460 PROCEEDINGS OF THE GEOLOGICAL SOCIETY, 



The presence of freshwater shells in some of these beds has heen 

 regarded as indicative of their fluviatile origin ; as far, however, as 

 the evidence at present extends, this condition is the exception 

 rather than the rule. When these gravels remain at what I regard 

 as their original place of deposit, viz. immediately upon the chalk 

 or gault surface, I believe that not a single river or lake shell has 

 ever been found associated with them, or lying below them, either 

 in the jlint-implement-bearing gravels, or in the very extensive beds 

 of similar gravel in the south and south-east of England and in the 

 north of France, which are not known to contain implements. 

 Certainly no shells have been seen in either of the four deposits 

 above described ; nor are there any at the Eeculvers, Bournemouth, 

 or Hill Head ; and the gravels at Madras are equally destitute of 

 them. The presence of these shells in the upper portion of these 

 beds by no means involves the conclusion that they are of the same 

 age as the underlying drift ; for, assuming that that was formed and 

 left as above suggested, the valleys and hollows would soon become 

 lakes and rivers, into which in process of time freshwater mollusks 

 would find their way ; and whenever the lower beds should be broken 

 up and reconstructed, the shells would be mingled with the debris, 

 and thus become un distinguishable from the older deposits. 



Another circumstance which has been relied upon as showing the 

 fluviatile origin of these gravels is the absence of any rocks except 

 those of the district through which the rivers take their course. I 

 do not think that this is very clearly established f; but, assuming it 

 to be so, it is quite consistent with the notion of diluvial transport 

 that the loose objects found on the surface should not be trans- 

 ported out of their own district : rocks and stones, if swept away 

 by a deluge, would very soon find their way into valleys and 

 hollows, and be left there when the waters had retired. 



In conclusion I would suggest that the distribution, in the first 

 instance at least, of these drift-beds, containing, as they do, so large 

 an admixture of chalk and tertiary and boulder- clay rocks, may 

 reasonably be attributed to the same forces or conditions, whatever 

 they were, by which the Tertiaries and Boulder-clays were broken 

 up and their materials so widely dispersed and intermingled. We 

 know nothing of these, except from their results ; but, whatever they 

 may have been, it seems quite certain that they are not ascribable 

 to fluviatile agency, and I am therefore disposed, with the French 

 geologists, to attribute them to some powerful cataclysmal action, 

 perhaps of short duration, and several times repeated. 



feet in flint-gravel. Two were found near the Cemetery, at a height stated to be 

 110 feet above high-water mark, and a mile distant from the beach; the other 

 was at a spot considerably higher and more inland. 



t M. Buteaux, in his very elaborate and careful description of the Somme 

 valley, says that in the diluvium of that valley certain rocks are found which 

 come from the Tertiary beds of the departments of the Oise and Aisne. Mr. 

 Prestwich considers that the quartzite pebbles at Brandon are derived from the 

 Boulder-clay series ; but I am not aware that there are any Boulder-clays in the 

 course of the river from which such a mass of these pebbles could have been 

 derived. 



