A. Von Morlet on Dolomisation. 79 



pound of one atom of each."* From this fact and other ob- 

 servations, he inferred that dolomite originated in a similar 

 change. Elie de Beaumont, in 1837, suggested the same 

 view, and thus accounted for the occurrence of open spaces 

 in the dolomite, often amounting to twelve per cent, of the 

 mass. 



The association of gypsum with dolomite had been noticed 

 by various observers. Haidinger, in view of this well-known 

 fact, concluded that it must arise from sulphate of magnesia 

 being the agent by which the change into dolomite vi^as pro- 

 duced. The magnesia of the sulphate of magnesia going to 

 a portion of the lime to form dolomite (or carbonate of lime 

 and magnesia), the sulphuric acid thus set free would form 

 with water and another portion of the carbonate of lime, 

 gypsum (sulphate of lime). 



But chemistry had shewn that when a solution of gypsum 

 was filtered through pulverised dolomite, sulphate of mag- 

 nesia was formed, and carbonate of lime set free. Hai- 

 dinger had also observed the efflorescence of sulphate of 

 magnesia in gypsum quarries, and traced it to a decomposi- 

 tion of this character. As these last are results of ordinary 

 exposure, Haidinger naturally inferred that this dedolomi- 

 sation required no unusual heat or pressure ; while for the in- 

 verse decomposition (or dolomisation), both heat and pres- 

 sure might be necessary. Experiments on this point were 

 projected in 1843, by Haidinger and Wohler, but were not 

 carried out. Von Morlot has at last applied this test, and 

 confirmed the view so far as to shew that when carbonate 

 of lime and sulphate of magnesia in the requisite proportions 

 are heated together under pressure, dolomite is actually 

 formed, together with sulphate of lime. The temperature 

 to which they were subjected was 200° C, and the pressure 

 15 atmospheres. An interesting problem was thus solved. 



[It is still a question, what is the least quantity of heat 

 requisite for this dolomisation. Many compact limestones 

 of our western states contain 30 or 40 per cent, of carbonate 

 of magnesia, as first shewn by Mr. D. D. Owen ; and these 

 rocks present no evidence of the action of heat. 



* Trans. Royal Soc. Edin., March 19, 1827. 



