16 Dr. Du Riche Preller—Permian in the. Alps. 
In so far as the degree of crystallinity, being the effect of 
metamorphism under pressure and high temperature, is a test of age, 
the Archean highly crystalline schists differ from the gneissiform 
Permian schists as much as do the latter from the still less crystalline 
Triassic schists, e.g. those of the Apuan Alps as part of the marmiferous 
zone, albeit both those younger schists often simulate a gneissose 
aspect. As regards the Archean schists, the presence of igneous 
rocks, whether primary or altered, is, of course, no absolute criterion 
of age, but in Piémont the enormous pietra verde masses of Monte 
Viso, of the Dora Riparia Valley, and of Val d’ Aosta are by alternation, 
eraduation, and lenticular intercalations, or again as irregular, 
obviously eruptive deposits, so closely associated with the mica- and 
cale-schists that their inclusion in the Upper Archean zone appears 
perfectly legitimate. As in the younger schist-formations, so also in 
that Archean zone the mica-schists always form the lower part 
of the zone, gradually passing into calc-schists which predominate in 
the upper part, with intercalations of saccharoidal limestone, quarried 
e.g. in the Susa Valley. It is with the upper parts of the mica- 
and the lower parts of the calc-schists that the pietra verde masses 
are more especially associated, and the intermediate position of the 
latter therefore points to their original subaqueous or superficial 
eruption in the corresponding period.' 
VY. Conctustion. 
In the necessarily small sketch-plan (p. 11, Fig. 1) I have traced 
the Permian zone from the Ligurian Alps near Savona through 
Southern Piémont, Dauphiné, and Savoy to Mont Blanc, a distance 
of 250 kilometres. It is seen that the curved alignment of that zone, 
which would equally apply to the concomitant Carboniferous and 
Triassic zones, runs, in the main, between and parallel to the two 
great primitive gneiss and granite belts indicated by dotted lines, the 
outer belt comprising the Mont Blanc massif and the Pelvoux group in 
Dauphiné, while the inner, more continuous one extends from Monte 
Rosa to Gran Paradiso and Mercantour in Southern Piémont.’ 
A third, smaller, but continuous inner belt may be said to lie between 
the Dora Riparia and the Maira Valleys, with Monte Viso midway 
1 In Piémont alone the crystalline schists, lying between the Mercantour 
massif in the south and Monte Rosa in the north, cover an area of 200 by 
30 kilometres, or roughly 2,400 square miles, of which the three principal 
pietra verde masses represent about one-fifth. These masses are all composed ° 
of basie roeks, more especially of diorite, diabase, gabbro, serpentinous and 
hornblendic rocks. The white marble of Susa is, as shown above, Archean, in 
contrast to the Triassic marble of the Apuan Alps, but both attest the process 
of the deposition of coarse calcareous material being followed by that of 
gradually finer to very fine material purified by solution and precipitation. 
The majestic triumphal arch at Susa shows that the marble of that locality, 
as that of Carrara, was quarried already by the Romans. Similar saccharoidal 
limestone intercalations are also worked in the Pellice, Upper Po, and Varaita 
Valleys. I propose to refer to these and the pietra verde areas, as also to 
Franchi’s recent divergent views as to their age, in a subsequent paper. 
2 GC. Diener outlines a similar series of belts in his Gebwugsbau der Westalpen, 
1891, but embraces in his generalizations the entire ¢hain of the Alps. 
