such excavations that they have been found; which would not have been the case had their presence in the gravel been owing to their interment by human agency; for, supposing it possible that some unknown race of men had been seized with a desire to bury their implements at a depth of from ten to twenty feet below the surface, they would hardly have selected for this purpose the hardest and most impracticable soil in their neighbourhood, a gravel so hard and compact as to require the use of a pickaxe to move it.
In the cultivated soil and made ground above, and at much less depth from the surface, ground and polished instruments, evidently belonging to the so-called Stone period, have indeed been found; but this again only tends to prove that the shaped flints discovered at a much greater depth belonged to some other race of men, and inasmuch as they certainly are not the work of a subsequent people, we have here again a testimony that they must be referred to some antecedent race, which had perished perhaps ages before the Celtic occupation of the country. The similarity in form between the flint implements from the drift, and those found in the cave-deposits that I have previously mentioned, is also a circumstance well worthy of observation.
Again, many of the implements have a coating of carbonate of lime forming an adherent incrustation upon them: this, as M. Douchet has already remarked, is for these weapons what the patina is for bronze coins and statues, a proof of their antiquity. The incrustation occurs on all the flints in certain beds of the gravel, and is probably owing to the percolation of water among them, charged with calcareous matter derived from the chalky sands above, which it has gradually deposited upon the flints and pebbles. It has probably been a work of time, commencing soon after the formation of the beds, and possibly is still going on. If, therefore, the flint implements had been introduced into these beds at a subsequent date to the other flints and pebbles which are found with them, we might expect them to be either free from incrustation, or at all events with less calcareous matter upon them; neither of these appears, however, to be the case, but all the flints in these particular layers, whether worked or not, are similarly incrusted. The presence of the coating upon them also proves that the weapons were really extracted by the workmen from the beds in which they state them to have been found, and that they are not derived from the upper beds or surface soil.
Another similar proof is found in the discolouration of the surface of the implements. It is well known that flints become coloured, often to a considerable depth from their surface, by the infiltration of colouring matter from the matrix in which they have been lying, or from some molecular change, due probably to
