PRESTWICH BRITISH AND FOREIGN TERTIARIES. 101 



This lower green-sand division of the Calcaire grossier, thin and 

 unimportant in the eastern portion of the Paris basin, acquires, there- 

 fore, greater development as it trends westward ; whilst at the same 

 time its organic remains become more numerous, although they never 

 abound as in the next overlying division of this formation. Judging 

 from the mineral character of the larger portion of the Bracklesham 

 Sands and from the position of the Venericardia planicosta, Ceri- 

 thium yiganteum, and Numinulites Icevicjatus in that series, I think 

 it probable that the expansion of this lower division of the Calcaire 

 grossier is continued in a nearly progressive ratio as it ranges further 

 to the north-west into the English area ; and that, taken together 

 witli the lower part or even the whole of the next French division, 

 they are here represented possibly by about the lower 250 to 300 feet 

 of argillaceons beds and yelloAv and green sands of Bracklesham and 

 White Chif {a& b (pars), p. 99). For in France the Cerithium y^gan- 

 teum marks a definite and regular zone, characterizing especially the 

 beds forming the base of the second division — those in near contact 

 with the Glauconie grossiere ; the Venericardia planicosta is also com- 

 mon in that zone, but more particularly marks the uppermost beds 

 of the Glauconie grossiere ; whilst the Niimmulites Icevixjatus is more 

 especially characteristic of the upper portion of the same lower divi- 

 sion. Now in Bracklesham Bay the beds containing the Cerithium 

 yiganteum,dind. those in which the V enericai'dia planicosta so abounds, 

 crop out in about the centre of the Bay ; whilst along the shore 

 southward tq^wards Selsea Bill a succession of other strata, with nu- 

 merous other fossils, outcrop in ascending order. In descending order, 

 although the junction of the lower beds with the London Clay can- 

 not here be traced, yet it is evident from the general character of the 

 whole group that fossiliferous beds descend very low in the series. 

 Here the Bracklesham Sands seem to be fossiliferous nearly through- 

 out ; in White Cliff Bay the lower beds are only partly fossiliferous ; 

 whilst at Alum Bay the whole series is perfectly unproductive. 



On the whole a greater development, at the commencement of the 

 Calcaire grossier period, of mineral mass, and conditions rather 

 more favourable for life, in England than in France, are probably the 

 causes why we find at Bracklesham so large a proportion of the shells 

 of the Lits coquilhers relatively to the total number of French spe- 

 cies occurring there. At the same time these early more favour- 

 able life-conditions led to the existence of a greater number of species 

 which died out before the period of the Barton Clays, and which 

 help, on one side, to give to the Bracklesham Sands more distinctive- 

 ness as regards that zone than the Calcaire grossier exhibits with 

 respect to the Sables moyens. 



2. The second and main division of the Calcaire grossier (the one 

 from which it derives its name) commences near Rheims and Epcrnay, 

 'between which places, at Courtagnon, it is only a few feet thick. It 

 however rapidly expands, and attains, five miles further west, at the 

 celebrated locality of Damery, a thickness of many feet. Near Chateau 

 Thierry it is 24 to 25 feet thick, and further westward, at places in the 

 neighbourhood of Chantilly and Creil, where these beds are very largely 



