200 Dr. Dw Riche Preller—Crystalline Rocks of Piémont. 
Of the mountains enumerated, the Argentera and Gran Paradiso 
massifs, with a gneiss nucleus in each case, are the only ones which 
have preserved their original ellipsoidal, dome-shaped outlines, while 
most of the others, lying in the calc-schist and pietre verdi areas, are 
conspicuous pyramids whose precipitous flanks, pre-eminently those 
of Monte Viso and Grivola, were chiselled probably quite as much by 
atmospheric as by fluviatile or glacially abrasive action. The six 
principal pietre verdi areas, of which the first three will be dealt with 
in the present and the other three in a subsequent paper, are as 
follows :— 
I. In Southern and Western Piémont: (1) the Maritime Alps; 
(2) Monte Viso; (3) the Dora Riparia, Sangone, and Avigliana group. 
II. In Northern Piémont: (4) the Lanzo Valleys; (5) the Dora 
Baltea or Aosta Valley ; (6) the Lanzo, Ivrea, and Val Sesia group. 
J. Tue Maritime Arps Group. (Fig. 1.) 
1. Montgioie Range.—The pietre verdi area between the Ellero, 
Corsaglia, Tanaro, and Bormida Valleys on the north side of the 
Montgioie range derives special interest from the fact that the 
deposits occur in the Permian and Triassic crystalline formations, 
already described in a previous paper,’ while further east, towards 
Savona and near Voltri in Liguria, similar deposits are intercalated 
in Triassic schists, and further west, along the French frontier, they 
appear in the cale-schist formation. Proof is thus afforded that the 
pietre verdi are not confined to any particular horizon, but are 
associated with both Mesozoic and Paleozoic formations. Some of the 
pietre verdi deposits on the northern slopes of the Montgioie range 
were already mentioned by Zaccagna’”; but their number and extent 
has more recently been considerably increased by Franchi,? who 
regards all the pietre verdi of the Ligurian, Maritime, and Cottian — 
Alps as links in the same Mesozoic horizon. 
The pietre verdi deposits between the Ellero, Tanaro, and Bormida 
Valleys, extending for about 30 kilometres along the lower hills from 
Villanova to Millesimo, are composed chiefly of lenticular masses of 
serpentinous, diabasic, and euphoditic rocks, the latter two largely 
altered to amphibolites and prasinites, all associated with Triassic 
crystalline and dolomitic limestone, in the Bormida valleys also with 
Permian schist, as already mentioned. In these, as also in the Lower 
Trias, occur frequent outcrops of laminated porphyric rock and masses 
of amphibolic schist often epidotic and garnetiferous, with abundant 
glaucophane.* 
West of the Montgioie range, in the border zone of the Maritime 
and Cottian Alps, and notably in the upper Grana and Maira Valleys, 
1 “The Permian Formation in Piémont, Dauphiné, and Savoy’’?: GEOL. 
MAG., January, 1916, p. 7 et seq. 
2D. Zaccagna, ‘‘ Alpi Marittime’’: Boll. R. Com. geol., 1889, p. 395 
et seq. 
3 §. Franchi, ‘‘ Zona Pietre Verdi fra 1’Ellero e la Bormida, Alpi Marittime ’’: 
ibid., 1906, p. 89 et seq. 
4 The nomenclature used throughout this paper is that given in the 
preceding one, GEOL. MAG., April, 1916, pp. 156-63. 
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