﻿Vol. 66.~] THE WESTEKN END OP THE WEALD. 669 



at any rate to the east of Bentley, and the Tilford Eiver, as we 

 know, is of much later date ; hence it is evident that the whole 

 system was still in the consequent stage. It may be urged that 

 much of this district was covered with Chalk, and that subsequent 

 streams do not readily arise on that formation ; this I am ready 

 to admit, and, indeed, I shall argue later that the difference between 

 the Blackwater and the neighbouring river-systems is largely due 

 to this cause : but the fact remains that, given time enough, sub- 

 sequent rivers do arise, even on Chalk, as can be seen in Hampshire 

 and in the Dean Valley (South Downs) at the present day. More- 

 over, why was there so much delay in founding a subsequent 

 system in the Lower Greensand, to the south of the Chalk escarp- 

 ment ? The lowest point of the Chalk must have been in the 

 syncline, approximately along the line of the Tilford River, and, 

 taking the central axis as lying between Hindhead and Black- 

 down (see fig. 6, p. 670), the Chalk must have retreated by the slow 

 process of subaerial weathering for a horizontal distance of about 

 7 miles before it reached the syncline. Seeing that soft beds were 

 exposed at the foot of the escarpment during the whole of this 

 time, the abseuce of a subsequent river seems to me surprising. I 

 am aware that opinions may differ as to the readiness with which 

 subsequent rivers can be developed — to that I shall return presently : 

 but the fact cannot be denied that the second cycle successfully 

 produced two such rivers in this region, while the first produced 

 none ; and if it is sought to explain this by supposing that the 

 second cycle was longer than the first, we are confronted with 

 the objection that, while the first cycle removed 1000 feet of 

 strata from the central axis, the second cycle has effected but little 

 reduction in the height of Hindhead, and none at all in the 

 Farnham Plateau. 



It appears to me, in fact, that those who uphold this hypothesis 

 are on the horns of a dilemma. If, in order to account for the 

 immaturity of the river- system, they push the Chalk escarpment 

 far to the south at the beginning of the second cycle, they have to 

 explain how this immense mass of Chalk was removed, while but 

 little denudation occurred elsewhere ; if, on the other hand, in 

 order to avoid this difficulty, they bring the escarpment nearly 

 into its present position, they increase the total distance over which 

 it retreated during the first cycle, and thereby heighten our astonish- 

 ment that the drainage-system should have remained so incomplete. 



Prof. W. M. Davis, it is true, does not regard a well-established 

 subsequent system of drainage as a normal product of one cycle of 

 denudation ; but, while attaching great weight to his opinion, 

 I fail, having regard to the nature of the Wealden strata, to under- 

 stand the grounds of his belief. All round the Wealden area the 

 Chalk ends in an escarpment, and has presumably done so ever 

 since it was first removed from the centre of the dome. But an 

 escarpment implies the lowering of the beds at its foot, some of 

 which (as, for instance, the Folkestone Beds) are extremely soft ; 

 and it appears to me incredible, unless all the consequent rivers 



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