1884.] on the Building of the Alps. G3 



is strongly in favour of a great break in some localities. On tho south 

 side of the St. Gothard we have in the Val Piora the Lustrous Schists 

 apparently in true succession with the representatives of the garneti- 

 ferous group of the Val Tremola, yet on the northern side, in the 

 Urseren thai, the latter series is wanting, and the gneisses which underlie 

 it appear to be immediately succeeded by the Lustrous Schists. This, 

 however, might be explained by a complication of faulting and folding. 

 What I have seen in the Binnenthal is harder to explain. At the 

 head of the Hohsand Glacier, just below the peak of the Ofenhorn, we 

 have a coarse but bedded gneiss, which I should correlate with the 

 series immediately overlying the granitoid gneiss so often mentioned 

 as the lowest rock of all. Glancing towards the north, across the snow- 

 field, we see this rock in the base of the Strahlgrat distinctly over- 

 lain by the Lustrous series, with its characteristic band of limestone 

 or dolomite. This series swoops down for some 2000 feet, and we cross 

 it in the upper basin of the valley below, while yet further down the 

 valley I detected the characteristic garnetiferous schist, of which, 

 however, there is no great development. If this be the result of 

 faulting and folding only, it is certainly very remarkable. 



But I must linger no longer over details. The passing time 

 warns me that I must attempt briefly to describe the general process 

 of the building of this great mountain group of Europe. I have, I 

 hope, proved that the metamorphic rocks of the Alps, if we may trust 

 mineral similarity and mineral and lithological sequence, are vastly 

 older than the Carboniferous period, and that in this ancient series a 

 certain succession may be made out. If we may reason from the 

 analogy of other regions, we may assign to the whole of their latest 

 group (the Lustrous Schists) an antiquity greater than the earliest 

 rocks in which indisputable traces of organic life have been found. One 

 point, however, I should notice before proceeding further. It might 

 perhaps be said — it has indeed been said — that the crystalline schists 

 and gneisses of the Alps are the result of the great earth movements 

 by which the mountains were upraised, when heat and pressure changed 

 mud into schists and felspathic sandstone into gneiss. I have shown 

 you that we can trace a mineral succession in the crystalline series of 

 the Alpine chain, and that some at least of these are earlier than the 

 Carboniferous period ; but I can add to the proofs that these great rock 

 masses had assumed in the main their present mineral structure when 

 these movements occm-red. We meet indeed with some rock masses 

 whose structure is doubtless due to the pressure which they have 

 undergone. This is the case with all cleaved rocks, as was lucidly 

 explained, twenty-eight years since, by Professor Tyndall in this very 

 room. We meet also with schists, where, from the arrangement of 

 the mineral constituents, we have good reason for supposing that they 

 were developed when the rock mass was exposed to a pressure definite 

 in direction. Here the lines of difierent minerals, which we believe 

 indicative of an original structure in the rock, are often wrinkled ; the 

 more flaky minerals commonly lie with their broader planes parallel, 



