384 MR. A. Y. JENNINGS ON THE [-^Ug. 1 899, 



regards them as * imbricated without regularity ' and presenting. 

 a striking analogy to the ' Klippen ' of Iberg. 



Commencing with the former group (ct), I proceed to consider 

 first 



(i) The Older Crystallines. 



This heading is vague, and has obviously no precise geological 

 significance, but it is a convenient term for descriptive purposes in 

 the region under review. The rocks so designated occupy the- 

 eastern part of the area, but are also evidently present in patches 

 and streaks on the west of the Davos Valley. They are a series 

 of gneisses and schists, building sometimes vast mountain-masses 

 such as those of the Silvretta and Scaletta groups, or thinning to 

 narrow layers such as the crystalline band under the Kiipfenfluh 

 and the Schiahorn. The dip is in general southerly and easterly, 

 as is the case over the whole area, but there are local variations 

 indicating the presence of acute-angled folds. The recurrence of 

 similar types of rock at different levels along roughly parallel lines 

 indicates that there is a considerable repetition of such folding, and 

 that the total thickness of the beds was not originally so great as 

 the height of such mountains as the Fluela Schwarzhorn and the 

 Kiihalphorn might at first lead the observer to suppose. 



In lithological character there is great variety. Besides the 

 white coarse-grained ' eye-gneiss/ conspicuous in the Muela Pass, 

 passing by gradations into quartzose schists, such as those seen at 

 the mouth of the Dischmathal, there occur brown biotite-gneisses, 

 of which the fragments are abundant in the Sertig Valley, and in 

 bands over the whole district occurs a compact ' hornblende- 

 schist' streaked with veins of a yellowish-green epidote. 



It is not proposed in the present paper to contribute evidence 

 as to the age or origin of these ' older crystallines.' It is probable 

 that the quartzose series represent crushed and altered granitic 

 rocks, while the ' hornblende-schists ' may with equal likelihood be 

 metamorphosed diorites. The biotite-gneisses, and many other 

 rock-varieties not mentioned here, may well be the representatives 

 of ancient sediments, but as they are, so far as we know, entirely 

 devoid of fossils, there is as yet no evidence for ascribing to them 

 any definite geological age. They are, however, undoubtedly much 

 older than any of the other formations present. 



Details as to the microscopic structure of various specimens of 

 the gneisses and schists will be found in Dr. Ball's paper.* It is 

 unfortunate that the limited time which he was able to give to 

 the study of the district prevented his work from being of other 

 than petrographic value. The distinction which appears on his 

 sketch-map between the crystallines of the eastern and western 

 sides of the lake does not really exist. He had not realized the 

 direction and distribution of the mountain-folds ; and the prominence 

 and crystalline character of the Casanna Schiefer on the south and 

 west of the lake evidently led him to the view represented in his 



^ ' Serpentine & Assoc. Eocks of Davos,' Ziirich, 1897. 



