558 REV. A. iRviNa oisr the plateau-geavels 



it suffered that amount and kind of lithological change* which, 

 with subsequent fluviatile transport for distances of 10 to 15 miles, 

 would give such materials the character and the subangular form 

 which they for the most part are found to present in the Plateau- 

 gravels. The flint pebbles, with which they are now intermingled, 

 were probably preserved from the action of those atmospheric agencies 

 which induced the lithological changes in the subangular flints, by 

 having been sealed up in the Eocene strata, after having been formed 

 hj shore-action f. These two chief constituents of the Plateau- 

 gravels, together with the subangular fragments of Neocomian chert, 

 were intermingled, no doubt, in the rivers which flowed from the 

 Wealden Hill-range, as the denudation of the Eocene beds in their 

 formerly southerly extension proceeded, with the increased accentu- 

 ation of the anticline, paon passu with the transport of the angular- 

 flint material by rivers from the Weald across the northward- 

 sloping plateau of Eocene land. 



These Plateau-gravels seem to have no necessary connexion in 

 time or otherwise with the " Mundcsley and Westleton shingle" of 

 Prestwich, since the flinty materials found in that might very well 

 have been derived from an elevated Chalk region of Mercia and 

 East Anglia. 



Even the high-level gravels of the country north of the Thames may 

 have had to a large extent a subaerial origin; for the fact that so many 

 of them are covered up by boulder-clay (and so protected from the 

 solvent action of carbonated atmospheric waters) renders it extremelj'- 

 difiicult to account for their non-fossiliferous character by the 

 hypothesis of " decalcification " j. The above explanation of the 

 intermingling of such different forms of the flinty material was put 

 forward in 1883 ; and was, as then pointed out, suggested to me 

 by my previous observations of the vast accumulations of angular 

 flint material (mere insoluble residue) found to-day on the top of 

 Saint-Boniface Downs in the Isle of Wight §. The quartz-pebbles 

 mentioned by Prof. Prestwich in his recent paper, and by Prof. 

 Eupert Jones II, are in my experience rare in the Plateau-gravels; 

 nor do I believe, after sifting the evidence, that Mr. Monckton's 

 large rolled block of vein-quartz came out of them %. 



Observation in the field tells us that as we work south the 

 presumably older gravels become, as we should expect, more angular, 

 and acquire a more massive development, most fully seen in the vast 



* See Appendix i. Note e, in my "Chemical and Physical Studies in the 

 Metamorphism of Kocks," p. 103 (1889). 



t See Proc. Geol. Assoc, vol. viii. 1883, pp. 167, 168 ; also the Quart. Journ. 

 Geol. Soc. vol. xliv. p. 184. 



\ Prestwich, op. cit. p. 146. The predominance of land and freshwater 

 remains in the list of organic remains given in Q.uart, Journ. Geol. Soc. vol. 

 xlvi. pp. 115, 116, seems to point to an estuarine origin for the beds at Westleton 

 and Mundesley, suggesting a terrestrial origin for the higlier beds inland. 



§ See also the new edition of the Geol. Survey's ' Memoir on the Geology of 

 the Isle of Wight,' 1890, p. 210. 



II See Proc. Geol. Assoc, vol. vi. p. 439. 



ir See Quart. Journ. Geol. Soc. vol. xlvi. p. 154. 



