ORGANIC REMAINS. 365 



pieces of the oak, yew, and fir, have, however, been deter- 

 mined at Hoxne. The mammalia, also, are but few; the 

 mammoth, the Eleplias antiquus, with species of Bos, Cervus, 

 and Equus, are the only ones which have yet occurred at St. 

 Acheul, though beds of the same age in other parts of England 

 and France have added the Rhinoceros licJiorhimts, the rein- 

 deer, and several other species. The mollusca are more 

 numerous ; they have been identified by Mr. J. G. Jeffreys, 

 who finds in the upper-level gravel thirty-six species, all of 

 them land or freshwater forms, and all belonging to existing 



' O O O 



species. It is hardly necessary to add, that these shells are 

 not found in the coarse gravel, but only here and there, where 

 quieter conditions, indicated by a seam of finer materials, 

 have preserved them from destruction. Here, therefore, we 

 have a conclusive answer to the suggestion that the gravel 

 may have been heaped up to its present height by a sudden 

 irruption of the sea. In that case we should find some marine 

 remains ; but as we do not, as all the fossils belong to animals 

 which live on the land, or inhabit fresh waters, it is at once 

 evident that this stratum, not being sub-aerial, must be a 

 freshwater deposit ; and as the most delicate shells are entire, 

 it is equally evident that they were deposited in tranquil 

 water, and not by a cataclysm. 



But the gravel itself tells us even more than this : the 

 river Somme flows through a country in which there are no 

 rocks older than the chalk, and the gravel in its valley con- 

 sists entirely of chalk flints and tertiary debris.* The Seine, 

 on the other hand, receives tributaries which drain other for- 

 mations. In the valley of the Yonne we find fragments of 

 the crystalline rocks brought from the Morvan.f The Aube 

 runs through cretaceous and Jurassic strata, and the gravels 

 along its valley are entirely composed of materials derived 

 from these formations. The valley of the Oise is in this 



* Buteux, 1. c. p. 98. t D'Archiac, Progres de la Geologic, p. 163. 



