520 
Mr. Buck land on the 
gravel, its quartzose pebbles, derivative by the course we have been 
tracing from the red sand strata of Warwickshire, occur less 
abundantly, though they are by no means unfrequent. They may 
be seen on the summit of the chalk hill immediately on the east 
of Henley and in the valley of Maidenhead, at Dropmore also, and 
in the gravel pits of Burnham between Beaconsfield and Windsor ; 
in all these last named places the great mass of the gravel is 
composed of imperfectly rolled flints derived from the neighbouring 
chalk. 
The occurrence of quartzose pebbles in such high situations as 
the top of Henley hill and Cumnor hill, and again on the highest 
summit of Witchwood Forest, and the elevated plains that flank the 
vale of the Evenlode above Oxford, goes far to prove the recent 
origin of the vallies through which the Thames and Evenlode now 
flow ; and compels us to refer the excavation of them (at least in 
certain parts) to the denuding agency of the subsiding waters of 
the most recent deluge that has affected the earth. It seems that 
the first action of these waters drifted forward the quartzose pebbles 
within the great escarpment of the oolite, and strewed them over 
the then nearly continuous planes of strata belonging to that 
formation; and that the present minor vallies were subsequently 
scooped and furrowed out by the retiring action of the same waters 
whose advance drove on before them the pebbles we are now 
considering ; for it is not easy to imagine any other solution of the 
fact of the pebbles being heaped together on the summit of the 
insulated, steep, and nearly conical hill of Wytham and the elevated 
ridge of Bagley Wood near Oxford, or on the highest crest of the 
oolite ridge of Witchwood Forest, or the chalky summit of Henley 
hill ; unless we adopt that which supposes the excavation of the 
vallies immediately subjacent to these hills to have taken place 
