386 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 26, 



this object the section at White-Chff Bay is best suited (see White- 

 CUff Bay section, fig. 3, PI. XIV.). 



From the great changes exhibited in the equivalent strata at Alum 

 Bay, the sequence is not so easily traced. We will therefore reserve 

 the comparative examination of that section to the end of the paper, 

 and confine ourselves at first to the one point where the evidence is 

 strongest. 



Comparison of the structure and physical conditions of the Bagshot 

 Sands and of the Bracklesham Bay series. 



We have shown that the Bagshot sands may be separated into 

 three divisions, of which the lower and upper ones are characterized 

 by loose light yellow siliceous sands, and the central one by dark green 

 sands and foliated brown and liver-coloured clays — the whole reposing 

 conformably on the London clay. This structure is subject to but 

 little variation throughout the London district. Now let us take the 

 central vertical strata Nos. 5 to 20 (see PI. XIV. Comp. Sec. fig. 3) 

 of White-Cliff Bay * and resolve them into their simplest elements, 

 and it will result that as a whole they may be classed into a lower 

 mass of light yellow unfossiliferous sands (stratum No. 5), to which 

 succeed thick beds of brown laminated clays and fossiliferous green- 

 sands (strata Nos. 6 to 13), more or less calcareous and argillaceous, 

 followed by sands and light brown and yellow sandy clays (strata 

 Nos. 14 to 20). This section exhibits a greater development of strata 

 and more complexity of structure than we find in the Bagshot sands. 

 In other respects the analogy of mineral structure is strong. This 

 we will now proceed to examine more in detail and at successive 

 sections. 



In the preceding paper I showed that the London clay at White- 

 Cliff Bay was probably limited to the 300 feet of argillaceous strata 

 (fig. 3, strata Nos. 3 & 4) which immediately succeeds the mottled 

 clays (No. 2). Conformably overlying this London clay is a mass of 

 light yellow siliceous sands without fossils, and 100 feet thick. At 

 the Southampton artesian well we again find that the sixty to seventy 

 feet of strata overlying the London clay consist of similar unfossiliferous 

 sands, but rather more argillaceous (see fig. 5. p. 388, stratum " b "). 



Proceeding to the London district we find these sands there con- 

 tinued, and forming a nearly exact counterpart to those of Hampshire. 

 Thus at Shapley Heath there is incumbent on the London clay, and 

 underlying the central green sands, about 1 00 feet of light yellow 

 unfossiliferous sands. At Goldsworthy, Chobham and Weybridge, 

 where the thickness of these sands can again be ascertained, they 

 exist in but slightly increased expansion (see PI. XIV. Comp. Sec. 

 figs. 4, 3, & 1). 



Over these sands (No. 5) at White-Cliff Bay are 100 feet oi foli- 

 ated broion clays and green and yellow sands, succeeded by 150 

 feet of impure green sands and brown and grey clays, with layers of 

 lignite and pebbles, and then 60 feet of pure dark green sands very 



* For fuller details of this section see Journal of the Geol. Soc. for August 

 1846, p. 252-255. 



