VALLEY AND ITS KELATION TO THE WESTLETON BEDS, ETC. 165 



apparently disturbed and displaced on the north side of the hill and 

 ])ushed southward. 



At Warley Heath (378 feet) the pebble-gravel is thick and little 

 disturbed. The flint-pebbles have a distinctive character of their 

 own. They are unlike those of Blackheath or of the Westleton 

 Beds. Dr. Mitchell speaks of them in his papers (MSS.) as the 

 Warley pebbles. They are larger and less shapely than those of 

 lilackheath, and are often weathered white. Of their derivation 

 from the Bagshot Beds, with which these shingle-beds are in close 

 association, there can be little doubt, for at Billericay there is a thin 

 bed of flint-pebbles intercalated in the yellow sands of the Bagshot 

 which cap the hill, and Mr. H. B. Woodward gives a section at South 

 Weald Park, near Brentwood *, showing a bed of pebbles 15 feet 

 thick in situ, and overlain by 6 feet of Drift-gravel. We have, in 

 some cases, therefore, this Eocene Shingle in situ, whilst in others 

 it seems to have been aflected by the Southern Drift and by subse- 

 (luent Glacial action. 



This range of hills formed here, as did the Hampstead and 

 Highgate on the north of London, and the Bushey and Stanmore 

 Hills to the south of Watford, the boundary to the advance of the 

 Boulder-clay ; for though Glacial gravels and evidences of Glacial 

 action are to be found further south, there is no Boulder-clay. 



Stanmore. — An important mass of shingle-gravel spreads over 

 Stanmore Heath (400 to 450 feet), from little Bushey to Bentley 

 Priory. It is composed in large part of : — 



1. Flint pebbles, a good many being white-coated. 



2. Very few subangular flints, stained brown. 



3. Some small white quartz pebbles. 



4. A few worn green-coated flints, from the base of the Lower Tertiary 



sands. 



Imbedded in a matrix of coarse yellow and ochreous sand, and 

 resting upon an indented surface of London Clay, as though due to 

 pressure (glacial) from above. Many of the pebbles also have their 

 longer axes upright. 



I did not notice any chert or ragstone in this shingle, and in 

 other respects it resembles the Brentwood and Warley, more than 

 the Westleton Shingle. The few quartz-pebbles may have been 

 derived from the Lower Tertiaries, which in the Pinner district 

 contain a few such pebbles. 



The hill (:i80 to 400 feet) between Pinner and Watford, as well 

 as Brockley (41 6 feet) and Elstrce Hills (450 feet), on the other 

 side of Stanmore, are capped by a small spread of similar shingle, 

 but it is not worked. 



There is no Boulder-clay to the west or south of these hills ; and 



* " The Geology of the London Basin," Mem. Geol. Survey, 1872, p. 324 ; 

 and ' Geology of London,' 1889, p. 273. 



