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strata separated by an intermediate and different condition 
of the valley. 
The mammalia found in this upper level gravel are but 
few ; the Mammoth, the Rhinoceros tichorhinus, with species 
of Bos, Ccrnts, and Equus, are almost the only ones which 
have yet occurred at St. Acheul, but beds of the same age in 
other parts of France have, in addition, supplied us with 
remains of the Bear, of a species of Tiger, of the Hycena 
spelwa, Ccrvus tarandus jiriscus, of a species of Dog, of the 
Musk Ox, and the Hippopotamus. The Mollusca, however, 
are more numerous ; they have been identified by Mr. J. Gr. 
Jeffreys, who finds in the upper level gravel 43 species, all of 
them land or freshwater forms, and all belonging to existing 
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 subaerial, must 
be a freshwater deposit. 
This, therefore, appears to indicate a change in the course 
of the river, and gradual excavation of the valley, which, by 
supplying the floods with a lower bed, left the waters at this 
height with a gradually diminishing force and velocity. 
Having briefly described the strata at St. Acheul, let us 
now visit some of the pits at the lower levels. At about 
thirty feet lower, as for instance at Menchecourt, near Abbe- 
ville, and at St. Eoch, near Amiens, where the gravels slope 
from a height of about sixty feet down to the valley, we find 
almost a repetition of the same succession : coarse subangular 
