6oo SCIENCE PROGRESS 



modified ' curves of the catenary ' except in accordance with 

 the mathematical law regarding these particular forces which 

 are brought into operation. 1 



If erosion attacked the surface as in other formations, the 

 surface, which all over the body of the chalk in the south of 

 England is mainly the upper chalk with its bands of flints 

 at vertical distances of a few feet apart, would, on erosion of 

 the soft parts, leave behind thick deposits of flints all over 

 the surface. 2 



Now, whereas the lie of the chalk of the adjacent southern 

 counties is comparatively horizontal, and the top stratum is 

 generally the flint-bearing upper chalk, while nowhere are there 

 deposits of residual flints left behind, as the insoluble products 

 of any weathering agency, the natural presumption, startling 

 though it is, is that we are treading the same surface that was 

 exposed ages ago, and that the turf-covered chalk, from a 

 surface point of view, is practically indestructible by ordinary 

 erosion. 



Further, it should be remembered that such residual flints, 

 if found, would be very different in many cases from ordinary 

 gravel, since where landslips have occurred the flint bed is 

 seen often as a weighty network of branches running root-like 

 in every direction, or perhaps in solid blocks sometimes of a 

 hundred pounds weight, and in tabular sheets. Of such there 

 are no signs, neither on the plateaus nor in the valleys. 



This negative evidence is very strong. A few valleys con- 

 tain deposits of flints, but they are not extensive, nor are the 

 flints of any large size. Mixed with these deposits, however, 

 we get occasionally the peculiar products of the lower green- 

 sand, as noticed by Mr. G. Clinch in The Sculpturing of the 

 Chalk Downs? who says : 



" Generally speaking the ' dry ' chalk valleys do not con- 

 tain any considerable amount of deposits of hard and in- 

 soluble matter. Many, indeed, are quite free from such 

 accumulations ; but some are partially occupied by beds of 



1 It might be mathematically demonstrated that such curves tnust be caused 

 by withdrawal of material from underneath them. 



s This has occurred in the Hythe beds, which contain bands of Ragstone (often 

 very cherty) and of Hassock, soft calcareous sandstone. Water percolating has 

 acted mechanically and chemically, removing the softer parts, so that a residual 

 drift of the insoluble parts of the Rag is left, forming a kind of gravel. 



1 Geological Magazine, vol. vii. February 1910. 



