186 DR. THOMAS STERRY HUNT ON THE 
this extension are these:—serpentines are not confined to the lower ophiolitic zone, but 
occur also alike among the newer gneisses and the succeeding crystalline schists. It 
is, says Gastaldi, “in contact with the gypsums and dolomites that we find the last limit 
of the serpentinous rocks which, for us, characterize the zone of the pietre verdi”’ This 
was in 1872, in his letter to de Mortillet, at which time Gastaldi was disposed to place in 
a separate group the crystalline schists above the horizon of the upper serpentines. He, 
however, subsequently included the whole of these schists in the zone of the pietre verdi, 
§ 57. As will be made apparent, the schists for a great distance below this horizon. 
are not to be separated from those above. We have in them, in fact, a third great crystal- 
line group, overlying the younger gneisses, but, by Gastaldi, included with these and the 
lower ophiolitic group under the common name of the pietre-verdi zone. At other times, 
Gastaldi used the term of pietre verdi in the more restricted sense in which it was em- 
ployed by Neri. He speaks in 1874, of “the pietre verdi properly so-called,” and in this 
sense he declares it to be comprised between “the ancient porphyroid and fundamental 
gneiss,” and “the recent gneiss, which latter is finer grained and more quartzose than the 
older.” He says farther: “I will not assert that when specimens of this newer gneiss are 
confusedly mixed with those of the more ancient, it would always be practicable to dis- 
tinguish them petrographically ; but I do not hesitate to affirm that, on the ground, the 
distinction is not difficult, on account of the frequent alternation of the younger gneiss with 
the other characteristic rocks of the upper series ; while the older gneiss, however wide its 
extent, is generally unmixed with other rocks.” * 
§ 58. The newest crystalline group, mentioned as overlying the younger gneiss and 
mica-schist series, is that of the argillo-talcose schists of Favre, the grey lustrous schists 
of Lory (glanzschiefer), with their included serpentine, gypsum, karstenite, dolomite, 
micaceous limestone, banded and statuary marbles, and quartzites ; a group very con- 
spicuous in Alpine geology. These rocks are well seen in the section from Turin to the 
French frontier, and are traversed in the Mont Cenis tunnel. (See also § 62-66.) 
§ 59. The vast thickness assigned by various observers to this entire series of newer 
erystalline schists, counting from the ancient gneiss below, is a remarkable fact in their 
history. We have seen the great breadth ascribed to the successive zones or groups in the 
sections already noticed. Gastaldi, in 1876, estimated the real thickness of the pietre- 
verdi zone, including the upper lustrous schists, at 24,000 meters, of which 8,000 meters, 
or one-third, was assigned to the lower ophiolitic group, or proper pietre verdi ; apparently 
without including the younger gneisses and mica-schists, which make up the middle 
group. To the upper group, as seen in the Mont Cenis tunnel, Sismondi and Elie de 
Beaumont assigned a vertical thickness of not less than 7,000 meters, and Renevier finds 
for it elsewhere an apparent thickness of 6,000 meters. 
§ 60. We have hitherto spoken of the Western Alps, and the sections as yet noticed do 
not extend to the eastward of Lago Maggiore. The map by von Hauer, of the Lombard and 
Venetian Alps, published in 1866-68, embraces the region from this meridian eastward, 
and shows the same order of succession as that laid down by Gerlach in the west. + The 

* Studii, part ii., p. 31. 
+ Gastaldi, Studii, Part I., p. 18, and Fr. von Hauer, Geologische Ubersichtskarte der Osterreichisch-Unga- 
rischen Monarchie, fol. y., West-Alpen u. fol. vi., Ost-Alpen ; Wien, 1866-68. 
ee sd. 
