AND PLEISTOCENE DEPOSITS OE THE STJSSEX COAST. 363 



high-water mark, the other at about the present mean tide-level ; 

 so that there was a priori reason to conclude that a subsidence of 

 100 feet or more would have been marked by at least some pauses 

 during which raised beaches would have been formed and rock- 

 platforms or notches cut at higher levels. 



In the second place he pointed out that, whilst the rude semblance 

 of stratification in the ' Head ' of Cornwall and Devon could readily 

 be explained by fluctuating meteorological conditions and local varia- 

 tions in the rocks disintegrated, there were no signs of current- 

 bedding in the ' Head,' although the rapid submergence and 

 emergence necessitated by Prof. Prestwich's explanation would 

 involve the operation of currents. 



He was pleased to find that Mr. Eeid, in correlating the ' Head ' 

 and the Coombe Rock, had come to pretty much the same conclusion as 

 that expressed by himself in 1879 respecting the ' Head ' on the Devon 

 and Cornish coasts, viz. that it indicated a more rigorous climate. 



Mr. J. Allen Brown believed that rubble deposits had been 

 formed at all times since the last period of emergence. He thought 

 Prof. Prestwich had not attached sufficient importance to the action 

 of subterranean waters, which, after saturating the Chalk, carried off 

 in solution and mechanically the carbonate of lime, thus massing 

 the strata of flints together by the removal of the Chalk, and causing 

 the formation of rounded chalk-rubble beneath as well as intermixed 

 with them. Prof. Prestwich had shown in previous papers that sub- 

 terranean water did not flow in direct lines, but followed the lines 

 of least resistance arising from th€ difference in density of the 

 Chalk, and that such agency was most frequently seen in action in 

 combes or valleys having egress to the sea. 



Such a valley was that at East Dean, which he had occasion to 

 examine recently, as implements of Palseolithic type had been found 

 there in the aggregated flint-bed. The section at Birling Gap, near 

 East Dean, from the contortion and irregularity of the deposits had the 

 appearance of being due to glacial action, but ou closer examination 

 was found to be formed by subterranean water-erosion, as the beds of 

 flint could be seen in situ in the adjoining cliff. Such rubbly deposits 

 could also be formed in depressions on the slopes of hills, by the same 

 action combined with subaerial agency. 



He noticed that Mr. Clement Eeid had thrown some doubt upon 

 the fluviatile origin of the high-terrace gravel deposits, as at High- 

 bury ; but he hardly thought there could be any uncertainty in the 

 matter, although his own investigations, which he hoped to complete 

 and submit to the Society, led him to believe that the action of ice 

 or of an ice-sheet impinging on the river carried with it much more 

 transported matter than had been generally admitted, and that such 

 ice-borne detritus varied locally according to the superficial deposits 

 of the country over which it travelled — here depositing the pebbles 

 of a Bagshot or Westleton bed, and elsewhere, perhaps, the foreign 

 rocks emanating from a distant glacier. 



Prof. Hughes felt that Prof. Prestwich's paper covered so wide a 

 field of enquiry that it was hardly possible to discuss it in one 



Q.J.G.S. x\o. 190. 2 c 



