.4- 



36 



ROCK SALT, ETC. 



Upper 

 Gallebs. 



Wall-case 40. 



irregular form, associated with marl and gypsum. The 

 number of saliferous beds in the district is five, the thinnest 

 of them being 6 inches, but the thickest nearly 40 feet 

 thick, and they are worked at a depth of from 50 to 180 

 yards below the surface. Upwards of 70,000 tons are 

 obtained from the Cheshire mines, and a large quantity i s 

 also manufactured from brine-springs, and other similar 



sources in Cheshire and East Woi 

 Catalogue, Great Exhibition, 1851.) 



(Official 



These beds of salt are regularly stratified, and occur 

 about the base of the Keuper marl ; the greater part is 

 like the red specimens, being coloured by marly and ferru- 

 ginous impurities ; the pure and transparent kinds, although 

 by no means scarce, are less common. The manner in 

 which the salt was originally formed in the rock is obscure 

 but it is not improbable that it was deposited in salt 

 lakes, where the evaporation of water being equal to the 

 supply no rivers flowed from them. All river waters 

 contain small quantities of salts in solution, and by this 

 means, in the course of time, the water of any lake (having 

 no outlet) will become saturated with salts, after which, 

 the supply continuing, deposition will ensue, in the manner 

 in which it now takes place in the great salt lake of 



Utah 



A. C. Ramsay. 



Pure Rock salt consists essentially of chloride of sodium : 



Chlorine 

 Sodium 



59-5 

 40-5 



100-0 



Mem 



of 



45. Sulphate op Strontian, occurring in large quan- 

 tities in Neio Red Marl, near Fate, in Gloucestershire, 

 probably replacing sulphate of lime. 

 Geological Survey", vol. i., p. 267. 



46. Keuper Sandstone, with pseudomorphous crystals 

 of Rock salt. 



These beds of Keuper sandstone lie in the middle of the 

 new red marl, and contain fossils, namely, B atrachian foot- 







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