and in several distinct cases, of objects of human industry with the remains of this extinct fauna, in which so many of the animals characteristic of the existing fauna are "conspicuous by their absence," in undisturbed beds, and for the most part beneath a thick coating of stalagmite, leads of necessity to this conclusion. This becomes, if possible, more secure when the results of the exploration of other caves on the Continent of Western Europe are taken into account. How long a period may have intervened between the extinction, or migration, of these animals and the present time is, of course, another question; but such changes in the animal world as had already taken place at least three thousand years ago, do not appear to occur either suddenly or even with great rapidity; and, leaving the stalagmite out of consideration, we have already seen that in some instances the physical configuration of the country in the immediate neighbourhood of the caves seems to have been greatly changed since the period of their infilling.
These changes are perhaps more conclusively illustrated in the case of the old river deposits, in which the remains of the same extinct fauna as that of the caves occur associated with implements manufactured by the hand of man, to which we must now direct our attention.
