GROUND-WATER 39 



estimated that there are 200 miles of passageways large enough 

 for a man to get through in an area of 10 square miles about 

 Mammoth Cave. 



Water is constantly seeping into caves from all sides and from 

 the tops. This water has mineral matter in solution, some of which 

 is deposited in the caves, either in icicle-like columns (stalactites) 

 hanging from the roof, or on the floor of the cave (stalagmites}. The 

 stalactites, stalagmites, etc. (Figs. 2 and 3, PL XI, p. 33) are among 

 the most interesting features of caverns. 



Cavern life. Though cavern life is no part of the chemical 

 work of ground-water it may be mentioned here. Caverns do not 

 furnish the conditions favorable for most sorts of life, for mqst 

 plants and animals need light; yet there are several varities of 

 animals in them, some living in the water and some in the damp 

 air. Cave animals are so like those living above ground in the 

 same region, that they are thought to be the descendants of 

 animals which got into the caves from the surface. 



The animals in the caves show some peculiar features. In the 

 first place, they are less brightly colored than their relatives above 

 ground. This is probably because of the absence of sunlight, which 

 seems to have much to do with producing color in animals. In the 

 second place, the eyes of cave animals are poor, or sometimes want- 

 ing altogether. Thus among the crayfish, some have good eyes, 

 some have imperfect eyes, and some have none. From these and 

 other facts we may infer that the eyes of animals in dark caves tend 

 to disappear. A third peculiar feature of cavern animals is the good 

 development of their organs of touch, such as antennae. In the 

 darkness the sense of touch is much more useful than sight. 



In Europe, caverns were sometimes the homes of primitive man. 

 The evidence of this is that the bones of men, as well as tools of 

 various sorts made by them, are found in the caves. Here, too, 

 are found the bones of large animals which were killed for food or 

 fur, and taken to the caves. On the bones of such animals and on 

 pieces of slate or wood, there are sometimes drawings, and some of 

 these drawings are of animals which no longer live in the region 

 where the caves are. From this we infer that the people who lived 

 in the caves lived there a long time ago. 



