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



lying bed of sand " c " at Alum Bay, may be considered as the first 

 and lowest group of the Eocene strata of the Isle of Wight (PI. IX.). 

 They appear to me to mark a distinct period in the hydrographical 

 condition of the tertiary epoch. Similar causes, judging from like 

 results, were then evidently in operation over the greater part of the 

 Paris, Isle of Wight and London basins. Whether the condition in 

 the Isle of Wight basin were a deep sea-bottom or shallow waters, or 

 whether the strata were accumulated rapidly or slowly, there is no 

 evidence here to decide. 



A careful examination shows that the surface of the upper thin 

 sand " c " of the last group at Alum Bay has been worn and eroded, 

 but in a much less degree than the surface of the chalk, by the ac- 

 tion of water, and that on it are deposited strata differing both in 

 lithological character and in their fauna from the preceding group, 

 and indicating, by its underlie of coarse sand and large rounded 

 flint pebbles, a considerable and sudden increase in the transporting 

 powers of the water. 



The organic remains of this division are extremely well-charac- 

 terized, and form in the Isle of Wight and London basins an excel- 

 lent geological horizon. Mr. G. Sowerby, as well as Mr. Bower- 

 bank, have noticed the fossils of this bed as being well-known Lon- 

 don clay fossils, and so far back as 1822 Prof. Sedgwick thought 

 that they resembled the fossils of the Bognor rocks. Dr. Mantell 

 and Mr. W. Parish have enumerated 30 or 32 species of fossils from 

 the Bognor rocks. Of the 20 species I have found in stratum "c?" at 

 Alum Baj^, 15 agree with those from Bognor. They include the 

 most typical forms and groups, such as a species of Pholadoniya^ 

 the Panopcea intermedia, Pinna afflnis, Pectunculus brevirostrisy 

 Dentalium planum, Vermetus Bognorensis and Rostellaria Sow- 

 erbii. If the preceding mottled clays maintained a striking con- 

 stancy of lithological character over a very wide area, these Bognor 

 beds present a no less remarkable constancy in their palseontological 

 character in the Hampshire and London basins. The fossils above 

 enumerated characterize them equally at Alum Bay, Bognor, Ba- 

 singstoke, Newbury, Sunning, Watford, Hertford, and many other 

 places in the neighbourhood of London. See sections 3, 4 and 5, 

 ante, p. 235. 



The uniformity of characters prevailing in the first divisions of 

 sands and mottled clays, which form the base of the tertiary forma- 

 tions throughout large areas of the Paris, Hampshire and London 

 basins, indicating a widely-spread and continuous sea, and suggest- 

 ing the origin of the detritus to have been probably from few and 

 like sources, ceases at the end of that period, after which the in- 

 creasing variety of the synchronous strata in the different basins 

 proves the increasing disruptions and severance in the original con- 

 nexion. Whatever may have been the depth and character of the 

 waters at this epoch in the Isle of Wight basin, a subject that we 

 shall be able to enter upon more fully in treating of the important 

 fossiliferous beds of this age in the north of France and south-east 

 of England, that a sudden change of some importance took place is 



