284 
THE GEOLOGIST. 
into the ice-floes, masses of fine gravel, sand, and earth, enclosing fra- 
gile shells, would also be brought down in the same way. Moreover 
the gravel deposits would chiefly be formed during the period of 
spring floods caused by the melting of the ice ; and consequently 
during the summer there would be a period during which mollusca 
might live under the influence of the quieter river actions, which ac- 
tions would naturally intercalate beds and streaks of sand and clay 
with freshwater shells amongst the coarser gravels. 3. That the 
Valley of the Somme ivas even then deeper than it is now ; and appears 
to have been filled up at the time of the arrival of the rolled flints. — 
All this has nothing to do with the question of man's antiquity at all; 
besides there is no proof given by Isl. Gras, "What he states as to 
the various deposits and their conditions go for nothing in this re- 
spect ; they siuiply do not bear upon the point at all. It matters 
not whether the valley was hollowed out, whether it was filled up or 
not, before the " rolled flints" were brought in, so long as the gravel 
deposit containing the flint-implements can be proved to be of geo- 
logical age — that is the point; and M. Gras, if we do not misunderstand 
him, admits the flint-implement-bearing beds are covered by other 
diluvial or alluvial deposits — a sufficient admission of their antiquity. 
As to a previous complete excavation of a valley before any depo- 
sits collected in it, such a notion in the main would be a very falla- 
cious one, for the scouring action of water and rainfalls is as great 
beneath a deposit as it is over its surface. Eains wash away visibly 
the fine soil on the surface, but the water that filters through also 
washes away invisibly the fine disintegrated surface of the rock on 
which the deposit lies ; so the whole mass of deposits gradually — 
slowly but surely — sinks into a greater and greater subterranean 
valley as age follows age. 
But to return to M. Gras — for he himself admits the position that 
the flint-implement gravel was covered over, in the following pas- 
sage :— - 
" By the help of these details a clear idea may be formed of the position 
of the worked flints ; they are found in the lower grey diluvium at variable 
depths, and often considerably below the surface of tlie soil. An attentive 
examination of the flinty mass which encloses them yields no re-arrange- 
ment of materials. Moreover, everywhere above these flints there is a 
thickness of two or three metres of diluvium of the latest date, of a brown 
colour. This itself appears to be perfectly intact, and sharply separated 
from the grey diluvium ; which excludes the possibility of the introduc- 
tion of foreign objects vertically through the argillaceous -sandy earth." 
But here follows what certainly shows either M. Gras' obliquity of 
