THE GEOLOGIST. 



into tlie 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 was even then deeper than it is now ; and appears 

 to have heen 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 M. Gras. What he states as to 

 the various deposits and their conditions go for nothing in this re- 

 spect ; they simply 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 sufiicient 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 

 W'ashes 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 fliut-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 llints ; they are found in the lower grey diluvium at variable 

 deptlis, niul often considerably below the surface of the soil. An attentive 

 exaniination of tlie flinty mass which encloses them yields no re-arrange- 

 mcnt of ui;itvM-ial:^. j\Ioreover, ever3-where above these flints there is a 

 thickness of [wo or tliree metres of diluvium of the latest date, of a brown 

 colour. This ilself appears to be perfectly intact, and sharply separated 

 from the grey dilnvinni; which excludes the possibility of the introduc- 

 tion of foreign objecls veriically through the argillaceous-sandy earth." 



But here follows what certainly shows either M. Gras' obliquity of 



