ORIGIN OF SALINE DEPOSITS 365 



estimated at 2.316 millions of metric quintals (254,760,000 short 

 tons). The niter fields lie between 50 and 100 miles from the coast, 

 and at elevations exceeding 2,000 feet. The crude sodium nitrate 

 or "caliche" occurs in deposits scattered over a large area and is 

 associated with salt and ulexite. A section of one of the "calichera" 

 or niter deposits in the Atacama Desert, 50 miles west of Taltal, 

 shows (Clarke- 1 0:207; 242) : 



1 . Sand and gravel oft. 1/2 inch 



2. " Chusca, " a porous, earthy gypsum o ft. 6 inches 



3. A compact mass of earth and stones 2 to lo ft. 



4. "Costra, " a low grade caHche, containing 



much sodium chloride, feldspar and earthy 



matter i to 3 ft. 



5. "Caliche " I to 3 ft. 



6. " Coba, " a clay +3 inches 



The caliche varies in its percentage of NaNOg from 31.9 to 56.25. 

 Sometimes it contains up to 7% CaSO^, at others up to 10% or over 

 MgS04, and again up to 34.6% Na^SO^. Insoluble impurities may- 

 range as high as 45% or over. No potassium salts appear in these 

 deposits, but anhydrite, gypsum, epsomite, halite and other minerals 

 are associated with the nitrates. 



In the Tarapaca desert the bed of "caliche" is from 4 to 12 feet 

 thick. Other localities are known in South America, but they are 

 of much less importance. Potassium nitrate, or saltpeter, is found 

 as an immense deposit near Cochabamba, Bolivia, associated with 

 borax. It contains 60.7% KNO3, 30.7% NagB^O^, and traces of 

 NaCl, N2O and some organic matter. 



Other Minerals Deposited Under Desert Climates. 



Among the minerals known to be found under conditions of in- 

 adequate rainfall is carnotite, a more or less impure hydrated vana- 

 date of uranium and potash. It is found as a yellow crystalline 

 powder or in loosely coherent masses, and contains radium. It oc- 

 curs somewhat abundantly in Montrose County and elsewhere in 

 Colorado, and has been found in the Mauch Chunk red shale of 

 Pennsylvania — a formation formed under comparatively arid condi- 

 tions. (Wherry-69.) 



ORIGIN OF THE SALINE DEPOSITS. 



The source of the various saline deposits is a subject of consid- 

 erable importance, since it promises to throw light on the condition 



