to be obliterated by the agencies of denudation. The older fluviatile deposits are manifestly those on the higher slopes, and their antiquity may be estimated by contemplating how long the particular river has taken to excavate the whole breadth of the valley down to its present bed. But this argument applies only to valleys that have unquestionably been so excavated. There are other valleys, such, for instance, as the lower portion of the Thames, which probably commenced to be excavated long before the advent of the Great Ice Age, and in these cases the washed-down materials might have been deposited in smooth water at an earlier period, and consequently their lowest strata would be the oldest. Examples of fluviatile deposits presenting this character are to be met with at Erith, Crayford, Ilford, and Gray's Thurrock, which, being outside the domain of the mer de glace, might, as was suggested by Dr Falconer, have been pre-glacial (Quart. Journ. Geo. Soc., xiv., p. 83).
G. de Mortillet claims that the deposits at Chelles (Seine-et-Marne), although only 8 metres above the present bed of the Marne, belong to the oldest Quaternary period (Le Préhistoric, 3rd edition, p. 499). Also in the valley of the Somme the same kind of implements and fauna are found, both in the upper and lower gravels. In the vicinity of Abbeville, as at Menchcourt and Mautort, the flint-bearing deposits are only 12 to 15 metres above the sea; at Moulin Quignon, 30 to 32 metres; and at Mareuil, 35 metres (Ibid., p. 563). Again, the Saint Acheul deposits, which have yielded an enormous quantity of flint implements of the coup-de-poing type, are 46 metres above the sea, and 26 metres above the river Somme. On the other hand, at Saint Roch and Montières, a mass of stratified gravels, only slightly elevated above the alluvial plain of the Somme, have yielded flint knives, tusks of hippopotamus, and an elephant's molar (identified by Dr Falconer as that of Elephas antiquus). (Antiquity of Man, p. 134.)
The stone implements from these widely separated localities have a strong resemblance to each other, and are readily distinguished from the more recent productions of Neolithic races. They may be classified under three types, viz.—a large pointed weapon, an oval-shaped instrument presenting a
