INAPPLICABILITY OF CATACLYSMS. 301 



meteorologiques, et paraissent etre le resultat d'immenses 

 inondations d'eau douce, et non d'eau marine, qui, se pre- 

 cipitant des points eleves vers la mer, auraient denude une 

 grande partie de la surface du sol, balaye la generalite des 

 etres organises et pour ainsi dire nivele, coordonne les bassins 

 hydrographiques actuels."* 



Such cataclysms as those supposed by M. D'Orbigny, and 

 many other French geologists, even if admitted, would not 

 account for the results before us. We have seen that the 

 transport of materials has not followed any single direction, 

 but has in all cases followed the lines of the present valleys, 

 and the direction of the present waterflow; that the rocks 

 of one valley are never transported into another; that the 

 condition of the loess is irreconcileable with a great rush 

 of water ; that the mammals and molluscs are the same 

 throughout the period ; while, finally, the perfect preserva- 

 tion of many of the most delicate shells is clear proof that 

 they have not been subjected to any violent action. 



We must, moreover, bear in mind that the gravels and 

 sands are themselves both the proof and the results of an 

 immense denudation. In a chalk country, such as that 

 through which the Somme flows, each cubic foot of flint, 

 gravel or sand, represents the removal of at the very least 

 twenty cubic feet of chalk, all of which, as we have already 

 seen, must have been removed from the present area of 

 drainage. In considering, therefore, the formation of these 

 upper and older gravels, we must not picture to ourselves the 

 original valley as it now is, but must, in imagination, restore 

 all that immense mass of chalk which has been destroyed in 

 the formation of the lower level gravels and sands. Mr. 

 Prestwich has endeavoured to illustrate this by a diagram, f 



* C. L'Orbigny, Bui. Geo. 2nd ser. V. xvii. p. 66. See also D'Archiac, I.e. 

 passim. 



f Proceed. Eoy. Soc. 1862, p. 41. 



