INAPPLICABILITY OF CATACLYSMS. 371 



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 water-flow ; that the 

 rocks of one valley are never transported into another ; that 

 the condition of the loess is irreconcilable with a great rush of 

 water ; while, finally, the perfect preservation of many of the 

 most delicate shells is clear proof that the phenomena are not 

 due to violent or cataclysmic 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 consider- 

 ing, 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 ;* and I must once more repeat 

 that this is no mere hypothesis, since the mass of sand and 

 gravel cannot have been produced without an immense removal 

 of the chalk. On the whole, then, we may safely conclude 

 that the upper-level gravels were deposited by the existing 

 river, before it had excavated the valley to its present depth, 

 and when consequently it ran at a level considerably higher 

 than the present. 



Far, therefore, from requiring an immense flood of water, 

 two hundred feet in depth, the accumulation of the gravel 



* Proceed. Roy. Soc. 1862, p. 41. 

 2B2 



