Dr. Du Riche Preller—Crystalline Rocks, N. Piémont. 311 
The upper part of this section is shown in Fig. 4.!_ Its characteristic 
feature is the Permo-Carboniferous zone which crosses the ridge 
about midway between and at right angles to the calc-schist 
formation. The zone or belt is composed of an enormous mass of 
sphenic diorite which constitutes the Valletta, Ruié, and Gran 
Nomenon peaks and the intervening Mésoncles and Belleface cols or 
saddles, and is flanked on either side by considerable banks of sericitic, 
gneissiform schist and psammitic, carbonaceous sandstone of the 
greywacke type. The diorite zone, about 4 kilometres in superficial 
width, extends east into the Cogne Valley and west across the 
Savaranche Valley to Mont Bioulé on the divide between the latter 
valley and Val Rhémes. Inthe Cogne Valley it was first recognized 
by Baretti* in 1876 and described as sphenic syenite, similar to the 
syenite of Biella; but Novarese showed it to be essentially dioritic, 
with 63 per cent of Si O,.° 
The Savaranche and Cogne dark-green diorite varies in structure 
from compact to granitoid, gneissoid, and schistose, and is normally 
composed of plagioclase, hornblende, quartz, black mica, aggregations 
of minute muscovite, and abundant titanite (sphene) crystals up to 
1 centimetre in length. Near Colle Mésoncles it exhibits secondary 
elements, e.g. albite, epidote, actinolite, with unaltered titanite, 
while on the Val Rhémes ridge it is essentially fine-grained and 
massive. ‘lhe mass thus presents an interesting example “of this rock 
both in its primitive and in its metamorphosed, re-composed, 
granitoid, and gneissoid form. In upward succession the diorite and 
gneissiform schist zone is followed by a bank of crystalline limestone, 
and thence to the summit of Grivola and beyond to Punta Galisia * 
‘by a constant conformable alternation of calc-schist and pietre verdi 
banks, the latter up to 500 metres in depth, as part of the belt which 
encircles the Paradiso gneiss massif. Here again the pietre verdi, 
predominantly prasinites with strips of serpentinous schist, appear in 
-all their varieties, more especially in the upper Savaranche Valley 
near Degioz (1,541 m.) immediately west of and below the Grivola 
1 This section is founded on the complete one given by Novarese in ‘‘ Profilo 
della Grivola’’, ibid., p. 497 et seq. 
2M. Baretti, ‘‘ Studi Gruppo Gran Paradiso’’: Mem. Acc. Linceo Torino, 
1876, p. 195 et seq. 
* V. Novarese, ‘‘ Diorite granitoide e gneissiche Val Savaranche’’: Boll. R. 
Com. geol., 1894, p. 275 et seq. 
* The cale- mee of Grivola and Galisia were assigned to the Mesozoic 
(Lias—Trias) as the equivalents and continuation of the schistes lustrés by 
M. Bertrand in his ‘‘Etudes dans les Alpes francaises’’, Bull. Soc. géol. 
France, vol. xxii, p. 69 et seq., 1894, which marked his return from his 
temporarily Archean to his earlier Mesozoic views on that formation. The 
latter were confirmed by P. Termier in ‘‘ Les schistes lustrés de la Grivola ’’, 
Bull. Service Carte géol. France, vol. vii, p- 150 et seq., 1895. The Piémontese 
cale-schists are, on the whole, more micaceous than the French schistes 
lustrés, which are more aluminous than the former and to which the designa- 
tion ‘‘ série cristallo-phyllienne’’ is therefore more appropriate. The super- 
position of cale-schists on Triassic limestone as verified by Franchi and 
Termier in various localities also occurs in the Roches d’Ambin massif (Petit 
M. Cenis, upper Susa Valley), where the minute gneiss and mica-schist are 
overlain by limestone upon which rests cale-schist. 
