r Vol. 55'] GEOLOGY or THE DAVOS DISTEICT. 411 



IV. Summary op Conclusions. 



The results of the present writer's observations round Davos may, 

 then, be stated as follows: — 



The ancient crj-stalline rocks, perhaps originally Palaeozoic sedi- 

 ments traversed by igneous rocks of different kinds, have been much 

 crushed and metamorphosed, thrown into a series of oblique folds, 

 and thrust over the grey (Liassic?) ' Biindner Schiefer ' of the west 

 and north. In the synclinals of these folds occur, south of the 

 Pratigau, a series of infolds of Triassic and Rhaetic limestones with 

 Verrucano and ' Casanna Schiefer' below them. 



Four such folds can be distinguished. The easternmost, forming 

 the mountains of the Ducan group, is the simplest, and is an open 

 fold though distorted. In the others, the two sides of the fold are 

 crushed together, and the changes due to dynaaiic agencies become 

 increasingly evident towards the west. In the second and third 

 folds the Casanna Schiefer, Verrucano, and Lower Trias, while very 

 variable, are, as in the first, of normal type, and not marked by special 

 metamorphism. In the fourth fold similar little-changed rocks can 

 be found at different points along the line of strike, but in other 

 localities they are scarcely recognizable. In the Cotschna district 

 the Casanna Schiefer are replaced by a band of breccia, folded on 

 itself perhaps more than once, and reappearingbelow the limestones 

 along the line of the great overthrust in a still more altered condition. 

 The Verrucano passes into red shales, the upper layers of which are 

 intercalated between strata of the shaly Lower Triassic limestones, 

 and in the red shales lie lenticular masses of red radiolarian cherts or 

 hornstones. This group of rocks is crushed, with the Lower Triassic 

 limestones, into a band of ' polygenic ' breccia on the underside of 

 the fold : that is, above the plane of the great overthrust. 



In addition to this, the structure of the fourth fold is vastly 

 complicated by the presence of a band of serpentine. This rock 

 is the representative of a peridotite-magma, injected apparently 

 at some period later than the Lower Trias, but the district does 

 not give satisfactory evidence for any later date. It probably cut 

 obliquely through the Casanna Schiefer and up into the Verrucano 

 and Lower Trias, but there is no conclusive evidence in this district 

 of its penetration into the Hauptdolomit. Where it has forced 

 its way through the stratified rocks, a remarkable formation 

 occurs, the ' Rothe u. Griiue Schiefer,' which consist sometimes of 

 laminae of serpentine and red argillaceous layers, sometimes of 

 serpentine and red calcareous bands, and occasionally of a confused 

 mass of all three elements veined and infiltrated with calcite. 

 The radiolarian hornstones occur in the red shales thus invaded 

 and altered. If the radiolarian rocks can be proved to be newer 

 than the Trias, the same must be true of the serpentine. If, on the 

 other hand, the view here suggested as to the nature of the fold is 

 correct, they are stratigraphically below the dolomite, and we have 

 here no evidence in favour of a post-Triassic date for the serpentine, 

 though there is nothing to disprove its post-Triassic, or even, as 

 others think, post-Cretaceous age. 



