XCiv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. lxXV, 



and south-east of England, and is not without its application 

 to the present distribution of the Glacial deposits. 



I have already hinted at the probable bearing of the factor on 

 certain occurrences of our Older Palaeozoic rocks, but shall not 

 venture farther in this direction, for reasons previously mentioned. 

 It seems, indeed, possible that the principle, with some limita- 

 tions dependent upon variability of rock-structure, may be of 

 universal application, since it is evident that, when denudation 

 plays upon a sedimentary mass of irregular thickness without other 

 inequality of conditions, it is the thinnest parts of the mass that 

 will first disappear and the thickest parts that will endure longest. 

 Formations accumulated in a subsiding trough or basin are neces- 

 sarily more or less lenticular in profile, so that, if brought at any 

 time equally under the influence of erosion or denudation while 

 still unprotected by later formations, they will lose area most 

 ♦quickly around the margin and will maintain it longest in the 

 middle of the lenticle. In the English examples under consideration 

 the lenticles have been tilted, so that one side only has been exposed 

 and lost, with the result that the remaining portions take the form 

 of wedges, in which the thick end sustains the present outcrop. 



The same conditions must have been operative during eveiy 

 cycle of erosion, and may have been effective at several different 

 periods on the same formation. Therefore the existing masses of 

 strata, considered broadly and without reference to exceptional 

 ■circumstances, may be logically held to denote by their survival 

 that they represent the thicker parts of the original formations. 



This is the assumption which I had in mind before, in mentioning 

 the Older Palseozoic rocks of Wales. If I were to go still farther 

 afield, I believe that I could gather a big body of evidence in 

 support of it, along with some which would tell against it. But 

 the point does not require elaboration ; it is obviously true as 

 regards the English Mesozoic rocks, and must be applicable in 

 other regions of similar history. Indeed, it may possibly have 

 already received more recognition than I am aware of. 



In concluding, I will rehearse the main steps of the argument 

 which I have sought to pursue. 



1. The Anticline of the Weald is a superficial structure depen- 

 dent upon an underlying syncline. The lenticle of sediments thus 

 bounded was deposited in a gradually deepening trough, which was 

 afterwards shallowed by partial recovery. 



