140 
A. E. SALTER-THE GRAVELS 
from above. Their constituents are also usually much weathered, 
the whole pointing to their having been surface-features for a very 
long time. Sections may be seen at Coles Hill near Amersham, 
and Tyler’s Hill near Chesham, Bucks ;* and at Sarratt, Chipperfield, 
Abbot’s Langley (at the back of Mr. J. S. Burrage’s house in 
Abbot’s Hoad), Bedmond (near the school on the road to King’s 
Langley), Bennett’s End, Stanmore Common, Shenley, Arkley, 
Potter’s Bar, Bell Bar,f Mimmshall Wood near South Mimms, 
Bayford, Hertford Heath, etc., Herts. 
Of the non-local constituents of these deposits may be mentioned 
the following:—Quartz-pebbles of various kinds, e.g. white, pink, 
and translucent; small blocks of rough quartz, dark chert, some 
with intricate quartz-veining, jasper, and small pieces of Car¬ 
boniferous chert showing crinoid stems. In places where the 
level approximates to that of the succeeding set of deposits a few 
Bunter quartzites, and more rarely pieces of rhyolite, much decayed 
as a rule, make their appearance. An important substance is 
often found in the more southerly deposits, as at Hampstead 
Heath, High Barnet, Newgate Street, and Brickendon Green, 
viz., Lower Greensand chert from the Hythe Beds of the Wealden 
area. As this substance is not found in the Lower Greensand of 
the Midlands and does not occur in the gravels in the northern and 
central parts of the county, it is reasonable to suppose that, at the 
time these deposits were formed, streams from the Wealden area 
entered this district. This substance also occurs plentifully in the 
high-level gravels of Essex. 
Similar deposits are found in the vicinity of the Stevenage Gap 
at corresponding levels, of which sections may be seen at Ayot 
brickyard (beneath a drift-clay), j Potter’s Heath, Harmer Green, 
Sacombe Green, Collier’s End, etc. No Lower Greensand chert 
occurs in them, and their constituents are of a rather more varied 
character than those already mentioned. |[ 
It is evident from the above that in order to understand the 
origin of these high-level drifts it is necessary to temporarily 
banish from our minds the present configuration of this part of 
the country. The region of higher ground lying south of the 
main slope, described in the Introduction to this paper, had three 
main lines of drainage converging towards it from the west, north, 
and south respectively, which united here to form an easterly- 
* Upheld Green, “Excursion to Boxmoor,” ‘Proc. Geol. Assoc.,’ vol. xvi, 
p. 501 ; “Excursion to Chesham and Cowcroft,” op. cit., vol. xv, p. 87; and 
“Excursion to Cowcroft,” op. cit., vol. xvii, p. 370. W. P. D. Stebbing, 
“ Excursion to Penn and Coleshill, Bucks,” op , cit., vol. xv, p. 311. 
f A- E. Salter, “Excursion to Potter’s Bar and Hatfield,” ‘Proc. Geol. 
Assoc.,’ vol. xiv, p. 420. 
X J. Hopkinson and A. E. Salter, “Excursion to Ayot Green and Hatfield 
Hyde,” ‘Proc. Geol. Assoc.,’ vol. xv, p. 308; see also op. cit., vol. xvii, p. 396. 
H. W. Monckton, “On a Section of the Westleton Beds at Ayot Brickfield,” 
‘ Geol. Mag.,’ 1899, p. 59. 
|| For a fuller account of these deposits see the author’s paper “ On the 
Superficial Deposits of Central and parts of Southern England,” ‘ Proc. Geol. 
Assoc.,’ vol. xix, p. 1. 
