STUDER—GEOLOGY OF SWITZERLAND. 29 



tine, slate, and limestone : Saussure devoted more than three days 

 to the study of them. 



In the region of the Alps of the Tessine the gneiss and mica-slate 

 have almost entirely lost their alpine character. A well-characterized 

 gneiss predominates, and next to that mica-slate is an important 

 member of the group. The latter rock abounds in many kinds of 

 concretions, especially at the Cima di Zambro, at the foot of the 

 P. Forno, at Sponda, &c. &c. The limestone and slate mass of the 

 Levi- and Dever-Alps is in the strike of the green slates and lime- 

 stone, which may be followed from Saas to Zwischbergen, and is 

 doubtless their prolongation. The rocks at Naret, at the junction of 

 the romantic valleys of Bavona, Peccia, and Campo la Torba, are 

 extremely disturbed. In the deep ravine of Val Bavona, on the 

 eastern base of the Gran Pasodon, hitherto unknown to the geolo- 

 gist, the gneiss which surrounds the Suena Alp on its western side 

 overlies the dolomite belonging to the calcareous zone, and is inter- 

 twisted with it and with schists, while further on the gneiss is clearly 

 seen as the fundamental rock of the range. 



The Alps of the Adula range present a very unusual character. 

 The longitudinal and transverse valleys seem to have exchanged their 

 usual conditions. Distant as they are from the axis of the Tessine 

 Alps, their remarkable elevation en masse proves them to have been 

 disrupted from the latter. 



Closely as the Tessine Alps are connected with the Adula range, 

 they are still more nearly related to the gneiss which spreads 

 out from Schams to the Rofla and to Perrara, and which reaches its 

 greatest development in the Sureta Alps with their snowy pinnacles 

 surrounded by glaciers. The pass of the Spliigen gives great facili- 

 ties for studying this group. To the west rises the noble pyramid 

 of the Tambo Horn, consisting of beds of gneiss dipping east. With 

 these are associated in the background of the Toga Alp talcose and 

 micaceous slate, hornblende slate, and quartzite, mostly of a decom- 

 posing quality. The main road from the Spliigen, following the 

 romantic pass of the Rofla, penetrates into the central nucleus of the 

 group. The grey micaceous and calcareous schists which have pre- 

 vailed from Spliigen, begin at Suvers to give way to chlorite slate 

 and talcose gneiss, alternating with white marble. On the road from 

 Pignen to Nezza, for about five hundred metres above the bottom of 

 the valley, are seen, horizontally disposed, slates forming the founda- 

 tion of a vast wall of white marble and grey limestone. The Despin 

 Alp above Zillis is an enclosed circular basin [Thal-Kessel], the back- 

 ground of it rising to the lofty peak of the Curves. On the west a 

 plateau of limestone and dolomite shuts in the basin, leaving only a 

 narrow exit for the waters from the mountain. In the lower part of 

 the valley there were formerly many mines of argentiferous galena and 

 of copper pyrites, which are found in talcose gneiss accompanied by 

 large crystals of felspar. More than a dozen deserted mines can be 

 counted along the edge of the stream, which is precipitated over many 

 cataracts, and along the rocky descent of the mountain towards Nezza. 



The crystalline slates which appear between the groups mentioned 

 and the next zone to the south cannot readily be described, or sub- 



