536 Rk. H. Chandler—Drift at Bostall Common. 
of this small patch of London Clay, and agrees very closely in com- 
position with the Shooters Hill gravel at a level of about 200 feet 
higher. 
The extent of the spread of drift was revealed during the last 
two winters, when the top of the hill on Bostall Common was 
removed by the London County Council unemployed, and all the 
moderately large stones hand-picked and placed on one side. By 
looking over these heaps it was possible to form an accurate opinion 
of the composition of the drift, and it was then that the similarity 
to Shooters Hill gravel became so apparent. I have had the corroded, 
split, and zoned pebbles here in abundance, also two quartzite pebbles 
(this quartzite is curiously marked — precisely like one obtained 
from Shooters Hill), and a piece of the Lower Greensand Chert. 
Quartz pebbles I have not found, but as they would probably be 
small (as at Shooters Hill) they would not stand such a chance 
of being picked as the larger pebbles; this may account for their 
apparent absence. 
The height of 234 O.D. is above any of the terraces associated 
with the Thames in this neighbourhood; moreover, the gravel is 
different from the Terrace gravels in that it contains no (or very 
few) subangular flints, no Bunter quartzite, Rhanella chert, or 
igneous rocks, all of which are plentiful in the terraces. 
Mr. F. C. J. Spurrell has suggested! that this drift might be 
the remains of a Boulder Clay, or of its subjacent gravel, but con- 
sidering its curious composition I suggest that it is more likely to 
have been derived as a ‘trail’ from the gravel on Shooters Hill, at 
a time when that mass of London Clay and its capping of gravel 
was much more extensive than at present. A reference to the sketch 
will show that this source of supply has been cut off for a long 
time ; for the East Wickham stream, which rises on the slopes of 
Shooters Hill (as soakage from the gravel), and finds its way to 
the Thames at Plumstead, has now separated the patch of London 
Clay at Bostall Common from the mass of Shooters Hill by a valley 
150 feet deep (in the line of section), and there has been uncovered 
an outcrop of the Lower London Tertiaries 13 miles wide. 
An alternative hypothesis is that the Bostall Common drift was 
once continuous with Shooters Hill gravel and at about the same 
level, and that it has been separated from Shooters Hill by the 
cutting back of the East Wickham stream, whilst denudation has 
lowered Bostall Common vertically from about 404 feet O.D. (the 
height of Shooters Hill less the gravel cap) to 284 feet O.D., by 
reducing the London Clay from 180 feet to 10 feet; possibly because 
its original capping of gravel was not so thick, and hence unable 
to act so protectively.’ 
The suggested hypothesis seems more workable (i.e. a trail from 
Shooters Hill down the slope of London Clay), and this feature 
1 “A Sketch of the History of the Rivers and Denudation of West Kent, etc.”’ : 
ene W. Kent Nat. Hist. Soc., 1886, p. 19. ‘This appears to be the first and only 
reference. 
* There is a remarkable agreement between these figures. 
