82 Professoi' Favre on the Geology of the German Tyrol. 



much more certain than that of the Silurian formation. It 

 is developed at Stangalp, to the west of Gmund, and to the 

 north of Villach, as is mentioned by M. Morlot, in his ex- 

 planation of the Geological Map of the Alps, and as is proved 

 by specimens in the Museums of Vienna and Linz ; the lat- 

 ter come from Rosaninalpe to the south of the Radstadter- 

 Tauern. 



Ascending in the geological scale of formations, we find 

 the red sandstones, the trias and dolomite, formations which 

 are associated with and traversed by the quartziferous and 

 pyroxenic porphyries. The observations made by us on these 

 varied rocks are the following : 



Turning eastward from Klausen, in the valley of the 

 Eisack, by the Grodner-Thal, as far as St Cassian, we pass 

 over a transverse section of the most interesting nature. But, 

 in order to obtain a general view of the whole, it is neces- 

 sary to make several detours, such as those of Castelruth, 

 the Seissei*-Alp, and Langkogl. The Eisack cuts through 

 different porphyritic rocks, which seem to form the base of 

 the sedimentary formations ; then, ascending to reach the 

 Grodner-Thal, we walk over argillo-micaceous and talcose 

 slates ; and near the village of St Peters, we arrive at 

 masses of red quartziferous porphyry, which, considered on 

 a large scale, appear to form a bed rising towards the west, 

 but to which two systems of fissures, which cross each other, 

 have given an irregular prismatic structure. This porphyry 

 is usually altered on the surface ; it is covered by the red 

 sandstone, the beds of which have a stratification conform- 

 able with the porphyry. M. de Buch has long since shewn 

 that the porphyry was the mother-rock of the red sandstone. 

 Above the red sandstone, which is highly developed in the 

 neighbourhood of Castelruth, are found difi'erent beds which 

 are referred to the trias system ; but it is not always easy 

 to seize exactly their geological position, for the vicinity of 

 the quai'tziferous porphyry, especially that of the pyroxenic 

 porphyi'y and the immense quantity of pyroxenic tufa, which, 

 after alternating with these, have altered them, and intro- 

 duced among them the elements of the plutonic rocks, which 

 ]-enfler tlieir characters very vai-iable. Above the red sand- 



