72 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



kind of stratification*. At Airolo we find a yellowish dolomitic 

 rock which I regard as an infolded mass of mnch more recent 

 date. 



I proceed next to the section given by the northern part of the 

 Lukmanier pass. On commencing the ascent from Dissentis, we 

 find a group of mica-schists, the continuation of the trough of the 

 Casanna schists already mentioned, which have obviously been ex- 

 posed to tremendous crushing, so that the dominant structure is a 

 cleavage-foliation which has a general W.S.W.-E.N.E. strike, and 

 is nearly vertical. Its surfaces are coated with a silvery mica, and 

 the rock breaks into flakes thin as millboard, being so friable that 

 specimens of any size are hard to obtain. As we pass through the 

 numerous tunnels in the glen of the Medelser Rhein we note occa- 

 sional mineral differences, such as bands of greener schist, one being 

 a well-marked talcose schist about a yard thick, and some of a 

 whiter and more quartzose schist, which has to some extent re- 

 sisted the crushing. As we ascend, the effects of this become less 

 marked, and some indications ai^e found of an earlier stratifi- 

 cation-foliation, which is parallel with the apparent bedding, and is 

 here and there to be distinguished from the dominant cleavage- 

 foliation. Before finally quitting this series of more or less cleaved 

 schists, we pass two masses of augen-gneiss, the second containing 

 crystals of felspar of definite but rather rounded outline, which are 

 sometimes quite three inches long, and lie in different directions in a 

 rather fissile foliated ground- mass. I feel certain that both these 

 rocks are really granite, intruded prior to the great compression 

 which has affected the whole range. Near Casalia we have another 

 augen- gneiss and an infold of rauchwacke, evidently a rock of much 

 later datef. We now pass a group of rocks lithologically gneisses, 

 sometimes porphyritic, sometimes very fissile from crushing, until, 

 about a mile below S. Gion, we reach a mass of granitoid gneiss, 

 somewhat resembling the Pibbia gneiss of the St. Gothard. Here, 

 however, there is abundant evidence that the rock is a true granite, 

 intrusive into an ordinary moderately fine-grained gneiss, and that 

 both rocks exhibit a cleavage-foliation resulting from subsequent 

 pressure. This granite, so far as I know, continues till we approach 

 Santa Maria (nearly at the summit of the pass). Generally it is 

 fairly massive, but occasionally it becomes rather fissile. Then 

 occurs one of those singular complexes which, if judged by the 

 ordinary laws of stratigraphical sequence, would lead us to the most 

 extraordinary theoretical results. According to the map and sec- 

 tions of the Swiss surveyors, which I have to a great extent verified 

 on the ground, the granite is succeeded by gneiss, and this by quart- 

 zose mica-schists or micaceous quartz-schists. Then comes a slate, 

 assigned to the Lias, then a black mica-schist with melanite garnet, 

 then " rauchwacke," then another band of the last-named schist, 



^ I shall hereafter refer to these as the Tremola schists. 



t This, on the opposite bank of the valley, is associated with a very fissile 

 "schist," referred by the Swiss geologists to the schistes ^Msz'rees, which I was not 

 able to examine. The new map, however, refers it to the Carboniferous series. 



