256 OBIGINAL AETICLE9. 



" qu'ils convergaient des bords du bassin vers sou centre, suivant les 

 " depressions preexistantes, et qne leur elevation ou leiir force de 

 " transjwrt ne suffisait j)(is pour f aire passer les debris qu'ils charriaient 

 " d'une de ces valUes dans C autre.''''* 



Coiisideriug, however, all these facts, reinembering that the con- 

 stituents of the upper level gravels are, in all cases, derived from beds 

 now in situ along the valley, that they have not only foUoAved the 

 lines of these valleys, but have done so in the direction of the 

 present waterflow, and without in any case passing across from 

 one river system to another, Ave may surely, I think, follow Mr. 

 Prestwich in his conclusion that these gi-avels have been brought 

 down, and deposited by the present rivers. 



The sandstone blocks which occur in the gravel appear indeed at 

 first sight to be irreconcileable with any such hypothesis. In some 

 pits they occur frequently, and are of considerable size ; the largest 

 I have myself seen is represented in the section, Eig. 1, taken 

 close to the railway station at Joinville. It was 8 ft. 6 inches in length, 

 with a width of 2 ft. 8 in., and a thickness of 3 ft. 4 in. Even when 

 we remember that at the time of its deposition the valley was not 

 excavated to its present depth, we must still feel that a body of water 

 with power to move such masses as these must have been very different 

 from any floods now occurring in those valleys, and might fairly per- 

 haps deserve the name of a cataclysm. But whence could we obtain 

 so great a quantity of water ? AVe have already seen that the gravel 

 of the Oise, thovigh so close, is entirely different from that of the 

 Somme, w^hile tliat of the Seine again is quite different from that of 

 any of the neighbouring rivers. These rivers therefore cannot have 

 drained a larger area than at present ; the river systems must have 

 been the same as now. Nor would the supposition after all account 

 for the phenomena. We should but fall from Scylla into Charybdis. 

 Around the blocks we see no eAddence of violent action ; in the section 

 at Joinville, the grey subangular gravel passed under the large block 

 abovementioned, with scarcely any alteration. But a flood which could 

 bring down so great a mass would certaiidy have swept away the 

 comparatively light and moveable gravel beloAv. "We cannot therefore 

 account for the phenomena by aqueous action, because a flood whicli 

 would deposit the sandstone blocks would remove the underlying 

 gravel, and a flood which would deposit the gravel Avould not move 

 the blocks. The Deus ex machina has not only been called in most 

 unnecessarily, but Avheu examined turns out to be but an idol 

 after all. 



Driven, then, to seek some other explanation of the difficulty, 

 Mr. Prestwich falls back on that of floating ice. Here we have an 

 agency wdiich would satisfactorily explain all the difliculties of the 

 case. The " packing" and propelling action of ice would also ac- 

 coimt for some irregularities in the arrangement of the beds which 



• L.c, p. 163. 



