Dr. 0. 8. Du Riche Preller—Pietre Verdi. 161 
II. Rocks with secondary elements. 
(1) Essential. (a) Prasinite group: with a dominant non- 
felspathic element, viz. chloritic, amphi- 
bolic (actinolite and glaucophane), or epidotic 
prasinite, and varieties. 
(6) Euphodite and its varieties. 
(2) Subordinate. (a) Amphibolite group: felspathic and epidotic 
amphibolite with frequent glaucophane. 
(6) Epidotites and zoisitites, felspathic. 
(a) Amphibolite group: epidotic and garnetiferous 
amphibolite with dominant glaucophane, 
eclogite. 
(6) Epidotite, zoisitite. 
(c) Serpentine, serpentinous, chloritic, and talcose 
schist. 
FELSPAR 
(3) Absent. 
It will be seen that the old generic group of amphibolites or 
hornblendic rocks is separated into amphibolites proper and prasinites, 
the last-named designation having been adopted from Kalkowsky and 
Zirkel as basic rocks or ‘Griineschiefer’ of a felspathic basis with 
chlorite, hornblende (the bright-green actinolite or the bluish-green 
or violet fibrous glaucophane) and epidote, one of these being dominant 
as a non-felspathic element. The amphibolites, largely derived from 
diorite and composed of albite, epidote, and dominant amphibole, 
are mostly compact, passing to schistose, although the hardest, 
massive amphibolite, viz. ‘hornblendite’ or ‘ Hornblendefels’, is, in 
large masses, comparatively rare in the Piémontese Alps. The 
prasinites, on the other hand, are on the whole less compact and 
more often schistose, and in the main, like the amphibolites, altered, 
transformed, or metamorphosed from massive eruptive rocks. They 
often contain, as an accessory mineral, white mica, but rarely 
biotite, and include, as a largely diffused variety, the chloritic rock 
‘ovardite’, first recognized and so named by Striiver’ from Torre 
d@Ovarda, a ridge in one of the three Stura di Lanzo valleys. It is 
composed of epidote, microscopic amphibole, and predominant chlorite 
in a plagioclase groundmass. Amphibolic schist, the equivalent of 
‘ Hornblendeschiefer’, is intermediate between amphibolites proper 
and prasinites.? 
A further distinction made is that between gabbro and euphodite 
in the sense that gabbro is restricted to the primary eruptive rock 
with its elements unaltered, while in euphodite the triclinic felspar 
is already altered to saussurite and the diallage to smaragdite—the 
latter being, like epidote and the amphibole varieties, a largely 
diffused mineral in the Piémontese Alps. 
Again, massive serpentine, as the direct product of altered lherzolite 
and peridotite, is distinct serpentine schist, which is a further 
1 Striiver, Una Salita alle Torre d’Ovarda, Torino, 1873, and Bucca, 
loc. cit., 1886, p. 453. 
2 The felspar-actinolitic rock noticed by Professor Bonney near Fenestrelle in 
the Chisone Valley (‘‘ Two Traverses of the Crystalline Rocks of the Alps”’ : 
Q.J.G.S., 1889, p. 80 et seq.) is an amphibolic prasinite, viz. ovardite, while 
the schist with glaucophane, the epidiorite, and the dark-green porphyrite 
mentioned by Professor Gregory in his ‘‘ Waldensian Gneisses’’, loc. cit., 
come under the category of prasinites (ovardites) and amphibolites. 
DECADE VI.—VOL. III.—NO. IY. 11 
