regarded merely as the characteristic fossils of certain river-valley gravels, without reference to the condition of either previous to their being brought together. But although the conditions of either deposit can hardly fail to throw light upon the history of the other, each has undoubtedly a history and (geologically) a date of its own; the implements, although in the gravel, are not of it, except in a certain limited sense. The one is the product of human skill, the other the result of natural causes; and it is essential to consider them separately, as well as in their connexion with each other.
When first observed, the implements had always been found in the immediate neighbourhood of river-channels, and assuming (as it seems usually to have been assumed) that they had been carried from the places in which they were made, it was reasonable to ascribe their transport to those rivers; but this was but a presumption which, however reasonable, was liable to be rebutted. Because certain objects are found in or near the banks of rivers, it by no means follows that they must of necessity have been carried thither by the rivers; they may have been deposited by other means, and possibly even before the rivers had an existence, and there seems good reason for believing that as regards many, or indeed most, of these flint implements this may have been the case.
At the commencement of the Quaternary epoch, when, by the retiring of the sea, or the elevation of its bed, the Cretaceous and Tertiary strata became dry land, it cannot be doubted that the surface, in many places, was, as it still remains, strewn, especially in valleys and hollows, with fragments of various rocks—the wreck and ruin of beds which had been broken up and dispersed. Of these a large proportion would consist of nodules of flint which had been washed out of the upper chalk-beds, or from which the chalk had been removed by decomposition. Abundant materials would thus be provided for the makers of implements and weapons, and the fol- lowers of this primitive industry would naturally resort to those spots on which the best material was to be found. The condition in which we find them is quite consistent with the belief that the stone from which the implements were formed had previously been long exposed upon the surface. At one time, therefore, the raw material and the manufactured were alike lying upon the surface, and after some interval of unknown but probably very extended duration, both were alike overwhelmed by those masses of sand and gravel beneath which we now see them. This interval doubtless involved important changes, including perhaps the obliteration of ancient river-channels and the formation of new ones.
If, as has been sometimes supposed, the implements were carried about by river-floods, or by deluges, whether marine or of fresh water, we should expect to find them confusedly intermingled with the sands and gravels, and they would be strewn continuously along the whole course of the valleys. This, however, seems not to be the case; for although the gravel-beds are continuous (frequently for several miles), the implements hitherto have been found only at detached spots, often far apart, and which were probably visited on
