OF THE BAG SHOT BEDS OF THE LONDON BASIN. 175 



than about 30 feet thick, as compared with the 92 feet of the Col- 

 lege-Well Section, a marked instance of attenuation. 



Obviously enough the determination of this horizon is very impor- 

 tant, so far as concerns the actual thickness of the lower (juartz-sand 

 series (Nos. 11 and 12) on the margin of the area ; and, as I showed 

 in my former paper, the lithological character of bed No. 10 varies 

 sufficiently within certain not very wide limits to introduce an ele- 

 ment of uncertainty, if inferences were drawn from a few discon- 

 nected and small exposures taken at random. "But I thiuk it must 

 also be equally obvious to any one who peruses carefully this and 

 my former paper, that the lithological evidence is strengthened and 

 controlled by the stratigraphical, the beds recognized as on the 

 horizons of Nos. 9 and 10 of the typical well-section being found 

 either cropping out from beneath the green-earth series or in direct 

 stratigraphical alignment with beds that do thus visibly crop out 

 from beneath them. 



Section S will be seen to be on the same contour with Section P 

 at Wick HiU. Pinchampstead Rectory, at 250' O.D., is on beds 

 which crop oat also on the same contour from beneath the Upper 

 Sands, which cap the Church Hill, and the well here (50 feet deep) 

 fihowed that the green beds become very feeble also in that direction, 

 very little green sand having been brought up in the digging of it, 

 within the lifetime of the present Hector *. At the foot of this hill 

 beds Nos. 9 and 10 crop out, and they can be traced all along the road 

 to near Eversley Bridge. There are many exposures of these in 

 small sections ; they are cut through by a small transverse valley of 

 erosion between the Rectory and Bannister's I'arm, which stands on 

 an outlier of them, and some fifteen years ago they were worked for 

 bricks near the lower road, at about the 200-foot contour. Their 

 passage down into the dirty fine quartz-sands of iSTo. 11 is well 

 shown in some rather large ditch-sections in the fields below the 

 Curate's house, only a few feet above the Blackwater, and above the 

 place where the London Clay is marked on the Survey Map. 



On the south flank of The Ridges the clays of No. 5 crop out in 

 the road-cutting below Sunnyside, and continue down to East 

 Court. The green earthy sands (Nos. 7 & 8) crop out next below, 

 and below these the clays and loams (Nos. 9 & 10) are exposed in 

 many small sections about the village. In 1886 a new well was 

 dug at the village school by John Walter, Esq., of Bearwood, who 

 kindly drew my attention to it. 



Section T. Well at Village School, Flnchampstead (210' O.D.). 



feet. 



a. Laminated hard clayey sand 10 (No. 10). 



h. Dirty blackish-green quartz-sand, with pyrites, ^ 1 /aj- i in 

 c. The same dirty sand mixed with black clay ... 5 J ^ ' ^' 



Total 20 



* The assignment of the beds in the Eectory Hill to the Upper Bagshot 

 (Geol. Mag., January 1885) was a mistake based on the reported non-appearance 

 of green sands in the Aveli-section. 



