Page:Popular Science Monthly Volume 85.djvu/149

Rh 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 Range. It is admitted that electrically generated atmospheric nitrate may also be present.

Headden 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 explain 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 suggested, that instead of being formed in one way only, the nitrates owe their origin to several sources.