72 ENGULFED RIVERS NEAR LifiGE. chap. iv. 



calcareous matter and forms stalactite. So long as water 

 flows, even occasionally, through a suite of caverns, no layer 

 of pure stalagmite can be produced; hence the formation of 

 such a layer is generally an event posterior in date to the 

 cessation of the old system of drainage, an event which might 

 be brought about by an earthquake causing new fissures, or 

 b}^ the river wearing its way down to a lower level, and 

 thenceforth running in a new channel. 



In all the subterranean cavities, more than foi'ty in num- 

 ber, explored by Schmerling, he only observed one cave, 

 namely, that of Chokier, wdiere there were two regular layers 

 of stalagmite, divided by fossiliferous cave-mud. In this 

 instance, we may suppose that the stream, after flowing for 

 a long period at one level, cut its way down to an inferior 

 suite of caverns, and, flowing through them for centuries, 

 choked them up with debris; after which it rose once more 

 to its original higher level: just as in the mountain-limestone 

 district of Yorkshire some rivers, habitually absoi'bed 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 Avas at some former 

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

 by the fluviatile gravel still contained iu it. 



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

 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-sjH'ing where they 

 issue again; so that they must be slowly filling up cavities 

 in the interior with mud, sand, pebbles, snail-shells, and 



