1878.] 
Superficial Gravels and Clays. 
343 
states that “ So little indeed has the aspedt of the country 
changed in post-glacial times, that in many places the larger 
rivers are even now above the bases of the adjoining drift- 
mounds, whose present form can hardly be referred to any 
other than glacial adtion ; and post-glacial denudation gene- 
rally has effedted so little that by far the greater part of the 
present surface-configuration has, in one way or another, 
resulted from the former presence of the great ice-sheet.”* 
Mr. D. Mackintosh, and I can quote no higher authority 
on the glacial beds of the West and North-west of England, 
in a recent ledture, at Chester, brought forward a great 
number of fadts tending to show that the time which has 
elapsed since the close of the Glacial period need not have 
been so much as ten thousand years. Mr. Geikie and other 
geologists often refer to the recent appearance of the ice- 
markings in glaciated distridts, and to the very small modi- 
fication of the surface that has taken place since the 
outspread of the drift ; but I need not refer more particularly 
to these opinions, as the neighbourhood of London itself 
affords sufficient evidence to the same effedt. 
At Finchley we see the Upper Boulder-clay mantling the 
hills and descending the slopes into the valleys, proving con- 
clusively that the surface-features of that distridt, when it 
was spread out, were the same as they are now. The upper 
part of the valley of the Brent was then in existence, and at 
the most has not since been lowered more than 10 or 12 feet. 
The unconsolidated clay lies as it was deposited, and runs 
down to about 150 feet above the sea-level. It covers the 
hill continuously, and even on the steeper slopes has not 
been entirely denuded. Can it be for a moment considered 
possible that the great valley, several miles in width, has 
been worn out by denuding agencies below the level to which 
the boulder-clay reaches, and that above that line the adtion 
of the elements has been stayed, no appreciable change 
effedted, and not even the uppermost bed of the glacial 
series denuded ? How often must the river have changed 
its course, and travelled across from one side of the wide 
valley to the other, to remove the enormous mass that has 
been swept away in its excavation ! Yet we are asked to 
believe that during all this time the denuding agencies did 
not operate on the uplands, but were stayed in their course, 
like the sun on Gibeon and the moon in the valley of 
Ajalon. 
If we look at the country below the level of 150 feet above 
* Quart. Journ, Geol. Soc;, vol. xxxi., p. gg. 
