66 PEOCEEDIXGS OF THE GEOLOGICAL SOCIETY. 



tatingly referred to original stratification, but which can be shown 

 to be only a form of pseudostromatism, the results of a crushing 

 in situ of zones of the original coarse-grained rock. 



With these prefatory remarks, I proceed to sketch out, as briefly as 

 possible, the results of my examination of certain districts in which 

 metamorphic rocks are largely developed. I will commence with the 

 Central Alps, where, as we shall see, we find excellent illustrations 

 of all the structures noted in these preliminary remarks. 



Tlie Alps. 



The crystalline massif of the Oberland Alps is orographically 

 limited on the southern side by the uppermost parts of the valleys 

 of the Rhine and the Ehone together with the headwaters of the 

 Reuss. On the northern side it is bounded geologically, but not 

 orographically, by Mesozoic strata, with which it is marvellously 

 interfolded, and over which in the middle part its peaks seem to 

 rise almost like breaking waves of the sea. Here the watershed is 

 quite at the northern side of the massif. At the eastern and 

 western ends the crystalline rocks, which, in the central parts, 

 constitute summits varying from at least twelve to more than four- 

 teen thousand feet above the sea, gradually decline until they are lost 

 to view beneath masses of Mesozoic rock, disappearing at elevations 

 not exceeding about eight thousand feet above the sea, and often less 

 than half that height, especially at the eastern end. Towards that 

 end the deep gash occupied by the Reuss affords admirable sections. 

 The dominant rock, lithologically speaking, is gneiss. Commencing 

 at the part where the scalpel of nature appears to have made the 

 deepest cut into the anatomy of the mountain mass, namely, in the 

 valley of the Eeuss about Wasen, we find the rock for a considerable 

 distance to be a granitoid gneiss, sometimes granular, sometimes 

 very distinctly porphyritic, the felspar crystals being occasionally as 

 much as an inch long. Foliation is generally but slightly marked, 

 being only indicated by wavy micaceous lines ; its strike is about 

 W.S.W.-E.N .E. ; its dip very high, but on the whole inclining 

 towards the southern side ; occasionally flaggy or schistose and 

 more micaceous bands occur with the dominant strike and dip ; but 

 the more these are examined, the more doubtful it becomes 

 whether they are anything but cases of pseudostromatism. As we 

 ascend the valley to the mouth of the tunnel at Goschenen and so 

 onwards to the Devil's Bridge and the Urner Loch, the gneissoid 

 aspect becomes very slightly more pronounced; that is, the rock 

 would be readily recognized as a gneiss, though not one of the 

 banded varieties, while below we should sometimes be puzzled to 

 difl'erentiate a hand-specimen from a granite. Micaceous bands, 

 also, of a schistose or a slabby rock, simulating bedding, are perhaps 

 more frequent ; until just beyond the Urner Loch, an abrupt change, 

 presently to be noticed, coincides with the expansion of the valley 

 into the open basin which forms a part of the limiting trough already 

 mentioned. 



Returning to our former position and descending to Amsteg, we 



