^Ol. 55.] THE GEOLOGY OE THE DAVOS DISTKICT. 381 



25. The Geology of the Davos Disteict (Switzeeland). By A, 

 Vaughan Jennings, Esq., F.L.S., F.G.S. (Read May lOth^ 

 1899.) 



[Plates XXVI & XXVII— Map & Section.] 



Contents. 



Page^ 

 I. Introduction. — Position and General Geological Structure of the 



District 381 



II. The Rocks of the District ' 383 



{a) The Chief Rock-sj'stems present. 

 {b) The Rocks of Limited Distribution. 



III. The Tectonics of the District 399^ 



(a) The Nature and Number of the Mountain-folds. 



{h) The Three Eastern Folds, and the Formations present in 



them, 

 (c) The Western Fold, and its' Special Features. Suggested 

 Explanation of these, and Correlation of the Rocks with 

 those of the other Folds. 

 IV. Summary of Conclusions 411 



I. Introduction. 



TowAEDS the east of Canton Graubiinden lie the mountain-ranges^ 

 which surround the Valley of Davos, a valley now so renowned for 

 the healing value of its climatic conditions, but till lately both 

 difficult of access and remote. 



Those who know Davos only when the individuality of the surround- 

 ing mountains is lost in the white brilliancy of its wondrous winter 

 may, naturally enough, never be led to think of the nature and origin 

 of the walls of their splendid prison ; but to the yearlj^-increasing 

 number of those in comparative health who remain or arrive during" 

 the summer months there are features in the landscape which must 

 attract attention if they do not excite enquiry. It is difficult for 

 the most casual observer to avoid noticing the abrupt crags of the 

 Cotschna ridge above Klosters, the steep-tilted slopes of the twin 

 Schiahorner, the long level ridge of the Alteingrat, and in the 

 southern distance the sharp silhouettes of the Tinzenhorn and the 

 Piz Michel shutting off this mountain-valley from the western world. 



Some explanation of the changing contours and the varied colours 

 of these barrier-mountains may be of interest to those who have 

 looked and wondered ; but it is not only on such general grounds 

 that a detailed description of the district is desirable. 



There are problems in the structure of the district of the greatest 

 interest to all geologists, and regarding the nature and relative date 

 of the great earth-movements which have resulted in the Alps as 

 now known, it is a district which should afford evidence to the 

 enquirer, if not in all cases explanation. The age of the ' Biindner 

 Schiefer,' the origin and date of the serpentine and its associated 

 red-and-green schists, the meaning of the great * overthrust ' and 



