Yol. 55.] GEOLOGY OF THE DAVOS DISTRICT. 399 



III. The Tectonics of the District. 



Having thus obtained some idea of the local distribution of the 

 various rocks, an endeavour may now be made to distinguish the 

 interrelationship of the diiFerent outcrops and to form some idea of 

 the true structure of the district, so as to represent it by a series of 

 sections or by a model. 



While Theobald's map is on the whole remarkably accurate, it 

 will be at once evident to a geologist that the sections which accom- 

 pany that author's memoir are far from representing the conditions 

 which actually prevail. The nature of mountain-folds was in 

 Theobald's time but inadequately realized, and it seemed impossible 

 to represent the ancient crystalline rocks as lying above and parallel 

 to sedimentary strata of Mesozoic age. Hence we find the dolomite 

 and its associated rocks represented as forming shallow basins on the 

 edges of uptarned schists and gneisses. 



Since the publication of Theobald's memoir no attempt, I 

 believe, has been made to explain more exactly the structure of the 

 Davos region, and to bring our reading of it more into accord with 

 the growth of our knowledge of mountain-building. The view which 

 I here venture to put forward explains, I think, as nearly as possible 

 the different outcrops actually observed ; at the same time it perhaps 

 throws some light upon the nature of the doubtful rocks of the district, 

 and brings new elements into the consideration of its more inter- 

 esting problems. It may be added that the explanation suggested 

 was arrived at from observation of the mountains themselves, not 

 from a study of the map ; and that the sections here reproduced are 

 sketches made in the field from such comprehensive points of view 

 as the summits of the JElplihorn, the Jacobshorn, the Schiahorn, 

 and the Kiipfenfluh. 



The repetition of such rocks as the Yerrucano and the Casanna 

 Schiefer on each side of the different outcrops of limestone and 

 dolomite shows at once the presence of a series of folds in the 

 district, while the almost constant south-easterly dip of all the 

 strata indicates that the folds are, as a rule, compressed or flattened 

 and have undergone pressure and thrusting from that direction. 

 A study of the simplest fold, that of the Ducan, shows that the 

 Secondary rocks occupy the troughs of the folds, while the older 

 crystallines form the anticlinals between them. 



It is by no means easy to be sure of the number of the folds 

 present, more especially where they are approximated in the south 

 and west: but I believe that, within this area, there are four 

 distinct synclinals, which may be enumerated as follows : — 



(1) The First, Eastern, or Ducan Fold. 



(2) The Second or Wiesen-Amselfluh Fold. 



(3) The Third or Strela Fold. 



h (4) The Fourth, Western, or Arosa-Cotschna Fold. 



The first three are of comparatively simple character, composed 

 of rocks referable with more or less exactness to definite geological 



