608 MESSES. GAEDNEK, KEEPIDSTG, ANT) M0]STE:T0]N" OIT THE 



green grains; but, judging from what occurs in the Hampshire 

 basin, this reason is unsatisfactory, and the difficulty of drawing a 

 line in the middle of a sand-bed has prevented the mapping being 

 executed with consistency *. 



It has been recently suggested that a bed of pebbles which occurs 

 very persistently over the whole area, some 10 to 20 feet above 

 the green sand with Bracklesham fossils, should be taken as the 

 base of the Upper Bagshot, and in this opinion we concur f. 



Taking the pebble-bed as the base, the greatest proved thickness 

 of the Upper Bagshot is 228§ feet at the Albert Asylum Well (15 

 on sketch map), and this may be far from the original thickness, as 

 no overlying beds but drift are present. 



The various levels at which the pebble-bed is found show that 

 the formation rests in a syncline of the Bracklesham Beds, and, 

 probably, is conformable with them. 



The Upper Bagshot Beds consist of whitish-yeUow sands, a little 

 loamy in some places. Paint bands of colour denote the original 

 bedding with occasional iron concretions, pipings, and small blotches, 

 the latter having once been fossils. Sometimes, as at Tunnel Hill, 

 between Aldershot and Brookwood, the original forms are preserved 

 as ferruginous casts, either of the interior or retaining the markings 

 of the exterior of the shell. Becognizable fossils have only been 

 found at this locality in beds of sand ranging from 70 or 80 to 118 

 or 128 feet above the base of the series, so that the overlying beds, 

 nearly 100 feet thick, may represent a higher portion of the Barton 

 Series. 



It has recently been suggested that sands at Aldershot, Bearwood, 

 Wokingham, Buckhurst, Bracknell, and Ascot are Upper Bagshot, 

 though mapped as Lower Bagshot (see Q. J. G. S. vol. xli. p. 492, 

 vol. xliii. p. 374) ; but, after considering the evidence, we have no 

 doubt that the mapping is in these instances correct. Our reasons 

 are stated in the Quart. Journ. Geol. Soc. vol. xlii. p. 402. 



The point marked 1, near Ascot, on our sketch map, is the rail- 

 way-cutting, the section of which is published Quart. Journ. Geol. 

 Soc. vol. xxxix. p. 349, and from which large quantities of Brackle- 

 sham fossils have been obtained. The pebble-bed at the base of 

 the Upper Bagshot is well seen about 13 feet above the fossiliferous 

 green sand. 



Pebbles derived from this bed are found in great abundance 

 capping Hagthorn Hill, to the north of Tower Hill, also at the point 

 marked 2 on the sketch map, and at Bed Lodge, above the 300-feet 

 contour-line. There are good sections in the Bracklesham clays at 

 a brickfield in the northern slope of Tower Hill, (3) on the same 

 contour, and there are good sections in Upper Bagshot yellow sands 

 at the point marked 6, at Gravel Hill, 4, and at Caesar's Camp, o, 

 whence we have two casts of shells. In Duke's HiU there is a satis- 



* See Mem. Geol Surv. iv. pp. 329, 330, 333. 



+ See Quart. Joum. Geol. Soc. vol. xxxix. pp. 348, 353, vol. xli. p. 492, 

 vol. xlii. p. 402 ; Proc. Geol. Assoc, vol. iv. p. 334, vol. viii. p. 149. 



