521 , 
Quartz Rock of the Lie key Hill, &c. 
subsequently to the transport of the pebbles to their present 
situation on the highest summits. Nor is this hypothesis unsup- 
ported by the fact, that it is on the elevated plains that flank the 
vale of the Evenlode, no less than in the lower regions which form 
its present water-course, that the pebbles are scattered in an almost 
uninterrupted line, marking distinctly the course by which they 
have been propelled from Warwickshire into the valley of the 
Thames, descending along the back of the inclined and once 
continuous planes of the oolite strata that dip to the south-east, 
from their highest escarpment in the Cotswold hills. 
There is another strong fact tending to prove the excavation of 
the vallies of the Evenlode and of the Thames near Oxford to have 
been subsequent to the transport of the Warwickshire pebbles, 
namely, the total absence of pebbles of oolite in the caps of 
Warwickshire gravel that crown the summits of Wytham Hill and 
Bagley Wood. Hence we may infer that the destruction of the 
oolite strata did not begin with the first rush of the advancing 
deluge, but was the effect of its subsiding waters returning to 
the lower levels, excavating combes and vallies on every side 
of the higher ridges, and covering the bottoms only of these 
with gravel composed of the wreck of the oolite strata imme- 
diately inclosing them, mixt up also with that which its rising 
waters had transported from more distant regions ; and that the 
lower trunks of the vallies of the Thames and Evenlode, i. e. 
those portions of them which may be fairly attributed to the 
exclusive action of denudation, and which lie below the average 
level of the table-lands which flank their course, did not exist 
at the time of the first advance of the diluvian waters, which 
brought the pebbles in from Warwickshire, but were excavated by 
3 u 2 
