ORIGIN OF NITRATES IN CAVERN EARTHS 133 
shown in the preceding analyses, points forcibly to the probable 
origin of these salts in cavern earths. 
It was found from analyses of many samples taken from 
Saltpeter Cave, Indiana, so as to cover practically the whole floor 
of the cavern from the opening to the end, that nitrates were 
distributed throughout the entire extent of the dry chamber, 
irrespective of distance from the entrance. Since bats do not 
go far inward from the entrance of caves, and since we find no 
organic matter in cave earth to indicate an animal origin for the 
nitrate contained therein, it is evident that we cannot regard the 
nitrates in cavern earths as originating from bat guano. 
The conclusion reached from this investigation is that the 
nitrates in caves were brought in by water percolating through 
the soils above the caves and were deposited on the floors. Cur- 
rents of air in and out of the caverns removed the water, and the 
various salts it previously held in solution were left as an inherit- 
ance to the cave earth. A cavern acts, therefore, merely as a 
receptacle for stopping a portion of the surface drainage. This 
accumulation of salts occurs only in caverns where the inflow of 
surface water does not exceed in amount the water removed by 
evaporation. In wet caves the soluble salts are washed onward 
with the water bearing them and so are not deposited. 
Nitrates found under overhanging cliffs are of a, similar 
origin. Water bearing dissolved nitrates percolates through the 
soil and finally oozes out at the surface. The water evaporates 
and leaves behind an incrustation of its soluble materials. The 
nitrates thus formed under overhanging cliffs remained perma- 
nently stored there, being securely protected from rain. They 
served, along with the nitrates found in the caves of Alabama 
and Georgia, as a source of saltpeter used by the South during 
the Civil War for the manufacture of gunpowder. 
When vegetable matter is piled up and allowed to decay, an 
incrustation of potassium nitrate forms on the surface. The 
vegetable or organic nitrogen has been oxidized to nitric acid. 
The nitric acid combines with the potash of the plant to form 
potassium nitrate. The water evaporates from the pile and 
