184 ME. H. ^Y. MOiS^CKTON ON SOME GRAVELS [May 1898, 



13. On some Gravels of the Bagshot District. By Horace W. 

 MoNCKToif, Esq., F.L.S., T.G.S. (Eead January 19tli, 1898.) 



In 1891 I broTiglit before the Society a paper on the beds of gravel 

 which occur on the hills and in the valleys of the district south of 

 the Thames between Guildford and J^ewbary. In that paper I drew 

 particular attention to the composition of the gravel, and showed 

 that gravel of a very uniform character extends in some cases over 

 a considerable area (in one case over a length of nearly 10 miles), 

 whereas other gravels in the near neighbourhood have different 

 and yet curiously persistent characteristics. These peculiarities 

 seemed so difficult to explain, on any theory which attributed the 

 formation of the gravels to the action of the sea, that I arrived at 

 the conclusion that they were river-gravels — their peculiarities of 

 composition depending upon the geological structure of the drainage- 

 areas of different rivers. 



Sir Joseph Prestwich appears to have been inclined to the same 

 conclusion. He says, writing in 1890 :- — 



' As the channels of the earlj^ streams became deeper and larger, 

 and the Lower Greensand more exposed, the mass of debris carried 

 down increased, and the proportion of chert and ragstone became 

 greater. It was then that were formed the extensive plateaux of 

 gravel of the Chobham and Frimley Downs, and of the other hills 

 we have named in Berkshire, Hampshire, and Surrey.' ^ 



With this I quite agree, but in the next paragraph Sir Joseph 

 says, ' We are without a clue as to whether fluviatile or marine 

 action had to do with their origin ' ; but, he continues, ' It is not 

 improbable that* they are in part of subaerial origin.* 



In 1883 the Rev. Dr. Irving suggested an estuarine origin for the 

 highest plateau-gravels of the area with which I am dealing,^ and 

 in 1890 he expressed the opinion that their origin was fluviatile, 

 though, if I understand him rightly, he attributed the formation of 

 gravels at lower levels to marine action — ' the work of floating ice 

 ... in the old Thames Straits.' ^ 



It would seem, therefore, that I have the support of both Sir 

 Joseph Prestwich and Dr. Irving as to the fluviatile origin of the 

 highest-level gravels, and the evidence of composition on which I 

 largely rely was not brought forward by those authors, though both 

 agree that the materials came from the south and south-east. 

 I think, therefore, that I may safely say that on this point I am on 

 fairly sure ground. 



All are, I think, agreed that the low-level gravels of the Thames 

 Valley are of fluviatile or at least of subaerial origin, and I have 

 failed to find evidence which points to the presence of the sea in this 

 area at any time during or since the deposition of the highest gravels, 

 that is, those of Upper Hale, Aldershot, and of the North Downs. 



^ Quart. Journ. Geol. Soc. vol. xlvi, p. 173. 



^ Proc. Geol. Assoc, vol. viii, p. 143. 



' Quart. Journ. Geol. Soc. vol. xlvi, p. 562. 



