^^^' 55-] GEOLOGY OF THE DAVOS DISTRICT. 387 



series of peaks, as in the neighbourhood of the Arosa Rothhorn, 

 mixed up with other strata. When, however, this latter group is 

 traced northward into the Davos district, it will be found to con- 

 tinue in definite and separate ridges, the tectonic meaning of which 

 will be discussed at a later stage. The westernmost line includes the 

 Arosa Weisshorn and its surrounding slopes, and crosses the Arosa 

 and Upper Plessur valleys to the Weissfluh, the Casanna, and the 

 Cotschna ridge. The second forms the great series of crags on 

 the east of the Arosathal: the Schiesshorn,Thiejerfluh, Madrigerfluh, 

 Kiipfenfluh, and the twin Schiahorner above Davos. The dolomite- 

 region of the Lower Landwasser spreading round Wiesen is not 

 prolonged so far to the north, but ends in the long ridge of the 

 Alteingrat and the cliff-like wall of the Amselfluh. The south- 

 easterly dip is prevalent in all these ridges, though occasionally, 

 as near Davos itself, there may be a north-westerly inclination 

 indicating the presence of minor folds. 



(3) The Mittelbildungen. — Theobald used this term as a 

 general name for the beds which occur in Graubiinden between 

 the Hauptdolomit and the Verrucano ; and though the name does 

 not express a sharply-defined geological series, it is convenient to 

 retain it. In this position in the Austrian Alps occur various for- 

 mations defined by characteristic fossils ; but in the Davos district 

 we find only much reduced and widely varying representatives of the 

 Arlberg-kalk, Partnach Schiefer,yirgloria-kalk, and Streii'en Schiefer, 

 with their associated beds of gypsum and rauchwacke. 



In the north of the district, beyond Klosters, the Hauptdolomit 

 disappears, and in the limestone-band which runs thence towards 

 the Calanda and Arlberg Theobald has traced almost all these 

 beds. In other parts thin layers of the Arlberg-kalk and Virgloria- 

 kalk can be often traced, with local patches of the other members 

 of the group ; but frequently, as in the Strela-Schiahorn ridge, the 

 whole series is reduced to a thin layer of shaly limestone. 



(a) The tJpper Rauchwacke. — Rauhwacke or rauchwacke is 

 a yellowish limestone, sometimes dolomitic, with a characteristic 

 vesicular or porous structure. It occurs on two horizons in the 

 Trias. The Upper Rauchwacke often lies immediately below the 

 Hauptdolomit, separating that formation from the Liiner or Raibler 

 Schiefer below, and it is commonly associated with beds of gypsum. 

 In the Davos district it is frequently absent, but may be observed 

 in the valleys north of Wiesen, and with gypsum-beds on the 

 Gypshorn and the Strehl of the Ducan basin and on the north of 

 the Casanna-Cotschna ridge. The latter is perhaps in the same 

 geological position as the patch which appears between the Weissfluh 

 dolomite and the serpentine of the Todtalp Schwarzhorn. 



(/j) The Arlberg-kalk is generally a compact, fissile, dark- 

 grey limestone, often partly siliceous. It is but slightly developed in 

 this area, although fairly constant. A good example may be found 

 on the Parsenn slope above Schwarzseealp, though it is not marked 

 on Theobald's map. 



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