352 Dr. Dw Riche Preller—Crystalline Rocks, N. Piémont. 
kinzigitic gneiss is largely developed in its schistose form, associated 
with gneissiform, schistose diorite, norite, gabbro, and peridotite. 
The gneissic sedimentary rocks, known as stronalites,' are frequently 
intercalated in the eruptive series and vice versa. This high-level 
complex, reaching up to 2,500 metres altitude and including the 
schists of Fobello and Rimella, constitutes Gerlach’s second, separate, 
upper dioritic zone; but, as Franchi and Novarese” have shown, it 
forms an integral part of the entire Lanzo—Ivrea-Verbano (Lake 
Maggiore) dioritic-kinzigitic area. A branch of the kinzigitic 
gneissic schist extends from the upper Sesia Valley west by Val 
Vagno and Croce Rossa into the, upper Gressoney Valley, and thence 
connects with the eclogitic mica-schist of Val Pellina. In Val Sesia 
the mica-schist extends from Varallo down the valley, and is 
succeeded by the transverse granite belt, and then by the great 
porphyry mass of Borgosesia already mentioned.’ It is a noteworthy 
feature that the Lanzo—Lvrea—Sesia zone descends to the very edge of 
the Po Plain, whereas along the western ridge of Lake Maggiore and 
beyond the kindred rocks are only found at high levels, the general 
direction of dip being thus north-east to south-west. 
Stratigraphically the whole Ivrea—Val Sesia area within, the 
Piémontese Alps presents the important phenomenon that all the 
eruptive masses are infolded in the mica-schist and gneiss formation 
conformably with the latter without any evidence of angular 
intrusion. This close association and relationship points to the 
entire crystalline, viz. both the sedimentary and the eruptive, series 
being of the same age, that is, Permo-Carboniferous. Lithologically, 
it is noteworthy that while the eruptive series includes every 
conceivable combination of felspar, quartz, and mica as primitive 
elements, the only rock conspicuous by its absence is diabase, 
probably because it associates more readily with the more highly 
magnesian calc-schist than with the mica-schist and gneiss formation. 
It is, of course, quite impossible within the limits of this paper to 
describe in detail the outcrops in the numerous localities between the 
terminal points of Lanzo and Val Sesia. Suffice it therefore to state 
that from Lanzo to Ivrea and Biella the general vertical sequence is, 
in ascending order, mica-schists and eruptive rocks overlain by 
subordinate and isolated masses of indubitably Lower Trias crystalline 
limestone, while from Biella to Val Sesia the sequence is essentially 
one of juxta- instead of superposition. Of this superficial sequence 
the most typical example is the section, about 12 kilometres in 
length, along the Cervo Valley from Montesinaro to Andorno above 
Biella, which is shown in Fig. 4, and includes the whole eruptive 
series of old parallel lava streams infolded in the mica-schist 
1 The rocks of the Val Sesia and Val Strona region are described in detail 
in E. Artini and G. Melzi’s ‘‘ Ricerche petrogr. e geol. Val Sesia’’: Memorie 
R. Ist. Lomb., xviii, p. 219 et seq., Milano, 1900. ' 
2 Op. cit., 1905, 1906. 
3 There is apparently no passage from the granite to the porphyry or vice 
versa, but Franchi found (op. cit., 1906) a vein of porphyry in the granite 
mass, pointing to a somewhat later stage of eruption of the former within the 
same geological period. 4 
