1862.] WHITAKER LONDON" BASIN. 273 



borough, just where we should expect, on quite independent grounds, 

 that the Bagshot Sand at one time rested at once on the Chalk, 

 proves, as far as indirect evidence can, that there they have come 

 from that formation ; and it seems to me that their sudden abundance 

 in that neighbourhood, where they almost form a giant pavement 

 along some of the valleys, cannot be in any other way so well ac- 

 counted for as by that westerly thinning of the Lower Eocene beds 

 treated of in the second part of this paper, and the result of which 

 has been to bring the Bagshot Series without doubt very near to, 

 and most likely actually on, the Chalk in that neighbourhood. 



According to this view, it is in that district where the greywethers 

 have suffered least vertical displacement (through the denudation of 

 the softer beds of the formation to which they belonged), in their 

 subsidence from their original position to the one they now occupy, 

 that they occur in the greatest abundance. 



On the Sands of Neiley and Headley Heaths. — It may be as well 

 to mention here that Mr. Godwin- Austen is disposed to class with 

 the Lower Bagshot Beds some outliers of sand that occur on the 

 Chalk of Surrey, to the east of Guildford. For my own part, how- 

 ever, I do not think that the sands of Ketley Heath and Headley 

 Heath are of so great an age. I take them to belong to the same 

 set of beds as the sands of Chipsted (south of Croydon) and Paddles - 

 worth (near Folkestone), which have been referred by Mr. Prestwich 

 to the age of the Crag *. I think that their method of occurrence, 

 or their " lie," is too irregular to allow us to class them with the 

 Lower Bagshot Beds. At Headley they seem to abut against an 

 outlier of the Lower Eocene Beds, with which series most surely 

 they have no kinship ; and they here and there spread some way 

 down the slopes of the valleys. 



From what has gone before it is clear that, just to the north of 

 the district where these sands are found (in Surrey), the London 

 Clay is not less than 400 feet thick : I cannot think it likely that 

 that formation should thin off so suddenly southwards, without any 

 sign, and that the Lower Bagshots should also cut through the Wool- 

 wdch and Eeading Beds and the Thanet Sand to the Chalk. This 

 would show a great unconformity between the Middle and Lower 

 Eocene Series, which we have no other reason to look for; the 

 resting of the Bagshot Beds on the Chalk, that I have shown to be 

 most likely to take place at the western end of the London Basin 

 (see p. 262), being caused chiefly by " overlap." 



Nevertheless, as all that one can say of the Headley Sands is that 

 they are newer than the London Clay, there is just a possibility that 

 they may belong to the Bagshot Series ; but, from what I have seen 

 of them (in many places), I take this opportunity of stating my belief 

 that they are much more likely to belong to the Crag, or even to a 

 later formation, though I can as yet see no evidence as to their 

 exact place in the geological series. 



However, should they turn out to belong to the Bagshot Beds, 



* Qviart. Joiirn. Geol, Soc. vol. xiv. p. 322. 



T 2 



