186 Proceedings of the Royal Physical Society. 



feroiis sandstones near Juniper Green, where large pseudo- 

 morphs of Rock Salt were pointed out to the writer by 

 Miss Eobina Orrock, of Edinburgh. These pseudomorphs 

 probably represent crystals deposited from concentrated 

 estuarine waters in a lagoon. Another occurrence is in the 

 marls of the New Eed,^ near Kildonan, at the southern end 

 of Arran. Here, also, the mineral is represented by pseudo- 

 morphs. There can be little doubt in this case that the 

 Chloride of Sodium was formed under arid climatal condi- 

 tions, and, possibly, in the warp of an old lacustrine delta. 



Grypsum, the second mineral in this category, has likewise 

 been formed under diverse circumstances, some of which 

 may be conveniently noticed here. In a few cases it is 

 due simply to the action of solutions derived from vitriol- 

 escent sulphides (usually Pyrites) upon solutions of carbonate 

 of lime. Formed in this way, it is by no means of un- 

 common occurrence in Carboniferous shales. G-ood stellate 

 groups so formed occur, for example, on the shore at 

 Dalmeny, just east of the Forth Bridge. It also occurs in 

 the same manner in the Yoredale shales on the Fife shore, 

 about a mile KE. of Kinghorn. A second mode of occur- 

 rence is in that of veins of Satin Spar, in which form it 

 occurs in the Ballagan Shales (Lower Limestone Shales, d}) 

 of Tweedside. The veins probably represent what was 

 formerly diffused sulphate of lime, formed under the sub- 

 arid conditions which prevailed during the time when 

 the Ballagan Beds were being deposited. These latter 

 occurrences are probably due to occasional concentrations 

 of estuarine waters in shallow lagoons, the sulphate of lime 

 having been derived either direct from sea-water, or else 

 from the solutions transported seawards by the rivers. 

 More usually beds of Gypsum (which, however, have not 

 yet been found in Scotland) represent what were originally 

 thin films deposited upon surfaces of mud in inland lakes, 

 and which films have been dissolved, carried to lower 

 levels, and there redeposited in a concentrated form. Such 



1 This is employed here as a convenient general name for any of the Red 

 Rocks which are intermediate in age between the Carboniferous and the 

 Rhsetic Rocks. A term having that meaning is very much needed. 



