BAG SHOT STKATA FROM ALDERSHOT TO WOKINGHAM. 507 



The base of the Upper Bagshot, for example, is found at the respec- 

 tive altitudes of 350 feet at Aldershot, about 130 feet at Parnborough 

 and Mytchett, 250 to 260 feet at Camberley and about Welling- 

 ton College, and again about 260 feet at Bracknell. There must 

 therefore have been earth-movements accompanied by alterations of 

 level since the Bagshot strata were deposited, as if caused by lateral 

 pressure acting in a north- an d-south direction. Such movements 

 may have been synchronous with the greater movement which 

 produced the Isle-of- Wight anticline, and placed the whole Bagshot 

 Series at a high angle of inclination along the north side of its axis. 

 In the greater elevation of the Bagshot horizons at Aldershot, 

 there seems to be some indication of an additional elevation of the 

 line of the Hog's Back, and therefore probably of the Wealden 

 anticline, after the Bagshot Strata of the London Basin were 

 deposited. 



5. The great thickness of the Lower Bagshot Sands in the deep- 

 well sections, taken together with their passage downwards into 

 the London Clay, their diminution in thickness southwards, and 

 the apparent absence of them, in the sections described, along the 

 northern and southern margins of the district, are good reasons 

 for believing that previous to the deposition of the Lower Bagshot 

 Strata the London Clay was thrown into a slight syncline, and 

 suffered a considerable amount of denudation during Bagshot times, 

 both on the northern and southern sides of the area ; a strong case 

 for the overlap of the Upper Bagshot Sands seems thus to be made 

 out. 



6. This last conclusion seems to be borne out by a comparison of 

 some ascertained thicknesses of the London Clay itself. 



(a) At W^okingham this has lately been proved to be only about 

 270 feet. In the well for the W^okingham District waterworks, of 

 which a complete section has been recorded by Prof. Rupert Jones *, 

 the boring commenced in the Loudon Clay and passed through 

 263 feet of that formation ; and the Bagshot Sands rest upon the 

 London Clay near by, at a level only a few feet above the mouth of 

 the well. 



(6) In the Wellington-College well, the Chalk is said to have 

 been reached at about 650 feet. Deducting from this rather more 

 than 200 feet of Bagshot Strata (c/. jSg. 1), we have over 400 feet 

 for the vertical range of the London Clay and the Eeading beds. 



(c) Quite recently the Chalk has been reached at Brook\^'ood, as 

 I am informed by Mr. Thomas Tilly, of 15 Walbrook, at a depth of 

 640 feet from the surface. This gives us over 400 feet for the 

 thickness of the London Clay at this spot. 



(d) At Aldershot the thickness of the London Clay was proved a 

 few years ago, in the Aldershot town well, to be 120 feet. The 

 mouth of this well, which begins in London Clay, is 250 feet above 

 O.D. level, and the Bagshot Sands are seen resting upon the London 

 Clay at a level not much more than 50 feet higher, so that the thick- 



''^ Geo]. Mag. dec. ii. vol Tii. p. 421 



