206 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



volcanic magmas. The great majority of caves occur in lime- 

 stone, dolomite, or gypsum deposits, and owe their origin 

 primarily to the solvent agency of the water circulating through 

 the ground. Water as it passes down rock-fissures attacks the 

 sides of the rock and widens its own channel, the solvent 

 action of the water being greater when it is surcharged with 

 carbonic acid. Larger water-courses find their way into the 

 widened fissures and may erode complicated systems of tunnels 

 and grottoes like those in Carniola, where the subterranean 

 streams act both chemically and mechanically on the neigh- 

 bouring rock. The streams partially dissolve the material, 

 partially carry it away in suspension, or leave a finely-ground, 

 insoluble deposit on the floor of the cave known as "red 

 earth." 



The caverns may be further enlarged by collapse of the roof 

 from time to time. Frequently surface-material, or organic 

 remains imbedded in the deposits above, are thus introduced 

 into limestone caverns. A stream or river-channel eroded in a 

 limestone bed may be intercepted by the occurrence of clefts 

 and swallow-holes, and the superficial stream may thus be 

 guided into the system of subterranean intricacies which had 

 been previously excavated by the chemical action of under- 

 ground water. 



Many caverns were undoubtedly used by the mammals of 

 the diluvial period as shelter-places, just as they were after- 

 wards used by primaeval man. Often, however, the remains of 

 mammals that are found imbedded in the soft clay, sand, or 

 loam have been subsequently swept into the caves from the 

 surface in consequence of roof collapse. During the latter half 

 of the nineteenth century it has been a matter of controversy 

 among the authorities on cave remains whether man was or 

 was not a contemporary of the cave-bear, the mammoth, the 

 woolly-haired rhinoceros, and other extinct mammals in Europe. 

 The newest contributions to the literature of ossiferous caves 

 deal more with their topography, physiography, and acces- 

 sibility. The year 1894 was marked by the publication of two 

 pioneer works in this particular aspect of the study of caves, 

 the one by the Austrian writer, Franz Kraus, the other by the 

 French writer, E. A. Martel. 



The purely mechanical activity of running water is expressed 

 in the removal and transportation of loosened fragments of 

 rock (ablation), in the grinding action of the transported 



