OP THE BAGSHOT BEDS OF THE LONDON BASIN. 167 



along Nino-milo Ride, and a similar slight rise of beds of the same 

 horizon from Wokingham to Bracknell *. It also acconnts for the 

 slight dip to the west of the clay-and-sand beds at Bracknell noted 

 below. As a stratigraphical fact its effect must be allowed for in 

 correlating altitudes. 



Sunningdah f. — The succession here is clearlj' marked. Close to 

 the Station the Middle Group forms almost an escarpment. The 

 hill is capped over a considerable area with a pebble-bed a little 

 below 240' O.D. This must be on the horizon of No. 3, as it passes 

 with a gentle dip to the south under hills of the Upper Sands. On 

 the eastern flank of this hill, below Titlark Farm, we find the 

 section noted in the Quart. Journ. Geol. Soc. vol. xlii. p. 404, 

 including about 10 feet of quite normal green earthy sands, with 

 the underlying clays of the Middle Group. 



The lower clay-beds (Nos. 9 & 10) crop out at the foot of the 

 hill about the level of the Station, and were worked for bricks a 

 little further north only a few years agoj. The fine quartz sand 

 (No. 11) is seen beneath the laminated clay-and-sand bed, in an 

 old pit there at about 200' O.D. At a rather lower level the 

 London Clay is exposed along the banks of the brook south of 

 Broomhall Farm§, and from this it would appear that about 30 feet 

 is the most we can assign to the thickness of the Lower Sands at 

 Sunningdale, beneath the Middle Group. The outlier (mapped i. 5) 

 on Shrub's Hill is more extensive, probably, than is there repre- 

 sented. Its assignment to the Middle Group is verified by the 

 occurrence of a strong dark-green sand (which did not appear, when 

 I dug into it, to be reconstructed) all across the floor of an extensive 

 gravel-pit in Potnall Woodjl. A little way further north the 

 London Clay is exposed on the south side of Virginia Water, 

 according to the Survey-map, which I have verified. Due south of 

 this outlier is Chobham Place, where 100. feet (? more) is recorded % 

 for the thickness of the Lower Sands in the well-section. 



There is apparently considerable attenuation of the quartz-sand 

 series (Nos. 11 & 12) in this hill. 



The beds of the Middle Group are well developed in the Long- 



* See fig. 2 of my last paper, vol. xliii. of the Quart. Journ. Geol. Soc. 



t To my friend Lieut. H. Gr. Lyons, R.E., F.G.S., I am indebted for many 

 stratigraphical details about this neighbourhood, to which he has drawn my 

 attention. 



\ On the opposite side of the valley (i. e. the west side) a similar bed overlies 

 the fine quartz sands in a road-cutting at a corresponding altitude : it is also 

 exposed in Brick -kiln Lane, at Sunningdale village, with quartz sand in the 

 valley below. 



§ The Survey mapping here needs to be reconsidered. 



II That part of the horizontal section of the Survey which cuts through this 

 hill would be in perfect accord with the results of my observations, if the base 

 of the Middle Group were drawn in the same line as it is in the section further 

 south. 



^ Mem. Geol, Surv. vol. iv. p. 543. It is difficult to account for the record 

 of 100 ft. of Upper Sands in this section. Prof. Prestwich tells me an old 

 workman gave him the account from memory. The sections in the immediate 

 vicinity give abundant evidence (clays and green earths) of horizons to justify the 

 Survey-mapping, which represents Chobham Place on the Middle Beds (i. 5). 



