400 MK. A. V. JENNIK'GS 01^ THE [^^g- i899j 



systems. The western fold is that which is thrust over the grey 

 Biindner Schiefer of the Scharifigg and Pratigau, and is complicated 

 by minor folds as well as by the presence of the serpentine with 

 its associated diorites and variohtes, red cherts, red-and-green schists, 

 and breccias ; all of which, as to their age and origin, are still the 

 subjects of controversy. 



The First or Ducan Fold. (PL XXYII.) 



The first fold comprises the mountains of the Ducan district. The 

 pass of that name, which connects the head of the Sertigthal, by a 

 narrow saddle at a height of 2760 metres, with the valley leading 

 down to the Albula, is flanked on either side by conspicuous masses 

 of the Hauptdolomit and its associated limestones ; while a broad zone 

 of Yerrucauo and Casanna Schiefer fringes the isolated tract and 

 shuts it off from the surrounding sea of crystalline rocks. 



From the fact that a distinct south-easterly dip is observable on 

 the Davos side, while a corresponding north-westerly inclination is 

 noted near the Sertig Pass, it might be concluded that, in this 

 case at least, one is dealing with a simple trough or basin ; but 

 no geologist who has crossed the Ducan Pass or approached the 

 ridge from Monstein can fail to see that so obvious an explanation is 

 remote indeed from the truth. 



The vertical position of the limestone-strata along the ridge 

 formed by the Gypshorn, the Krachenhorn, and the Strehl, and the 

 contortion of the overlying beds, show that a simple open synclinal 

 is far from an adequate representation of the facts ; while the 

 occurrence along the axis of a sort of ' inlier ' of the Lower 

 Limestones suggests that there is a minor anticlinal, a ' knee ' 

 projecting upward in the centre. In other words, there is evidence 

 that even the Ducan ' basin ' is double and oblique, affected by 

 that pressure from the east which is conspicuous in the surrounding 

 area, but far more evident in the western folds. The diagrauimatic 

 section (PL XXYII ), of course, indicates only the dip of the strata 

 in an east-and-west line, but it should be remembered that the 

 ' ends ' of the synclinal area dip respectively southward and north- 

 ward, thus accounting for the apparent southerly dip seen from 

 Sertig on the Mittaghorn and Plattenhorn. 



The Eauchwacke, with its associated gypsum-beds, is well deve- 

 loped, and a detailed study of the whole ' Mittelbildung ' series in 

 this area is likely to prove of much value. 



It is, however, the presence of strata newer than the dolomite 

 that gives to this region its special interest. On the west of the 

 Ducan Pass several peaks are capped by beds which are of Rhsetic or 

 Liassic age. As already noted, the LitJwde7idron-'kalk (Dachsteinkalk) 

 is present on the Strehl, the ^Iplihorn, and the Krachenhorn ; and 

 the two former are also capped by dark shales with fossil bivalves, 

 doubtless correctly referred to the Avicula condor ^«-beds. 



