22 R. A. F. PENROSE, JR. 



in some plants, but in quantities so extremely minute as to make 

 such sources answerable for only a very small amount of the 

 borates of the pampa. On the other hand, when we consider 

 the vast areas of igneous rocks in the Andes and even in the Coast 

 Range, the source mostly from boron-bearing minerals and springs 

 seems very plausible. The boron materials from such sources were 

 probably carried down into the waters of the inland basin, where they 

 were concentrated and deposited in the same manner as the other 

 saline materials. 



In concluding the subject of the origin of the nitrates and other 

 sahne deposits of the pampa, it must be said that the present dis- 

 cussion is intended only as a most brief and general one. A vast 

 amount of geological and chemical details must be worked out both 

 in the field and the laboratory before the subject can be fully under- 

 stood. The determination of the exact conditions of deposition 

 and the various chemical transitions through which the saline mate- 

 rials have gone, require far more data than are at present available. 



INDUSTRIAL FEATURES IN THE TARAPACA REGION 



Mining and refining oj nitrate. — Mining in the nitrate regions is 

 done in surface openings. The capping of costra is thrown aside 

 and the nitrate below mined and raised to the surface (see Figs. 

 4 and 5). The quantity of nitrate often varies greatly in different 

 parts of a deposit and the change from rich spots to lean spots is 

 often very abrupt, so that nitrate is usually worked in isolated pits 

 or short trenches on the spots where it is richest, and not in long 

 trenches running systematically through the deposit, as would be 

 the most economical way if the deposits were uniform. Hence, most 

 properties that have been extensively worked present the appearance 

 of an upturned tract studded with numerous pits, some close together 

 and some more or less separated. In some cases, where the capping 

 of costra is hard and compact, or very thick, the miner finds it easier 

 to go under it in search for nitrate than to remove it, and thus small 

 underground workings in the form of caves have sometimes been 

 formed, but these are the exception, and the usual mining is in open 

 pits. 



When the richest parts of a deposit have been exhausted, the miner 



