MINERAL NATURE OF SOILS 



361 



remarked sinee the subject was first broached by Humboldt 

 and Boussingault. According to Miintz and Maraeano, nitrates 

 occur in the soils of Venezuela, the valley of the Orinoco, and 

 other localities sometimes to the amount of 30% of their mass. 

 These nitrates they show to be due to the oxidation of organic 

 nitrogen through the agency of bacteria. They state that in 

 the caverns of the regions, a guano composed mainly of the 

 excreta of birds and bats, but admixed also with the dead bodies 

 of these and othei animals, has accumulated to the amount of 

 millions of cubic metres. Through the gradual nitrification of 

 this guano, and a combination of the nitrogen with the lime 

 of bones, or existing as a carbonate in the soil, a gradual transi- 

 tion is brought about wherever there is free access of air or 

 the temperature is sufiSciently high to stimulate the nitrifying 

 organisms to their fullest activity. There is thus a gradual 

 change in the character of the nitrogeneous combination from 

 the interior to the exterior portions of the cave, as shown in the 

 following : 



Analysis op Ba.t Guano 



Constituents 



Guano teom 

 Interior of 



Earth from 



THE Entrance 



Earth from 



SOME DiSTANCS 



FROM Entrance 



Organic nitrogen 



Nitrate of lime 



11.74% 

 0.00 



2.41 % 

 3.03 



0.80% 

 10.36 



These authorities would account for the presence of extensive 

 deposits of nitrates as in Chili, on the assumption that the solu- 



NlTEOGEN AND NITRATES IN SOILS 



Constituents 



San Juan 



Los MORROS 

 DK PaRAPARA 



El Enoantado 



Nitrate of lime 



Organic nitrogen 



2.85% 

 0.16 



3.50% 

 0.27 



0.62 % 

 0.21 



ble nitrate, originally derived from the decomposmg organic mat- 

 ter, as noted above, had been leached out from its place of origin 

 by percolating water and redeposited elsewhere on evaporation. 



