NATUEE AND VALUE OF THE EVIDENCE. 
297 
strong and permanent, that no subsequent exposure will remove it. In studying the 
drift deposits, I have found it a convenient test whereby to trace one set of flints from 
the gravel of one period to that of another, when the general appearance of the two 
gravels has been so much alike, that, but for the presence of these derived portions, it 
would be difficult to separate them. Now in looking over M. Bouchee de Peethes’ fine 
collection, you are at once struck with the fact, that the flint-implements from each 
locality present a colouring in perfect accordance with the lithological character of the 
bed of which they had formed part, indicating, I believe, not only a real derivation from 
such beds, but also a sojourn therein of equal duration to that of the naturally broken 
flints occurring in or forming part of the same beds. Some of those from the sand d 
of Menchecourt are not discoloured ; others, however, exhibit a more or less white por- 
celanic coating. This depends probably upon the occasional presence in the sand d of 
white clayey and marly seams {d!). Those from the ochreous gravel of Moulin Quignon 
are, on the contrary, stained of a bright yellow or ferruginous colour. The same varia- 
tions exist at St. Acheul ; some of the Hint-implements still retaining their fresh black 
sui’faces, whilst others are weathered white or ochreous, according to the character of the 
particular seam of gravel in which they are met with, the unaltered ones being the most 
frequent, as the white gravel is in the largest proportion. 
In the next place, these Hint-implements, not being ground or polished, present a 
rough surface, often with many small hollows and angles in which the matrix can lodge ; 
and in all the specimens from the different localities, which still retained portions of the 
Fig. 8. Fig. 9. 
matrix, either in such cavities or adhering to the surface, the material was invariably in 
accordance with that of the bed from which they were reported to have come. 
Further, many of the worked Hints, especially those at St. Acheul, are coated, more 
