THE NITER FAMILY. 787 



material of the sedimentary rocks may be placed, and, as already 

 explained, the remaining 10 per cent is provided for by compound names. 

 We are now prepared to consider the manner of formation of the 

 various families of original sedimentary rocks, their transformation, and 

 resultant alteration forms. 



NONFRAGMENTAL CLASS. 

 NITRATE ORDER. 



NITER FAMILY. 



Natural niter is mainl} T soda niter (NaN0 3 ), although potash niter 

 (KN0 3 ) does occur in subordinate quantity. The sodium and potassium 

 of the niter are mainly derived from the many alkaline-bearing silicates by 

 their decomposition in the zone of katamorphism, and chiefly in the belt of 

 weathering, through the process of carbonation. The original source of the 

 nitrogen of the niter is the atmosphere. This is oxidized in the zone of 

 katamorphism, mainly in the belt of weathering and very largely in the 

 soil, to nitric acid. (See Chapter VI, pp. 465-466.) The nitric acid unites 

 for the. most part with the alkalies, forming the nitrates. The nitrates, 

 once formed, are dissolved from the soils by the circulating ground water 

 and carried to the sea or to lakes with no outlets. In the lakes niter is 

 chemically precipitated in consequence of continual addition of salts in 

 solution and evaporation of water. Niter is the most readily soluble of the 

 important natural salts, and therefore is the last of the series of chemical 

 precipitates to separate. It forms in the final stages of desiccation of the 

 lakes as the top deposit. Therefore niters are wholly the products of the 

 zone of katamorphism, and mainly of the belt of weathering. 



The most extensive known deposits of niter are those in the extremely 

 arid regions of Chile. Niter deposits also occur in Bolivia, in Nevada, and 

 in southern California. 



The alterations of niter are those of recrystallization and solution. 

 The process of recrystallization need not be dwelt upon, as it is in no way 

 different from the recrystallization of other readily soluble compounds. 

 Niter is so readily soluble that, unless the region be one of extreme aridity, 

 the rock, after having been precipitated, is redissolved and transported else- 

 where. Even where niter becomes buried under other rocks, it is likely 

 to be dissolved by the ground, waters and again brought to the surface. 

 Consequently niter as a deeply buried rock is rare. 



