﻿Vol. 66. J THE WESTERN END OF THE WEALD. 659 



planed off by marine denudation before the present rivers arose, the 

 relation of the latter to the synclines would not be so marked ; both 

 anticlines and s}-nclines might indeed be occupied by rivers, as a 

 result of secondary action, but none of these streams would deserve 

 to be called consequent. At first sight, then, it appears as if we 

 might obtain from this source some important evidence as to the 

 course of denudation ; but, unfortunately, the problem is complicated 

 by other considerations. 



The Wealden area seems to have been raised above the sea at 

 the close of the Eocene Period, but the principal longitudinal folds 

 are generally attributed to Oligocene or Miocene times. In that 

 case, assuming that there has been no more recent marine action, 

 the river-system was antecedent to the folds, and their effect upon 

 it would depend on so many factors — for instance, the degree of 

 maturity of the rivers, the intensity and rapidity of the move- 

 ments, etc. — that it seems impossible to lay down any definite rules 

 which will guide us in distinguishing between such an antecedent 

 river- system and one developed upon a marine plain after the folds 

 were formed. The transverse folds are perhaps more helpful, but 

 unfortunately they are for the most part less forcibly developed, 

 and therefore harder to trace. That transverse synclines arising 

 •during upheaval would attract consequent streams, while anticlines 

 would repel them, is obvious enough; but the effects of the planation 

 •of such folds are worthy of closer study. Transverse synclines thus 

 planed off would form salient angles in the line of Chalk upon the 

 plain, while anticlines would form re-entering angles. If, then, the 

 plain were tilted, in the manner already suggested, the edge of 

 the Chalk would be higher along the synclines than along the anti- 

 clines, and this would give a decided advantage to those consequent 

 streams which happened to coincide with the latter. For, although 

 the initial rivers probably ran over a thin covering of marine de- 

 posits, yet the moment this was removed, one of the most important 

 factors in determining the relative success of different consequent 

 rivers in extending their territory through the 'hinterland' of soft 

 beds would be the height at which they crossed the hard Chalk, or 

 the rate at which they could cut it down. This principle may be 

 illustrated by concrete examples. If we continue the dotted summit- 

 line in fig. 2 (p. 642) to the point at which Topley supposes the 

 Rother to have crossed the Chalk (26, pi. ii), we find that the latter 

 only rose to 560 feet above present sea-level, and it is quite in 

 keeping with this that the Bother should have captured, by means of 

 subsequent streams, a large area of territory on both sides of the 

 channel. It is tempting also, though probably not altogether safe, 

 to attribute to the same causes the comparative failure of some of 

 the more central rivers. The highest point in the North Downs is 

 Botley Hill (882 feet O.D.), and it is certainly a curious feature 

 that immediately to the east of it is the Darent- — the only Wealden 

 river which does not reach the Weald Clay ; while on the west lies 

 the Wandle, which, after obtaining a firm hold on the Weald, 

 probably at more than one point, has now been completely severed 



