182 HEV. A. mYTN-G ON THE STRATIGRAPHY 



interesting question. At present I think we must say with Dr. 

 Barrois (ojj. cit. p. 115), " Je ne sais comment on pourrait recon- 

 naitre ici I'importance de ce qui a ete enleve par les denudations." 



The General Syndine. — We have seen that there is evidence of 

 the " Farnborough Syncline " * being continued to the west, at 

 least as far as Highclere. A glance at the map shows, by the trend 

 which the general strike of the Tertiary Beds makes to the north- 

 east from Guildford to about Ewell, that the axis of this syncline 

 must pass nearly through Woburn Park, near Chertsey. This is 

 quite enough to account for the low altitude of the strongly-deve- 

 loped clays which are mapped (and, I believe rightly) as belonging 

 to the Middle Group there, and at Ongar and Eow Hills. 



On Mr. Hudleston's last paper t we note therefore : — (i.) that 

 the apparent abnormal thinness of the Lower Sands about Chertsey 

 is but an instance of that slight unconformity for which he had 

 himself contended in his previous paper t ', (ii.) that the identity of 

 the horizon of the clays in the Hatch brick-yard with that of 

 certain intercalated patches in the Walton cutting requires more 

 evidence than has been yet adduced for it to be generally accepted ; 

 (iii.) that the dark-coloured laminated sandy clay (Mr. Hudleston's 

 ' No. 4 Bagshot ') bears a striking resemblance to the higher beds of 

 the London Clay exposed in the Aldershot brick-yards, where a 

 very similar succession may be studied, and (until the contrary is 

 proved by excavation) may be maintained to be only an inljing 

 portion of the London Clay, a result of that previous local erosion 

 of the surface of that formation of which the section nearer the 

 Station gives us good evidence. 



It is with much pleasure that I find the general relationship 

 which I have all along insisted upon between the London Clay and 

 the Lower Bagshot (' fluviatile sands ') borne out, not only by the 

 well-sections published by Lieut. H. G. Lyons, E.E., P.G.S. §, but 

 also by the more extensively-informed judgment of Prof. Prestwich, 

 This relationship of the ' London Sands,' as he now proposes to 

 name them (as the equivalents of the Upper Tpresian), is seen on 

 comparative grounds and from palaeontological evidence obtained in 

 other Eocene areas, to be closer than has been generally supposed, 

 notwithstanding marginal erosion and local unconformities on the 

 northern flank and in the Walton cutting. jN'ow that the varia- 

 bility of the thickness of the Lower Sand Series is admitted, there 

 is really no serious difference between us. Whether or not this 

 amounts to an unconformability along the northern margin, or is only 

 a marked instance of "contemporaneous erosion" (Jukes), is a question 

 on which there is room for difference of opinion. That the move- 

 ments which gave a slight accentuation to this great pre-Eocene 



* Quart. Journ. Geol. Soc. vol. xli. As a piece of eTidence for estimating 

 this syncline, the new well at Minley Manor (1886) at 250' O.D. gave 62' of 

 uniform Upper Sands without reaching the pebble-bed or the Middle Clays. 



t Quart. Journ. Geol. Soc, August 1887. t Ibid. May 1886. 



§ Quart. Journ. Geol. Soc, August 1887 ; see also paper by the author, 

 " The Bagshot Beds and the London Clay," Geol. Mag. for September 1886. 



