THE WEALD 603 



It is very difficult to visualise the process outlined by 

 former geologists in their attempts to explain the denudation 

 of the Weald, but one fact emerges from their assumptions, and 

 that is, they one and all find the position and direction of 

 the ' transverse valleys ' to be a tough problem to work out. 



Seeing that the prevailing idea among them was that of 

 an original chalk ' dome ' all over the Weald subsequently 

 pared down into a pene-plain by the sea, removing the chalk 

 and thus exposing the underlying anticlinal strata from which 

 sub-aerial erosion has produced the present features, it is 

 hard to understand why the results of differential erosion, 

 advanced in this paper, should not have been recognised. 



It stands to reason that if at one time the Weald, with its 

 covering of chalk, was planed down to one level, thus removing 

 the chalk ' dome,' the Weald clay, greensands and the chalk 

 left on their flanks must have been exposed to the same con- 

 ditions ; so that it follows that the present inequality in their 

 elevation must, in that case, be the result of a much more 

 rapid erosion of the sands, clay, etc., of the Weald, than of 

 the chalk. 



The gaps in the escarpment through which the rivers run 

 — the transverse valleys — must have been created by the 

 rivers themselves, as the chalk has only been subjected to a 

 very small extent to ' fault ' movements since it was laid 

 down. 



Therefore the present rivers are merely the descendants of 

 the rivers which first found their exit to the sea through the 

 chalk escarpments some 500 ft. above their present beds ; and 

 one only has to substitute a hilly region of wealden strata for 

 the planed-down chalk ' dome ' to explain completely these 

 transverse valleys and the debris of these wealden strata 

 found lying on the summits and in some of the valleys of the 

 Downs. 



In this theory of an initial plain of marine denudation, 

 in order to permit of an explanation of these north and south 

 river-valleys, Mr. Topley, who is one of the chief exponents 

 of the process by which denudation was effected, is obliged to 

 postulate a slight elevation of the wealden beds above the 

 chalk left on the flanks of the " plain of marine denudation " 

 in these words : " In the plain of marine denudation we should 

 have a comparatively plane surface sloping from a central line 

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