NITRATE DEPOSITS 139 



ciently large to be of commercial value have been removed for use in the 

 manufacture of fertilizers. Samples taken from some of the caves where 

 the guano has undergone decomposition have been analyzed by the writer 

 and found to run as high as 75 per cent, of potassium nitrate. Other 

 samples have been examined which consisted of very pure elongated 

 white crystals of calcium nitrate, and which had been taken from crevices 

 in a cave. When placed in a humid atmosphere these soon melt in the 

 moisture which they absorb from the air, but may be kept indefinitely in 

 a desiccator. 



"While guano is usually considered to be the source of the nitrates 

 found in caves, other theories are occasionally advanced to explain the 

 origin of some of the deposits. Thus Hess 4 considers that guano could 

 not be the source of the large store of nitrates which have been taken from 

 the Mammouth Cave at distances of over five miles from any opening 

 which leads to the surface, since bats go, as a rule, but a short distance 

 from the entrance to the cave. Moreover, in the bottom of many caves 

 there are to be found earths from which nitrates can be extracted, but 

 which do not contain any animal remains as would be expected if the 

 nitrates were derived from guano. To explain the occurrence of nitrates 

 in caves of this kind, the view is put forward that the nitrates do not 

 come from guano, but originate in the surface soil above the eaves 

 through the oxidation of organic matter by nitrifying bacteria. As the 

 soil in limestone regions is usually loose and porous, the nitrates are con- 

 sidered to be carried down by percolating water and deposited in the 

 floor of the caves. Air currents in and out of the caves would remove the 

 water by evaporation, and the nitrates would consequently remain and 

 would not be washed away so long as the inflow of water did not exceed 

 that lost by evaporation. 



A similar explanation is given for the origin of nitrate deposits under 

 overhanging cliffs. Thus, water carrying nitrates dissolved from the soil 

 percolates through the earth and a portion finally oozes out at the surface 

 underneath where it evaporates and leaves the nitrates behind. Being 

 protected from the rain in this position, the nitrates in this way are en- 

 abled to accumulate. 



The theory advanced by Hess to account for the origin of nitrates in 

 caves has not met with universal acceptance. Nichols 5 has argued that 

 bats do frequent remote parts of caves; that cave earth does contain 

 organic matter; and that the proportion of phosphates to nitrates in the 

 cave earth is much too great to be accounted for on the supposition that 

 they were brought in by percolation from the surface soil. It is con- 

 sidered that while small deposits may be found in the way described by 

 Hess, the great bulk of the nitrates that are found in caves results from 



iJour. Geol., 8, 129, 1900. 

 s Jour. Geol., 9, 236, 1901. 



