THE MAMMOTH CAVE. — 49 
way the process of excavation was conducted, 
until communications were established with run- 
ning water, by 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 tliese 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 
