192 
THE GEOLOGIST. 
in flood time, grounding on the brick-carili and prisliing a portion of it 
into the underlying beds of sand, where, as the ice gradually melted, it 
would be left, caught, and squeezed in by the sand pressing itself into 
place again. 
The two classes of evidence are, therefore, conformable. It is in har- 
mony also with the existence of the large iDeds of brick-earth or loess 
overlying the gravel, and which is, doubtless, the deposit of the old river 
during floods, usual in a severe climate at the time of the melting of the 
winter snows. The w inter climate may probably have been as rigorous as 
that of jN^orthern Eussia or Northern Canada. Such a climate would not 
be any bar to the presence of man, whose works are found in these old 
sliingie beds. It is true that none of his remains have yet been found in 
these deposits, but they are found in caves of the same age. The abun- 
dance of animal remains is the almost inevitable consequence of a country 
subject to great river-floods, by \A"hich large numbers of animals are always 
destroyed and swept down ; man, on the contrary, guards against such 
risks. Along the ]S[orthern American rivers of the present day, although 
the remains of the buflalo and other animals occur in profusion, the re- 
mains of man are scarcely ever met with. There is every reason to expect 
that this further and desirable proof may be forthcoming at no long 
distance of time. 
Lastly, the speaker stated that the present river Somme only carries 
down fine silt and mud, wiiercas the old river transported large masses of 
coarse shingle ; therefore, it is to be inferred that the old river was one of 
much greater power than the present one. During floods especially its 
power must have been very great ; with greater transporting power the 
river would possess greater excavating power ; at the same time the dis- 
integration of rocks, especially such soft rocks as the chalk of this district, 
produced by severe cold, combined with the effects of ground ice lifting 
up from the bed of the river large quantities of the shingle, w ould hasten 
the deepening of the valley. As it deepened, terraces of shingle have 
been left at places on the slopes. It may be difficult to imagine a river 
with so limited a collecting ground filling a valley a mile wide, but this 
the speaker supposes to have been the case only during floods, and that 
the ordinary channel of the river was very much smaller. He instanced 
a case in India where Dr. Hooker mentions a river which was only eighty 
yards wide when he crossed it, but which, after the rains, covered a 
channel three miles wide, and ran ten to twelve feet deep. I he melting 
of the snow in the spring produces the same result in arctic regions as 
heavy and continued rains in southern regions. 
Mr. Prestwich next exhibited a diagram to show what he conceived to 
be the different phases of the phenomena, from the period w hen the beds 
of St. Acheui were formed, until the valley assumed its present form and 
dimensions. The plan, which was formed of a series of superimposed sec- 
tions, showed — 
1. The old r'ive?' during the deposition of the shingle and sand hanlcs of 
St. Acheui. — In this the bed of the river was occupied with large shingle 
banks, which w ere left dry during the time the river was low. Mr. Prest- 
wich supposes these to have been resorted to by earl}^ man, in consequence 
of the number of large flints they contained, for making flint imi3lements 
on the spot. This may be one of the reasons why they are so numerous 
at St. Acheui, w hich was shovAu to be one of those old shingle banks pre- 
served from that time. Ice-floes dropped large blocks of sandstone into 
the shingle. A space shut off" in part by a shingle bank vAOuld account for 
