President of the Geological Society for 1850. 21 



porous and cavernous nature of the dolomite are referred to 

 by MM. E. de Beaumont and Morlot as a character implying 

 the alteration of a compact rock into one of more open 

 texture which had been permeated by gases.* *' It is now 

 more than twenty years," says De Beaumont, writing in 1847, 

 *' since I first advocated Leopold Von Buch's views, who 

 attributed the gypsums and dolomites of the Alps to epigmie, 

 or to the alterations of calcareous masses by mineral springs 

 and gaseous emanations which came up from the interior of 

 the earth at the time when the porphyries called melaphyre 

 were formed-t M. Frapolli, in reference to similar meta- 

 morphic action, has adduced numerous facts illustrative of 

 the manner in which carbonates of lime may have been 

 turned by sulphurous vapours into gypsum ; and Sir R. Mur- 

 chison reminds us that the well-known thermal waters of 

 Aix do now actually change the ordinary Jurassic limestone 

 into sulphate of lime ; while, according to M. Coquand, 

 another example of the like metamorphism is afforded by 

 Mofettes, where the sulphuro-hydrous emanations turn the 

 cretaceous limestone into gypsum along the lines of fissure 

 which they permeate. J M. Favre, as before stated, has 

 shewn that the period when the porphyries called melaphyre 

 were erupted agrees well with this hypothesis, and that the 

 heat and gases disengaged during such volcanic outbursts 

 might well have transformed the calcareous into magnesian 

 rocks. Thus it is supposed that the carbonate of lime con- 

 taining shells of the Jurassic epoch has been slowly trans- 

 fonned into magnesian carbonate, and perhaps an increase 

 of volume was gradually acquired by the gypseous and dolo- 

 mitic masses in proportion as they derived fresh accessions 

 of mineral matter from below. If so it may have caused 

 expansion, and have furnished an irresistible lateral pres- 

 sure. 



If in the central parts of the Alps we suppose heat to have 

 accompanied the metamorphic action which has converted 

 into gneiss and mica-schist, not only the Jurassic and creta- 



* Bulletin, 2d Series, vol. vi. p. 318. t Ibid. vol. iv. p. 1282. 



\ Ibid. vol. vi, p. 124. 



