342 Superficial Gravels and Clays . [July, 
for what small amount of difference exists between the con- 
tents of the two deposits. 
I should, I believe, have little difficulty in establishing the 
position I have taken up, — that the gravels and clays of 
Ealing are simply the valley representatives of the glacial 
beds at Finchley, and that they were deposited at the same 
time, — if I had only the faCts of the case themselves to deal 
with. I have, however, a much harder task before me ; I 
have to contend against the general acceptance by geologists 
of Prof. Prestwich’s theory, — that the valley clays and 
gravels are quite distinct from and newer than the drifts on 
the slopes and tops of the hills. I shall, in consequence, 
have to examine this theory in detail. 
Briefly, Prof. Prestwich’s celebrated theory is, — that after 
the distribution of the glacial drift, the valley of the Thames 
was gradually excavated, and the gravels and clays deposited 
during the process. It implies, therefore, that the whole of 
the Thames Valley, from the level up to which the gravels 
in question extend, has been cut out since the Glacial 
period. 
The objections that may be urged against this view are 
many and serious. The gravels at Ealing reach to a height 
of 120 feet above the river, and the width of the Thames 
Valley at that level is more than 9 miles. If filled to that 
height there would be an expanse of water stretching from 
the northern side of Haven Green, at Ealing, to Morden, in 
Surrey, with some small islands consisting of the tops of the 
hills near Kingston, Richmond, Wimbledon, and Putney. 
A few miles farther west the valley is still wider, and without 
hills rising above the 120-feet line. All the valley below this 
line is supposed to have been excavated since the distribution 
of the glacial drift. Col. Lane Fox has shown us that there 
has been no appreciable change in the course or level of the 
river during the last two thousand years.* The theory there- 
fore requires that we should put back the occurrence of the 
Glacial period many tens — and possibly many hundreds — 
of thousands of years, to allow time for the excavation of 
the valley from the 120-feet contour-line. 
When, however, we go northward, to the region of un- 
doubted ice-aCtion, we find everywhere traces of the recent 
adtion of the glaciating agent, and that very little change 
has taken place in the configuration of the country since it 
was covered with ice. Thus Mr. Goodchild, in his descrip- 
tion of the glacial phenomena of the North-west of England, 
* Quart. Journ. Geol. Soc., vol. xxviii., p. 463. 
