250 DR. J. W. GREGORY ON THE WALDEKSIAN [May 1 894, 



type of talcose gneisses, and is of a faint green colour ; this no doubt 

 it has acquired from the absorption of some of the ' pietre verdi.' 

 The microscope shows it to consist of the usual pegmatitic quartz- 

 felspar mosaic with bands of white mica ; the dark colour of hand- 

 specimens is seen to be due to inclusions of an indeterminate 

 opaque material, which appears reddish-brown by reflected light. 

 A series of broken and corroded garnets, often showing double 

 refraction, also represents material collected from the surrounding 

 schists. The foliation of the gneiss flows round the included frag- 

 ments, like a true fluxion-structure. Though we did not find 

 similar inclusions in situ at the Col, the exact resemblance of the 

 gneisses leaves little doubt that it was derived from the dyke which 

 we examined, or from a similar one. 



Fig. 7. — Gneiss, with included fragments of the ' pietre verdi' 

 series at Mustione. 



South of the gneiss, along the northern arete of Punta Costa- 

 bruna, the serpentinous schists (probably an altered Iherzolite) rise 

 into a sharp crag ; south of this, the mica-schists recur again, and 

 these form the summit. On the eastern side of the pass and ridge a 

 long gradual slope of meadow-land extends down to the Sangonetto 

 Valley, and consequently there are no exposures. The gneiss, how- 

 ever, occurs extensively developed on both sides of this valley ; on 

 the north it forms the ridge of Monte Salancia, from the crags of the 

 llocca del Moutone to Monte Luzera (the Punta Siudre of the 1 



map). On the south side it forms the northern arete of Eocca Possa, 

 see fig. 8, p. 251. The gneisses of the two sides of the valley are at 

 first separated by the schists, a wedge of which appears to extend 

 into the gneiss, as far as the 1500-metre contour, down the Poirent 

 Valley (a tributary of the Sangonetto). East of this point, as far as 

 Dirotto, all the exposures seen were of gneiss. Still farther down 

 the valley widens, and, as we had no time to leave the road, we could 

 see no rocks in situ. 



