﻿Yol. 66.~] THE WESTEKN END OF THE WEALD. 677 



runs nearly due north — again with no obvious relation to the 

 strike — while on the Tertiary beds the north-westerly direction of 

 the Wealden portion is for a time resumed. Further observation 

 shows that, as regards the Weald Clay itself, there is a change of 

 strike along part at least of the Mole's course, as may be seen if 

 we follow, on the map of the Geological Survey, the belt of Palndina 

 Limestone : this may account for the direction of the river across 

 the Weald Clay, but leaves unexplained the change of course in 

 •crossing the Chalk. 



The numerous tributaries which reach the Mole from the west 

 follow approximately the direction of the strike, and are nearly at 

 right angles to the consequent stream : only one of them lies in the 

 Lower Greensand, the rest being all in the Weald Clay. On its 

 east side the Mole receives but one important tributary, and since 

 the strike on this side reverts to the normal east-and-west line, this 

 stream, which follows it, differs markedly in direction from the 

 longitudinal rivers on the west. On this eastern side there is no 

 subsequent branch in the Lower Greensand, but we are introduced 

 to streams of a type which is extremely common between Maidstone 

 arid Dorking, though unknown farther west — namely, obsequent 

 streams traversing the Lower Greensand at right angles to the 

 strike, and joining subsequent rivers in the Weald Clay. The most 

 important of these in the region of the Mole is one which rises near 

 Merstham, and cuts through the Lower Greensand escarpment at 

 Hedhill ; but there are others on a smaller scale farther west, also 

 belonging to the Mole, as well as several of importance farther east, 

 belonging to the Medway. 



Although the latter are outside the scope of this paper, they 

 must be included in a general sketch of the origin of such streams, 

 since they appear to me to have a possible bearing on the hypothesis 

 of a marine plain. Whatever were the advantages possessed by the 

 Medway and the Mole, they seem to have pushed out subsequent 

 streams very rapidly in the soft Weald Clay (which ex hypothesi 

 was from the first exposed), so that at a comparatively early stage 

 they had wrested all the central area from their less fortunate 

 neighbours. Meanwhile the latter had been cutting down the Chalk 

 and spreading laterally in the Lower Greensand as fast as they 

 were able, but after the decapitation which they had suffered in the 

 Weald Clay, their progress was not very rapid. The Medway 

 itself spread for some distance westwards in the Lower Greensand ; 

 but, owing to the narrower outcrop and (on the whole) less yielding 

 material, its success was far less than in the Clay : while the only 

 other river which extended laterally for more than a mile or two 

 was the Dareut. The Mole, for some reasons yet to be studied, made 

 practically no advance eastwards in the Lower Greensand, though 

 it established a small tributary on the west. The comparative 

 success or failure to reduce the level at which they crossed the 

 Chalk was of the utmost importance to the several streams which, 

 though severed from the Weald Clay, survived for a time in the 

 Greensand ; for, unless they could cut down their valleys below tho 



