﻿654 ME. H. BURT ON THE DENUDATION OF [Nov. I9IO, 



(fig. 3, p. 642). The same influence may have been at work in 

 lowering the hills to the east of the River Ouse, but in that region 

 there may possibly have been, from the first, a decided tilt towards 

 the east, corresponding to the tilt already traced in the North Downs. 

 There is also a fall from Butser Hill to Ditchling Beacon, but it is 

 by no means clear that this is a primary feature. The raised sea- 

 beach of the south coast shows that movements, more recent than 

 the plain, have lifted the western end of the Sussex coast fully 

 100 feet more than the eastern, and if we permit ourselves to make 

 allowance for this along the Downs, we obtain an actual fall from 

 Ditchling Beacon westwards in the uplifted plain. 



Besides the broad warpings already noticed, there existed no 

 doubt a certain number of minor irregularities in both the North 

 and the South Downs. It is to this period that I attribute most of 

 the transverse folds ; but, as my belief rests on their relation 

 to the rivers, the discussion of it must be left to the third section 

 of this paper. 



Along the escarpment of the Lower Green sand, and along the 

 central axis of the Weald, we have, as already indicated, no 

 evidence regarding the summit-line of the plain on which, if taken 

 alone, reliance can be placed. But, in connection with what has 

 gone before, the following points are worthy of consideration. 

 Assuming that Leith Hill and Hindhead both approximately 

 represent the plain, there is a fall in the Lower Greensand 

 area towards the west. It is very slight (about 5 feet per mile), 

 but, then, Hindhead is much nearer to the central ridge than 

 Leith Hill and therefore higher up the slope of the plain ; making 

 allowance for this, the gradient probably differs but little from 

 that shown in fig. 1 between Botley Hill and the Farnham 

 Plateau — that is, about 1\ feet per mile. Again, measuring from 

 Blackdown (918 feet O.D.) to Wheatham Hill (813 feet) in the 

 Western Downs (Alton Hills), we find a gradient of 9 feet per 

 mile. It is true that Butser Hill (889 feet O.D,) is higher than 

 Wheatham Hill, and that .the latter may have had a capping 

 of Eocene deposits ; but, taken together, these gradients seem to 

 point to the conclusion already arrived at, that the plain had a 

 slight inclination towards the west. 



We now turn to the warpings of the plain along transverse 

 lines. Prestwich's sections enable us without difficulty to measure 

 the gradient of the Chalk Plateau in the Darent region. A careful 

 survey of it farther west, as far as the Mole, would be of con- 

 siderable interest ; but, in default of it, I think that the most 

 satisfactory method is to take a few of the more important summits 

 along the edge of the Downs, and measure the average gradients to 

 points some 4 or 5 miles farther north, ignoring the minor valle3"S 

 which sometimes intervene. We then have the following series, 

 working from east to west : — 



1. Terry's Lodge Hill (770 feet) to West Yoke (460 feet), about 

 3^ miles distant. Average = 95 feet per mile. There seems, however, to be 

 some additional disturbance near the escarpment ; and, if we measure to 



