204 Dr. Dw Riche Preller—Crystalline Rocks of Piémont. 
peak of Visolotto. In all the alternating banks the gradual passage 
into, and compenetration with each other is very marked, and-so is 
more especially the tendency to chloritic decomposition forming 
serpentinous schist, which in contact with narrow bands of crystalline 
limestone imparts to the latter its greenish colour. 
The descent from Monte Viso may, on the southern side, be 
conveniently effected by the Forciolline gorge, and thence through 
the Vallante ravine and the Varaita Valley by Sampeyre and Venasca 
to Saluzzo in the Po Valley. In those deeply eroded ravines the 
calc-schist formation reappears in contact with amphibolie, prasinitic, 
and serpentinous schist. At the junction of the Vallante and Varaita 
Valleys the last-named schist predominates, and lower down the 
latter valley is replaced by alternating banks of cale-schist, serpentine, 
and chloritic amphibolite. 
2. The Gneiss, Mica-schist, and Graphitic Area.—Parallel to and 
east of the pietre verdi area of Monte Viso runs, as already mentioned, 
the Dora—Maira primitive gneiss massif, about 60 kilometres in 
length and 5 to 10 kilometres in width, at an altitude of 1,500 to 
2,000 metres, the visible thickness being about 700 to 1,000 metres. 
Its superficial continuity is, however, frequently interrupted by great 
intervening, overlying, or intercalated masses of minute, granular, 
and tabular gneiss, with which are associated masses of erystalline 
limestone, quartzite, steatite, and dioritic, amphibolic, and prasinitic 
rocks. ‘he primitive gneiss is the typical rock with large elements, 
glandular, often granitoid, and tourmaliniferous; the mica- 
schists, often garnetiferous, and the minute, tabular gneiss flank the 
primitive gneiss both on the eastern and western side. Of the 
gneissoid dioritic rocks associated with the minute and tabular gneiss, 
which latter reaches, e.g. in the Pellice Valley, a thickness of 
1,500 metres, an intercalated mass 700 metres in thickness occurs 
near Barge; another, 1,000 metres, near Angrogna (Pellice); and 
again, in the Chisone Valley, another 1,500 metres in thickness, 
where the dioritic rock is associated with and altered to amphibolites 
and prasinites, including the ovardite of Fenestrelle. Both the tabular 
gneiss and the crystalline limestone, often associated with steatite, are 
extensively quarried on the eastern side of the Dora—Maira massif, at 
Vernasca, in the Varaita, near Luserna, in the Pellice, and near 
Malanaggio, etc., in the Chisone Valley, as are also the fissile, tegular, 
quartzite masses (bargiolina) of Monte Bracco (1,305 m.) near Barge. 
In the same mica-schist and minute gneiss horizon occur masses of 
graphitic rock with intercalations of graphite, which, flanking Monte 
Bracco on its western side, extend about 20 kilometres south, and 
about the same distance north of Barge. It is here, in the Pellice 
and Chisone Valleys, that the graphitic zone is. associated with the 
gneissoid dioritic rocks already mentioned. The whole mica-schist, 
minute gneiss, graphitic and dioritic zone is now assigned to the 
Permo-Carboniferous. 
3. Summary.—Vhe Monte Viso and Dora—Maira areas may be 
grouped, in ascending order from east to west, viz. from Barge in the 
Po Valley to Crissolo and the summit of Monte Viso, in a distance of 
20 kilometres, in four horizons as follows :— 
