GEOLOGICAL HISTORY OF SERPENTINES. 185 
rounding gneiss. From my own observations, I conclude that while these recent gneisses 
in the Alps, as in North America, assume a highly granitic aspect in certain beds, they are 
not to be confounded with veritable intrusive rocks which penetrate them. 
§ 54. Gastaldi has described in detail and figured a section in the Biellese, a region 
carefully mapped by Quintino Sella and G. Berutti, and studied both by Gerlach and 
Gastaldi. * Here, in the section as given by the latter, the granite or granitic gneiss is 
bounded to the northwest by serpentine, diallagic rocks “ and other greenstones,” followed 
by a band of diorite. To this succeeds a great breadth of the newer gneisses, in which is 
included a large dyke of melaphyre, evidently of eruptive and posterior origin, and, farther 
to the westward, a mass of syenite, which is extensively quarried, and has been studied 
with great care and described by Cossa in his work already mentioned. I had the good 
fortune to visit this well-known region in 1881, in company with Signor Quintino Sella. 
The granitic rock of the eastern part of the section appeared to be a part of the ancient 
gneissic series so largely developed elsewhere near Biella, and consisting of reddish gra- 
nitoid gneisses, sometimes hornblendic, but scarcely micaceous, often thinly banded, highly 
contorted, and indistinguishable from much of the gneiss of the Laurentides, or of the 
South Mountain in Pennsylvania, east of Schuylkill. Interstratified with it, near Biella, 
are beds of coarsely crystalline impure limestone, holding graphite, mica and hornblende, 
and resembling closely some Laurentian limestones. Elsewhere in the Alps, it may be 
noted, similar gneisses include serpentinic limestones, as for example the pale green ophi- 
calcite found by Favre in the gneiss of Mattenbach near Lauterbrunnen, which is indis- 
tinguishable from that of the Laurentian of Canada, and like it contains Æozoon Cana- 
dense. + It is well-known that similar serpentinic aggregates are often found with the 
limestones in the ancient gneisses of Scandinavia and Finland, as well as in North America. 
§ 55. This ancient gneissic series in the Biellese is directly overlaid by the ophiolitic 
and dioritic belt (pietre verdi), and this is followed to the west by the newer gneisses and 
mica-schists, which cannot be distinguished from those found in the vicinity of Philadelphia, 
or in the White Mountains of New Hampshire, which I have called Montalban. The 
intruded mass of syenite, made up of reddish orthoclase with some albite, hornblende, 
and a little sphene, presents, inthe extensive quarries which I visited, the massive character 
and the comparative homogeneousness which belong to a pleutonic rock. The usually 
great breadth of ophiolitic rocks met with in this part of the Alps is here, as pointed out 
to me by Signor Sella, rapidly reduced, to the southward, by the encroachment of the 
newer gneisses on the westward side, and where the crystalline rocks sink beneath the 
alluvial plain, does not excede a kilometer. These relations suggest a transverse super- 
position of the newer eneiss series alike upon the ophiolitic group and the older gneiss, af 
which we shall find evidence elsewhere. 
§ 56. It has been seen that the designation of pietre verdi was by Neri restricted to the 
ophiolitic group beneath the newer gneisses, which he referred to a later and distinct 
geological period ; Gastaldi, on the other hand, extended the term so as to include not only 
the newer gneisses and mica-schists, but the vast mass of crystalline strata between these 
and the anthracitic series, with their included gypsums and dolomites. The grounds of 

* Gastaldi, Studii, ete., part L., pp. 3 and 26, 
+ Favre, Recherches géologiques dans la Savoie, etc., iii., 320, and also Chem. and Geol. Essays, p. 342, 
Sec. IV., 1883. 24, 
