92 CHEMISTRY OF DOLOMITES AND GYPSUMS. [VIII. 



solutions, permanent in the air, holding, as bicarbonate, 21.0 

 grammes of monocarbonate of magnesia to the litre; so that 

 the solubility of carbonate of magnesia under these conditions 

 is about nine times as great as that of sulphate of lime. (Amer. 

 Jour. Science (2), XXVIII. pages 170-178. 



The fact that the separation of the carbonate of magnesia 

 necessary for the production of dolomites and magnesites re- 

 quires the absence of chloride of calcium from the waters in 

 which it is deposited, whether this carbonate is generated 

 by the reaction of bicarbonate of lime on sulphate of magnesia 

 (with simultaneous production of gypsum), or by the interven- 

 tion of bicarbonate of soda, and that in both cases isolated 

 and evaporating basins are indispensable conditions of the 

 formation and deposition of this magnesian carbonate, was 

 clearly pointed out, as above, in 1859. The legitimate de- 

 ductions from this as to the geographical and climatic condi- 

 tions of regions during the formation of magnesian limestones 

 were further insisted upon in a paper upon the Geology of 

 Southwestern Ontario, in 1868, and again in 1871, in paper 

 XIII. of the present volume. (See also ante, page 74.) 



It was not, however, I believe, till 1871 that these views 

 of mine found recognition, when Professor A. C. Ramsay, by 

 the investigation of the magnesian limestone of the Permian 

 in England, was led to reject as untenable the notion held by 

 Sorby (and by others), that this was once an ordinary lime- 

 stone of organic origin subsequently impregnated with magne- 

 sian carbonate under conditions not explained ; and to con- 

 clude that the carbonates of lime and magnesia of which it 

 is composed had been " deposited simultaneously by the con- 

 centration of solutions due to evaporation," " in an inland salt 

 lake." To this view, as he informs us, he was led by physi- 

 cal considerations, and by the depauperated condition of the 

 organic remains contained in these strata, without being, at 

 the time, aware that I had twelve years previously announced 

 the same conclusions for all magnesian limestones, and estab- 

 lished them on chemical grounds. (Quar. Geol. Jour., 1871, 

 page 249.)] 



