1862.] WHITAKEE— LOin)ON- BASIN. 261 



the Chalk. The former, here many feet thick, consists, in descend- 

 ing order, of bluish-grej clay (partly mottled yellow), light-green 

 sandy clay, and Hght-green sand. I saw no flints in it. Sonth of 

 this there are '^ swallow-holes*" at the junction of the Reading 

 Beds and the Chalk. 



West of Castle HiU there is another outlier, equally well marked, 

 forming the wooded hill that stretches for three-quarters of a mile 

 from the northern end of Wilton Common nearly to Broil, and the 

 top of which consists, without doubt, of London Clay ; for at Wilton 

 "K"i1ti, at the southern end of the outlier (where the dip is sharp to 

 the north), whilst in places the brown and light- coloured sands of 

 the Reading Beds are found at the surface, I saw, close by the edge 

 of the wood, and near the middle of the brick-field, about four feet 

 of stiff bluish-grey and brown London Clay, with a line of ironstone 

 ccmtaining fossils. The fossils were all casts, and amongst them I 

 made out Nautilus (casts of detached chambers), Calyptrcea, Fusus 

 (or Pleurotoma), Cardium, and Ostrea. 



On the line of hill to the west of the Bedwins there is a large 

 outlier of Lower Bagshot Sand, London Clay, and Beading Beds, 

 forming the high ground from Chisbury Barrow to the south-eastern 

 part of Tottenham Park, a distance of about two and a half miles 

 nearly N.E. and S.W. The outlier is from a quarter to three- 

 quarters of a mile in breadth ; its boundary is for the most part 

 well marked, and along it there are many swaUow-holes, especially 

 within a radius of half a mile from Stoke Parm to the west of Great 

 Bedwin. At the southern end, near the Chalk escarpment, the dip 

 is fairly sharp ; but it soon lessens northward, and the beds becom^ 

 flat or nearly so : perhaps, indeed, the direction of the dip may have 

 changed from north to south at the northern end of the outlier ; but 

 not having any datum-heights by which to judge, I cannot say with 

 certainty. Down the northern flank of the hill just south of Stoke 

 Farm deep drains were made in January 1859, and I was fortunate 

 enough to see part of the work in progress. The following beds 

 were cut into, beginning at the bottom of the hill, and taking them 

 in ascending order : — 



1. ChalJc (and the reconstructed bed described in Quart. Joum. 

 Geol. Soc. vol. xvii, p. 527). 



2. Reading Beds. — Variously coloured mottled plastic clay, with a 

 little sand. 



3. London Clay. — Stiff blue and brown mottled clay, not plastic, 

 with large rounded flints at the lower part (basement-bed). 

 Higher up the clay is sandy. 



4. Lower Bagshot Sand, — Brown and buff sand, partly clayey. 



* For an account of these underground water-courses, see a paper by Mr. 

 Prestwich, Quart. Journ. Geol. Soc. vol. x. p. 227 ; and also the Memoir illustra- 

 ting Sheet 13 of the Map of the Geological Survey, p. 24. In the latter their 

 frequent occurrence near the junction of the Tertiary beds and the Chalk ia 

 noticed. 



