The Origin of Bock-Salt. 



33 



dissolved in the summer. Thus the composition of the 

 Elton Lake, in which the proportion of sulphate of lime 

 is always small, varies according to the season of the 

 year." ^ 



The Dead Sea is another well-known example of an inland 

 lake in which concentration is proceeding at a high rate. 

 It is fed almost entirely by the Jordan, which carries into 

 the Dead Sea 6,500,000 tons of water daily during the 

 melting of the snows of the Lebanon, the whole of which 

 is dissipated by evaporation. Chloride of sodium and chloride 

 of magnesium are among its preponderating dissolved con- 

 stituents. "At a depth of 300 metres, the salts in solution 

 in the Dead Sea amount to 278 per thousand, with a specific 

 gravity of 1*2563. In this are contained, in the following 

 percentages : — 



Chloride of sodium, . 

 Chloride of magnesium, 

 Chloride of potassium, 

 Chloride of calcium, . 

 Bromide of magnesium. 

 Sulphate of lime, 



Thus the chloride of magnesium 

 that of sodium. Hence precip 

 sodium takes place as fast as it arrives from the rainfall 

 of the Jordan basin. Thick deposits of salt, inter-stratified 

 with clay and other detrital material, occur to heights of 

 about six hundred feet above the level of the Dead Sea. 

 [Photographic views of those of Jebel Usdem, taken by 

 Mr M. Cotsworth of York, were exhibited when this address 

 was last given before the Eoyal Physical Society.] It is 

 said that it is only during exceptionally high floods that the 

 waters of the Dead Sea rise to the level of the foot of the 

 Jebel Usdem cliffs ; hence it is usually considered that the 

 quantity of salt derived by the Dead Sea from its ancient 

 deposits here must form but a very small proportion of its 

 saline constituents. It may be well to remark again that 

 the presence of the excess of the chloride of magnesium in 



1 Justus Roth, op. cit. , \). 246. 2 7^^^;. , p. 247. 



VOL. XV. C 



61-27 

 3-21 



18-10 

 3-13 

 0-34." 2 



is considerably in excess of 

 tation of the chloride of 



