NITRATE DEPOSITS 141 



nitrates, they are not considered of much commercial importance, and 

 the same may be said of all other deposits so far discovered in this 

 country. 



Small nitrate deposits are also to he found in various other parts of 

 the world, as in the Sahara, in Eussian Turkestan, and in Egypt, where 

 nitrate earths occur which contain about 15 per cent, of calcium and 

 sodium nitrates. The earth has long been used locally as a fertilizer, and 

 its use is supposed to be increasing. The source of the nitrates in this 

 region is not known. 



All known deposits, however, which occur, like the ones just referred 

 to, in various desert regions throughout the world are insignificant com- 

 pared with the well-known deposits in the deserts of Atacama and Tara- 

 paca in the north of Chile. These deposits command a great deal of 

 interest, not only on account of their commercial importance, but also 

 for the many attempts which have been made to explain why the quantity 

 of nitrates in this particular region should be so large compared with 

 any other known deposit. 



The first shipment of nitrates to Europe from Chile was made in 

 1825. Since then the annual exportation has continuously increased 

 until in 1912 the total quantity exported amounted to 2,485,860 tons 

 of which 1,925,590 tons went to Europe, 469,100 tons to the United 

 States, and 91,170 tons to other lands. 



The arid region in which the nitrates are found extends for about 

 430 miles between 13° and 25° south latitude and lies between the 

 Andes in the east and the Coast Eange on the west. This area lying 

 between the two mountain ranges does not form a continuous valley, 

 but is broken up by transverse ranges into a series of elevated basins or 

 plateaus. These plateaus are generally flat or undulating, and have an 

 elevation from less than 2,500 feet to more than 5,000 feet. They have 

 a general slope from the foot of the Andes towards the Coast Eange, and 

 as a result the lowest part of this plateau region, or pampa as it is called 

 in Chile, lies along its western border where it joins the foothills of the 

 Coast Eange. It is along this zone that the nitrate deposits occur. The 

 surface of the surrounding region is dry and sandy and vegetation is 

 totally absent. 



The nitrate beds as they occur in different parts of this region vary 

 in thickness up to about six feet. They are usually found at or near the 

 surface, but may in some cases be covered with an overburden to a depth 

 as great as thirty feet. The nitrate deposits are never found pure, but 

 are always mixed with sodium chloride and other salts, and are impreg- 

 nated with insoluble earthy material. Crude nitrate may sometimes run 

 as high as 60 to 70 per cent, of sodium nitrate, but a deposit running 50 

 per cent, is considered high-grade material. Material containing less 

 than 16 per cent, is too low grade to be mined at a profit at present. 



