268 PEOCEEDING^S OF THE GEOLOGIGAL iSOCIETY. [Apr. 16, 



That this lower sand belongs to the "Woolwich and Reading Beds 

 there can be but little doubt, as it abounds in some of the character- 

 istic fossils of that formation. The upper sand groups itself naturally 

 with the lower, the only difference being that the former contains 

 but few fossils. If such be the case, it follows that the basement- 

 bed of the London Clay is here altogether absent. It is possible, 

 however, that the upper sand and the loamy bed beneath may belong 

 to it, although the former is utterly unlike the undoubted basement- 

 bed wherever I have seen it, that is, from Marlborough Forest to 

 near Hemel Hempstead on the northern side of the London Basin, 

 and from Peckham and Croydon to Chiselhurst on the southern. 



It is but right to state that Mr. Prestwich is very doubtful in 

 separating the Blackheath pebble-bed from the "Woolwich and Eeading 

 Beds, and that he has also some doubt as to the place which should 

 be given to the sands that underlie the London Clay near Heme 

 Bay. Thus he says, " The difficulty is, whether we are to consider 

 any of the peculiar, fossiliferous, sandy, or conglomerate beds of 

 "Woolwich, Bromley, and adjacent districts as a fuller development 

 of the basement -stratum of the London Clay, or whether they all 

 belong to a distinct and underlying series. I am rather inclined, on 

 structural evidence, to the latter opinion ; nevertheless on palaeonto- 

 logical grounds it might be presumed that a passage here exists 

 between the two series*:" and again, "I feel slightly doubtful 

 whether some of the thick pebble-beds under and around Shooter's 

 HiU may not belong to the upper part of the "Woolwich series, rather 

 than to the basement of the London Clay ; the beds which at Upnor 

 and Heme Bay I have included in the ' Basement-bed ' may also 

 possibly belong to the upper section of the "Woolwich series. I 

 mention these doubts, which, however, do not affect the superposition 

 and grouping of the three divisions here proposed " (Basement-bed of 

 London Clay , "Woolwich and Reading Beds, and Thanet Sand) ," although 

 it would modify the exact lines of separation, in order to direct atten- 

 tion to any new facts which may arise to throw light upon those ques- 

 tions where I consider the evidence not quite conclusive t«" 



If the upper sands of Upnor, &c., be classed with the Woolwich 

 and Reading Beds, we need feel no surprise at so many fossUs of that 

 formation being found in them. 



If the above-noticed beds be classed with the "Woolwich and 

 Reading Beds, that formation will have a thickness of about 50 feet 

 near Heme Bay, instead of only 30 ; and at Croydon of 45 feet, instead 

 of 36. At New Cross they are 54 feet thick ; under parts of London 

 from 40 to 70 feet ; at Ealing 60 feet ; at Hanwell 75 feet, and at 

 Isle worth and Chiswick as much as 87 and 90 feet respectively J. 



From London westward, by "Windsor, Reading, Newbury, and 

 Hungerford, the Reading Beds have a general thickness of fram 40 

 to 60 feet (being subject to slight local changes), until near Great 

 Bedwin, to the west of which place I have shown, in the first part 



* Quart, Journ, Geol. Soc. vol. vi. p, 262. t Ibid. vol. x. p. 130, foot-note. 

 t Ibid. pp. 94, 96, 105, and 142 to 151. 



