﻿Vol. 66.~\ THE WESTEKN END OF THE WEALD. 6d3 



central axis, and so being affected by the transverse warping which 

 will be considered presently. There is also the same relation of the 

 highest points to the river-valleys, including the Wandle (Merstham 

 Gap) and Blackwater, except in the interval between the latter 

 river and the Wey, where the general low level of the Hog's Back 

 is due to causes which will be dealt with later. That the summit- 

 line has again a definite relation to the original plain appears to me 

 certain, but the suggestion of a fall towards the west is complicated 

 by the changes in the dip. The latter increases steadily from Croydon 

 to Guildford, remains extremely high between Guildford and Farn- 

 ham, and then decreases again. If we assume that the retreat of 

 the escarpment since the plain was uplifted has been uniform all 

 along the line, it is obvious that its effect in lowering the summit 

 of the Chalk must have been much greater where the dip is high 

 than where it is low, and it is quite possible that some at least of 

 the fall in the summit-line of fig. 1 (p. 642) is due to this cause. I 

 think, however, that the assumption of a uniform retreat of the 

 escarpment is most improbable. Where the dip was low, the Chalk 

 on the plain would thin out gradually, and only a small part of its 

 southward extension would consist of Chalk-with-Elints, which 

 is usually harder than the Lower Chalk ; it would, moreover, be 

 entirely devoid of all Tertiary covering which would serve to pro- 

 tect it, except over a narrow belt, where the dip was high. Again, 

 with a slight dip the escarpment would at first be very low, and its 

 rise in height would be gradual as compared with the rate of its 

 retreat northwards ; whereas, with a high dip, the maximum height 

 would be reached almost at once. So far, therefore, as I can judge, 

 the rate of retreat of the escarpment might, in the early stages, be 

 almost in inverse proportion to the steepness of the dip. 



The lowness of the Hog's Back must certainly be attributed to 

 the excessive inclination of the strata, and the removal of the 

 Eocene beds which formerly Covered the Chalk ; but, all things con- 

 sidered, I see no reason for assuming that the plain to the west of 

 Guildford ever attained a much greater elevation in the neighbour- 

 hood of the present escarpment than is indicated by the summit- 

 line in fig. 1. It is clear from the form of the Wealden area, and 

 the distribution of its component strata, that there is a general 

 structural fall to east and west about a transverse axis running 

 approximately through the Medway gap and Beachy Head; and 

 the evidence embodied in figs. 1 & 2 (p. 642) seems to point to the 

 plain having undergone a similar deformation, although the axis 

 was apparently farther west, and the inclination much smaller, 

 especially perhaps on the western side. 



The South Downs are composed of at least two distinct lines of 

 upfold, and are divided by several embayments into four portions, 

 two of which project northwards into the Wealden area, Avhile the 

 other two are withdrawn farther south. Having regard, therefore, 

 to the southward tilt which, as the rivers show, the plain must have 

 had, it is not surprising that Chanctonbury Iiing, which belongs 

 to one of the southern lines of hills, fails to reach the summit-line 



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