In many natural excavations, both in the old and the new world, mostly in the secondary limestone strata, the result of fracture of the earth's crust, of chemical action of acid waters, of erosion by powerful currents, and of slow disintegration by the elements, have been found the bones of extinct post-tertiary mammals, mingled sometimes with the works and bones of man. The most celebrated of these caves in Europe are near Kirkdale, England, 25 m. N. N. E. of York, fully explored by Dr. Buckland; at Bristol; Kent's cave, near Torquay; in the valley of the Dor-dogne, France, especially those of Moustier and Cro-Magnon, described by Christy and Lartet; and at Gailenreuth in Bavaria. There are many others in Belgium, near Liege; in Sicily, at Gibraltar, in Mexico, in several parts of the United States, and in Brazil. These caves may consist of several chambers at different levels, and show on their walls the erosive action of water, and at the bottom and top various deposits of stalagmite and stalactite from the infiltration of lime-bearing waters. Under this lime floor ancient bones have been discovered, mingled, both as to size and species, in the most indiscriminate manner; they are often rolled, as if from the action of floods, sometimes fissured, but often unchanged.

The bones most abundantly found are those of the great car-nivora of the quaternary period, the bear, hyaena, lion, etc.; with those of the great pachyderms, as the mammoth and the rhinoceros; and of many herbivora and rodents. The English caves were mostly occupied by hyaenas, while those of the continent were chiefly caves of bears. At Kirkdale Dr. Buckland found the remains of at least 75 hyaenas, of the extinct or cave species, mixed with those of the extinct pachyderms, carnivo-ra, ruminants, and rodents; from which he believed that the hyaenas dragged the carcasses there and fed upon them, cracking their bones with the marks of their teeth peculiar to this animal, and leaving behind them their fossil faeces. In Gailenreuth have been found the bones of the cave bear, of at least 800 individuals. Caves containing bones of post-tertiary mammals are rare in North America; but in those of Brazil, explored by Dr. Lund, remains of gigantic rodents, pachyderms, and edentates were found, especially of the extinct mega-therioids. The bones found in the caverns have a uniform appearance over large areas of country, and evidently belong to the geological period intermediate between the tertiary and the present epochs.

Though some of these caves owe their remains to the fact that they were the dens of hyaenas and bears, or were the* retreats of sick and wounded animals, there can be no doubt that most of their contents have been brought to the caves by temporary torrents of water independent of marine action; the bones could not have come from a great distance, as they belong to the then existing animals of the region, and are the same as those met with in external transported sediments. Remains of man and of his works have been found mingled with the bones of the above post-tertiary extinct mammals in the caves of Europe, and especially of southern France by Messrs. Christy and Lartet, seeming to place it beyond doubt that man began his existence at this remote epoch. The implements found are invariably those of the early stone age, and the bones never those of the domestic animals afterward subjugated by man. - See ArchAEology, and the works of Dr. Buckland, Constant-Prevost, Lyell, and the Reliquim Aquitanicm of Christy and Lartet.