144 TEE POPULAR SCIENCE MONTHLY 



decomposition of ancient guano deposits. In defending this theory Pen- 

 rose 8 has assumed, in the same way as those who favor a marine origin 

 for the nitrates, that the pampa region was once a part of the ocean 

 bottom, but as the region gradually rose it became a more or less enclosed 

 basin. At this time guano beds were supposed to have been deposited 

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

 neighboring shores of the Pacific. It is considered quite possible that 

 marine plants might also have collected in the basin at the same time, 

 and that these constituted the source of the iodine, although it is pointed 

 out that this element might also have originated in minerals, or mineral 

 springs occurring in the region. The formation, as suggested, of inland 

 basins of sea-water, which would ultimately evaporate, would furnish 

 also a source for the common salt associated with the nitrates, as well as 

 for the soda of the nitrates. 



The guano theory, however, has been objected to on the ground that 

 no accumulation of phosphate has ever been found in the nitrate country, 

 and such must necessarily occur in amount corresponding to the nitrates 

 if the latter have been derived from guano. It is argued, on the other 

 hand, that such phosphates may actually exist, but that they have not 

 yet been discovered, and it is further explained that the absence of the 

 remains of birds and of sea shells may be accounted for on the ground 

 that sufficient time has elapsed since the beds were deposited to admit of 

 the decay of all such materials. 



There is still, however, a further objection which applies to both the 

 sea-weed and guano theories. Thus, if the region was at one time a sea- 

 beach it must have taken ages, as Newton has pointed out, for the nitrate 

 pampa to be elevated to its present level. During these ages the region 

 must have passed through varying climatic conditions, including most 

 probably rains. It has, therefore, been argued that the nitrate deposits 

 are, geologically speaking, of very recent origin. 



In suggesting another organic source from which the nitrates may 

 have been derived, Kuntze has called attention to the fact that vicunas, 

 and llamas, which are at home in this portion of the Andes, have the 

 peculiar habit of always depositing their manure in one and the same 

 place. Immense herds of these animals are supposed to have roamed 

 over the region from time immemorial, each herd having a definite 

 dunging place at some convenient point. As the manure accumulated its 

 nitrification would progress rapidly under the prevailing arid conditions. 

 The common salt would be derived from the urine and excrements, while 

 the decomposition of rocks throughout the region is considered sufficient 

 to account for all other salts occurring in the crude niter. 



Newton 9 is of the opinion that the source of the nitrates is the 



s Jour. Geol, 18, 1, 1910. 



9 Jour. Soc. Cliem. Ind., 19, 408, 1900. 



