separation of Britain from the continent. Under any circumstances its presence seems to indicate that the volume of the rivers was probably in excess of what it is at the present time. But whatever may have been the degree of winter cold, or the amount of the snow and rainfall, the one was not so extreme as to prevent there being an abundance of animal life, nor the other so great as to interfere with the growth of a sufficient supply of vegetable food on which it might subsist.
It has, indeed, been supposed by some that the remains of the early mammals occurring in the gravels are derived from older beds, and that their presence in association with flint implements no more proves the contemporaneity of the men who made those implements with the old Quaternary fauna, than their association with Chalk fossils proves that mankind were originally inhabitants of the bed of the Cretaceous ocean. Did the gravels only occur at such levels as are within reach of existing streams, there might be some reason in such a view, which is, moreover, in certain cases and within certain limits, probably correct. For we have seen how in the course of the excavation of a valley, the beds deposited at one time are liable to be disturbed at another, and re-deposited in a fresh place; which could hardly happen without an admixture of fresh materials, some probably of a more recent date. In the process of transport, however, not only the implements but the still softer bones are liable to wear and abrasion of the angles, and it is impossible to conceive that, assuming the Quaternary fauna to have disappeared from this region before the valleys were excavated, and the implement-bearing beds deposited, their bones could still exist in such numbers, and so often in an unrolled condition in the low-level beds.
Had this older fauna disappeared, it is evident that man could not have subsisted here alone, unaccompanied by other animals to furnish him with food; and if these animals belonged to the later or "prehistoric" fauna, where, as Sir John Lubbock pertinently asks, are their bones? If, however, we acknowledge that the pleistocene mammals still occupied this country at the time of the low-level beds being formed, and if we find their remains also in those at a high level, and at all intermediate heights, it is evident that they must have persisted here during the whole period of the excavation of the valleys; while, if we find also flint implements in an unrolled and unworn condition at all heights, it is evident that those who made them must also have been co-occu-
