PRESTWICH — BRITISH AND FOREIGN TERTIARIES. 237 



that I would place the central green sands and marls of Cassel {h 

 and i of Ly ell's section) and the green sands of Bagshot. 



In consequence of this parallelism of these green sands of Bagshot 

 with the Bracklesham series of Hampshire, I had on a former occa- 

 sion {op. cit. p. 399) suggested that the lower unfossiliferous sands of 

 the Bracklesham series and the Lower Bagshot sands might possibly 

 be of the same age as part of the " Sables and Gres inferieurs," but 

 that, in the absence of fossils, the evidence was not sufficiently posi- 

 tive*. The other course we have now followed through Flanders has, 

 by the extension of many of the fossils of the " Lits Coquilliers," 

 by the lithological structure and dimensions of the mass, and by the 

 recognition of the London Clay, afforded the further evidence required. 



These considerations induce me to place the Lower Bagshot Sands 

 on the level, on the one hand, of the three upper divisions of the 

 *' Sables inferieurs" (but chiefly of the Sables divers) of M. d'Archiac, 

 or the '* Glauconie moyenne " of M. Graves ; and, on the other hand, 

 on that of the *' Sables Ypresiens " and the Systeme Paniselien, and 

 including possibly the lower part of the Brussels Sandsf. 



§ 10. Conclusion. 



If the synchronism of the Bracklesham series with that of the 

 " Calcaire grossier" be admitted, then the independence of the London 

 Tertiaries with respect to the former deposit will apply with equal 

 force to the latter. For I have lately shown J that the London series 

 contains 485 species of organic remains (plants excluded), and that 

 only eighty-eight or 18 percent, of these pass upwards into (or through) 

 the Bracklesham series ; or taking the fossils of the two series together, 

 there are only 9*4 per cent, common to both. There are altogether 

 397 species peculiar to the London group, and they form — the Fishes, 

 Reptiles, Crustaceans, and Echinodermata especially — a very charac- 

 teristic fauna. The distinctiveness of age and origin shown by the 

 fauna is fully corroborated by the physical evidence. 



The large proportion of species peculiar to the three lower divisions 

 of M. d'Archiac also shows a well-maintained distinction between 

 these beds and the Calcaire grossier ; although in this case the fauna 

 of the Lits Coquilliers serves as an intermediate link, and tends to 

 lessen the apparent force of that difference. Nevertheless, these lowest 

 French divisions are evidently in closer relation with our more distant 

 London Tertiaries than with the overlying series in the Paris area. 



I conceive, therefore, that we may take the " London Tertiaries " 

 as a good natural group, constituting an important and independent 

 division of the Eocene period perfectly well marked by its organic 



* M. Dumont has since visited the Bagshot district, and without hesitation 

 referred the Lower Bagshots to the Ypresien Sands. Quart. Journ. Geol. Soc. 

 vol. viii. p. 370. 



t I am incHned to place in this series (the equivalent of the " Glauconii; 

 moyenne ") the 40 feet of siliceous sands without fossils, and possibly even the 

 " Gres lustre " (strata b & c, op. cit. p. 334), included in the base of the Brussels 

 group. 



X Quart. Journ. Geol. Soc. vol. x. p. 435. 



