological Survey is really 

 Middle Old Park. 



