ANNIVERSARY ADDRESS OF THE PRESIDENT. CXV 



volume which a cuhe metre of Umestone would occupy if converted into 

 dolomite, by the substitution of one atom of carbonate of magnesia 

 for one atom of carbonate of lime in each double atom of carbonate 

 of lime, which show that hollows or pores would result equal to 1 2 

 per cent, of the total volume of the rock, explaining the cavernous 

 structure of many dolomites. M. de Morlot, desirous of ascertaining 

 how far the theoretical view of M. de Beaumont was borne out by 

 fact, carefully chose a piece of the dolomite of the Prcdiel, believed 

 to represent its mean cavernous state, and with many precautions, 

 ascertained the relation of the pores or hollows to the volume of the 

 rock. This he found to be 12*9 per cent., a remarkable coincidence 

 he infers, all the circumstances being taken into consideration, and a 

 result confirming the views of M. Elie de Beaumont. M. de Morlot 

 however regards the metamorphic character of dolomite, with M.Elie 

 de Beaumont, as placed beyond doubt by the fact, that part of the 

 Silurian corals of Gerolstein were formed of crystallized dolomite, 

 and are cavernous, without having lost their organic form. He also 

 notices, and gives a figure of, a coral from the Seisser Alp, from the 

 structure of which he infers that there has been metamorphic action, 

 and that the atom of lime thus displaced has been removed. 



The frequent association of dolomite with gypsum in many places, 

 and a careful examination of specimens collected near Vienna, induced 

 Ilaidinger to suspect that the magnesia had been introduced in the 

 form of a sulphate, and that this salt, so commonly existing in nature, 

 had so reacted upon the limestone to which it was conveyed in so- 

 lution in water, that the double carbonate of lime and magnesia, and 

 gypsum were the results. A solution of sulphate of lime was, how- 

 ever, known, if filtrated sufficiently long through pulverized dolomite, 

 to transform the latter into carbonate of lime, sulphate of magnesia 

 being formed. From reasoning upon some circumstances observed, 

 in connexion with this subject, Haidinger concluded, that though at 

 a low temperature and solely under ordinary atmospheric pressure, 

 a solution of sulphate of magnesia decomposes dolomite, under a 

 high pressure and heat the reverse would take place. Estimating 

 the increase of temperature from the surface of the earth downwards, 

 and the probable pressure beneath a certain amount of mineral accu- 

 mulations, M. Haidinger inferred, that at a temperature of 200° 

 Centigrade, and under a pressure equal to 1 5 atmospheres, this would 

 happen. The experiment was made ; a mixture in atomic proportion 

 of svdphate of magnesia and carbonate of lime was subjected, in a tube 

 of glass, hermetically closed at both ends, and exposed in a modifi- 

 cation of Sir James Hall's gun-barrel apparatus, to the pressure and 

 heat calculated. The experiment was perfectly successful ; there was 

 complete double decomposition, and the formation of the double car- 

 bonate of lime and magnesia and of sulphate of lime was the result. 

 Although, to make this experiment applicable to the occurrence of 

 mixed masses of dolomite and gypsum in nature, we have to suppose 

 like conditions on the great scale, and a very large proportion of that 

 soluble salt, sulphate of magnesia, intermingled with carbonate of 

 lime, it is one of considerable \ alue, as showing what would happen 



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