THE MAMMOTH CAVE. 49 



way the process of excavation was conducted, 

 until communications were established with run- 

 ning water, Jby which the mechanical agency of 

 that fluid was made to assist the chemical. The 

 little niches and recesses which are observed in 

 various parts of the Cave, and which seem to 

 have been chiseled out and 'polished by artificial 

 means, were formed in this manner ; for when 

 these points are closely examined, a crevice will 

 be observed at the top or back of them, through 

 which water issued at the time of their forma- 

 tion, but which has been partially closed by crys- 

 tals of carbonate of lime or gypsum. At the 

 time these niches were forming, water flowed 

 through the avenues in which they are found. 

 Examples of the action we have been describing 

 may be seen in Sparks' Avenue, leading to the 

 Mammoth Dome. 



"The grooves which are observed in rock over 

 which water is or has been flowing are also 

 formed by the solvent action of water contain- 

 ing carbonic acid ; for in all such instances the 

 water has no solid matter in suspension. Ex-^ 

 amples of this kind of action may be seen in 

 operation in Mammoth and Gorin's Domes ; and 

 evidences of its former action may be observed 

 in Lucy's Dome. What are termed the ' pigeon- 



5 



