40 Proceedings of the Royal Physical Society. 



occurrence which has received much less notice — perhaps 

 because writers did not see their way to account for the facts 

 — is the very general association of rock-salt with hydro- 

 carbon compounds. I have ventured elsewhere ^ to discuss 

 this point. It is, I think, due to the action of the sulphates, 

 which are present in larger or smaller quantities in all salt 

 lakes, upon decomposing matter of vegetable origin, whereby 

 these latter are converted into other hydro -carbon com- 

 pounds, especially into bituminoids. 



The other minerals associated with Eock-Salt are Carnallite, 

 Kieserite, Mirabilite, Polyhalite, and other " abraum " salts. 

 Furthermore, seeing that the waters from which Rock-Salt 

 has been deposited have all traversed the rocks of the land 

 before reaching the area of concentration, it might be 

 expected that every substance which water can possibly 

 carry off in solution from the land, in quantities however 

 minute, may be thus concentrated in like manner to chloride 

 of sodium and its other associates. Thus, in the Triassic 

 rocks of Alderley Edge in Cheshire, it has long been known 

 that these rocks, which are closely associated with the strata 

 in which the salt is worked, yield a long list of elements and 

 compounds. Woodward, in his " Geology of England and 

 Wales," gives Platinum, Copper Ores, Cobalt, and Galena. 

 He might have added, various ores of iron, especially Haema- 

 tite and Turgite, and a Vanadium compound largely used in 

 making Vanadic acid. Various other substances have been 

 detected in the Sandstone associated with Eock-Salt, Barytes 

 being one of them, and quite lately Dr Mackay of Elgin has 

 added Eluor to the list. I see no reason why any of these 

 should be excluded from the list of substances carried down 

 in solution in rivers to the area of evaporation, and why 

 they should not represent the concentrated form of sub- 

 stances which were formerly in a state of extremely minute 

 quantities in solution, originally derived from the land and 

 not from the sea. 



As for the influence of chloride of sodium upon other 



1 "On some Modes of Origin of Oil Shales," Trans. Edin. Geol. Soc, 

 vol. vii. p. 121; "On the Bituminoid Cement of the Caithness Flagstone," 

 Froc. Boy. Phys, Soc.y vol. xiii. p. 316. 



