1867.] Mineralogy, Mining, and Metallurgy. 417 



rest must have been made, not on the Partzite itself, but on the 

 main body of the Blind Springs ore.* 



Few men have a better right to speak on the chemical origin of 

 minerals and rocks than Dr. Sterry Hunt, of the Geological Survey 

 of Canada. This indefatigable chemist has recently laid before the 

 French Academy of Sciences his views "On the Formation of 

 Gypsums and Doloraites."t Alluding to his former researches, Dr. 

 Hunt shows that the reaction of a solution of bicarbonate of lime on 

 sulphate of magnesia gives rise to the formation of sulphate of lime 

 and bicarbonate of magnesia. It is, however, extremely difficult to 

 obtain, on evaporation, a complete separation of the two salts pro- 

 duced by this double decomposition ; for the bicarbonate of magnesia 

 on exposure to the atmosphere loses a portion of its carbonic acid, 

 and passes to the condition of a neutral or a sesqui-carbonate, which 

 easily decomposes the sulphate of lime, reproducing carbonate of 

 lime and sulphate of magnesia. To obviate this loss of carbonic 

 acid, Dr. Hunt conducts the evaporation in an atmosphere highly 

 charged with carbonic acid ; such an atmosphere effectually prevent- 

 ing the decomposition of the bicarbonate, and allowing the gypsum 

 to separate in a pure crystalline form. To apply these laboratory 

 experiments to the explanation of the natural origin of gypseous 

 and dolomitic rocks, the author has recourse to the opinion still 

 entertained by some geologists, that the proportion of carbonic acid 

 in the atmosphere must have been much greater in the earlier 

 periods of the world's history than at the present time. This 

 admitted, his experiments afford a simple explanation of the formation 

 of beds of gypsum, and also of the magnesio-calcareous rocks with 

 which they are commonly associated. The water of most natural 

 springs holds in solution more or less bicarbonate of lime, which, 

 when carried down to the sea, reacts on the sulphate of magnesia 

 present in sea-water, producing sulphate of lime and bicarbonate of 

 magnesia ; and the water containing these mixed salts, on evapora- 

 tion in a basin of limited area and under an atmosphere rich in car- 

 bonic acid, deposits the sulphate of lime in the form of gypsum, 

 while the magnesian carbonate, uniting with carbonate of lime, may 

 be precipitated as a dolomitic sediment. 



At a subsequent meeting of the Academy, Dr. Hunt followed up 

 the subject in a paper " On Certain Reactions of Magnesian Salts, 

 and on Magnesia-bearing Eocks."J 



The same eminent chemist gives the result of much philo- 

 sophical thought in a memoir " On the Objects and Method of 



* * San Francisco Mining Press,' 1867, Jan. 19. Feb. 9, and April 13. 



t " Sur la Formation des Gypses et des Dolomies : " ' Comptes Kendus,' 1867, 

 No. 16, p. 815. 



X " Sur quelque3 Reactions de Sels Magnesiens et sur les Roches magnesiferes:" 

 4 Comptes Rondus,' 1867, No. 17, p. 846. 



