252 GEOLOGICAL DESCRIPTION OF THE EAIITH'S CRUST. 



some cases granular limestone may not have been formed 

 in the interior, and raised to the surface by gneiss and 

 syenite, ( 281 ) where it occupies fissures, as at Auerbach or 

 in the Bergstrasse, is a question on which I do not 

 venture to express an opinion, because I have not personally 

 visited the localities. 



The most remarkable instance of metamorphism produced 

 by erupted rocks on compact calcareous strata, is that which 

 Leopold von Buch has pointed out in masses of dolomite, 

 especially on the southern Tyrol, and on the Italian declivity 

 of the Alps. ' The alteration of the limestone appears to 

 have been effected by means of fissures traversing it in every 

 direction ; the cavities are everywhere covered with rhorn- 

 boidal crystals of magnesia, and the whole formation con- 

 sists of a granular agglomeration of crystals of dolomite, 

 without any trace of the original stratification, or of the 

 fossils which were previously contained in it. Laminae of talc 

 are partially disseminated in the new rock, and it is interspersed 

 with masses of serpentine. In the valley of the Passa 

 the dolomite rises perpendicularly in smooth walls of daz- 

 zling whiteness to a height of several thousand feet. It 

 forms groups of numerous sharply-pointed conical moun- 

 tains, clustered but separate. These features recal the 

 lovely mountain landscape with which the imagination of 

 Leonardo da Vinci has adorned the background of the por- 

 trait of Mona Lisa. 



The geological phsenomena which we are here describing, 

 and which interest both the imagination and the intellect, 

 Result from the action of augitic porphyry, which has ele- 

 vated, shattered, and transformed the beds which are above 

 it. (282) The illustrious geologist who first brought into 



