THE NITRATE DEPOSITS OF CHILE 17 



of alkaline carbonates, that the protoxide compounds of iron, which 

 are common in the rocks of the pampa, are easily oxidized under 

 ordinary conditions forming peroxide compounds of iron, and he 

 thinks that the alkaline carbonates, under such environment, have 

 caused the oxidation of the nitrogen of the air with the ultimate forma- 

 tion of nitrates. 



David Forbes' thinks that the nitrates were derived from the 

 decay of vegetation around and in salt water swamps and lagoons, 

 which he believes once occupied the site of the present pampa. A 

 certain amount of nitrogenous matter might be derived in such a 

 manner, and this subject will be discussed again later on. 



It seems, however, as if a source of nitrogen more abundant and 

 ready than any of those mentioned might have existed in the immense 

 accumulations of guano which for ages have been characteristic of 

 this coast, and this suggestion has been offered by a number of other 

 writers. Incidentally it may be stated that in many parts of the 

 world, especially in warm regions, nitrates are found in small deposits 

 in caves, in association with bat guano, and that the source of the 

 nitrogen from this guano is very generally recognized.'' 



It is well known that the part of the coast of Chile where the 

 nitrates occur has been gradually rising in recent geologic times, and 

 that the pampa region already described was once a part of the ocean 

 bottom. During this elevation, as the region gradually rose up to, 

 and then above, the ocean level, it probably passed first through the 

 condition of an open bay or gulf, then became more and more sepa- 

 rated from the ocean, and finally, when raised completely above 

 it, became a more or less inclosed interior basin occupied by an inland 

 sea, or a series of basins occupied by salt lakes, lying between the 

 Andes and the Coast Range. Guano beds were doubtless deposited 

 along the borders of these waters, just as they are now deposited on 

 the neighboring shores of the Pacific. 



Guano consists largely of nitrogenous materials, phosphates, and 

 water, with other substances in smaller quantities. The nitroge- 



1 "On the Geology of Bolivia and Peru," Quarterly Journal of the Geological 

 Society of London, Vol. XVII (1860-61), pp. 13-16. 



2 A. Muntz et V. Marcano, Academie des Sciences, Comptes Rendus, Vol. CI (1885), 

 pp. 65-68. See also A. Muntz, ibid., pp. 1265-67. 



