242 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 25, 



all, or almost all, the fossils which occur at White Cliff Bay, in the 

 strata marked 9 to 11, are met with at Bracklesham ; but at this 

 latter place they are associated with numerous other species, identi- 

 cal for the most part with those of the glauconie grossiere and lower 

 calcaire grossier. More than sixty or seventy species have already 

 been identified as common to the Bracklesham beds and the calcaire 

 grossier (moyen), and Mr. Edwards and. Mr. Bowerbank are daily 

 adding to the list*. 



In addition to the greater vertical range of organic remains in this 

 series at White Cliff Bay than at Alum Bay, the fauna of these two 

 localities presents some differences both in genera and species. As 

 the superposition is however identical, the beds being in both cases 

 overlaid and underlaid by similarly characterized strata, there can 

 be little doubt of their synchronism; and the difference of the faunas 

 must be attributed to the different hydrographical conditions under 

 which they v/ere accumulated. 



In further evidence of the gradual changes in operation during 

 this period, it may be noticed, that in the London clay at White 

 Cliff Bay and Alum Bay we meet with indications cf those fluvio- 

 marine conditions, which at a later period prevailed in fuller deve- 

 lopment ; for I have found in the upper London clay atr Alum Bay 

 the " Cyrena ohovata,' and in the same division at White Cliff Bay 

 the ^^Potamides cinclus" or if not that species, at all events a species 

 identical with one in the overlying freshwater deposits, and a Natica 

 or Ampullaria also analogous with one occurring in the overlying 

 beds. Of the freshwater deposits the Cyrena obovata is one of the 

 most characteristic shells. 



Again at Alum Bay in the centre of stratum No. 29 may be seen 

 a well-defined line of separation, marked by a sudden passage from 

 clayey greensands to tough brown clays accompanied by a drift of 

 pebbles underlying the latter. These two divisions of stratum No. 

 29 are also marked by different groups of testacea; the Pectunculus, 

 Sanguinolaria, Solen, Pecten^ 8zc. of the lower division being suc- 

 ceeded in the upper one by Voluta, Pleurotoma, Conns, &c. These 

 latter constitute a deeper sea group than the former, showing a de- 

 pression of the sea-bottom, and delaying for a period those fresh- 

 water conditions to which this locality was tending; for it was in 

 the former or lower part that the Cyrena obovata occurred. Such is 

 also the case with Potamides cinctus at White Cliff Bay; but the di- 

 vision of the strata is not there so well exhibited, as that portion of the 

 cliff is much covered and broken. There is however there an evi- 

 dent difference, both palaeontological and lithological, in the upper 

 and lower strata of the London clay, although it is not so visible as 

 at Alum Bay, which appears to have been nearer the centre of dis- 

 turbance, as all the changes are there more abrupt and marked than 

 at White Cliff' Bay, where they exhibit more gradual transitions, 

 indicating a disturbing force decreasing in effect as we proceed 



* Since writing the above I have seen in M. A. d'Orbigny's collection a series of 

 specimens from the glauconie grossiere of Chaumont. As a group they present 

 a strong analogy with those from Bracklesham Bay; and the same remarkable abun- 

 dance of the Venericardia planicostata characterises both locahties. 



