436 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 7, 



tlie clays of London, the sands and clays of Bracklesham, and the 

 clays of Barton, under one name of London Clay. 



Although I had endeavoured, in 1847, to prove that these three 

 deposits vi^ere not synchronous, but in a definite order of superposi- 

 tion, still, owing to the circumstances named above and to the 

 confusion produced by the difficulty of unravelling organic remains so 

 long mixed up together, the extent of the differences between the strata 

 of London and of Bracklesham were not then fully developed, and the 

 evidence in support of these views has not been considered sufficiently 

 conclusive by some foreign geologists who yet adhere to the former 

 views on this question. One of the objects of this paper is to confirm, 

 by a further inquiry into the organic remains of these two deposits, 

 the distinction before pointed out, and with the lists given in the last 

 paper*, to enable more especially our foreign colleagues to judge of 

 the extent of these distinctions, and to afford them specific fossiliferous 

 zones for comparison with their own rich and attractive tertiary 

 series. So late as 1850, one of the most able of the French natu- 

 ralists, in comparing the corals of the English marine eocenes vrith 

 those of the Calcaire grossier, is led, by adopting the old meaning of 

 the " London Clay," to a theoretical difficulty in the explanation of 

 the range of species, which, by taking the more restricted meaning, 

 would not exist, and which restriction the work itself, in fact, 

 directly corroborates by the distinctive determination of the London 

 and Bracklesham species. Thus M. Milne-Edwards, after remarking 

 on some points of resemblance between the English fauna and that 

 of the "Calcaire grossier," observes nevertheless, that "most of the 

 corals found in the environs of Paris have not been met with in the 

 Eocene strata of the London Clay, and many of the corals belonging 

 to the last-mentioned deposits have not been discovered elsewhere f;" 

 and then states, that, as " at the present period similar differences to 

 those existing in these French and English Eocene series exist at 

 small distances in the same zoological region, and appear to depend 

 principally on the depth of the sea and the nature of the bottom, 

 by analogy we are therefore led to suppose that in the Eocene ma- 

 rine fauna they are only indicative of some such local peculiarities |." 



M. Hebert, who has so thoroughly studied the French Tertiaries, 

 still considers that the differences existing between the fauna of the 

 Calcaire grossier and that of the London Clay proper, are to be 

 accounted for by such causes as above-named, and is there- 

 fore unwilling to admit any difference of age in these deposits §. 

 Wliilst the distinguished palaeontologist, M. A. d'Orbigny, writing 

 in 1852, and speaking also of our three Enghsh groups taken 

 together, observes that " the identity of the London Clay and of our 

 'Etage Parisien ' (i. e. the Glauconie grossier e, Calcaire grossier, and 



* See above, p. 411-19. 



t Monog. Palffion. Soc, vol. for 1850. Brit. Foss. Corals, p. 12. 



X M. Agassiz also seems to refer the differences in the fishes to similar causes. 

 Rep. Br. Assoc. 1846, p. 52. 



§ Bull. Soc. Geol. de France, 2nd ser. vol. ix. p. 350, and Comptes Rendus, for 

 1850, p. 852. M. Hebert considers the Basement-bed of both alike. 



