80 Professor Favre on the Geology of the German Tyrol. 



these two rocks pass into one another. It will be further 

 remarked, that the circumstances which have developed the 

 garnets in the argillo-talcose slates have produced the same 

 effects in the green slates, for in these garnets are abundant. 

 The green slates are developed in the neighbourhood of the 

 serpentines and amphibolic rocks ; and we may regard both 

 of these rocks as being the maximum of alteration in tliis 

 great formation of slates presenting such varied characters. 



On ascending Pfitsch-Joch from Zell, we find porphyroidal 

 amphibolites, other varieties in which the amphibole is radi- 

 ated, argillo-talcose slates, green garnetiferous slates, and 

 dolomites ; these rocks constitute the mountain Greiner (8800 

 feet), celebrated for its minerals. It is near the granitic 

 chain of the bottom of the Ziller-Tlial. 



The green slates, containing a variable quantity of epi- 

 dote, form a great part of the mountains of the valley of 

 Gastein, particularly between this valley and Kauris. 



The serpentine, as T have mentioned, is disposed in masses 

 throughout the formations of which we are treating. In gene- 

 ral, it is placed in beds, or in fragments of beds, parallel to the 

 central chain. Tliis arrangement indicates that this rock is 

 not one of eruption, but that it is the produce of strongly de- 

 veloped metamorphic action. I have found this rock at 

 Pfitsch-Joch with a species of euphotide, near Dollach in Ca- 

 rinthia, at Matrey between Innsbruck and the Brenner, where 

 it is mined along with ophicalce ; it is everywhere surrounded 

 with large masses of green slate. 



The non-fossiliferous stratified formations are, therefore, 

 composed of argillo-talcose slates, green slates, limestones, 

 dolomites, amphibolites, serpentines, and ophicalces, the va- 

 rieties of which are infinitely numerous. The principal rock 

 is the first of those we have indicated ; the others occur in 

 the form of beds, or fragments of beds, parallel to the central 

 chain. 



The presence of the Silurian formation in the Tyrol has 

 been determined a few years since. The following are our 

 observations on this subject. 



When traversing the valley of Gastein, from south to 

 north, and receding from the granitic and central chain, we 



