BAGSHOT BEDS OF BAG SHOT HEATH. 53 



yellow sand full of casts of marine shells Lower Bagshot. In his 

 paper of 1887 ^ and in his last paper,^ Dr. Irving deals with this 

 question ; but, as a matter of fact, neither Mr. Herries nor I 

 say that the presence of pipeclay seams is conclusive evidence of a 

 Lower Bagshot horizon (see this Journal, vol. xliii. (1887) p. 378), 

 but that it distinguishes the Lower from the Upper Bagshot — a 

 very different thing. 



I now propose to describe the localities in dispute : — 



Farley Hill, mapped as Lower Bagshot, but claimed by Dr. Irving 

 as probably Middle capped by Upper Bagshot.^ He adds that 

 further exploration is needed, and 1 was so fortunate as to find a 

 small section at the top of the hill in a gravel-pit showing 6 feet of 

 yellow Bagshot Sand with many white clay laminae below the gravel. 

 This is certainly not Upper Bagshot, and it proves there is none of 

 that division on the hill. It is like ordinary Lower Bagshot, and 

 though admitting that one or two sections in the Middle Bagshot 

 not unlike it are to be found, still I should say that if it stands 

 alone no one will hesitate to regard it as Lower Bagshot Sand. 



Bearwood, mapped as Lower Bagshot. Described by Dr. Irving 

 as " an outlier of Upper Bagshot Sands on London Clay,'' ^ and 

 shown in his diagram^ as Upper Bagshot Sand with a pebble-bed at 

 the base resting on London Clay. 



On Aug. 25, 1887, I visited the locality in company with 

 Dr. Irving, and he pointed out four places where he claimed Upper 

 Bagshot Sand above the pebble-bed : — 1, a hole in Coombe Wood ; 

 2, the loamy sand above the pebble-bed in the pit of which a 

 section is given ; ^ 3, some small holes in a wood north of Birtle 

 Heath ; 4, a large sandpit near Dowles Farm. 



On Jan. 15, 1888, 1 wrote to him expressing the opinion that the 

 Dowles Farm sandpit was below the pebble-bed, and not 20 feet 

 above it as he had thought, and was Lower Bagshot/ This Dr. 

 Irving now admits,*^ and as the sands at Birtle Heath are clearly on 

 the same horizon as the Dowles Farm pit, the only possible Upper 

 Bagshot left is that in the hole in Coombe Wood and in the pebble- 

 pit. But in both layers of whitish clay occur, and they are in my 

 opinion clearly not of Upper Bagshot age. 



Dr. Irving further says in his ' Recent Contributions,' p. 16, that 

 there is Lower Bagshot Sand underlying the clays and pebble-bed 

 shown in the diagram (loc. su'pra cit.).^ The idea of an overlap 

 here or of Upper Bagshot Sand resting on Loudon Clay seems there- 

 fore to fall to the ground ; but a difficult question remains, namely, 

 whether the pebble-bed with the clayey beds both above and below 



1 Quart. Journ. Geol. Soc. vol. xliii. p. 378. 



^ 'Eecent Contributions,' &c., 1891, p. 13. 



3 Quart. Journ. Geol. Soc. vol. xliv. (1888) p. 177. 



* Geol. Mag. for 1887, p. 111. 



5 Quart. Journ. Geol. Soc. vol. xliii. (1887) p. 388, fig. 2. 



^ Geol. Mag. torn. cit. p. 116. 



"^ Ibid. p. 114. 



^ ' Eecent Contributions,' &c., 1891, p. 15. 



^ See also Quart. Journ. Geol. Soc. vol. xliv. (1888) p. 176. 



