Dr. Du Riche Preller—Crystalline Rocks of Piémont. 201 
similar euphoditic and diabasic masses occur in the calc-schist forma- 
tion, but intensely metamorphosed, the former to epidotic and chloritic 
prasinites with or without gastaldite (blue secondary hornblende), 
the latter to felspathic prasinites and amphibolites.' These pietre 
verdi masses bear close analogy to the euphoditic and diabasic, also 
variolitic masses with overlying serpentine in the cale-schists of 
Maurin and of the Chabriére Valley, near Pointe de Mary, about 
30 kilometres further north-west, as also to those of the Mont Genévre 
group another 30 kilometres further north, and to those between the 
Ripa and Troncéa Valleys about 20 kilometres east of Genévre. From 
the occurrence of all these crystalline masses both of eruptive? and 
sedimentary origin on the northern and eastern flank of the Permian 
horizon, Franchi has rightly concluded that that formation separates 
the Trias into two distinct zones: an external one on the left, composed 
of the ordinary, fossiliferous limestone, gypsum, and cargneules or 
Briangonnais facies, and an internal zone, the crystalline and semi- 
erystalline facies composed of the cale-schists and crystalline and 
dolomitic limestone with pietre verdi.* 
2. The Argentera Massif (Fig. 1).—This massif, also called Mer- 
eantour, is an oval-shaped ellipsoidal group of 60 by 25 kilometres in 
approximate length and width, extending west of Col di Tenda along 
the French frontier, and bordered on the north by the Stura di Cuneo 
Valley, which separates the Maritime from the Cottian Alps. The 
massif includes, besides Monte Argentera (3,397 m.) and Monte 
Matto (3,057m.) in the centre, some of the highest mountains of 
the Maritime Alps, e.g. Mercantour (2,775m.) and Monte Clapier 
(3,046 m.) at the south-eastern, and Monte Tinibras (3,032 m.) at the 
north-western end. The access to the central part is by the Gesso 
Valley from Valdieri, whose well-known hot sulphur springs rise 
in the upper valley, at 1,346 metres altitude, almost in the centre of 
the massif. The latter is, like the Dora-Maira and Gran Paradiso 
gneiss massifs, entirely free from pietre verdi on its surface; even the 
fringe of pietre verdi which surrounds those massifs is absent on its 
periphery. Zaccagna attributes this isolation of the Argentera massif 
to a great fault along the Stura Valley, which latter is, some 20 kilo- 
metres north-east of Valdieri, crossed by a succession of pietre verdi 
outcrops descending from the Maira and Grana Valleys towards Cuneo 
and S. Dalmazzo, and thence running along the base of the 
Montgioie range to Villanova and Millesimo. 
The Argentera massif consists, in the main, of three crystalline 
formations: a nucleus of primitive, glandular, large-grained, granitoid, 
1 §. Franchi, ‘‘ Aleuni Metamorfisi di eufotidi e diabasi Alpi Occid.’’: Boll. 
R. Com. geol., 1895, p. 181 et seq. The transformation described in this 
important memoir applies equally to similar phenomena in all the other pietre 
verdi areas of the Piémontese Alps. In the massive and schistose amphibolites 
of the Grana and Maira Valleys, as also in Val Chisone, at Pegli, Liguria, and 
in the Tuscan archipelago, Franchi found the equivalent of the Californian 
mineral lawsonite, a secondary pseudomorphic plagioclase corresponding to the 
formula of hydro-anorthite felspar (Boll. R. Com. geol., 1898, p. 308). 
* The term ‘ eruptive’ is used in this paper in preference to ‘igneous’ as 
better corresponding to the non-intrusive character of the Piémontese rocks. 
