PRESTWICH BRITISH AND FOREIGN TERTIARIES. 91 



beds is free from the sand which at other times often covers them. 

 Under these circumstances it would be difficult to say whether, on 

 the one side, any of the Lower Bagshot Sands (supposing they 

 might be here fossiliferous), or, on the other side, some portion of 

 the Barton Clays, may not have contributed to enrich the Brackles- 

 ham collections. Not that I believe this foreign element to prevail to 

 any extent ; still it is possible that some fossils, especially of the ad- 

 jacent Barton series, may under such circumstances have been asso- 

 ciated with those of the Bracklesham Sands*. The error, however, 

 if it do exist, is probably not a very serious one, and will not mate- 

 rially affect the question we have in view ; whilst, on the other hand, 

 we may feel assured that, thanks to the able and indefatigable re- 

 searches of Mr. Edwards, the fossil shells of these beds have been 

 worked out and determined with an accuracy and to an extent in no 

 instance surpassed and rarely equalled f. 



In a paper read in November 184/1 referred the Bracklesham 

 Sands to the lower part of the Calcaire grossier — a position which 

 I yet partly assign to them, though I am now disposed to give 

 them a much greater extension. There are many points to be noted 

 in common between these Bracklesham Sands and the lower Calcaire 

 grossier. In the one as in the other, green sands are more or less 

 mixed ; whilst at the base of the series, both in England and France, 

 there is an occasional band of small flint pebbles, that, taken together 

 with a certain prevailing coarseness of the sands, form physical fea- 

 tures which, although not very strong, are sufficiently persistent and 

 sufficiently on the same plane to give a distinctive character to the 

 commencement of the Calcaire grossier series both in this country 

 and in France. With these is combined the appearance of a distinctive 

 group of organic remains that continues in successive and changing 

 phases through the Middle Eocenes up to the period of the Sands of 

 Fontainebleau and the Limburg beds, when we find the fauna of 

 this Paris group replaced by another, still of the same type, but 

 equally distinctive in individual characters, as the former is from that 

 of the London Group which it had supplanted. In this paper I will 

 confine myself to the inquiry connected with the correlation only of 

 the marine beds of the Bracklesham and Barton periods, lea^-ingthe 

 inquiry connected with the freshwater conditions subsequently pre- 

 vailing in part of the latter to a future occasion. For the lower divi- 

 sion of the Eocene series, or the London Group, I took the strata in 

 this country as types. With regard, however, to the Middle Eocenes, 

 they are so well developed in France, have been so admirably worked 

 out by Cuvier and Brongniart and many subsequent observers, and 



* As, however, the greater part of the fossils are obtained from the centre of 

 the Bay — from those beds containing the Venericardia planicosta, Cerithium gi- 

 ganteum, and Valuta sjunom, or from otliers closely associated with them — there 

 can be little doubt that the great bulk of the organic remains procured from 

 Bracklesham Bay belong truly to the Bracklesham series. 



t The collection of Mr. Bowerbank is also xevy extensive, as likewise was tliat 

 of the late Mr. Dixon, to whom we are indebted for an important list of all the 

 fossils known to occur at Bracklesham, with valuable monographs on the several 

 classes of organic remains contributed by various scientific friends. See Dixon's 

 'Geology of Sussex,' London, 1850. 



