ON THE BAGSHOT BEDS OF THE LONDON BASIN. 403 



position in the series. We shall, we believe, show that the premises 

 from which he draws his conclusions are incorrect. 



The Ascot- Chertsey District. 

 In our previous papers we pointed out that the Middle Bagshot 

 of Bagshot Heath consists of a very well-marked and persistent 

 series of beds, the most important of which is a green sand, as a 

 rule containing casts of marine shells. Above and in this green- 

 sand bed are usually more or less irregular lines of flint pebbles, and 

 still higher we usually find the pebble-bed which marks the base of 

 the Upper Bagshot sands. 



In the Ascot Railway -section described in our former papers, 

 these pebble-beds are seen undoubtedly in situ. Passing eastwards, 

 the Middle Bagshot Hills are frequently found to be capped with 

 masses of pebbles, and we feel no doubt that these are often the 

 remains of the Middle Bagshot pebble-beds, though in most instances 

 not in situ, but more or less re-arranged in post-Bagshot times. 

 This is well shown at the locality three quarters of a mile west of 

 Long Cross, which is referred to by Prof. Prestwich (Quart. Journ. 

 Geol. Soc. vol. iii. p. 389, note). There the green-sand bed is found 

 near the bottom of the hill, and is full of casts of shells ; above it is 

 a few feet of yellowish sand, and the hill is capped by a consider- 

 able mass of pebbles, obviously not in situ ; still further east, 

 near Chertsey, is St. Ann's Hill, on the north-eastern side of which 

 are two pits, which, owing to the kindness of the Lord of the Manor, 

 Mr. Bennett, we have been able to examine. The section in the 

 larger pit is published in vol. iv. of the ' Memoirs of the Geological 

 Survey' (p. 332). There is in the upper part of the pit a vast mass 

 of pebbles with green sands and clays mingled together in the most 

 curious manner ; and below and down to the bottom of the pit is a 

 considerable thickness of white and yellow sands. Pebbles also 

 occur in whitish sands low down in the pit ; but whether in situ 

 or not, it is difficult to determine. 



The smaller pit is at a lower level than that of the clays and 

 green sands above mentioned ; at the east end of it are 20 or 30 feet 

 of fine yellow sands, with thin bands of white clay (which we believe 

 to be the ' pipe-clay ' of other observers) and iron-sand, and at the 

 west end yellow sands with irregular patches and non-continuous 

 lines of small pebbles. 



The pebbles in the large pit sometimes form a conglomerate, in 

 which we have been fortunate enough to find several casts and im- 

 pressions of univalve shells, not, however, sufficiently perfect for 

 identification. 



The whole of this hill is marked Lower Bagshot on the Geological 

 Survey map, and we admit that the yellow and white sands at the 

 bottom of the large pit and the whole of the small pit belong to that 

 division of the scries, but the fossiliferous pebble-beds and the green 

 sands are, we think, clearly of Middle Bagshot age, though we also 

 think it possible that considerable re-arrangement may have taken 

 place in post-Bagshot times. 



