94 Professor Favre on the Geology of the German Tyrol. 



tified formations, and in pai'ticular in Chablais and Faucigny. 

 Is the doloniite, in these localities, the result of submarine 

 eruptions, analogous to those of the Tyrol ? that is to say, 

 did there exist in the sea which deposited this rock, a greater 

 quantity of sulphate of magnesia and chloride of magnesium 

 than in the present seas \ Without being certain, this appears 

 to us probable ; for we likewise find in Savoy evident traces 

 of submarine eruptions. These traces are furnished by the 

 rock long known under the name of Taviglianaz sandstone,* 

 in a locality in the chain of Diablerets, where it is much de- 

 veloped. 



This rock, which is widely diffused in Savoy, and in the Can- 

 tons of Vaud and Berne, has not the same composition as the 

 pyroxenic rocks of the Tyrol ; but it has a close relation, in 

 its geological position, with the pyroxenic tufas of this 

 country. 



The sandstone of Taviglianaz, of which we can distinguish 

 many varieties, is usually formed of white felspar in small 

 crystallized fragments ; blackish or greenish amphibole, in 

 fragments of imperfect crystals, but in which we can deter- 

 mine an angle of 124' ; of white or black mica in scales by 

 no means abundant, and of quartz in small fragments, some 

 of which are so rounded that they appear to have been rolled. 

 Some specimens of these rocks eflFervesce with acids. This 

 is not, therefore, a pyroxenic tufa ; but rather, if we might 

 venture to make this supposition, a syenitic tufa. This rock 

 has a position analogous to pyroxenic tufa; in this sense, 

 that it is stratified, and alternates with beds really formed 

 by way of sediment, such as limestones more or less argil- 

 laceous. It is a rock of igneous origin, triturated and stra- 

 tified by the waters. With regard to the age of its for- 

 mation, it differs considerably from that of pyroxenic tufas, 

 with which we are at present specially pccupied ; for it 

 usually covers the nummulitic formations, and is itself covered 

 by the flysch, or Alpine macigno. 



Is this rock connected with the pyroxenic eruptions which 



* As early as 1834, M. Studer, in his work on the Western Alps, compared 

 the sandstone of Taviglianaz to a volcanic tufa. 



