That forgery of drift implements has been practised latterly, especially by the French workmen, is indisputable, but this need not affect the question. The facts connected with their discovery had been on record for nearly a century and a half before their significance was perceived; and specimens lay unheeded in the British Museum and in the collection of the Society of Antiquaries of London, with their human workmanship undisputed, so long as their origin was ascribed to Celtic art.[13] In reality the explorers of the drift have been perplexed by the very abundance of the traces of art which it discloses. Dr. Rigollot states that in the pits of St. Acheul alone, between August and December 1854, upwards of four hundred specimens were obtained. The lowest estimate of the number recovered in the valley of the Somme is 3000; but this is exclusive of the more dubious flint-flakes, styled knives, estimated by Sir Charles Lyell at many thousands more.[14] In England flint implements of the same peculiar type have already rewarded research in many localities; so that Mr. Evans justly remarks: “The number found is almost beyond belief.”[15] Some reasons tending to account for their accumulation in such localities are discussed in the following chapter, in the light of analogous discoveries in the New World. But while it is no longer possible to question their artificial origin, and the consequent evidence of the presence of man in those localities where they abound, the haunts of those primeval hunters and fishers were the river-valleys of an elder world; and any attempt at estimating the time required for changes of climate, extinction of fauna, the succession of races implied in the phases of palæolithic and neolithic arts, and the gradual introduction and development of metallurgy, involves so many unknown quantities, that at present it must suffice to recognise as no longer disputable that the whole historic period of Northern Europe is insignificant when compared with the time requisite to account for all the phenomena in question. The relative chronology of the French drift is: _1st_, superficially, tombs and other remains of the Roman period, scarcely perceptibly affected in their geological relations by nearly the whole interval of the Christian era; _2d_, in the alluvium, seemingly imbedded by natural accumulation, at an average depth of 15 feet, remains of a European stone-period, corresponding to those of the recently discovered pfahlbauten, or lacustrine villages of the Swiss Lakes; and, _3d_, the tool-bearing gravel, imbedding works of the Flint-Folk, wrought seemingly when the rivers were but beginning the work of excavating the valleys which give their present contour to the landscapes of France and England.