Vol. 54.] SCHISTS OF THE ST. GOTHARD PASS. 359 



Many of the actinolites seen in these schists exhibit a tendency 

 to ' fray out ' at the ends ; often they have a tufted arrangement 

 (see figs. 2 & 3, p. 362). While many of them lie in the planes of 

 cleavage-foliation ^ (which is sometimes consiucuous), others make 

 all angles with it. Bands in which actinolite is more than usually 

 abundant sometimes seem to show traces of a granular or even of 

 an ophitic structure, the whole suggesting that the mass originally 

 may have alternated from a hornblendic biotite-granite, more or less 

 garnetiferous, to a coarse diorite (also containing the last-named 

 mineral), the two not having been at the outset very sharply dis- 

 tinguished, and being now, owing to the effects of pressure, still more 

 difficult to separate. In the upper part, though actinolite may still be 

 observed, the rock comes nearer to an ordinary hornblende-schist. 



After a time, when the zigzags are ended, and the road runs at the 

 base of the crags bounding the right side of the more level part of the 

 Yal Tremola, biotite- gneiss sets in, and here and there are stratiform 

 masses of a rather dark variety of hornblende-schist. 



In the above-mentioned series the actinolites, judging from their 

 appearance, are later in date than the cleavage-foliation. The 

 garnets, however, though often well preserved, are perhaps more 

 generally either a little distorted or crushed, so that they probably 

 are anterior to the main disturbance. It is difficult to form an 

 opinion of the age of the biotite, but the abundant small tiakes of 

 silvery mica ( paragon ite ?) are most likely posterior to that dis- 

 turbance. 



(b) Val Canaria. 



This valley descends from the watershed of the Lepontine Alps, 

 and joins the Yal Bedretto about | mile below Airolo. The floor 

 is strewn hereabouts with large boulders of garnet-actinolite schist, 

 together with the ordinary biotite-gneisses of the district and 

 some other schists. The first afibrd instructive subjects for study, 

 and correspond with the rocks exposed on the St. Gothard road. 

 Though I have often spent a spare hour or two among them, 

 I have not ascended the Yal Canaria to the outcrops from which 

 they have come. Still, when I was examining the noted section 

 (once supposed to prove that the ' Upper Schists ' were more recent 

 than the rauchwacke) in the lateral glen on the western side 

 of the Yal Canaria,^ I climbed up till I reached the garnet-actinolite 

 rocks in situ at a height of about 1200 feet above Airolo. I see no 

 reason to doubt that the rocks exposed in the V"al Canaria are 

 practically identical with those studied on the St. Gothard. 



^ The strike, where I have measured it, of this structure (which often corre- 

 sponds with the mineral banding) varies from N.N.E. to N.E., on the whole 

 nearer the former, and it dips at a high angle (60°-70°) to the western side. 

 The significance of this fact is noticed below. Crushed-out quartz-veins may 

 be seen. 



2 Quart. Journ. Geol. Soc. vol. xlvi (1890) p. 187, & vol. 1 (1894) p. 285. 



