CHAP. iv. STALACTITE IN CAVES. 71 



angular pieces of limestone and shale, besides sand and mud, 

 together with bones, chiefly of the cave-bear. Connected with 

 this main duct, which is from one to two feet in width, are 

 several minor ones, each from one to three inches wide, also 

 extending to the upper country or table-land, and choked up 

 with similar materials. They are inclined at angles of 30 

 and 40, their walls being generally coated with stalactite, 

 pieces of which have here and there been broken off and 

 mingled with the contents of the rents, thus helping to 

 explain why we so often meet with detached pieces of that 

 substance in the mud and breccia of the Belgian caves. It is 

 not easy to conceive that a solid horizontal floor of hard 

 stalagmite should, after its formation, be broken up by run 

 ning water ; but when the walls of steep and tortuous rents, 

 serving as feeders to the principal fissures and to inferior 

 vaults and galleries are encrusted with stalagmite, some of 

 the incrustation may readily be torn up when heavy fragments 

 of rock are hurried by a flood through passages inclined at 

 angles of 30 or 40. 



The decay and decomposition of the fossil bones seem to 

 have been arrested in most of the caves by a constant sup 

 ply of water charged with carbonate of lime, which dripped 

 from the roofs while the caves were becoming gradually filled 

 up. By similar agency the mud, sand, and pebbles were 

 usually consolidated. 



The following explanation of this phenomenon has been 

 suggested by the eminent chemist Liebig. On the surface of 

 Franconia, where the limestone abounds in caverns, is a 

 fertile soil in which vegetable matter is continually decaying. 

 This mould or humus, being acted on by moisture and air, 

 evolves carbonic acid, which is dissolved by rain. The rain 

 water, thus impregnated, permeates the porous limestone, 

 dissolves a portion of it, and afterwards, when the excess of 

 carbonic acid evaporates in the caverns, parts with the 



