
Ea us e 
4 
356 DYNAMICAL GEOLOGY. [Boos IIL, 
and land-shells and land-animals fall into the holes, or the caverns 
are used as dens by beasts of prey, so that the remains of terrestrial 
animals are preserved under the stalagmite. Not unfrequently, 
caverns, once open and freely used as haunts of carnivora, have had 
their entrances closed by the fall of débris, as at d in Fig. 102, 

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Fie. 102.—Srction or a Limestone CAVERN WITH FALLEN-IN ROOF AND 
CONCEALED ENTRANCE (B.). 
where also the partial filling up of a cavern (aa) from the same 
cause 1s seen. Where the collapse of a cavern roof takes place 
below a watercourse the stream is engulfed, In this way brooks 
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Fic. 103.—Snorion or Tom OuANNEL or AN UNDERGROUND STREAM. 
and rivers suddenly disappear from the surface, and after a long sub- 
terranean course, issue again in a totally different surface area of 
river-drainage from that in which they took their rise, and sometimes 
