1861.] FISITER BRACKLESnAM BEDS. 67 



the whole series into foiir principal groups of strata distinguished by 

 the letters A, B, C, D. 



A is the upper group, generally abounding in Gasteropoda, and 

 has one of its fossil-beds, in the eastern part of its range, full of 

 NummuJina variolaria. It contains foui jprincipal fossil-beds, di- 

 stinguished by the letters a, b, c, d. 



B is the next member of the group, more sandy in its general 

 condition tlian the last, and marked by the presence of Cerithiiim 

 gi(iantenm. It contains two fossil-beds, e, f, of which /is the most 

 noteworthy. Nummid'uia variolaria is found in this member of the 

 group at "WTiite Clift' Bay. 



C, the next division, is sandy, like the last, but rendered remark- 

 able by the profusion of Nummidince Icevigatce which crowd its prin- 

 cipal fossil-bearing bed, g*. 



D embraces the lowest fossiliferous sands of Bracklesham Bay. 

 The distinctive shells are Cardita acnticosta and Cyprcea tuber- 

 culosa. 



The whole group consists of alternations of beds of sand and sandy 

 clay, — the clays being more prevalent in the highest member, and the 

 sands in the lower. Green grains aboimd in all the beds. Many of 

 the beds are laminated, being formed by alternations of very thin 

 bands of clay, separated by sandy layers. Such are generally devoid 

 of shells, but contain much vegetable matter. They appear to have 

 been caused by the deposit of sediment, in a quiet estuary, from a 

 great river, the changes to the coarser sediment being caused by the 

 state of flood. 



The beds of sand point to a shallower condition of the sea-bottom, 

 subject to drifting water. The shells in such beds are often drifted 

 into patches, and are sometimes exceedingly abundant at one spot, 

 while a few yards off scarcely a specimen will be found. The beds 

 of clay were deposited in a deeper sea, and the species found in them 

 agree with such a supposition. 



Bracklesham Beds at White Cliff Bay. — The Bracklesham Beds 

 are unquestionably better exhibited, in respect conjointly of develop- 

 ment and display, at Bracklesham Bay than at any other place. 

 But, because many pai-ts of the series are there covered up by more 

 modern deposits, while the relation of the whole to overlying and 

 underlying deposits is indifferently shown, the section at White 

 Cliff Bay becomes of much value ; for there we have an unbroken 

 sequence throughout, from the Chalk to the Bembridge Marls f. 

 Mr. Prestwich has given a detailed account of this section in the 



* Sir C. Lyell found the same change in the species of the Nummulitcs at the 

 Cerithhim giganteum bed at Cassel. Quart. Joum. Geol. Soc. vol. viii. p. 328. 



t Wlien examining the White Clifl' Bay section, I was much interested in 

 finding the equivalent to, and so fixing the position of, the very remarkable 

 foeailiferoufl bed of Brockenhurst. It occurs in the upper part of bed No. 21 of 

 Mr. Prestwich's section, Quart. Joum. Geol. Soc. vol. ii. pi. 0. p. 253. In plate 

 10 (by E. Forbes and W. II. Bristow) of the Memoir on the Isle of Wight (Geol. 

 Surv. 18.06), it is described as "brown clay, with irreg\ilar fracture, shaiy in 

 places, often with clayey nodules, containing fi.sh and marine shells- Cardiiu 

 acuticosta " {delfoidea, Edw. M.S.). 



v2 



