Ch. X.] ORIGIN OF THE STALACTITE. 123 



creasing in volume after rainy seasons, betray their dependence for a 

 supply of -water on atmospheric sources. The rain derives some of 

 its carbonic acid from the air, but much more from the decay of 

 vegetable matter in the soil which it percolates, and by the excess 

 of this acid, limestone is dissolved, and the water becomes charged 

 with carbonate of lime. The mass of solid matter silently and un- 

 ceasingly subtracted in this way from the rocks in every century is 

 considerable, and must in the course of thousands of years be so vast 

 that the space it once occupied may well be expressed by a long suite 

 of caverns. The varying size and shape of these w T ill be determined 

 by innumerable local accidents, such as the direction of pre-existing 

 rents and faults, or the unequal purity and consequent solubility of 

 the limestone in different strata, or in. different parts of the same 

 stratum. 



If there be a series of convulsions and movements of upheaval and 

 depression, during which old valleys are gradually deepened and 

 widened, or new ones formed, accompanied by the rending of rocks 

 in many places, the surface drainage may in time be so altered that 

 streams sweeping along angular and rounded stones may break into 

 cavities once having no such connexion with the surface. Such 

 streams may introduce fine mud, or angular and rounded pebbles and 

 land-shells, with portions of skeletons of various quadrupeds, or of 

 man, together with fragments of works of art, and fill up a large part 

 of the underground rents, galleries, and chambers with heterogeneous 

 materials. The whole of these may sometimes be united into solid 

 breccias and conglomerates by stalactitic infiltrations. 



In the descriptions given of violent earthquakes we read of the 

 sudden appearance of new fissures several feet wide, often of great 

 depth, and some of which remain permanently open. Wild animals 

 chased by beasts of prey fall into such natural pit-falls ; the pursued 

 and the pursuer perishing together. Their bones, during the slow 

 decay of the carcase, may be carried separately into subterranean 

 vaults, or many of them still bound together by ligaments ; even 

 entire skeletons may sometimes be washed into caves and be there 

 preserved. 



The quarrying away of large masses of Carboniferous and Devo- 

 nian limestone, near Liege, in Belgium, has afforded the geologist 

 magnificent sections of some of these caverns, and the former com- 

 munication of cavities in the interior of the rocks with the old sur- 

 face of the country by means of vertical or oblique fissures, has been 

 demonstrated in places where it would not otherwise have been 

 suspected, so completely have the upper extremities of these fissures 

 been concealed by superficial drift, while their lower ends, which 

 extended into the roofs of the caves, are masked by stalactitic incrus- 

 tations. 



The origin of the stalactite is thus explained by the eminent 

 chemist Liebwy. On the surface of Franconia, where the limestone 



