Dr. Dw Riche Preller—Crystalline Rocks, N. Piémont. 307 
Arpone to Ceres and Monte Bellavarda, as shown in Fig. 3. On the 
north, the western division is bounded by the Gran Paradiso gneiss, 
and the eastern division by mica-schist and minute gneiss. The 
Paradiso gneiss, being the fundamental substratum, probably extends 
south below the oale: schists and pietre verdi to the Dora—Maira 
gneiss massif; the mica-schist formafion with pietre verdi is the 
continuation of the Rocciacorba and Avigliana belt south of the 
Lanzo valleys and extends north-east from Lanzo to Ivrea and 
Val Sesia. The calc-schists are in evidence chiefly at the lower 
levels of the valleys where they alternate with pietre verdi; at the 
higher levels and on the crest-lines they are very subordinate, and, 
except on the western ridge from Rocciamelone to Ciamarella, and in 
the dividing strip already mentioned, appear only in the eroded gaps 
or saddles of the more resistant pietre verdi masses. 
From Mattirolo’s beautiful ‘‘ geo-lithological ”’ contour-map of the 
Lanzo valleys 1 : 100,000 (1904),' the distribution of the crystalline 
rocks of the entire area works out approximately as follows :—? 
sq. km. cece 
Lias—Trias Cale-schist with crystalline limestone . 48 = 8 
(western division) \Pietre verdi : : . 240 = 40 
Permo-Carboniferous /Mica-schist and minute gneiss : 5 OO = IG 
(eastern division) | Pietre verdi ; ‘ é 5 on LO — 
Pre-Carboniferous. Gran Paradiso gneiss . ; ; - § 96) 3 16 
600 100 
The pietre verdi of the two divisions thus represent collectively no 
less than two-thirds of the aggregate area. The lithological distri- 
bution of those masses, intercalated in, and resting on the crystalline 
schists, is extremely complex, for, except the transverse dividing 
line already mentioned, there is in their kaleidoscopic association no 
demarcation, sequence, or distinction of level. Yet, on closer 
examination, the broad limits of certain groups can be defined along 
the four parallel ridges which, flanking and separating the three 
valleys, run west to east and converge at the Lanzo defile. The 
principal groups, generally circumscribed by morainic, alluvial, and 
detritus belts round their bases, are shown in the plan, Fig. 3, and 
specified in the following table, in which the names and altitudes 
refer only to the culminating points. In almost every case the 
groups, varying in area from 5 to 20 square kilometres, comprise 
a cluster of minor peaks and spurs, and alike by their formidable 
bulk and their often pinnacled crests attest the great resistance of 
pietre verdi to denudation, to which the once overlying crystalline 
sedimentary schists more readily and long since suecumbed.® 
1 Boll. R. Com. geol., 1905, p. 191. At the time of the compilation of this 
map all the crystalline rocks of the Lanzo valleys were still considered of 
Archean age without distinction between the age of the mica-schist and the 
cale-schist formation, the new classification dating from 1911. 
2 The earlier works dealing with the Lanzo valleys, etc., by Gastaldi, 
Strtiver, Baretti, and Bucca from 1871 to 1886 were already quoted in the 
preceding papers. 
3 The ‘local designations Uja, Ciama, Punta, Becca, Bric, Truc, Torre, 
Rocca, etc., all denote point, peak, summit, crest, crag, etc. 
