﻿MR. H. BURT ON THE DENUDATION OF [Nov. 10,10, 



they present an intelligible picture of the warpings which it under- 

 went during upheaval. The central region remained extremely flat, 

 with a slope to north and south of (probably) less than 10 feet per 

 mile. Possibly, too, there was, west of Botley Hill, a similarly 

 gentle inclination towards the west. Along the line of the North 

 Downs the gradients increased considerably. The figures tabulated 

 above show a maximum of 80 to 90 feet per mile, in the region of 

 Botley Hill, gradually diminishing to 30 feet per mile near Farnham, 

 and taking therefore little or no notice of the increase in the dip of 

 the strata towards the west. It must be remembered, however, that 

 in the case of Farnham the gradient is calculated almost up to the 

 central axis, whereas in only one other case (Leith Hill) is there 

 any point of observation outside the Downs themselves ; and the 

 figures obtained elsewhere as to the flatness of the central region 

 make it not impossible that there was a considerable increase in 

 steepness immediately north of the Farnham anticline. Neither 

 here nor elsewhere, however, is there any indication that the great 

 North Down fold belongs, as a whole, to this period ; on the con- 

 trary, Prestwich's diagrams of the Chalk Plateau seem to show that 

 there were two distinct movements, and that the axis of the earlier 

 (and stronger) one lay somewhat farther north than that of the 

 second. The rivers, too, as will be pointed out later, negative the 

 suggestion that the principal longitudinal anticlines and synclines 

 are contemporaneous with the present drainage-system. 



It may be noted in passing, although evidence is not yet available 

 to prove this, that the flattening of the central region, and conse- 

 quent low elevation of the Wealden dome, give a clue to that 

 absence of glaciation which is now generally admitted. 



III. Evidence of Rivers. 



(A) Their Relation to the Rock-Folds. 



Prof. W. M. Davis (3), in his masterly exposition of the general 

 theory of river- evolution, naturally takes the simplest case — that of 

 a plain sloping steadily down to the sea, at a slightly lower angle 

 than the dip. In the Wealden area, however, this simplicity does 

 not exist, for besides the main anticline, forming the central 

 watershed, there are numerous other longitudinal anticlines and 

 synclines parallel with this axial ridge, as well as a certain number 

 of transverse folds at right angles to it ; and it is, therefore, desir- 

 able to make some enquiry into the part played by those disturbances 

 in river-development. If the longitudinal folds were contempo- 

 raneous with the initial stages of the present drainage-system, we 

 should expect to find many of the synclines occupied by longitudinal 

 consequent rivers ; and these might help us to understand that 

 combination of a bevelled escarpment with a mature river-system 

 to which Prof. Davis calls attention. As a matter of fact, however, 

 such rivers are rarely, if ever, found in that part of the Weald 

 which is here examined. If, on the other hand, the folds were 



