living creatures being proved to demonstration by other evidence than that of their actual remains (for those have never been discovered) in some of the chelonians, saurians, and batrachians of the new red-sandstone and other formations. Footprints of these animals, or ichnolites, are found in abundance, but the bones of the various species which have left these records of themselves "upon the rock for ever" have still to be found. Dr. Hitchcock enumerates no less than fifty-three species from the Jurassic, liassic, or triassic beds of the valley of the Connecticut, of which the existence has been determined by their foot-prints alone.
In the case of the Pfahlbauten lately discovered in the lakes of Switzerland and elsewhere, though implements of all kinds have been found in great abundance, yet human remains are of excessively rare occurrence. It is, however, almost beyond the bounds of probability to suppose that the flint implements from the drift are relics of a race of men who in like manner placed their dwellings upon artificial islands, though in far more remote antiquity than those who constructed the Pfahlbauten.
The question of the contemporaneous existence of man with the mammoth and other animals of the same age is of great importance, as the best if not the only means of fixing some approximate date to these flint implements, though from the nature of all geological evidence, and the possibility of the same results upon the earth's surface being attained in a greater or less period of time according to the greater or less energy of the agent producing them, any estimate of their age will always be liable to objections. But if the co-existence of man with this now extinct fauna be proved, then the basis of induction is enormously extended for arriving at some estimate of the antiquity of man : for the condition and probable age of drift-beds containing the mammalian remains alone, and unassociated with human relics, will then fairly enter as elements into the calculation. It is, however, at present premature to say more upon this point.
I will only add that the presence, in the drift of the valley of the Somme, of the Cyrena consobrina, or trigonula, a bivalve no longer European, though still found in the waters of the Nile, and which is frequently associated with elephant remains in the drift of our valleys, is also of significance in considering the question of the age of these implement-bearing beds.
If we are compelled to leave the mammalian remains out of the question, it seems to me by no means easy, in the present state of our knowledge, to assign even an approximate age to these deposits. Ranging as they do all the way up the slopes of the valley of the Somme near Amiens and Abbeville, there is great difficulty in arriving at any exact conception of the conditions under which they were
