LUBBOCK ON THE iJS^TIQUITT OF MAJS-. 255 



quenoise a Hirson* la vallee en preseute que des fragmeuts plus ou 

 luoins roiiles des roclies de trausition que traverse le eours de la 

 riviere. Eu descendant a Etreaupont, on y trouve des calcaires juras- 

 siques et des silex de la craie, formations qui ont suceede aux roches 

 aneiennes. A Guise, le depot erratique est com- 

 pose de quartzites et de schistes de transition de quelques grucs plus 

 recent, de silex de la craie, et surtout de quartz laiteux, dont le 

 volume varie depuis celui de la tete jusqu'a celui de grain de 

 sable .... Au dela les fragments de roches aneiennes diminuent 

 graduellement en volume et en nombre." At Paris we found the 

 granitic debris brought down by the Tonne to form a notable 

 proportion of the gravel; and at Precy, near Creil on the Oise, the 

 fragments of the ancient rocks were abundant ; but lower down the 

 Seine at Mantes, they had both diminished -very much in quantity, 

 and at Eouen and Pont de I'Arche we saw none, though a longer 

 search would doubtless have shown us fragments of them. This case 

 of the Oise is however interesting, not only on account of the valu- 

 able evidence contained in the above quotation, but because, though 

 it flows, as a glance at the map wiU show, immediately across and at 

 right angles to the Somme, yet none of the ancient rocks which form 

 the valley of the Oise, have supplied any debris to the valley of the 

 Somme : and this though the two rivers are at one point within six 

 miles of one another, and separated by a ridge of only 80 feet in height. 



The same division occurs between the Seine and the Loire : "bien 

 " que la ligne de partage des eaux de la Loire et de la Seine, 

 " entre St. Amand (Nievre) et Artenay, au nord d' Orleans, soit a 

 " peine sensible, aucun debris de roches venant du centre de la France, 

 " par la vallee de la Loire n'est passe dans le bassin de la Seine. "f 



In the Vivarais near Auvergne, " Les depots diluviens, sont com- 

 " poses des memes roches que celles que les I'ivieres actuelles entrai- 

 " nent dans les vallees, et sont les debris des seules montagnes de la 

 " Lozin, du Tanargue et du Mezene, qui entourent le bassin du 

 *' Vivarais.]: 



Again, 



" Le diluvium des vallees de I'Aisne et de I'Aire ne renferme que 

 " les debris plus ou moins roules des terrains que ces rivieres coupent 

 " dans leur cours."§ 



Other instances of the same law may be quoted ; Mr. Prestwich 

 has found it to hold good in England, but as it is an important link 

 in the chain of evidence on which his views depend, it seemed better 

 to take the facts from other observers. The conclusion deduced by 

 M. D'Archiac from the consideration of these observations, and spe- 

 cially from those concerning the valley of the Seine, was " que les 

 " courants diluviens ne venaient jDoint d'une direction unique mais 



* D'Archiac, 1. c. p. 155. J D'Archiac, 1. c. p. 160. 



t D'Archiac, 1 c. p. 1G4. ^ Malbos. Bull Geol. Vol. III. p. 631. 



