Geological Society of France for 1847. 159 



This communication was followed by one from M. Virlet d'Aoust, 

 on normal metaraorphism, and the probability of the non-existence 

 of true primitive rocks on the surface of the globe. He refers to 

 the memoir of Scheerer as suppoi'ting the opinions he had previously 

 advanced on metamorphic granites, and points out that it is not ne- 

 cessary, as is too commonly sujjposed, that the temperature capable 

 of producing normal metamorphism and granitic transformations 

 should be very high, since M. Schafhautl has shewn that, under 

 pressure, steam above 212^ Falir. can dissolve silica, and that pro- 

 bably, as has been pointed out by Sir David Bi-ewster, other gases 

 may have considerably influenced crystallisation in altered rocks. 

 M. Virlet considers that geological discoveries, as well ns the advance 

 of inorganic chemistry, tend to shew that there does not probably 

 exist, and cannot now exist, any really primitive rocks on the sur- 

 face of the eartli ; that is to say, any rocks which have not suffered 

 some chemical or molecular transformation, including water chemi- 

 cally combined, since their original cooling. Normal metamorphism, 

 thus extended to all the rocks commonly called primitive, is only, lie 

 observes, a corollary of the theory of central heat and of the original 

 igneous fluidity of the earth ; conditions during the consolidation of 

 the crust having caused changes of surface heat, and the returns of 

 great heat at various times having assisted considerably in producing 

 normal metamorphism. M. Virlet refers to the mechanical aggre- 

 gation of crystalline I'ocks as affording a proof of general metamor- 

 phism, and as due to conditions which the researches of Schafhautl, 

 Brewstei", Biess, and Scheerer, would lead us to expect. 



In an elaborate account of analyses of some of the siliciferous 

 thermal waters of Iceland, M. Damour considers that water, acting 

 at a temperature of more than 120° Cent., under very considerable 

 pressure and during a long period, upon the trachytic and zeolitic 

 rocks beneath, would dissolve many of the elements of which they 

 are composed ; among others silica, alumina, soda, potash and lime. 

 The alumina and lime would not long continue dissolved in the sili- 

 ceo-alkaline solution, while the silica, potash, and soda, would remain 

 in different proportions, as is found in the thermal waters of Ice- 

 land. 



M. Descloizeaux communicated the results of investigations made 

 jointly with M. Bunsen, of Marbourg, on the two principal Geysers 

 of Iceland. Experiments were made in the pipe of the Great Geyser, 

 by which it was found that the temperature at the bottom was va- 

 riable, being highest immediately before and lowest immediately after 

 the great eruptions. It is inferred that the source of heat is not 

 situate immediately beneath, but at a distance, probably consider- 

 able, and that the column of water communicates by a long and 

 winding channel with the space where the direct action of tlio sub- 

 terranean heat is felt. After a great eruption, during which a 

 large body of water and steam is ejected, the lower part of the liquid 



