90 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. DgC. 4 



that the upper pebble-bed of High Cliff changes into a fossil-bed, with 

 scarcely any pebbles, in the range of about a mile, it is not surprising 

 to find no pebble-bed in its place at Alum Bay. The tabular iron- 

 stone septaria hold a similar place in each section, and are identical 

 in appearance. The great pebble -bed of Alum Bay appears to be 

 equivalent to the lower and less important one of High Cliff, and the 

 coloured sands of Alum Bay to represent the white sand at the base 

 of the High Cliff section. (See figs. 3 & 4.) 



The casts of fossils at both these localities are in a rather peculiar 

 condition. They are not casts of the inner, but of the outer surfaces 

 of the shells. After the shell had been dissolved away, the matrix 

 which filled it appears to have been pressed into the mould left by 

 the outer surface ; and in some cases traces of the epidermis seem to 

 have remained. Thus it will be seen that these casts are more suited 

 to the determination of species than is usually the case. 



It may also be noticed that High Cliff is the only locality referred 

 to where there appears to be a natural physical break and distinct 

 change in the character of the deposit between the Bracldesham and 

 Barton beds. The division is probably, in reality, one of convenience 

 only, the two groups forming a continuous series changing gradually 

 throughout in its Kthological character and fauna. And if we take 

 a comprehensive view of these two portions of the Eocene series in 

 Hampshire, it will appear that the amount of depression of the sea- 

 bottom*, on the whole, exceeded the depth of sediment deposited 

 during the Bracklesham period, while the reverse was the case during 

 the Barton period ; so that the tendency in the former case was from 

 an estuarine to a deep-sea condition, while towards the close of the 

 Barton period an estuarine condition again prevailed. This, how- 

 e /er, again gave way to a marine condition during the deposition of 

 the Hempstead series ; and we have no means of carrying the record 

 further in our district. 



PehUe-heds.—U White Cliff Bay, Alnm Bay, and High Cliff, and 

 in a less degree at Bracklesham, we meet with several pebble-beds ; 

 and the sequence in which they occur seems usually be this : — The 

 character of the deposits in ascending order, that is, in the order of 

 events, changes gradually from clay to sand ; and when a sandy 

 condition has obtained for some time, we meet with a bed of pebbles ; 

 these are again followed by clay, and a like sequence recommences. 

 It is also very evident that the pebble-beds at localities not far 

 distant from each other occur on different horizons. 



Now the pcbble-bod at High Cliff affords an opportunity for 

 studying one of these deposits for about a mile ; and the changes in 

 it in that short distance are very remarkable. At the western part, 

 where a fallen block fortunately gave me an opportunity of studying 

 it, it is a conglomerate of rolled pebbles of flint, with a few of quartz 

 and other rocks, imbedded in a clayey matrix, which contains im- 

 pressions of fragments of shells and of vegetable matter. But as it 

 is followed towards the west the pebbles become gradually less 

 numerous, until, at the point where it sinks beneath the beach, 



^ Prestwich, Quart. Journ. Geol. Soc. vol. ii. p. 251. 



