122 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Prof. J. D. Dana,' after the discovery of magnesian limestone 
from the island of “ Metia” (Makatea), advanced a theory of dolomiti- 
zation, as applied to coral islands, which has been very largely accepted. 
He stated that the sea-water was the source of the magnesium, and that 
this is introduced during the consolidation of the limestone below the 
surface. 
T. Sterry Hunt? stated two ways in which dolomite might be formed. 
The first consisted in the action of bicarbonate of lime upon solutions 
of magnesium sulphate, in which case gypsum was a subsidiary product. 
The second method was the reaction between river-water, containing 
sodiumb icarbonate, and sea-water in shallow basins, and the consequent 
decomposition of calcium chloride and magnesium sulphate into calcium 
magnesium carbonate, which, by subsequent heating, was converted into 
dolomite. 
E. T. Hardman,® in his paper on the dolomites of the Carboniferous 
limestone of Ireland, contended that the alteration of Irish limestones 
to dolomite was due to the greater solubility of calcium carbonate in 
limestones containing some magnesium carbonate when acted on by 
water containing carbon dioxide in solution at atmospheric pressure. In 
support of this he quoted experiments he had performed on limestones 
containing some magnesium carbonate. He found, lke Bischof, that 
under atmospheric pressure the calcium carbonate was dissolved and 
the magnesium carbonate was unaffected. Under high pressures mag- 
nesium carbonate alone was dissolved * from the mixed carbonates, and 
this method was formerly used commercially in the preparation of 
magnesium carbonate from dolomite. 
In 1895 Klement® published a paper on the artificial formation of 
dolomite. He heated the finely powdered mineral or organism together 
with crystallized magnesium sulphate and a saturated solution of sodium 
chloride in a closed retort to a temperature of about 100° C. for two or 
three days. He then determined the percentage of magnesium car- 
bonate in the washed precipitate. Under these conditions calcite took 
up only a trace, aragonite absorbed 34,6 per cent, while various corals 
yielded from 38.5 to 41.9 per cent of magnesium carbonate. 
1 Geology of United States Exploring Expedition, 1849, p. 153. 
2 Chemical and Geological Essays, p. 90. 
3 Proceedings Royal Irish Academy, 1877, pp. 705-730. 
+ Dingl. Polyt. Journ. CC. IX., p. 467; also Abs. Journ. Chem. Soe., Vol. XII, 
p. 96. 
5 Ueber die Bildung des Dolomit, Tscherm, Min. Pet. Mitt., 1895, XIV., p. 526. 
ee 
