NITRATE DEPOSITS 145 



organic matter occurring in the soil of the great plain lying between the 

 nitrate beds and the Andes. It is pointed out that there exists in this 

 region all the conditions which favor the rapid conversion by nitrifying 

 bacteria of the nitrogen of organic matter into nitrates. The soil is 

 porous and basic in its nature, and contains organic matter chiefly of 

 ancient vegetable origin ; the temperature is high and, on account of the 

 absence of rain, there is no growing vegetation to absorb the nitrate, and 

 therefore it must accumulate. The mountain floods which swamp the 

 plain once in every seven or eight years are considered chiefly responsible 

 for transporting and concentrating the nitrates from the superficial 

 layers of the pampa soil to the lower western part of the pampa region 

 where the deposits are found. The nitrate deposits are thus looked upon 

 as the concentrated fertility of the thousands of square miles of land 

 between the watershed of the Andes and the Coast Eange. It is admitted 

 that electrically generated atmospheric nitrate may also be present. 



Headden 10 has suggested that the nitrates of Chile may have been 

 formed by the direct fixation of the nitrogen of the air by nitrogen fixing 

 bacteria in the same way as accumulations of nitrates have been shown to 

 have been formed in certain soils of Colorado. 



It is apparent from the views which have thus been advanced to ex- 

 plain the origin of the Chilean nitrates that no single theory has yet been 

 proposed which is adequate to account for all the conditions under which 

 the deposits are found, and it seems most probable, as some have sug- 

 gested, that instead of being formed in one way only, the nitrates owe 

 their origin to several sources. 



10 Col. Agr. Expt. Sta., Bull. No. 155. 



