Schmerling examined more than forty caves in the Valley of the Meuse and its tributaries. The access to some of these caves was so difficult that in order to reach them it was necessary for the explorer to let himself down by a cord, and then to crawl flat on his face through narrow galleries, so as to make his way into the great chambers; there he was obliged to remain for hours, and sometimes whole days, standing up to his knees in mud, with water dripping from the walls upon his head, while overlooking the workmen breaking up with their pick-axes the layer of stalagmite, so as to bring to light the bone earth--the records on which are inscribed the palpable evidences of the high antiquity of man. Schmerling was compelled to accomplish a perilous expedition of this kind in his visit to the cave of Engis, which has become celebrated by the two human skulls found there by him. Nearly all the caves in the province of Liége contain scattered bones of the great bear, the cave-hyæna, the mammoth, and the rhinoceros, intermixed with those of species which are still living, such as the wolf, the wild boar, the roe, the beaver, the porcupine, &c. Several of them contained human bones, likewise much scattered and rubbed; they were found in all positions, and at every elevation, sometimes above and sometimes below the above-mentioned animal remains; from this it may be concluded that these caves had been filled with running water, which drifted in all kinds of _débris_. None of them, however, contained any gnawed bones, or the fossil excrement of any animal species, which puts an end to the hypothesis that these caves had been used as dens by wild beasts. Here and there bones were found belonging to the same skeleton, which were in perfect preservation, and lying in their natural juxtaposition; they were probably drifted into the cave by gently flowing water, while still covered with their flesh, and no movement of the ground had since separated them. But no complete skeleton has as yet been discovered, even among the smaller species of mammiferous animals, the disjunction of which is generally less complete. In almost all the caves Schmerling met with flint implements chipped into the form of hatchets and knives, and he calls attention to the fact "that none of them could have been introduced into the caves at a posterior epoch, as they were found in the same position as the animal remains which accompanied them." In the cave of Clokier, about two and a half miles from Liége, he picked up a polished bone in the shape of a needle, having an eye pierced at the base; in the cave of Engis he likewise found a carved bone, and also some worked flints.