188 DR. THOMAS STERRY HUNT ON THE 
as altered trias, a view in which Renevier acquiesces. They are, for the most part, soft, 
glistening, and talcose in aspect, and have been variously described as argillo-micaceous 
and argillo-talcose schists, being sometimes, according to Lory, true sericite-schists. * 
They closely resemble the crystalline schists with hydrous micas which abound in the 
Primal and Auroral divisions of Rogers, (Taconian) as seen in eastern Pennsylvania. These 
schists in the Alps are traversed by veins of calcite and of quartz, and include besides 
great beds of quartz-rock, often a detrital sandstone, beds of limestone, sometimes micaceous, 
of banded and of white granular marbles, of dolomite and of gypsum. This latter in the 
subteranean exposures made in the Mont Cenis tunnel, is répresented by anhydrous 
sulphate of lime (karstenite), and is accompanied by rock-salt and sulphur. Magnesian 
silicates are also found in this group; nodules of tale are imbedded in the karstenite, chlo- 
rite occurs in veins and layers, and beds of serpentine (and of euphotide, according to Gas- 
taldi) are interstratified with these shining argillo-talcose schists. 
§ 63. The resemblances in mineral character between these upper argillo-talcose schists 
with chlorite and with interstratified serpentines, and the lower or true pietre-verdi zone, 
are obvious. Lory has moreover remarked the likeness between these upper schists with 
limestones and the mica-schists with limestones in the horizon of the newer gneiss series, 
included by him in the primitive schists, as leading to the confounding of the two. This 
resemblance, he suggests, “may have thown some obscurity” upon the relations of these 
various rocks, and the structure of the region It will not have escaped the notice of our 
readers that in the description of the section of the Simplon there is no recognition what- 
ever of the great mass of serpentines, euphotides and other ophiolitic rocks belonging to 
the pietre verdi, which elsewhere are found at the base of the newer crystalline schists, 
occupying a horizon between the older and the younger gneisses. 
§ 64. It will also be noted that Lory places a horizon of tale-schists, with chloritic 
rocks, etc., at the summit of the newer gneisses, and the view naturally suggests itself that 
Lory has himself confounded the lustrous schists of the upper series and their magnesian 
rocks, with the great lower ophiolitie zone. This latter would appear to be wanting in the 
section of the Simplon, where it is not noticed by Renevier. Lory thus places above the 
younger gneisses a talc-schist series to which he refers many of the types of rocks 
met with in the great ophiolitic and talc-schist zone, which elsewhere, underlies 
these younger gneisses, and in which the protogines are probably included. In this way 
the apparent discrepancy between Lory and all the observers hitherto mentioned is 
explained, as suggested by the present writer in 1881. The relations observed in the 
Biellese, as already noticed, suggest that the younger gneisses were deposited unconformably, 
alike upon the older gneisses and the great ophiolitic group, as is the case in many other 
regions. 
§ 65. In like manner, according to Lory, the lustrous schists themselves, with included 
serpentines (which he regards as contemporaneous eruptions) rest directly upon the ancient 
gneisses in the Levanna, between Susa and Lanzo. Other evidences of a want of confor- 
mity between these various groups of ancient schists in the Alps are not wanting. At the 
Col de Mont Genévre, as described by Lory, there appears through the lustrous schists a 

* Bull. soe. géol de France, x., 29. 
