360 PEOF. T. G. BONNET ON THE GAENET-ACTINOLITE [Aug. 1 898, 



(c) Val Piora. 



The lower slopes on the right bank of this valley are excavated 

 in the group described in my papers on ' ITesozoic Kocks & Crystal- 

 line Schists in the Lepontine Alps,^ ' nameh', in micaceous schists, 

 often dark, sometimes containing blackish garnets abundantly, and 

 occasionally staurolite, which pass on the one hand into marbles, on 

 the other into rather impure quartz-schists. Eauchwacke, some- 

 times with gypsum, occurs locally, and is more abundant in the 

 upper part of the valley. The actinolitic and garnetiferous rocks 

 apparently overlie these, and are followed by gneisses of the type 

 usual in this district.^ The former appear to be thinner than at the 

 St. Gothard, but constitute a line of craggy slopes and cliffs some- 

 times inaccessible. We examined numerous fallen blocks, and 

 worked along the crags as best we could, from the Lago Cadagno to 

 the Lago Tom. 



It may suffice to give a description of two sections, and then a 

 general summary of the remainder of our work. Of these two 

 sections, one is above the north-eastern, the other above the north- 

 western end of the Lago Tom. 



The former (one of the lowest set of outcrops visible) showed, 

 in descending order : (1) A considerable mass of hornblendic 

 or actinolitic rock, the crystals of the latter varying in length, 

 but usually not exceeding g inch. This seems to pass (in the lower 

 part) into a darker variety of hornblendic rock. Occasionally 

 it is distinctly fissile from the effects of pressure,^ but in places 

 it exhibits a streaky structure, which this agency alone seems 

 inadequate to explain. The rock sometimes resembles the horn- 

 blende-schist of the Lizard district, but it becomes, in its lowest 

 part, markedly actinolitic, the crystals ranging up to nearly 

 1 inch in length, and being confusedly scattered. In this rock 

 we find len tides of a variety described in the next section ; these 

 sometimes are about | yard long and 2 or 3 inches thick. (2) A 

 more felspathic variety of the actinolite-rock,^ the ' blades ' from 

 I to I inch in length lying in all directions, though in places the 

 mineral is, so to say, condensed in streaks (fig. 1, p. 361). (3) After 

 an interval of about 8 feet vertical (hidden by turf) and a little 

 to the west comes an outcrop of the typical garnet-actinolite 

 gneiss, in which are two or three bands of rather coarse horn- 

 blendic rock suggesting an intrusion.^ (4) An outcrop, some 

 distance lower down, of garnetiferous gneiss or micaceous schist, 

 apparently passing, as on the St. Gothard, into very typical 

 garnet-actinolite schist. Similar varieties were seen in the fallen 



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



- In reality this is an inversion, the true order (descending) being 

 (a) rauchwacke, (b) upper schists, (c) garnet-actinolite schists, and (d) biotite- 

 gneisses. 



2 The force appears to have acted roughly perpendicular to the mineral 

 banding. 



* The more fine-grained varieties being seemingly the more fissile. 



^ The total vertical distance in which (1), (2), and (3) cropped out was some 

 8 or 9 yards. 



