Tol. 55.] GEOLOGY or THE DAVOS DISTRICT. . 397 



presented by the weathering of the rounded glaciated surface 

 above. It will be observed here that two masses of the breccia 

 occur, separated by a considerable thickness of red schists ; but 

 this duplication I take to be due to a fold. On the opposite side of 

 the Lareterthal the same band is present, but apparently, like the 

 other associated rocks, it thins out rapidly ; it is yet, however, to 

 be distinctly traced along with the serpentine above Monbiel. 

 Westward from the Cotschna it seems obliterated by the over- 

 thrusting of the serpentine, but is probably continuous with the 

 crystalline band running below the serpentine towards Arosa. 



The constituents of the breccia are mainly white-mica schists 

 and fine-grained gneisses, with fragments of white granite and 

 aplite. I have not observed in it either the brown biotite-gneisses 

 or the green hornblende-epidote schists which are so characteristic 

 of the older crystallines of the eastern part of the district. 



On the north side of the Cotschna, below the dolomite-wall, there 

 is also present a band of brecciated crystalline rock, which, if the 

 view suggested below as to the structure of the country be correct, 

 may really be a more highly altered part of the Parsenn and Laret 

 band. It differs in having a considerable amount of interstitial 

 black or ferruginous material, and in the fact that the crystalline 

 fragments are oval and drawn out at the ends like the eyes of an 

 augen-gneiss, while the sinuous curves of the intermediate laminae 

 give to the surface of the rock ail the appearance of a flow-structure. 



The polygenic breccia occurs also on the northern slope 

 of the Cotschna toward the Pratigau, and immediately above the 

 last-mentioned rock. This northern aspect is very difficult of 

 study, owing to the enormous accumulations of detritus which fill 

 the woods of its lower slopes. Only high above the chalets of 

 Hinter dem Zug, and after crossing the stony plateau that lies above 

 the tree-level, is it possible to meet with clear sections of the 

 mountain-rocks in situ. Here, above the' mass of angular frost- 

 detached blocks which lies along the foot of the great dolomite-cliff, 

 will be found a band of breccia composed of angular fragments of 

 grey dolomite and of yellow limestone of the ' Mittelbildungen ' 

 embedded at all angles in a paste of dark red Yerrucano with blocks 

 of red hornstone and green schists.^ (See fig. 2, p. 396.) 



(vi) The Diabases and Yariolite. 



In neighbouring districts, along the outcrop of the serpentine 

 there are several other basic igneous rocks, but their relationship 



^ I wish to note the occurrence at this point of a very interesting rock 

 made up of calcite with rounded grains of serpentine. I was unable to find 

 its exact position in situ ; but as it seems of very limited horizontal extent, and 

 as it is associated with a green rock of evidently igneous nature, I am inclined 

 to regard it as a result of contact-metamorphism. It seems that the crushing 

 of such a rock might easily produce something like the ophicalcareous grits 

 described above. Prof. Bonney, however, thinks that the serpentine may be 

 derived. See also note on p. 398. 



