Vol. 50.] 



GNEISSES IN THE COTTIAN SEQUENCE. 



251 



Unfortunately lack of time prevented any attempt at a precise 

 determination of the boundaries of the gneiss, even if such be pos- 

 sible ; but it seems most probable that tbe dyke at the upper 

 Col de Vento is an offshoot from the great mass of gneiss about 

 Pale. 



Fig. 8. — Sketch-map of the gneiss exposures round Col de Vento. 



' A M. Salancia x i - Ti '" 





Alpe 



Piano delle 



Cavalle 



Inferior e "-iW > T ^ J~ *" 

 ._3.1e.tfo Rocca Rossa- 1 < -i ? v- . , > 



'/Superiore ^ ;n> y'A XmH'-; 



Mica-Schist Series. ____] Serpentine. !____] G. Waldensian Gneiss. 



Scale : -J — = 1-267 inch to the mile. 



50,000 



[For ' Sangoretto ' read ' Sangonetto.'] 



3. Meano, Perosa, and Chisonc Valley. — On Zaccagna's map the 

 gneiss band is shown to cross the Chisone Valley between Meano 

 and Eoure ; two unnamed streams are marked as traversing the 

 gneiss, and these occupy the positions of the Eorsetto on the south 

 side of the Chisone and the Balma on the north. Meano is itself 

 placed as on the extreme eastern margin of a granite which here 

 separates the schists and the gneiss. Eastward . from Meano to 

 Pinerolo the whole valley of the Chisone is coloured as schist. There 

 are, however, at S. Germano, large quarries of a pale coarse gneiss, 

 which seems to be a typical ' central gneiss.' But in this part of the 

 valley the chances of actual junctions are very remote ; and, as 

 Prof. Bonney has already described the rock and remarked on its 

 possibly intrusive nature, 1 it did not seem necessary to stop to 

 examine it. 



After leaving Perosa Argentina the road rises gradually, and there 

 are no exposures worth mentioning, though the hills on either side 

 are clearly of mica-schist ; \\ kilometre distant, however, a quarry 

 in the pale-coloured gneiss occurs on the northern side of the road. 



1 • Two Traverses, etc.,' Quart. Journ. Geol. Soc. vol. xlv. (1889) p. 83. 



s 2 



