M. Virlet on the Transformation of Rocks, 97 



stratified, like the other rocks to which they may be found sub- 

 ordinate ; while the dolomites of which I now speak, and which 

 I shall call dolomites of transmiitatiofi (such as are described by 

 M. de Buch as occurring among the Alps, and many others which 

 I could mention), are without stratification, presenting irregular 

 masses, combined with other characters which individuals accus- 

 tomed to observe modified rocks can seldom mistake. No one 

 who has visited the dolomites of the Alps can entertain any 

 doubt of the reality of the phenomenon of dolomisation, however 

 difficult the explanation of it may at first appear, since chemistry 

 teaches us that carbonate of magnesia is not volatile, or that it is 

 decomposed at a red heat, an objection which has been urged by 

 M. Thenard. It was in fact these considerations that caused me 

 to be among the first to publish my doubts on the subject, at a 

 time when no one undertook to ascertain, by chemical analysis, 

 that the parts of the deposit which had not been modified, were 

 not equally magnesian ; that is, did not form beds of primitive 

 dolomite — a circumstance which would have reduced the pheno- 

 menon of the change of limestones into dolomite, to a simple 

 phenomenon of modified crystallization, analogous to that, for 

 example, which has determined the change of the compact Jura 

 limestone of Carrara, and that of the compact chalks of some 

 parts of the Pyrenees, into granular limestones or statuary mar- 

 ble. One of my friends, M. Des-Genevez, who possessed a very 

 extensive knowledge of chemistry, and whose early scientific 

 works afford so much reason to lament his premature death, has 

 unhnppily been lost to the sciences before publishing the results 

 of his chemical researches on dolomisation. These, he has many 

 times assured me, had demonstrated to him that there existed 

 an insensible passage from beds of unaltered carbonate of lime to 

 dolomite or double carbonate of lime and magnesia. Thus the 

 transformation of certain calcareous rocks into dolomite, poste- 

 riorly to their formation, appears to me to be a well established 

 phenomenon, and requires, in my opinion, only to be properly 

 explained in order to be admitted by all. 



Who does not know how many facts, perhaps among the most 

 difficult to comprehend previously,havealready been explained by 

 the excellent researchesofM. Becquerel in electrical chemistry, and 

 the important labours of M. Fournet, regarding the formation of 



VOL. XXr. NO. XLI. — JULY 1836. 



