xliv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



consequently to prevent the formation of glaciers upon them ; hut 

 there is nothing in the facts observed to justify this conclusion as a 

 necessary one. And even if it were so, a merely local circumstance 

 of this kind could scarcely justify the notion of two distinct glacier- 

 periods without a guarded limitation of the expression as one of 

 merely local signification. I throw out this caution lest the language 

 of the author should lead to interpretations more general than the 

 observed facts might justify, or than the author himself may possibly 

 have intended. The facts described in this paper have been reviewed 

 and confirmed, I believe, since it was read, and, as proceeding from 

 so able an observer as Professor Ramsay, have been thought far too 

 important to be omitted in this discussion, although they have not yet 

 appeared in a printed form. 



There is another class of superficial deposits, entirely different from 

 those of which I have hitherto been speaking, and to which Mr. 

 Austen has especially directed our attention*, — I mean the sub- 

 aerial accumulations formed by the descent of disintegrated portions 

 of rock which fall from the higher parts of the steep escarpment of a 

 cliff or mountain, and collect at its bottom or along its face. Super- 

 ficial portions of rock-masses, disintegrated in situ, may frequently 

 also be associated with the accumulations just spoken of, the only 

 difference being that, in the one case, the disintegration takes place 

 in localities from which the disintegrated masses necessarily fall by 

 their own weight, or by the action of the elements ; and in the other 

 case, those causes are not sufficient to detach them from their original 

 positions. Mr. Austen has not only described the beds which he 

 considers to belong to this class on the coast of the English Channel, 

 but he also makes them subservient to the determination of the oscil- 

 lations of level which he considers to have taken place along that and 

 the adjoining coasts. 



The last coast-line antecedent to the existing one, as recognized by 

 the author, is about 8 or 10 feet higher than the latter. The 

 next line, in backward order of time, is about twice as high as the 

 first above the present level, estimating them all as high-water levels. 

 These two ancient sea-lines, therefore, indicate two successive eleva- 

 tions of the land of about the same amount. A third sea-line is 

 again recognized at nearly the same elevation as the first of the two 

 above-mentioned. Taking the events in the reverse of the above 

 order, or the proper order of time, we have 



(1.) A sea-beach, when the land was lower than at present, by a 

 variable amount in different places, sometimes amounting to 60 or 

 70 feet. This is indicated by a marine bed which was formed at that 

 level. 



(2.) A subaerial bed of shingle was then formed over this marine 

 bed, by the disintegration and fall of the rocks immediately above it. 



(3.) The land was depressed about 8 or 10 feet, and a thin marine 

 bed was formed on the subaerial bed of shingle. 



(4.) The land was elevated into a position a little higher than that 



* Quarterly Journal, May 1851, p. 118, " On the Superficial Accumulations of 

 the Coasts of the English Channel, and the changes they indicate." 



