Professor Favi-e on the Geology of the German Tyrol. 93 



logical position is found to be sufficiently explained by this 

 theory. Some of them are regularly stratified, as in the moun- 

 tains of the Tyrol; this is a regular sedimentary formation simi- 

 lar to that of limestone, although, perhaps more complicated. 

 The other dolomites are crystalline, saccaroidal (at St Goth- 

 ard, Pfilsch-Joch), in their position corresponding to that of 

 the saccaroidal limestone ; they have undergone a metamor- 

 phism similar to that of this rock ; and, as M. Fournet says, 

 in speaking of pi'edazzite, we may assert that we ought not 

 to see in saccaroidal dolomite an effect of magnesian cemen- 

 tation, but rather the simple fusion of a limestone already 

 magnesiferous.* 



We perceive, then, that this theoi'v on the origin of dolo- 

 mites does not rest on the vaporisation of the magnesia, an 

 occurrence which is known neither in nature nor in labora- 

 tories, but is founded, 1*^, On the consideration that the 

 eruptions of melaphyres (magnesiferous rocks) are anterior 

 to the formation of dolomites ; 2d, That these eruptions were 

 submarine ; 3</, That they were accompanied with acid vapours 

 which formed salts of magnesia, which, under the circum- 

 stances of pressure, and suitable temperature (somewhat high), 

 have modified the composition of the newly- formed limestone. 

 There is no fact in this theory whicli was not previously 

 known, and which is not daily repeated, so to speak, both in 

 nature and in laboratories. 



" More to the west, in Switzerland and in Savoy," says 

 M. de Buch, in the conclusion of his celebrated Memoir on 

 the Dolomites of the Tyrol, " we observe none of those pheno- 

 mena we have been discussing, and which, considered in their 

 mutual connection, may thi'ow some light on the formation of 

 the high chain of the Alps." — (Annales de Chimie, xxiii., 

 p. 407 ; 1823.) 



This assertion .appears to us to be too positive. Indeed, 

 although we can see nowhere in Savoy great chains of moun- 

 tains formed by dolomites so white and remarkable as those 

 of the Tyrol, this rock is still abundant in the regularly stra- 



* Annales de la Sociite irA^'rirulturc de liyon, iv., p. 12. 



