C PEOCEEDIXGS OP THE GEOLOGICAL SOCIETY. 



the sedimentary rocks also have been affected by it — a process 

 which is still going on. 



The author then proceeds to describe the physical features of 

 the different mountain-masses in the district under considera- 

 tion, and describes in detail the order of stratification and their 

 disturbances, changes, and metamorphisms in the twelve different 

 groups examined. It is impossible to give even a slight sketch of 

 the various complications, upheavals, inversions of stratification, 

 and distortions whicli these sedimentary rocks have undergone 

 during the oft-repeated elevatory action, as well as the correspond- 

 ing subsidences, to which they have been subjected. I will only 

 observe that the sedimentary rocks here treated of consist of all the 

 known formations of the Alps, from the Triassic system i;pwards 

 to the Elysch. It is, however, suggested that the Verrucano, 

 which overlies the Casanna and hornblende-schists, may possibly 

 be of Permian age. 



The description of each group or central mountain-mass is fol- 

 lowed by an account of the results arrived at by its examination. 



The first group described is the Hhseticon, and the following are 

 some of the results at which the author has arrived. 



All its formations lie in zones around the central nucleus, which 

 consists of the outlier of the Selvretta mass towards the west. The 

 northern Trias-liassic zone, which, following the 111 and the Arlberg 

 road as far as the Inn, forms the north side of the Selvretta mass, 

 has been already alluded to, but it does not belong to the district 

 under consideration. 



The crystalline rocks show a decided fan-shaped structure to- 

 wards their flanks, and overlie the sedimentary rocks, so that the 

 formations appear inverted. 



This crystalline nucleus consists of gneiss and hornblende- 

 schist, so that the former appears to form the true nucleus, and 

 the latter the outer layers, although internally they alternate, and 

 mica-schist alternates with both. The boundary towards the 

 sedimentary rocks consists everywhere of Casanna-schist, which 

 passes into the former or crystalline rock. 



The sedimentary rocks participate in this inversion even where 

 the crystalline rocks are not seen, or at least not in large masses. 



The Verrucano is seen along the whole line, bvit very variably 

 developed. In one place it forms a broad zone of red conglome- 

 rate, in another it is reduced to thin bands of quartzite and varie- 

 gated schists. 



The middle formations are much less strongly developed along 

 the whole southern base of the lihseticon than on the north side, 

 so that it is diffi.cult to distinguish the separate members, particu- 

 larly as they have been much altered by the proximity of the crys- 

 talline formations, and fossils are wanl^ng. 



The most persistent is the Virgloria limestone. The lower 

 Ranch wacke only appears on the Saaser Alp. Towards Monbiel 

 the whole zone thins out completely, and is replaced by thin slaty 

 limestone beds. 



