994 A TREATISE ON METAMORPHISM. 



of the major part of it. The natural direction to which we first turn to 

 account for the deficiency is the ocean. According to Dittmar's estimates 

 the amount of magnesium in the ocean is 1,743,000,000,000,000 metric 

 tons, which corresponds to 2,887,800,000,000,000 metric tons of magnesia. 

 It is at once seen that the total amount in the ocean is vast, the magnesia 

 being between three and four times as abundant as lime. But this enormous 

 amount accounts for only 19.45 per cent of the deficiency. 



Another large portion of the deficiency is probably accounted for by 

 magnesium in classes of the sedimentary rocks not considered — that is, the 

 saline deposits. In all salt deposits magnesium salts are important impu- 

 rities. In the water of Great Salt Lake the magnesium varies from 0.3 to 

 2.6 per cent of the total solids in solution; " in the water of the Dead Sea 

 it is given as 14.41 per cent of the total solids. 6 In the salt deposits of 

 New York and Michigan the magnesium in the brines varies from .034 to 

 .454 per cent. c In the rock salts of Louisiana the magnesium varies from 

 0.003 to 0.06 per cent/' These figures may be taken as representative of 

 ordinary salt deposits, but in certain exceptional salt deposits, as those of 

 Stassfurt, the magnesium salts are much more abundant. In such deposits 

 a great portion of the mag'nesium salts with the accompanying potassium 

 salts is likely to be found in a more or less distinct bed above the rock salts. 

 As illustrating the abundance of these compounds Precht states that at 

 Stassfurt, from 1876 to 1880, there were mined 699,136 metric tons of car- 

 nallite (KMgCl 3 .6H 2 0), kieserite (MgS0 4 +H 2 0), andkainite (MgS0 4 .KCl-f 

 3H 2 0) and only 96,856 tons of rock salt. A considerable amount of 

 magnesium occurs also, in accompanying polyhalite. " It is plain that the 

 total quantity of the magnesium in saline deposits is great, but what portion 

 of the deficiency is thus accounted for can not be stated until very careful 

 studies have been made of the volumes and compositions of the salt deposits 

 of the world. 



It is believed that the explanation of a larger part of the deficiency is to 

 be found in the concentration of magnesia in the zone of katamorphism in 

 consequence of the alterations of that belt, the magnesia as is explained 



a Gilbert, G. K., Lake Bonneville: Mon. U. S. Geol. Survey, vol. 1, 1890, p. 253. 



l> Encyclopedia Britannica, 9th ed., 1877. 



'•Tenth Census, vol. 2, p. 1017. 



d Mineral Resources, 1883-84, p. 841. 



f Precht, H., Die Salz-Industrie von Stassfurt und Umgegend, 1889, p. 12. 



