pr LA Uet 
Prof. Bonney—Crystalline Schists of the Alpine Chain. 507 
lava-flows—but found in process of work that there was generally 
an abrupt boundary between them and the associated micaceous 
schists. Only one section above Windisch Matrei* suggested a 
passage from the one to the other, and I should like to re-examine 
this as -I might have overlooked slight thrust faults. But in not 
a few places” one can trace the transformation of clearly intrusive 
diabases into quite ordinary green schists. 
The above-mentioned green schists are sometimes intrusive into 
certain varieties of gneiss and mica-schist of dubious origin, sometimes 
into the great group of crystalline schists, obviously metamorphosed 
sediments, which exhibit almost every gradation from schists con- 
sisting largely of mica into quartz-schists on the one hand and 
(through calc-mica-schists) into saccharoidal marbles on the other. 
The serpentines can be found intrusive into the green schists; the 
gabbro into the serpentines;* occasionally also an aplitic granite cuts 
the green schists, but I do not know its relation to the other two 
intrusives. Thus, though all these rocks (except the granite) are basic 
and more or less green in colour, I prefer to follow the Swiss 
geological maps in distinguishing as schistes vertes the pressure- 
modified diabases, and grouping them (though only provisionally) 
with the above-mentioned calc-mica and associated schists. 
Since I began to pay special attention to the petrology of the Alps 
I have not seen much of the dioritic belt which extends from near 
Ivrea by Biella and Andorna to the Val Sesia, near Varallo; still, 
I have come across it two or three times, enough to refresh my 
memory and give me a general idea of its characters. Its members 
may very well have been drawn from the same source as the schistes 
vertes and their associates, but they have probably consolidated under 
different (deeper-seated) conditions, and may thus be conveniently 
distinguished from them. As, however, this question does not seem 
to me to have any very direct bearing on the nature and origin of the 
schistes vertes, I shall venture to pass by it, merely remarking that 
I greatly doubt whether the porphyrite north of Biella can be included 
in the dioritic belt. That rock, which is more extensively developed 
in the neighbourhood of the Lago Maggiore, seems to me the western- 
most extension of the great zone of porphyrites, Permian in age, 
which are so largely developed near and to the east of the Adige in 
its course from Meran to Trent. 
The second and most important point is the geological age of the 
schistes vertes and certain other schists associated with them. This, 
according to the authorities followed by Dr. Preller, is from Permo- 
Carboniferous to Trias; one division of the pietre verdi with certain 
mica-schists and minute gneisses belonging to the former, the other 
division with the cale-schists and crystalline lmestones, to the 
Lias—Trias.* Much apparent, but very little real, evidence is cited 
to support these determinations, and I do not hesitate to say, after 
1 Q.J.G.S., 1889, pp. 87, 88, 108. 
2 Id., 1893, pp. 94-103 ; 1894, pp. 279-84; 1903, pp. 55-6. 
° Gabbro intrusive into serpentine is, of course, a very common thing. 
I may add that locally the schistes vertes are cut by eclogites. 
* See p. 307. 
