36 LONDON DISTRICT. 



are yellow, but somewhat finer than the Bagshot; their structureless 

 appearance presents a marked contrast to the current-bedding of that 

 division. Some 40 ft. are exposed in an old road-cutting near the north- 

 eastern angle of the ' British Camp.' The sands are also dug in the gravel 

 pits on the summit of the hill, and were here recognised as of Barton age 

 by H. B. Woodward (op. cit.). 



West of the Wey the main mass of the Bagshot Sand is diversified 

 by a number of outliers of Bracklesham Beds. On Woburn Hill, south- 

 east of Chertsey, the following section was seen at the Hatch Brickworks 

 in 1911 : 



Ft. 

 Lilac and brown laminated brick-earth, strongly 



current-bedded, planes dipping south-east about 6 

 Horizontally-bedded sands, thinning towards the 

 south-east to a horizontal parting - 01 



Bracklesham 

 Beds. 



Brick-earth, similar to above, bedding planes dipping 



north-west - - 6 



Thin iron parting - 



Pale lilac loam, very dense - - 1-1 



Ironstone - | 1 



Bagshot Sand White sands - - seen to 5 



Here, again, the Bracklesham Beds rest in a basin cut in the Bagshot 

 Sand with an ironstone at the junction. At Ongar Hill, where 30 ft. of 

 lilac clays are exposed in a brickyard, the ironstone is replaced by a 

 band of iron nodules. At Brox Church the pebble-bed at the base of the 

 Barton Beds caps the hill; unfortunately, this outlier, the only one of 

 that bed within our area, is indicated on the London map (Sheet 3) as 

 two tiny patches of Plateau Gravel. Round Ottershaw there are several 

 patches of the Bracklesham pebble-bed, which is also probably the bed 

 which caps the St. Ann's Hill west of Chertsey, though Messrs. Gardner, 

 Keeping and Monckton regarded it as the Barton bed. 1 At the bottom 

 of this hill are several pits in the Bagshot Sand, which locally contains a 

 thin pebble-bed; these are succeeded in turn by the lilac clays and the 

 glauconitic sands of the Bracklesham Beds which have a combined 

 thickness of about 30 ft. ; this amount does not seem sufficient to allow 

 of the pebble-bed at the top being referred to the Barton Series. 



The particulars of the Bagshot, Bracklesham and Barton Beds in the 

 south-western area are taken mainly from the Windsor Memoir, where 

 they will be found set out in greater detail. 



CHAPTER V. 



STRUCTURAL GEOLOGY. 



It has already been mentioned (p. 17) that the Chalk had 

 been thrown into gentle folds before the deposition of the Tertiary 

 strata; these folds have, however, little if any influence on the 

 present structure, and it is to post-Eocene movements that the 

 ' London Basin ' owes its form. The term ' London Basin ' has 

 been used so constantly that it must be accepted, though many 

 writers have pointed out that it is a misnomer. The structure 

 would be better described as a shallow trough, with an axis running 



1 Quart. Journ. Geol. Soc., vol. xliv, 1888, p. 609. 



