The flint implements are said also to occur occasionally in the beds of sandy clay above the white sand, but the pit has of late years been but little worked, and in consequence the implements but rarely found. In the section of the Menchecourt beds given by M. Boucher de Perthes,[1] the place where two of the worked flints were found is shown at about thirty feet from the surface, and another was discovered at about fourteen feet; they are, however, said to have been most commonly met with in the lower beds. At the Moulin Quignon, the Porte St. Gilles, and at other places in the arrondissement of Abbeville, as for instance at Yonval, the gravel-pit at Mareuil, the sand-pit at Drucat and at St. Riquier, similar flint implements are stated by M. de Perthes[2] to have been found under similar circumstances; but these last-mentioned places I have not visited.
The whole of the drift which I have described is of fluviatile origin; and in the beds of sand and clay, land and fresh water shells of existing species are frequently found in abundance, though at Menchecourt, as has been already mentioned, they are mixed with others of marine origin, which gives more of an estuarine character to the deposit at that place.
I think that it is by no means impossible that these arenaceous beds at Menchecourt may eventually be proved to be rather subsequent in date to the higher and more gravelly beds at the Champ de Mars, and Moulin Quignon, on the opposite side of Abbeville; their elevation above the river Somme is not much more than from twenty to thirty feet, so that under ordinary circumstances it might be considered by some, that they are due to its action under a state of things not very materially different from that at present existing, did not the mammalian remains, found at both Menchecourt and St. Roch, point to an entirely different fauna from that of the present day. In any case, as it is but reasonable to suppose the drift deposits on the higher slopes of the valley to be at least coeval with those at the bottom, even if not of greater antiquity, the mammalian remains of the lower deposits become of extreme importance, as a means of ascertaining the age of those at a higher level, from which precisely similar remains may be absent. This is, however, a purely geological question, into which I need not at present enter.
Mr. Prestwich, in the able Memoir upon this subject which he has communicated to the Royal Society, has gone so fully into the geological features of this part of the valley of the Somme, that any further details are needless, and I shall therefore content myself with this very general sketch of the position of the drift at Abbeville and Amiens, and refer those who desire further information to
