210 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



division apart, but nearly allied to the three underlying subdivi- 

 sions of **the Lower London Tertiaries." In Belgium, on the 

 contrary, M. Dumont, on physical evidence, unites into one group 

 the sands and clays of Ypres ; and forms a second group of the 

 beds beneath, dividing it into the Upper and Lower Landenian ; 

 whilst Sir Charles Lyell, mainly on the evidence of the organic 

 remains, places the Ypresian Sands at the base of his middle Eocene 

 group ; the Ypresian clays and the upper Landenian in his lower 

 Eocene group ; and the lower Landenian in a separate intermediate 

 group between the Tertiaries and the Chalk. In France the con- 

 stant recurrence of very similar mineral characters in all the strata 

 beneath the Calcaire grossier has rendered the division of this part 

 of the Tertiary series rather unsettled and difficult of exact determi- 

 nation. So much is this the case, that M. D'Archiac observes *, 

 that " where the ' Lits coquilliers' are wanting, there is no mode of 

 separating the third member of the * Sables Inferieurs' from the first, 

 and that at those places where the sandstones, or even the lignites, 

 with their beds of clay and oysters do not exist, there is no distinction 

 to be seen between these sands of the third division and the Glauconie 

 inferieure." M. Graves also states f, that *' as the division into series 

 of the * Sables glauconieux ' is entirely artificial, when the fossils are 

 wanting at the same time as the lignites and sandstones, all distinc- 

 tion ceases, and the beds of sand continue uninterruptedly from the 

 Chalk to the Calcaire grossier, without the possibility of distinguish- 

 ing any divisions." 



It was this unbroken sequence which before caused me to hesitate 

 in assigning to the London clay its exact parallel in the French 

 series. From the close agreement of the Calcaire grossier with the 

 Bracklesham sands, I felt no doubt of the infraposition of the London 

 clay to the former deposit, whilst, from the agreement of the Woolwich 

 fluviatile beds with the lignites of the Soissonnais, I was satisfied of 

 its superposition to the latter deposit. But then in France the beds 

 beneath the Calcaire grossier were in perfect sequence, and showed 

 no break. Therefore, if we looked only to the limits afforded by 

 these two undoubtedly good geological horizons, the London clay in 

 England held exactly the place occupied in France by the " Lits 

 coquilliers" and associated sands (Et. 1, 2, 3, D'Arch.). But the 

 fossils of the latter presented a far closer agreement with those of the 

 Calcaire grossier than with those of the London clay, although the 

 number of known species common to these beds and the London clay 

 appeared at that time larger than that of any other member of the 

 English series. Consequently, though I considered the London clay 

 to be more closely connected with the Lits coquilliers than with the 

 Calcaire grossier, with which it had previously been associated, I 

 stated J, that "possibly the London Clay may have been formed 

 during a period not represented, or only very partially so, in the 

 French series ; " and further remarked, that I was inclined "to con- 

 sider that the London clay period immediately preceded that of the 



* Hist, des Prog, de la Geol. vol. ii. p. 604, f Op. cit. p. 257. 



t Quart. Journ. Geol. Soc. vol. iii. pp. 376-7, note. 



