264 COSMOS. 



According to the admirable observations of Leopold von 

 Buch, the masses of dolomite fomid in Southern Tyrol, and on 

 the Italian side of the Alps, present the most remarkable in- 

 stance of metamorphism produced by massive eruptive rocks 

 on compact calcareous beds. This formation of the hmestone 

 seems to have proceeded from the fissures which traverse it in 

 all directions. The cavities are every v/here covered w^ith 

 rhomboidal crj'^stals of magnesian bitter spar, and the v^hole 

 formation, without any trace of stratification, or of the fossil 

 remains which it once contained, consists only of a granular 

 aggregation of crystals of dolomite. Talc laminse lie scattered 

 here and there in the newly-formed rock, traversed by masses 

 of serpentine. In the valley of the Fassa, dolomite rises per- 

 pendicularly in smooth walls of dazzling whiteness to a height 

 of many thousand feet. It forms sharply -pointed conical 

 mountains, clustered together in large numbers, but yet not in 

 contact with each other. The contour of their forms recalls to 

 mind the beautiful landscape with which the rich imagination 

 of Leonardi da Vinci has embellished the back-ground of the 

 portrait of Mona Lisa. 



The geognostic phenomena which we are now describing, 

 and which excite the imagination as well as the powers of the 

 intellect, are the result of the action of augitic porphyry man- 

 ifested in its elevating, destroying, and transforming force.* 

 The process by which limestone is converted into dolomite is 

 not regarded by the illustrious investigator who first drew at- 

 tention to the phenomenon as the consequence of the talc being 

 derived from the black porphyry, but rather as a transforma- 

 tion simultaneous with the appearance of this erupted stone 

 through wide fissures filled with vapors. It remains for future 

 inquirers to determine how transformation can have been effect- 

 ed without contact with the endogenous stone, where strata 

 of dolomite are found to be interspersed in limestone. Where, 

 in this case, are we to seek the concealed channels by which 

 the Plutonic action is conveyed ? Even here it may not, how- 

 ever, be necessary, in conformity with the old Roman adage, 

 to believe " that much that is alike in nature may have been 

 formed in wholly difierent ways." When we find, over widely- 

 extended parts of the earth, that two phenomena are always 

 associated together, as, for instance, the occurrence of mela- 



* Leop. von Buch, Geognostische Briefe an Alex, von Humboldt, 1824, 

 «. 86 and 82 ; also in the Annalen de Ckemie, t. xxiii., p. 276, and in the 

 Ahhandl. der Berliner Akad. avs der Jahren 1822 i(?id 1823, s. 83-136 ; 

 Von Dechen, Geognosie, s. 574-576. 



