124 TRANSACTIONS OF THE [ FEB. 13, 
or bands two to six inches in width, which are quite black. 
The salt appears to have a uniform character in all parts of the 
mine, and is remarkable for its purity, especially in its freedom 
fromcalcium and magnesium salts. It is also quite free from 
potassium salts; for traces of Stassfurt salts I made especial 
search in vain. The following analyses show the great purity 
of this product : 
Analysis by Mr. F. W. Taylor, Analysis by 
(Smithsonian Institution) K. W. Hilgard. 
March, 1882. 18638. 
Sodium chloride, 98.731 99.880 
Calcium sulphate, 1.192 0.126 
Calcium chloride, Trace Trace 
Magnesium chloride, 0.013 — 
Silica, 0.024 100.006 
Tron sesquioxide, 0.010 
Water, 0.0380 
100.000 
Other analyses made by Professor Goessmann range from 98.88 
to 99.60. It is of interest to compare this with rock-salt from 
other localities. 
Cheshire. Stassfurt. Berchtesgaden. 
Sodium chloride, 98.30 94.57 99.85 
Potassium chloride, Trace. 
Calcium chloride, Trace. 
Magnesium chloride, 0.05 0.97 0.15 
Calcium sulphate, 1.65 0.89 
Insoluble, 3.99 
Water, 22 
100.00 100.00 100.00 
Partial analyses of the black salt have been made by Mr. 
McCalla, the resident engineer and chemist, who finds that it 
yields a white solution and about seven per cent of a white in- 
soluble residue, chiefly gypsum. ‘The black color, therefore, 
seems to be an optical phenomenon. These black bands form 
well-marked folds in the salt, the space between the ridges and 
above them being filled with coarser granules of salt than the 
rest. Near these black bands the finest cleavage crystals of 
transparent purity are found. These bands seem to indicate 
that at some time the rock-mass has been subjected to lateral 
pressure, causing ridges. 
The geological features of the island and the origin of the salt 
deposit have been discussed by both Professor Goessmann and 
Professor Hilgard. ‘The former thinks it is ‘* probably of ter- 
tiaryage,” and says, ‘‘many circumstances favor the theory that 
the deposit isa secondary one—resulting from the evaporation of 
