1852.] LYELL BELGIAN TERTIARY FORMATIONS. 359 



Roem. sp., both which (according to M. Bosquet*) occur in the 

 Eocene strata of France. The lower half was made up of stiffer clay 

 of a bright green colour, and lower down of darker colour, in which 

 I found no Nummulites. As the Brussels beds with Nautilus JBur- 

 tini occur in the trenches of the citadel at Ghent, I imagine the green 

 sands of this well to belong to E. 3 of Table I., or the Systeme 

 Ypresien of M. Dumont. It may perhaps be found possible and 

 convenient to draw here and elsewhere a line of demarcation between 

 the Ypres beds and the London Clay proper at the point where the 

 Nummulites cease. Whether the beds containing N. planulatus 

 near Ghent or Courtray may correspond in age with an upper division 

 of the London Clay proper, or with the lowest part of the Bagshot 

 series, cannot as yet be decided. 



[6.] Mons-en-Pevelle, near Lille. 



At no locality visited by me were the bands of Nummulitic lime- 

 stone so conspicuous as at Mons-en-Pevelle, about nine miles south 

 of Lille, to which my attention was directed by M. Meugy. The 

 thickness of the formation (overlying the London Clay) to which 

 they belong is estimated by that geologist at about 100 feet. I saw 

 the layers of nummulitic rock, from 6 to 8 inches thick, extending 

 throughout a thickness of about 60 feet of sandy and clayey beds. 

 Not only were the roads made of them, but several buildings were in 

 part constructed of the same, and I saw the yard of a farm-house 

 paved with nummulitic slabs. With the exception of a Bentalium 

 (D. Deshayesianum), I could find no fossils in the associated strata. 

 In this part of French Flanders the lower nummulitic beds are sepa- 

 rated from the Chalk by about 150 feet of London Clay, and nearly 

 100 more of Plastic clay and sand. 



§ 8. London Clay proper (F. 1. Table I.). Argile Ypresien, etage 

 inferieur, Dumont. 



I have already stated, p. 331, that at the railway-station at Cassel 

 a mass of brown clay with septaria was bored to the depth of 100 

 metres, and the bottom not reached. In uniformity of aspect it re- 

 sembled the clay of Highgate and other places near London, and 

 the absence of shells in the large heaps of clay extracted from the 

 well, which I examined carefully, might be paralleled by a similar 

 dearth of fossils in numerous sections in the London and Hampshire 

 basins. The green sands and clays above the London Clay in the Hill 

 of Cassel much resemble those containing Nummulites planulatus 

 elsewhere, although I could not meet with that fossil at Cassel. 



Near Lille a mass of clay, estimated by M. Meugy to be about 

 44 metres (or 145 feet) thick, underlies the Nummulites planulatus 

 sands and limestone of Mons-en-Pevelle already described, and under 

 that again are sands and clays, probably corresponding to the Plastic 



* Descript. des Entom. Foss. des Terrains Tertiaires de la France et de la 

 Belgique, Mem. Couron. Acad. lloy. Belg. vol. xxiv. 



