^^1* 55'] ^H^ GEOLOGY OP THE DAVOS DISTRICT. 405 



quarried on fche opposite shore afc the south-western corner of the 

 lake. Beyond this first cutting, the right-hand bank shows a small 

 exposure of shaly rock which proves to be certainly Verrucano. 

 Succeeding this is the exposure of dolomite through which the 

 second cutting runs, and as this dips down towards the lake we find 

 once more above it a still more reduced representative of the 

 Verrucano. Following immediately is a mass of Casanna Schiefer 

 like that with which we started, constituting the last exposure of 

 solid rock on the railway east of the lake. 



It is thus evident that all the elements of the Strela fold are 

 still present, though greatly reduced; that they cross the valley 

 from the Schiahorn to the foot of the Seehorn ; that they border 

 the lake on the east, and disappear at its northern end under the 

 Wolfgang-Drusatcha ridge. This disappearance is of great importance 

 in connexion with the view which I have suggested elsewhere,^ as 

 to the nature of the Davos Valley and the former courses of ita 

 rivers, and shows that an investigation of the solid geology of the 

 district confirms the opinions arrived at from physiographical con- 

 ditions only. If the Wolfgang-Drusatcha ridge were composed of 

 solid rock, in situ, one would expect to find this limestone-band 

 striking across it ; but, so far as I know, there is no trace of it. 

 It is only by the Monchalpthal that we find it again, but from 

 here it can be followed round the shoulder of the mountain above 

 E,uti toward the Silvrettathal. North of this it reappears, and 

 can be traced above Monbiel obliquely across the Rhatikon towards 

 the neighbourhood of the fault in the Verkolmtobel. 



The Fourth or Cotschna-Arosa Fold. 

 (PL XXVII & figs. 4-7, pp. 402, 404, 407.) 



In what I take to be the fourth of the series of folds comprised 

 within the Davos district, the limestone-outcrops, by which the 

 position of such folds is generally most readily traced, form the 

 conspicuous masses of the Weissfluh and the Casanna. Between 

 the Strela Pass and Langwies there seems to be a thinning of the 

 calcareous band, but there is little doubt that the Casanna- Weissfluh 

 line is continuous with that which crosses the Langwies-Arosa 

 valley, runs round the slopes of Pretsch and Maran, and merges 

 into the larger masses round the Arosa Weisshorn. 



It is true that, looking from the Strela Pass, one might at first 

 be inclined to regard the Weissfluh as a direct extension of the 

 Schiahorn fold, but the intercalation between the two of a well- 

 marked crystalline zone shows that such is not the case ; while the 

 expansion of this band on the east into the great mass of gneiss 

 and schists which constitutes the Dorfliberg (apart from the 

 question of the serpentine Todtalp) will soon convince one of the 

 distinctness of the two limestone-masses. The dolomite of the 

 Casanna, which follows the Weissfluh on the north, is continued 

 eastward to form the limestone-cliff's, so conspicuous from Klosters, 



^ Quart. Journ. Geol. Soc. vol. liv (1898) p. 279, & Geol. Mag. 1899, p. 259. 



