THE MAMMOTH CAVE. 45 



no existence in this subterranean world. In 

 fact, there is an eternal sameness here, which is 

 without a parallel. 



In many parts of the Cave, time itself is not 

 an element of change; for where there is no 

 variation of the temperature, no water, and no 

 light, the three great forces of geological trans- 

 formation cease to operate. 



The atmosphere of the Cave, contrary to 

 what might be generally supposed, is remark- 

 ably pure and wholesome. 



The proportions of oxygen and nitrogen bear 

 the same relation to each other in the Mam- 

 moth Cave that they do in the external air. 

 The proportion of carbonic acid gas is less than 

 that observed in the atmosphere in the sur- 

 rounding country, upon an average of many 

 observations. This noxious gas is one of the 

 necessary constituents of vegetable existence ; 

 and, as there is no vegetable life within the 

 Cave, its comparative absence is a natural in- 

 ference. 



In the dry parts of the Cave the proportion 

 of carbonic acid is said to be about 2 to 10,000 

 of air ; in the vicinity of the rivers, something 

 less. Not a trace of ammonia can be detected 

 in those parts of the Cave not commonly visited. 



