406 • ME. A. V. JENNINGS ON THE [^"g. 1899, 



and it seems to me therefore that the coutinuity of this ' Cotschna 

 ridge ' with the raifareous series west of Arosa can scarcely be 

 doubted. It seems equally certain that, since both Veriucano and 

 Casanna Schiefer have been traced alike above and below the 

 limestone series, one is dealing here with a crushed synclinal fold 

 such as that of the Strelagebirge and others already described. 



The difference lies in the greater intensity of the dynamical forces 

 which have been in operation along the strike of this fourth fold, 

 combined with the presence of rocks which are not represented in 

 the three folds so far considered. The serpentine is obviously a 

 new element; it is not present in the eastern folds. The main 

 geological problems of the district are, firstly, its age and origin ; 

 and, secondly, how far the rocks associated with it are represen- 

 tatives of formations distinct from those already dealt with, or may 

 represent the same strata modified or metamorphosed by the peculiar 

 conditions to which they have been subjected. 



Before, however, entering into the arguments for the age of these 

 problematic rocks, it is necessary to give some account of the local 

 distribution of the different members of the group, and the best 

 idea may be arrived at by following the successive outcrops north- 

 ward from the Davos Lake. 



Returning to the Davos Valley, where the northern edge of the 

 Strela fold crosses below the lake, the whole west side of the valley 

 is seen to be occupied by the crystalline schists of the Dorfliberg. 

 In the central part of this mass are the gneisses and the ' horn- 

 blende-schist ' already noted on the east as w^ell as on the Korbshorn 

 and Wannengrat ridges. The older crystallines are thus once more 

 present here. The northern and southern margins of the mass seem 

 to belong, however, to the Casanna Schiefer. The southern band 

 . includes the quarries at the south-western corner of the lake, and 

 (as we have seen) reappears on the easb. The northern outcrop 

 borders the serpentine by the railway along the Meyerhofer Thali, 

 and forms the jagged, saw-like edge of the Mittelgrat, where its 

 conspicuous element is a white micaceous or talcose granite. This 

 can be traced in close connexion with the serpentine across the 

 barren valley under the Schaflager, and so over the sharp ridge that 

 here forms the watershed of the Davos and Plessur valleys. 



The line of crystalline rocks which may be termed the Dorfliberg 

 anticlinal disappears in the rocky promontory at the north-western 

 corner of the lake, but is found again in the stream -bed north of 

 TJnter Laret, and runs along the eastern slopes of the Lareterthal, 

 over the Eiiti ' shoulder,' between the Strela limestone above and 

 the serpentine below, and so across to the Eastern Ehiitikon. 

 Westward it is continued as a narrow band under the Schiahorn 

 and Kiipfenfluh, and is here, I believe, thrust forward, together 

 with the overlying dolomites, causing the local disappearance of 

 the subjacent serpentine. Thus farther west, above Kiipfen, where 

 the latter rock reappears, the crystalline zone widens out, under- 

 lying the chalets of Madrigen, and striking south towards the 

 , Arosathal. 



