﻿Vol. 66.'] THE WESTERN END OP THE WEALD. 657 



retains its original elevation; but, even if we raise it as high as 

 Butser Hill, the gradient is still small compared with those that we 

 have just examined, and some evidence can be obtained elsewhere 

 that the central region was very flat. 



In the South Downs we seldom hind such direct lines of 

 observation as in the North Downs. The really high points along 

 the escarpment-line are, as fig. 3 (p. 642) shows, few and far apart ; 

 and the same is true of a parallel ridge, about 3 or 4 miles farther 

 south, with which comparison has to be made. Moreover, we have 

 no evidence, so far as 1 know, of a distinction between a pre-Eocene 

 and a post-Eocene planation of the Chalk, as we have in the North 

 Downs, nor of the Eocene beds having undergone two periods of 

 tilting; wherefore the gradients which we observe may possibly 

 have but little connection with the Pliocene plain, a great part of 

 which may, in this region, have been composed of Tertiary strata. 

 I give the following observations, however, for what they are worth, 

 premising that, except where otherwise stated, the hypothetical 

 summit-line (fig. 3) has been used in calculating gradients : — 



1. Butser Hill (889 feet; actual, not theoretical) to Windmill Hill 

 (600 feet). Gradient = 105 feet per mile. 



2. Linch Down (860 feet; 818 feet actual) to Bow Hill (624 feet). 

 G-radient = 54 feet per mile. 



S. Cocking Down (850 feet) to St. Roche's Hill (677 feet). Gradient = 

 48 feet per mile. 



4. Chanctonbury Ring (779 feet ; actual, not theoretical) to Cissbury Hill 

 (603 feet) Gradient = 70 feet per mile. 



5. Near Ditchling Beacon (810 feet) to Newmarket Hill (645 feet). 

 Gradient = 47 feet per mile. 



Although some of these gradients are not far removed from those 

 of the North Downs, yet their paucity and irregularity, coupled with 

 the doubts already expressed as to whether they are pre-Eocene or 

 post-Eocene, must make us hesitate to accept them as evidence of 

 marine action. The plain may, indeed, have existed; but, if a large 

 portion of it was covered with Eocene beds, there is nothing sur- 

 prising in the absence of evidence of it, for the South Downs, owing- 

 to their greater proximity to the sea, and perhaps to other causes 

 (9, vol. iii, p. 404), have undergone more severe denudation than the 

 North Downs. However this may be, we can safely assert that the 

 marine plain, if it ever extended to this region, cannot have been 

 continued in so steep an incline all the way to the central axis. 

 Such a gradient as 50 feet per mile, continued from Duncton Down 

 to Blackdown, would give an elevation of nearly 1300 feet ; but 

 there is reason to think that the Hythe Beds were already exposed 

 in the central region, and in that case Blackdown cannot have been 

 very much higher than at present (918 feet). It follows, therefore, 

 that the existing gradient from Blackdown to Duncton Down (about 

 8 feet per mile) is not far removed from that of the original plain. 



Although the data given above are very imperfect, and are by 

 no means sufficient, taken by themselves, to establish planation, yet, 

 if the existence of a marine plain be granted on other grounds, 



