THE ANTIQUITY OF MAN. 121 



the Mountain limestone district of Yorkshire some rivers, hab- 

 itually absorbed by a " swallow hole," are occasionally unable to 

 discharge all their water through it ; in which case they rise and 

 rush through a higher subterranean passage, which was at some 

 former period in the regular line of drainage, as is often attested 

 by the fiuviatile gravel still contained in it. 



" There are now in the basin of the Meuse, not far from Lidge, 

 several examples of engulfed brooks and rivers : some of them, 

 like that of St. Hadelin, east of Chaudefontaine, which reappears 

 after an underground course of a mile or two ; others, like the 

 Vesdre, which is lost near Goffontaine, and after a time re- 

 emerges ; some, again, like the torrent near Magnee, which, 

 after entering a cave, never again comes to the day. In the 

 season of floods such streams are turbid at their entrance, but 

 clear as a mountain-spring where they issue again ; so that they 

 must be slowly filling up cavities in the interior with mud, sand, 

 pebbles, snail-shells, and the bones of animals which may be 

 carried away during floods. 



" The manner in which some of the large thigh and shank 

 bones of the rhinoceros and other pachyderms are rounded, 

 while some of the smaller bones of the same creatures, and of 

 the hyeena, bear, and horse, are reduced to pebbles, shows that 

 they were often transported for some distance in the channels of 

 torrents, before they found a resting-place. 



" When we desire to reason or speculate on the probable anti- 

 quity of human bones found fossil in such situations as the 

 caverns near Liege, there are two classes of evidence to which 

 we may appeal for our guidance. First, considerations of the 

 time required to allow of many species of carnivorous and herb- 

 ivorous animals, which flourished in the cave period, becoming 

 first scarce, and then so entirely extinct as we have seen that 

 they had become before the era of the Danish peat and Swiss 

 lake dwellings ; secondly, the great number of centuries necessary 

 for the conversion of the physical geography of the Liege 

 district from its ancient to its present configuration ; so many 

 old underground channels, through which brooks and rivers 

 flowed in the cave period, being now laid dry and choked up. 



" The great alterations which have taken place in the shape, of 

 the valley of the Meuse and some of its tributaries, are often 

 demonstrated by the abrupt manner in which the mouths of 

 fossiliferous caverns open in the face of perpendicular precipices? 



