Dr. C.S. Dw Riche Preller—Pietre Verdi. 157 
the mica-and-cale schist zone with pietre verdi as associated rocks, the 
latter being, in point of superficial area, a subordinate, the former 
the predominant part of the whole formation. Zaccagna’s two 
Archean zones thus comprised: (1) a lower one, restricted exclusively 
to primitive gneiss and granite without pietre verdi; and (2) an 
upper one, graduating, in ascending order, from minute and tabular 
gneiss to mica-schists and cale-schists, each group with crystalline 
limestone and pietre verdi. This classification, in its logical sequence 
and convincing simplicity, received the imprimatur of the Italian 
Geological Survey under its eminent Director, the late Comm. 
F. Giordano,’ and was also accepted by the French Survey, by 
Bertrand, Termier, and other French geologists. It derived additional 
force from the more intense metamorphism and crystallinity, pro- 
gressing from west to east, of the rocks on the Piémontese as 
compared with those on the French side of the Western Alps; and 
this, together with the fact that until then, about 1890, no deter- 
minable fossils had been found even in the uppermost calc-schist 
horizon, warranted the entire crystalline series of Piémont being 
classed as of pre-Carboniferous, and, in the absence of the lower 
Paleozoic, of Archean age. 
But in 1894 Bertrand returned to his former view of the Mesozoic 
age of the schistes lustrés which, in opposition to the late Professor 
Lory’s Triassic and to Zaccagna’s Archean views, he and Termier had 
already pronounced Liassic in the well-known case of Mont Jovet in 
Tarantaise (Isére Valley). In his Etudes dans les Alpes Frangaises * 
Bertrand maintained the Liassic age of the calc-schists not only on 
the French but also on the Italian side, on the ground that lower 
Triassic masses frequently underlie the calc-schists. Even before the 
publication of that work, Professor Parona, of Turin, had discovered 
Radiolaria in the silico-calcareous mass associated with the cale-schists 
and pietre verdi (serpentine) of Mont Cruzeau, near Cesana,* 
a discovery followed a few years later by other evidence of 
characteristic Liassic, Rhetian, and Triassic fossils in the dolomitic 
and caleareous masses which, in the lower as well as in the upper 
valleys of both Southern and Northern Piémont, occur at varying 
levels of the cale-schist horizon, either resting on, or intercalated 
between, or in some cases at the base of, the crystalline calc-schist 
strata. These discoveries were due chiefly to the untiring 
industry and perseverance of Franchi, who, in two important 
memoirs of 1898 and 1904,° claimed to have established the Mesozoic, 
1 Boll. R. Com. geol., 1887, pp. 342-5. 
2p. Termier, ‘‘ Sur le Permien du massif de la Vanoise’’: Bull. Soc. géol. 
France, vol. xxi, p. 124 et seq., 1893. 
3 M. Bertrand, Bull. Soc. géol. France, vol. xxii, p. 69 et seq., 1894. 
“cC. F. Parona, ‘‘Sugli Scisti silicei a radiolarie di Cesana presso il 
Monginevra’’: Atti R. Ace. Sc. Torino, vol. xxvii, 17. Gennajo, 1892; also 
noticed in Davies & Gregory’s paper on ‘‘ The Geology of Mont Chaberton ’’, 
Q.J.G.S., 1894, p. 303 et seq. 
° §. Franchi, ‘‘ Sull’ et& mesozoica della zona delle pietre verdi nelle Alpi 
Occidentali’’: Boll. R. Com. geol., 1898, pp. 173, 325 et seq. ‘‘ Ancora sull’eta 
mesozoica, etce.’’: ibid., p. 125 et seq. Franchi, Novarese, and Stella were in 
charge of the detailed survey of the Piémontese Alps forthe new1:100,000 map in 
