observable in the Secondary Stratified Rocks. 2 1 5 



England and France, supporting the great mass of green-sands, 

 chalk and tertiary rocks, which constitute so large a portion 

 of both these countries, would at first sight be little prepared 

 to find this mass of light-coloured and often tender limestones, 

 with their mixtures of clays or marls, connected, from some 

 cause either original or from disturbance, into hard dark and 

 compact limestones, resembling those commonly called transi- 

 tion, sometimes mixed with gypsum and dolomite ; in fact, in 

 raineraiogical structure very different from the same formation 

 in England and the North of France, where it has suffered little 

 disturbance beyond the fractures called faults. 



M. Von Buch's letter on the Dolomite of the Tyrol, is dated 

 1822, and his account of the Southern Tyrol, 1823. In these 

 memoirs he states his opinion, that the dolomite mountains of 

 that country, so remarkable for their forms and their frequent 

 crystalline character, are probablythe limestones of the country 

 altei'ed by the intrusion of the black or augite porphyry among 

 them, which he supposes converted the compact limestone into 

 a very crystalline rock, highly charged with magnesia. It 

 would be here out of jilace to enter into a detail of the facts 

 he has brought forward: I shall content myself with a reference 

 to the map and sections, which will at least show the shattered 

 and broken state of this part of the Alps. This Tyrolese 

 limestone, though commonly referred to the Jura limestone, has 

 not yet been well determined ; but certainly a part at least of 

 their continuation towards the lakes of Como, &c. is of that 

 epoch. Those of the Tyrol are gray and shelly, and they 

 may represent in part the chalk or green-sand series. 



In 1825, M. Von Buch visited the lakes of Orta, Maggiore 

 and Lugano, for the purpose of more particularly examining 

 the porpliyries in those districts. The result was a note on 

 the pliaiuomena presented by the relative position of the do- 

 lomite, limestone, and porphyries of the Lago di Lugano, which 

 appeared first, I believe, in a Gernian Journal, ancl afterwards 

 in the Amialcs dcs Sciences Nalurclles (or February 1827. In 

 this he took occasion to insist on the analogy observable in 

 the phuenomena of this district and those of the Tyrol, point- 

 ing out the dolomite mountain of San Salvador as an excellent 

 example of the truth of his theory. — The following is his dc- 

 scri|)tion. 



After mentioning the red conglomerate of San Martino, con- 



ractcristic. We may take as an example the niimiiiulitc rocks of thcAIps. 

 'riiesc, when examined partially, liavc l>een, and no doubt will be by many 

 observers, c-onsidcTcd as tertiary ; but if they arc examined on the larj;(! 

 scale, and their conucction with other districts rnnfu//i/ examined, we can 

 scarcely refuse to consider them '.is referable to the {,'rten-sand series. 



tnining 



