SOURCES OF ALKALINE CARBONATES 369 



same source as the sodium chloride, being one of the constituents 

 of the sea water whether recent or fossil. Gypsum forms as an ef- 

 florescence or incrustation in caves, and it is also produced exten- 

 sively by the alteration of other rocks. Oxidation of pyrite in 

 calcareous rock often results in the formation of this mineral and 

 so does the double decomposition between other metallic sulphates 

 and calcium carbonate. 



Sources of Alkaline Carbonates. 



The origin of the alkaline carbonates deposited by many waters 

 has been attributed to the leaching of volcanic rocks. Near Owens 

 Lake some of the seepage waters percolate through beds of vol- 

 canic ash, and contain even a higher proportion of alkaline carbon- 

 ates than the lake itself. The rocks from which these salts were 

 originally derived seem to have been mainly rhyolites, andesites, and 

 others rich in alkalies and relatively poor in lime. (Clarke-io, 2d 

 ed. li'i'p.) 



Other sources of alkaline carbonates in natural waters and soils 

 are found in the double decomposition between calcium bicarbonate 

 and alkaline sulphates (T. Sterry Hunt) or alkaline chlorides (E. 

 von Kvassay) and in the reduction of alkaline sulphates by organic 

 matter and the subsequent absorption of COo from the air (E. Sick- 

 cnberger). Finally, Ochsenius suggested that alkaline carbonates 

 are formed by the action of CO^, commonly of volcanic origin, on 

 the mother liquor salts. In Egypt, Chile, and Bolivia he finds also a 

 lack of association of lime and sodium carbonate, but he notes the 

 occurrence of eruptive rocks as sources of CO2 exhalations. In 

 Utah and in the Sahara he finds an association of lime with the 

 mother liquor salts, but no sodium carbonate, because eruptive rocks, 

 the sources of COo, are absent. Finally, in Nevada he finds the 

 mother liquor salts associated with eruptive rocks and much soda, 

 lie concludes, therefore, that an association of lime with the mother 

 liquor salts alone produces no alkaline carbonates, but that CO, 

 emanations from volcanic sources (with or without the presence 

 of lime reaction on these salts) will produce the alkaline carbonates. 

 The widespread occurrence of sodium carbonate in the soils of arid 

 regions is attributed by Hilgard (23) to the reaction between al- 

 kaline salts and calcium bicarbonate. When by excessive irriga- 

 tion these salts are dissolved they rise to the surface by capillary 

 attraction to form the crusts of "alkali." 



