Dr. 0. S. Du Riche Preller—Pietre Verdi. 159 
in Zaccagna’s sense; and that the Piémontese Alps, in their elusive 
complexity, may J vet reveal the most sur prising phenomena just when 
the problem of the crystalline schists and pietre verdi appears to have 
_been solved. 
Thus, in the most recent Italian Geological Survey map 1: 100,000, 
as also in the one of 1 : 400,000 of 1904, the Piémontese cale-schist 
formation has been rejuvenated as equivalent to and contemporaneous 
with the schistes lustrés of the French, the Biindnerschiefer of the 
Swiss, and the Schieferhiille of the Austrian Alps. It figures,. 
therefore, as the Liassic—T'riassic crystalline ‘‘ Piémontese”’ facies, 
with two subordinate facies—the ‘‘ mixed ”’ and the “‘ ordinary ”’ Trias. 
This rejuvenation, which is practically a reversion, mutatis mutandis, 
to Sismonda’s ‘‘ metamorphosed Jurassic schists ” of the early ’ sixties, 
entailed a similar stratigraphical process as regards the mica-schists and 
the minute, tabular, and graphitic gneisses which, accordingly, are 
now assigned to the Permo-Carboniferous, corresponding to Bertrand’s 
and Termier’s ‘‘série cristallophylienne permo-carbonifére’”’. The only 
formation left to the Pre-Carboniferous (or Pre- Paleozoic) is therefore 
that of the primitive gneiss belt of the Mercantour, Maira-Dora, and 
Gran Paradiso massifs, which formation constitutes the practically 
undisturbed substratum of all the more recent series.! 
This primitive gneiss, often of granitoid and porphyroid structure 
with large felspar crystals up to 8 centimetres in length, differs 
lithologically from the more recent minute and tabular gneiss, chiefly 
in that the small-grained elements of the latter are conspicuously 
rich in quartz and predominantly white mica. As regards the calc- 
schists, they are composed prevalently of calcite, aggregations of 
quartz in minute granules, and with white or greenish mica, the 
rock being generally of grey and often blackish colour due to 
a carbonaceous pigment, with numerous minute crystals of pyrite 
and other metallic minerals. When this typical cale-schist is 
deficient in calcite or loses it altogether, it assumes an essentially 
phyllitic character; when, on the other hand, calcite predominates 
over the other minerals, the calc-schist. becomes micaceous crystalline 
limestone or ‘calcefiro’?; and when the crystalline limestone is, by 
contact, impregnated with serpentinous matter, it becomes ‘ophicalce’, 
as e.g. the green marble of Susa. 
1 The official geological map of France, 1: 1,000,000, published in 1904, 
which extends to the Italian side as far as the Po Valley, includes in the 
Permo-Carboniferous not only the minute and tabular gneiss and mica-schists, 
but also the primitive gneiss belt, for which there is no warrant. Similarly, 
Termier (‘‘ Les schistes cristallins des Alpes occidentales,’’ Comptes Rendus du 
Congrés géol. Vienne, 1913) embraces in his série cristallo-phylienne triassique 
compréhensive all the younger formations down to the Eocene inclusive. Both 
cases are ultra-synthetic, and are not accepted by the Italian Survey. 
Professor Gregory’s view that the gneisses which he terms Waldensian 
(Q.J.G.S., 1894, p. 232 et seq.) are Pliocene and intrusive runs counter to 
the accepted interpretation of the coarse-grained gneiss being the primitive, 
viz. ‘fundamental’, substratum of the Cottian and Grajan Alps. Professor 
Gregory’s conclusions are traversed also by Novarese, ‘‘ Rilevamento geol. Valle 
Germanesca (Alpi Cozie), 1894,’’ Boll. R. Com. geol., 1895, p. 277 et seq., and 
Franchi, ibid., 1897, p. 13 et seq. 
