76 PSOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



limestone, (4) a second mass of the dark-banded schists. We have 

 here a section of a slightly curved synclinal trough of the bedded 

 schists (2, 3, 4), and foliation appears to agree with bedding, as it 

 certainly does when this series comes down to the valley, dropping 

 more than 3000 feet vertically in rather less than eight miles. I 

 call especial attention to this section, because it can only be ex- 

 plained either as a case of very peculiar overthrust faulting or of 

 unconformity. The characteristics of the gneiss would lead me to 

 refer it as a whole to a lower position than those of the St. Gothard 

 and the Lukmanier, and this reference is supported by my exami- 

 nation of the Simplon Pass further to the east. Hence at this 

 place the Tremola schists (and probably the underlying Gothard 

 or Lepontine gneisses) are wanting. 



Turning back to Olivone, we find, as I have said, gneiss rising 

 from beneath the bedded dark schists on the right bank of the Val 

 Campra. This rock crosses the Val Blegno below Olivone. It 

 bears a general resemblance to, and is mapped as continuous with, 

 the Lepontine gneiss described as extending from the lower end of 

 Lake Ritom towards the Yal Bedretto. In places it appears to have 

 been subjected to great pressure, which often, but by no means 

 always, has acted at right angles to the original foliation. 



Gneiss of this character continues down the Yal Blegno (which 

 is now running almost south), but near Aquila is another infolded 

 trough of the brown-bedded schists. Lower down comes moderately 

 fine-grained gneiss, with a fair amount of dark mica, lithologically 

 not materially different from the last described. A little above 

 Ludiano a coarse porphjritic gneiss sets in, the felspar crystals 

 being often from one to two inches long. ISTotwithstanding the rather 

 rounded outline of these, and the fact that the rock is fissile enough 

 to be used for posts to support the vine-trellises*, careful exami- 

 nation has led me to the conclusion that it is only a porphyritio 

 granite to which a foliated structure has been imparted by subse- 

 quent crushing. Alternations of this with a finer gneiss continue 

 for some distance. Then a gneiss more resembling the former type 

 sets in, continuing to Biasca. Here the rock varies from fairly 

 coarse to moderately fine ; planes which suggest crushing being 

 universal, and dipping at about 30° to E.N.E. 



Erom Biasca to Bellinzona the rock, as a whole, exhibits so little 

 variation that I did not think it necessary to make a close exami- 

 nation, and thus confine myself to saying that a gneiss which at 

 first closely resembles that of Biasca, extends far down the valley, 

 but after a time becomes more granitoid, and is quarried for blocks 

 as well as for slabs. About Misocco a more schistose character is 

 again evident. After passing Bellinzona towards Lugano there is a 

 decided change in the character of the rock, and here I began again 

 a more minute examination. This rock is a dark mica-gneiss. In 

 the mass it exhibits a gradual mineral change which suggests bed- 

 ding, but is roughly parallel with a cleavage-foliation. This strikes 



* Slabs about 4 inches thick, a foot or so wide, and 6 or 7 feet long, are 

 readily obtained. 



