In many cases the bones found in ossiferous caves must have been washed into them by currents of water, or else they may be the remains of animals that accidentally dropped in through holes in the roof; but there can be no doubt that frequently the caves in which the bones of extinct carniverous animals have been found, served as their dens while they were living. The abundance of bony dung associated with the remains of the hyena, as well as the great number of bones all belonging to one species which are frequently found congregated in the same cave, is strongly confirmatory of this opinion, no less than the circumstance that the walls of several ossiferous caves, when deprived of their stalactital covering, have been found smoothed or rounded off from the frequent ingress and egress of their former inhabitants as they squeezed themselves or dragged their prey through a narrow passage. Besides, the hyenas and bears of the present day frequently live in caves, thus justifying the inference that their extinct predecessors had the same habit. The antiquity of many of the animal remains found in caves is proved not only by their being dissimilar to existing species, but by the manner in which they are entombed. For ages they accumulated on the floor of the cave, often to a considerable depth, mixed with mud or sand or fragments of rock—then, when, from a change of level or some other cause, the cavern became uninhabited, a thick crust of stalagmite was slowly formed, and burying them all, as under solid stone, preserved them undisturbed, until some accident revealed their existence after a time the length of which escapes all calculation. The dim vista into the past appears still more shadowy in the case of the cavern discovered by Dr. Schmerling at Choquier about two leagues from Liège, where three distinct beds of stalagmite were found, and between each of them a mass of breccia and mud, mixed with quartz, pebbles, and in the three deposits the bones of extinct quadrupeds! Ossiferous caves have been found and examined in many parts of the world: in France, in Belgium, chiefly in the valleys of the Meuse and its tributaries; in Austria and Hungary, in Germany and England.