254 MR. A. WADE ON THE EASTERN DESERT OE EGYPT. [May 19II. 



An analysis of the ' gypsumized ' beds of South Gaysum Island 

 gave the following result : — 



Per cent. 



CaO 30-20 



SiO. 2-14 



Na 2-35 



CO., 172 



SO," 39-38 



11,0 21-50 



CI" 2-69 



Total 99-98 



If it be held as proved that these raised calcareous beds are thus 

 altered under suitable conditions into gypsum, some difficulties con- 

 nected with Triassic and more recent Egyptian geology are evidently 

 nearer solution. 



A certain amount of encrustation, consisting of soluble salts, 

 occurs upon almost every fossil present on the islands in the Bed 

 Sea. In order to determine its character, I carefully removed the 

 encrusting salt from the fossils that I had collected, and subjected 

 it to analysis. The mean of four analyses on the very small quantity 

 available was as follows : — 



Per cent. 



CaO 28-78 



SiO., 6-48 



Na.,0 18-10 



MgO 227 



CO., 31-41 



SO: 2-71 



CI 8-92 



H.,0 1-45 



Total 100T 



The solution gave a distinctly alkaline reaction. 



There was some considerable variation in the amount of chloride, 

 sulphate, and silica present. Roughly speaking, the analysis indi- 

 cates the presence of about 50 per cent, of CaC0 o ; 7 of MgSO i ; 14 

 of Nad ; and 18 per cent, of Na 2 C0 3 . 



The presence of sodium carbonate is interesting, and suggests 

 mass action between the salt and the limestone *: — 



-*- CaCl„+Na 2 C0 3 . 



1 C. M. Guldberg & P. Waage, ' Ueber die cbemische Affinitat ' Journ. 

 Prakt. Chem. vol. xix (1879) p. 09. Since the above was written, Mr. S. R. 

 Tiling worth has drawn my attention to the fact that Berthollet has shown 

 that this reaction does take place on the shores of certain lakes in Egypt : see 

 G. Senter, ' Outlines of Physical Chemistry ' London, 1909, p. 139. 



