328 HARMER : THE PLEISTOCENE DEPOSITS OF EAST ANGLIA. 
Chalky Boulder-clay ; in that of the Waveney, along the sides 
of which the latter is found at a lower level than that which 
it occupies on the plateaux to the north and the south, and in 
many other places. Mr. Whitaker has, moreover, shown that 
an old and deep valley, running north and south, and apparently 
more or less coinciding with that of the Cam, in Sheet 47, is 
filled with drift, which was found at one place to extend to 
more than 140 feet below sea level.* Mr. J. Hopkinson, F.G.S., 
has also instanced a similar case in Bedfordshire, where in the 
plain at the foot of the Lower Greensand escarpment at Sandy, 
which latter reaches a height of 120 feet above it, a boring passed 
through 104 feet of boulder-clay to the Oxford Clay.f These 
and other similar facts indicate that the conditions of the Yare 
valley, which I originally thought anomalous, may be more 
or less typical of the general structure of the district. The 
" Cannon Shot " gravels of Mousehold Heath, the latest of the 
Glacial deposits of East Anglia, situated as they are on the brow 
of the valley 150 feet below, in which Norwich stands, in a 
position where the}^ could not have been accumulated under 
present conditions, seem also to support the view that during 
the latter part of the Upper Glacial period many of the valleys 
of this region were fiUed with ice.{ 
I offer no apology for treating this subject in a somewhat 
speculative manner — for indulging in what I hope I may call 
a " scientific use of the imagination." The collection either of 
facts, or of fossils, although a duty, often laborious and always 
useful, is nevertheless not the " whole duty of man." In a 
study as fascinating as is that of geology, it is not always possible 
while the hammer is busy to keep the mind at rest. Unless, 
moreover, we are to be crushed under the weight of our own 
accumulations, it is necessary to arrange, and from time to 
time to rearrange, our facts in orderly sequence, asking ourselves 
constant^ what they mean, and, where their meaning is obscure, 
as is so often the case, to what they seem to point. 
* Q. J. G. S., Vol. xlvi., p. 335, 1890. 
+ Proc. G. S., Xo. 767, p. 20. 1902. 
* As to this, see Proc. Geol. Assn., Vol. 17, p. 471, 1902. 
