﻿Yol. 66, ,] THE WESTERN END OF THE WEALD. 673 



river. It lies for the most, part just above the 600-foot contour, 

 while on the east the Downs rise to 733 feet O.D. On the west 

 there is no rise near the escarpment, yet a mile away to the north, 

 near Woodcote Lodge (Hook Wood), gravel is found at 678 feet O.D., 

 and this, if we allow a gradient of 50 feet per mile (see § II, p. 656), 

 would be equivalent to about 730 feet on that part of the marine 

 plain which overlay the present escarpment. Assuming that the 

 Netley Sands, and perhaps the Eocene Beds seen at Hook Wood, 

 were formerly thicker and more extensive than at present, but have 

 been removed except where specially protected by gravel, there is 

 no difficulty in understanding how the present configuration of the 

 Downs has been evolved from the original plain. Much of the 

 bevelling of the hill-crest is attributed to pre-Eocene causes, and 

 the consequent river which gave rise to the gravels is regarded as 

 having been cut off after it had excavated a valley about 120 feet 

 deep. By that time the Lower Cretaceous strata must have been 

 exposed a little to the south of the present escarpment, and the 

 formation of a subsequent stream would normally follow. 



About half way between Netley and Guildford is the gravel-bed 

 of Newlands Corner, which also contains chert, and is indeed 

 closely similar in composition to the Woodcote Lodge gravel (13, 

 p. 33). It stands for the most part at very much the same level 

 as that of Netley, and may also be ascribed to an early consequent 

 river. According to my reckoning, the Chalk extended over this 

 part of the plain for about 3 to 4 miles south of its present position, 

 and most of the territory between it and the central watershed 

 was occupied by Lower Greensand. W T hether the Weald Clay was 

 exposed is doubtful, but if not it would soon emerge, for its 

 covering of Lower Greensand must have been planed off to a very 

 thin layer. 



To the west of Guildford the geological structure of the plain 

 was more complex, and the evolution of the river-system is pro- 

 portionately difficult to determine. There is no drift on the Hog's 

 Back, and the only break in the even curve of its sky-line is a 

 shallow depression, about 50 feet below the summit, immediately 

 to the north of Puttenham ; but this absence of drift and passes is 

 not in the least surprising. The theoretical height of the plain at 

 Puttenham is (see fig. 1, p. 642) about 660 feet, and, owing to the 

 high inclination of the strata, this level would be reached at quite 

 a short distance (less than a mile ?) from the present summit ; the 

 latter, however, which hardly rises above 500 feet O.D., would be 

 buried under at least 150 feet of Tertiary strata, so that a river 

 might cut a valley as deep as that which we have already traced at 

 Crondall(that is, 200 feet below the level of the plain) without leaving 

 any lower pass across the Chalk ridge than we find above Puttenham 

 at the present day. It is quite clear from this that the even bevel- 

 ling of the crest of the escarpment along the Hog's Back cannot be 

 connected with the plain which I am endeavouring to establish. 



In the absence of drift the course of former consequent streams 

 is more than ever a matter of conjecture ; but it may be possible to 



