184 DR. THOMAS STERRY HUNT ON THE 
complete section, to the eastward of the central gneiss, shows also the serpentinic and 
dioritic rocks overlaid by mica-schists, and the same story is repeated in other sections. 
Subsequently, in his letter to Zezi, Gastaldi describes and figures a section from Monte 
Bracco through Monviso and Monte Pelvo, along the upper part of the valley of the 
Po, and the valley of Varaita, to the frontier. His conclusions from the study of all these 
sections may be thus summed up: The crystalline rocks of the Western Alps are classed 
in two great groups, the lower of which (the central gneiss of von Hauer,) was described 
by Gastaldi as the ancient gneiss, and by him compared with the Laurentian of North 
America. It consists chiefly of a highly feldspathic granitic gneiss, sometimes por- 
phyritic or glandular, and includes bands and lenticular masses of quartzite and 
crystalline limestone, with white steatite, and graphite. Reposing upon the ancient 
gneiss, is a great and complex group, designated by Gastaldi as the “newer crystalline 
series,” which, from the frequent presence therein of serpentines, diorites, diabases, and 
related rocks of a greenish color, is also called by him the zone of the greenstones, or the 
pietre verdi. 
§ 51. In a generalized diagrammatic section which accompanies Gastaldi’s last pub- 
lished statement, (his letter to Sella in 1878,) the first division of the newer crystalline series 
is described as a great mass of serpentine, followed by a second division consisting of 
euphotide, succeeded, after an interval of crystalline schists, limestones and gneissic rocks, 
by a series made up of many alternations of epidotic, dioritic and variolitic schists, with 
green steatite. In some localities are found great beds of lherzolite and of amphibolite, 
with varieties of diorite, and rocks in which a triclinic feldspar prevails, together with schists 
more or less calcareous, and crystalline limestones. The serpentines and their associated 
ophiolitic rocks, which constitute the lower members of the newer crystalline series, 
are described by Gastaldi as resting in some cases in nearly horizontal stratification upon 
the ancient gneisses, and, elsewhere, as overlying the limestones of this older series, from 
which their uncomformable superposition may be inferred. 
§ 52. The group of newer crystalline rocks, as given in Gastaldi’s section of 1878, 
includes also what he designates as recent gneiss and granite, besides various undescribed 
schists, with crystalline limestones, followed by a second horizon of serpentines, to which 
succeed gypsum and dolomites. All of these, as is shown in the section from Turin to 
the frontier, are intercalated, with quartzites, in a vast series of schists, which are placed 
above the recent gneiss and granite. Finally, the whole series is overlaid by the uncrys- 
talline sediments of the anthracitic group, of carboniferous age. 
§ 53. The lithological characters of the lower part of this vast series of newer crystal- 
line schists are sufficiently well defined in the various sections already noticed. As regards 
those which immediately succeed the serpentinic, chloritic and tale-schist zone, the group of 
“mica-schists” of Neri, the “recent gneiss and granite” of Gerlach and Gastaldi, we get 
additional light from various passages in the writings of the latter. They are spoken of, in one 
place, as gneissic mica-schists more or less rich in hornblende, in which, at Traversella, are 
also included serpentines. Elsewhere, the rocks of the same area are successively called 
mica-schist, recent gneiss and mica-schists, gneissic mica-schists, and also, a very mica- 
ceous gneiss, often passing into mica-schist and sometimes hornblendic. With these, or with 
the lower portions of the series, are associated granitic and syenitic rocks which, in the 
opinion of Gastaldi, are not eruptive, but the result of local modifications of the sur- 

