THE MAMMOTH CAVE. 51 
never entirely destitute of nitrifiable matter. 
The nitric acid which enters into its composition 
may, in some measure, be defived from the at- 
mosphere. The kind of nitre that is found in 
the Cave.is the nitrate of lime, which, when re- 
acted upon by the carbonate of potash, is trans- 
formed into the nitrate of potash, or common 
saltpetre. This was the course pursued by the 
saltpetre miners when that substance was manu- 
factured in the Cave in 1812-14. The nitrate of 
lime is found in the dryer parts of the Cave, 
but is not discoverable till the earth which con- 
tains it is lixiviated. 
“The mechanical agencies concerned in the 
excavation of the Mammoth Cave are trifling 
when compared with the chemical. They are 
instanced in the transportation of gravel, sand, 
and clay from one part of the Cave to another, 
and in the abraded appearances presented by 
the rock composing certain avenues. Thus, it is 
possible to tell the direction in which the water 
ran in most of the’avenues, and the rapidity of 
its motion, by observing the points at which 
gravel, sand, and clay are deposited, and the 
order in which they come. For example, the 
points at which gravel is deposited indicate a 
rapid current; where sand is found, the move- 
