NITRA TES IN CA VE EARTHS 24 T 



a very small quantity of nitrate from the surface may be mixed 

 with the much larger quantity leached from the bat guano above. 



There are, however, better indicators than the carbonate or 

 sulphate of lime. These are chlorine and the phosphates. The 

 chlorine has not been given in a sufficient number of Mr. Hess' 

 analyses to be available in this discussion, but the data regarding 

 the phosphates are more complete. Inasmuch as phosphates 

 "revert" or become insoluble, the total phosphate, not the 

 soluble, must be considered. Mr. Hess finds only traces of 

 phosphate in the drip or in the soluble extract from the soils of 

 the surface, while the quantity of phosphoric acid in the guano 

 and the niter earth is approximately equal and is very consider- 

 able, 2.62 per cent, and 2.10 per cent, respectively. While the 

 approximation to equivalence is doubtless accidental, yet it is 

 undeniable that there is in cave earth much more phosphate in 

 proportion to the niter, alkalies, etc., than the drip water could 

 bring in. An abundance of phosphate is found in soluble form 

 in the bat guano. Mr. Hess regards this excess of phosphate 

 as a concentration in the residual soil, of the calcium phosphate 

 of the limestone on account of its insolubility. But it appears 

 from the figures anven bv Penrose and others 1 that the percent- 

 age of phosphate of lime in limestone and in its residual clay is 

 approximately the same, the larger part of the phosphate going 

 into solution with the carbonate of lime. Penrose selected clay 

 from a hollow in the limestone where it was overlain by 15 feet 

 of similar clay and a chert cap, and compared it with the lime- 

 stone. He found phosphoric acid in the limestone 3.02 per cent, 

 and in the clay 2.53 per cent. It is not contended that under 

 exceptional circumstances phosphates may not be concentrated 

 as a residuum after solution of limestone, as Safford claims for 

 those of Tennessee, but it is contended that such concentration, 

 if it occur at all, is very unusual, and furthermore that it does 

 not occur in the cave regions of Kentucky and Indiana. 



Although no determinations of phosphoric acid in limestone 

 and its residual soil can be found for the immediate vicinity of 



1 Merrill : Rocks, Rock Weathering, and Soils, p. 23?.. 



