The Crag Deposits on the North Downs

Abstract

To students of Tertiary geology, the interest of Mr. Clement Reid's verification of Prof. Prestwich's judgment of many years ago as to the Pliocene age of certain outlying deposits at Lenham is so great that I must crave permission for space for a line or two with reference to other similarly situated deposits on the North Downs, which have been described as belonging to an horizon “somewhere between the Chalk and the moon.” The deposits to which I refer were described by Prof. Prestwich in the Q.J.G.S., vol. xiv., and of his paper Mr. Whitaker made free use in preparing the account of these outliers in vol. iv. of the “Memoirs of the Geological Survey” (pp. 336–42). The idea has been for some time growing up in my own mind, with reference to these unfossiliferous outliers, that some of them will have to be recognised as remnants of the once more widely extended Upper Bagshot Sands. This conclusion is at present based mainly on three facts: (1) the literal application of Prof, Prestwich's description of their lithological character to portions of those beds; (2) the occurrence of “similar beds on the Chalk Downs on the opposite side of the Channel, between Calais and Boulogne”; (3) the superposition of “analogous strata” on the top of Cassell Hill in French Flanders upon the Calcaire grossier series, the equivalent of our Middle Bagshot (so-called Bracklesham) Beds. I hope to deal with this more at length during the next session of the Geological Society, and only draw attention now to the suggestion which I threw out several years ago (Proceedings of the Geological Association, vol. viii. p. 170) for reasons assigned, that the oldest plateau-gravels of the London Basin are probably of Pliocene age. This may possibly have escaped Mr. C. Reid's notice.