LTE TORIGINFOR NITRATES IN CAVERN EARTHS 
Mucu interest has been taken in the great caverns of Vir- 
ginia, Kentucky, and Indiana by tourists, and considerable 
popular literature has been published, especially in description 
of Mammoth, Luray, and Wyandot caves. In this literature 
rather frequent allusion is made to the ‘“‘nitrates’”’ in cavern 
earths, and occasionally a theory is advanced to explain their 
origin. Popular interest is awakened in this question by the large 
amount of ‘‘saltpeter” known to have been taken from Mam- 
moth Cave during the war of 1812, and from similar caverns in 
Alabama and Georgia during the Civil War for the manufacture 
of gunpowder. 
The origin of this supply of nitrates is commonly ascribed to 
animal remains, and especially to the excrement of bats. In 
Mammoth Cave, however, the cavern earth was worked for 
nitrate for a distance of over five miles from the only open- 
ing known which leads to the surface, while bats as a rule 
go but a short distance from the entrance of the cavern. Again, 
on account of the antiseptic character of the atmosphere of 
caves, we would expect, in case the nitrate was derived from 
bats, to find some animal remains, in the form of their dried 
bodies, their bones, or their excrement; but organic matter of 
any kind is rare in cavern earths. The hypothesis ascribing 
such an origin to the vast stores of nitrates taken from Mam- 
moth and other caverns seems, therefore, inadequate. 
Caves in limestone regions are due to the solvent action of 
water containing carbon dioxide. This process must have been 
very slow and in most cases unaided by mechanical erosion, thus 
leaving the insoluble portion of the limestone as a deposit on 
the floor of the cavern. This residue is known as cavern 
earth. 
From the mode of formation of caves, it is evident that this 
residue must have been washed perfectly free from all salts. 
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