170 EEY. A. lEYIKG OlsT THE STEATIGRAPHT 



Ascot Hills. — As further evidence of the stratigraphical structure 

 of the hills between Bracknell and Ascot, represented in the right- 

 hand part of fig. 2 (former paper), I now submit the following : — 

 (1) On the south flank of Long Hill we find the two clayey beds 

 (No. 5, and Nos. 9 & 10) cropping out with the intermediate green 

 earths (5 to 6 feet). The latter, not being found on the north 

 slope, appear to thin away in the hill *. The Lower (fluviatile) 

 Sands occupy the valley on both sides of Bull Brook, and there is 

 a good exposure of them (about 2b' vertical) in a sand-pit on the 

 north side of Long Hill. The beds of this hill admit of direct 

 correlation with beds which crop out in Swinley Park and South- 

 Hill Park. (2) A mile and a half further east, along the same line 

 of hills, we find a similar succession of beds. Here, again, occur 

 the two clayey beds, with green earthy sands between them, cropping 

 out on the same flank of the hills, vis-d-vis of the Middle Group of 

 beds which crops out from beneath the Upper Sands of Tower 

 Hill in the Swinley brickfield f. The Lower Sands are exposed in 

 the railway-cuttings, and in many smaller sections of the valley 

 below, and have lately been proved to the water-bearing line, at a 

 depth of 28 feet in a new well near Englemere. 



These Ascot Hills, therefore, have a capping of Upper Sands, the 

 base of which (about 300' O.D.) corresponds in altitude with the 

 base of the same sands along the southern side of the valley. It 

 presents a very simple case of valley-erosion. The thinness of the 

 Lower Sands in the floor of this valley, towards the west, accounts 

 for the presence of Whitmoor Bog, which has somehow been 

 mapped as London Clay. Prom what has been now stated it is 

 pretty clear that the mapping by the Survey Officers all along this 

 piece of country needs some revision. 



If we could restore the beds removed by denudation across the 

 valley of Sunningdale and Virginia Water, we should doubtless find 

 the beds of the Middle Group continued along the southern portion 

 of "Windsor Park J, since at Englefield Green we have a succession 

 very similar to that which we have described at Bracknell. The 

 recent excavations in connexion with the new Beaumont College 

 have proved (after clearing the run of the hill) that the London 

 Clay reaches an altitude of 250' O.D. on the northern flank of the hill. 

 Upon this rests from 10 to 15 ft. of fine quartz-sand, which is found, 

 at N"ew Egham and Stroud §, to thicken southwards ; and the whole 

 hill is capped by a strong clayey bed, which there is no difficulty in 

 assigning to horizons l^os. 9 & 10, with a pnre pebble-bed in places 

 at or near the surface ||. 



* Compare Section M at Hagthorn Hill. t See Section L. 



J The low hills aroimd Virginia Water owe, I believe (from the small 

 exposures examined), their magnificent timber to the outcrop of the strong loams 

 ofNos. 9&10. 



§ Quart. Journ. Geol. Soc. vol. xlii, p. 404. 



II The altitude of the London Clay here is accounted for by a dip of the 

 Tertiary beds, see Mem. Geol, Surrey, vol. iv. fig. 50, p. 191 : it is also shown 

 by a comparison of the altitudes of the Chalk in well-sections at Windsor 

 and Old Windsor {ibid. App.). 



