86 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 4, 



to the BracldeBhara series, and, as I shall show hereafter, are in a 

 part of the series which Mr. Prcstwich has placed among the 

 Bracklesham Sands at High Cliff. 



Here, then, Ave have a proof that the Bracklesham Beds have not 

 all become imfossiliferous at Alum Bay *, but the same shelving of 

 the sea-bottom towards the coast-line t, which has here given an 

 estuarine condition J: to the shallower seas of the lower and middle 

 beds of the northern and eastern area, has converted the deep sea 

 of the upper part into a shallow sea, represented by beds 6 and 4 

 of the section. 



This shallower condition may account also for the disappearance 

 at Alum Bay of the Nummulina variolaria. The water, already con- 

 verted from an estuary into a shallow sea, seems to have continued to 

 deepen § ; and at No. 10 I^ummulites come in abundantly. But the 

 variety is not identical with that found in the upper beds of the 

 Bracklesham series || ; and the list of fossils from that bed contains 

 species of a Barton type, viz. Pleurotoma turhida (colon)^ P. conoides, 

 and Cassidaria amhigtia. 



High Cliff. — ^The well-known series of fossiliferous sands and 

 sandy clays of Barton Cliff and High Cliff terminate downwards 

 in a series of dark-green sandy clays ^, which are based upon 

 light-coloured sands**. These Mr. Prestwich considers to belong 

 to the Bracklesham series. 



There is an advantage in studying these beds at High Cliff, from 

 the fact that the same strata are visible for a considerable distance in 

 the cliff (fig. 2) ; so that the changes, due to horizontal range, which 

 took place in them can be observed, — an advantage which is not 

 offered by the vertical strata at Alum Bay and White Cliff Bay. 



* Quart. Journ. Greol. Soc. vol. iii. p. 394. 



t " Physical Geography of the Tertiary Estuary of the Isle of Wight," by H. 

 C. Sorby, Esq., Edin. New Phil. Journ., Apr. 1857. 

 X Memoir of Geol. Survey on Isle of Wight, p. 34, 

 § Edin. New Phil. Journ. ibid. 



II See Sir C. Lyell's paper on the Belgian Tertiaries (Geol. Soc. Journ. vol. viii. 

 p. 334, note). Mr. T. R. Jones informs me that this Nummulite is a variety of 

 N. planulata, as also is N. variolaria. The common Nummulite of the High 

 Cliff Sands is N. variolaria. The Alum Bay variety is here called N. Prestwich- 

 iana. See Appendix B, page 93. 



^ The green colouring-matter which is so common in the Middle Eocene beds 

 is remarkably abundant here. It occurs in grains, which, when separated from 

 the matrix, have the size and form of grains of fine gunpowder. 



Professor Livcing has kindly furnished me with the following analysis of this 

 substance, and informs me that it does not differ materially from the colouring- 

 matter of the G]*censand bed at the base of the Lower Clialk of Cambridge- 

 shire : — 



Water T002 



Silica 5011 



Iron, protoxide 2504 



Alumina G-12 



Magnesia 314 



Potash 517 



99-60 

 ** See Mr. Prestwich's paper " On the Strata of Christchurch Harbour," 

 Quart. Joiu-n Geol. Soc. vol. v. p. 44. 



