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ME. H. BURY ON THE DENUDATION OF [NOV. IC)IO,. 



level at which the underground waters of the pervious Lower 

 Greensand overflowed southwards on to the Weald Clay, they were 

 certain sooner or later to be captured by obsequent streams ad- 

 vancing from this direction. Perhaps the two diagrams given in 

 fig. 7 (below) will help to make this clear : in A the Lower Greensand 

 river is at least as low as that in the Clay, and has a chance of 

 surviving ; in B the Weald Clay river is lower than that in the 

 Greensand, and the latter is doomed to failure. In a rough and 

 diagrammatic way these two sections may be taken as representing 

 the conditions obtaining, A at Leith Hill, and B at Bedhill. In 

 the former case the Weald Clay was little, if at all, exposed upon 



Fig. 7. — Diagrammatic sections illustrating the drainage of the 

 Lower Greensand and the Weald Clay. 



Chalk I I Lower Greensand. 



Upper Greensand & Gault ■" Weald Clay 



[In A the Lower Greensand and the Weald Clay drainage are on about the 

 same level, and the former has a good chance of surviving ; in B the 

 Weald Clay drainage is the lower, and is certain, sooner or later, to capture 

 the Lower Greensand drainage.] 



the plain, and the subsequent rivers in it and in the Greensand 

 started on fairly even terms ; in the Redhill region, on the other 

 hand, the area of Clay exposed was large from the beginning, and 

 rivers developed in it with such rapidity that they first beheaded, 

 and then completely captured the Greensand streams. In the- 

 whole region between the Mole and the Medway the only Lower 

 Greensand river which has survived is the Darent : it does not; 

 seem to have long maintained its primary hold on the Weald Clay r 

 since the Lower Greensand escarpment is almost everywhere above 

 600 feet ; but it must have had some initial advantages, of which the 

 syncline described by Mr. Spurrell was perhaps the most important, 

 whereby it succeeded in combining into two subsequent streams in 

 the Greensand numerous small consequents which can now only be 



