374 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 26, 



am however inclined to think that we need not restrict the synchronism 

 of the Bognor beds of Hampshire to the lower part only of the London 

 clay, but that we may consider that the conditions, which in the Isle of 

 Wight were favourable to the prolonged existence of the characteristic 

 Bognor fossils throughout the whole of the London clay, were altered 

 as we approach the site of London by a greater depth of sea, whereby 

 the shallow water and littoral fauna of Bognor had its character 

 modified by the introduction of new forms, as the Nautilus, Penta- 

 crinites, and other deep-sea animals which abound in the central beds 

 of the London clay around London. The groups of organic remains 

 in the intermediate localities bear corroborative evidence. At Alum 

 Bay and Southampton we find a considerable number of Highgate 

 forms, but still with a general prevalence of the Bognor group*. In 

 the western portion of the London district we meet with a distribution 

 of the fauna approximating closely to that of Hampshire, and showing 

 a high range in the London clay of the Bognor group. At Newnham 

 and Cuffell the fauna begins to exhibit the lower range of the Bognor 

 group, and the introduction of a greater variety of Highgate forms ; 

 and in the neighbourhood of London we find the Bognor group, 

 although largely preponderating in the lowest beds, but faintly repre- 

 sented in the greater bulk of the middle beds, whilst in the highest 

 beds some species of the group reappear in the greatest abundance. 



This is a phaenomenon of considerable interest, inasmuch as it in- 

 dicates that that prolonged and gradual subsidence of the sea-bottom, 

 which I have before f endeavoured to show prevailed during the 

 formation of the London clay (BognoT beds) in the Isle of Wight, 

 extended in a nearly equal degree to the western portion of the London 

 district. Over all this area the increasing depth caused by the sub- 

 sidence appears to have been constantly neutralized by an accumula- 

 tion of sediment, equal, or nearly so, to the amount of depression. 

 By the joint and counteracting effects of these two causes, a nearly 

 uniform and moderate depth was maintained throughout the seas 

 then covering these districts, enabling the Panopcea, Pholadomya, 

 Pinna, and other shallow-water genera, to exist all through this geo- 

 logical period, to the exclusion of the more varied fauna which greater 

 changes of depth would have produced. But we have indications, as 

 we proceed further eastward in the London district to Highgate and 

 Sheppey, of a departure during part of this period from these uniform 

 zoological conditions ; for, as we have just mentioned, we here find 

 various species of Cephalopoda, Echinodermata, some Brachiopoda, 

 and of a generally deeper sea testacea, superadded in considerable 

 abundance to the more limited fauna of the same age in the Isle of 

 Wight. As the deeper sea forms here predominate, so do those of 



* The typical species of this (if we may so term it) rudimentary group are, 

 Cytherea obligua, Cardium Plumsteadiense, Infundibulum trochiforme, Natica 

 glaucinoides, PanopfRa intermedia, Pectunculus brevirostris, Pholadomya margari- 

 tacea, P. virgulosa, Pinna affinis, Pyrula tricostata, P. Smithii, Rostellaria Sowerbii, 

 Turritella imbricataria (var.), Teredo antenauta, Venerieardia Suessonensis, Ver- 

 metus Bognoriemis, and the Ditrupa plana. 



t Journal of the Geol. Soc. for August 1846, page 237. The reasoning upon 

 which this hypothesis is founded is there given, and need not therefore be re- 

 peated here. 



