DRIFT-STAGES OF THE DARENT VALLEY. 159 



crucial test. Though the Gault elsewhere at the foot of the Chalk 

 escarpment often shows a sprinkling of drift, there is no place 

 where the character of that drift has hcen so well shown as in the 

 sections on the line from Dunton Green to Westerham. 



At first sight these sections might seem to corroborate the view 

 of those who hold that the escarpment has been worn back by slow 

 subaerial denudation, for, as I have shown (p. 149), traces of the 

 Eed Clay with its flints, together with flints from the Chalk and 

 pebbles from the Lower Tertiaries, are there, though in very small 

 quantity, and only in local patches. 



But so far from possessing this uniformity and the special local 

 characters in accordance with such an origin, the drift-beds in the 

 valley present a marked diversity, while there are spaces free from 

 any drift. If we take, for example, the section across the valley 

 at Dunton Green, we find that instead of this uniform debris a 

 chalk- and-flint rubble extends from the slope of the escarpment to 

 Broughton Hill, which, on the other hand, is capped by a gravel of 

 Chalk flints and Tertiary flint-pebbles, with Lower-Green sand debris 

 brought from a distance ; at Dunton Green there is the peculiar 

 angular-flint drift with scarcely a trace of Lower-Greensand debris, 

 while the Low-level drift in the valley beyond consists of mixed 

 flints and Greensand debris. 



On the rising ground (of Lower Greensand) on the side south 

 of the valley the drift is composed almost entirely of local debris, 

 and there is scarcely the trace of a flint (see PI. YI. fig. 1). It is 

 obvious, therefore, that here we have not simply a local drift of 

 Chalk flints and Tertiary debris, left behind during a slow weather- 

 ing and recession of the escarpment, but successive streams of drift- 

 gravel, formed by erosion, and transported from other points higher 

 up the vallej'. Of course, in a slow recession, the effects of springs, 

 streams, and freshets are not to be overlooked ; but it is not to be 

 supposed that these would be of such a character as to remove or 

 alter all the evidence of the primary cause, and until some of that 

 evidence is forthcoming the hypothesis must, like that of the marine 

 origin of the escarpment, fail, not only for want of proof, but also 

 as against such evidence as we have. 



Instead of a slow gradual recession, due only to atmospheric 

 influences, in the direction of the dip of the strata, the evidence 

 rather shows that, after the first predisposing causes, glacial agency 

 was the great motor in developing the valleys, and, as a consequence, 

 the escarpment ; and that the denudation was afterwards further 

 carried on in the same lines by strong river-action and weathering, — 

 supplemented at times by renewed ice-action. It was, I conceive, 

 by these more energetic agencies, aided by the influence of a 

 heavy rainfall, and the issue of powerful springs on the face of 

 the escarpment, that the escarpment was gradually pared back 

 and brought into its present prominent relief. 



[Other observations in connexion with the denudation of the 

 Wealden area, and concerning the course and action of the rivers 

 during its early stages, will be found in my paper " On the Southern 

 Drift," in Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 160 et seq.'] 



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