354 
POHJLAR SCIENCE REVIEW. 
sive. They are called by Italian geologists the Rocce Antraci- 
t if ere delle Alpi , and under this name form a connected group 
of enormous thickness, repeated in this part of the Alps 
two or three times by anticlinal and synclinal axes, and 
generally very highly inclined. These are shut in on both 
sides by granite and protogine, sienite and diorite, and occa- 
sionally penetrated by these latter rocks and by a variety 
of serpentine and euphotide. The magnesian character of 
these rocks will be at once recognised, and is seen also in 
the talcose and steatitic nature of the metamorphosed schists. 
Although the tunnel does not cut through any of the intrusive 
rocks, and does not seem even to approach them, it shows very 
clearly the presence of magnesia as connected with the meta- 
morphosis. This is another matter especially and locally 
interesting. The great abundance of gypsum, the same in 
character and appearance in the tunnel and on the surface, is 
another point to be observed. We leave these matters to the 
careful study of geologists. 
EXPLANATION OF PLATE LXIV. 
Fig. 1. Section from N. 14° W. to S. 14° E. on the line of the great 
tunnel from the mountains on the northern side of the Arc 
valley, in Savoy, to the mountains between the lateral valley of 
Eochemotte, to the valley of the Dora, in Pidmont. This 
section is carefully drawn to the same scale of vertical and 
horizontal distances. 
Fig. 2. Plan of the country immediately adjacent to the tunnel, showing 
the position of the principal valleys on each side the central axis. 
N.B. — The following are the rocks as identified by Professor 
Sismonda, and met with in the tunnel commencing with the 
north or French entrance. 
Actual thickness. 
Distance tun- 
nelled thi*ough. 
Weathered and fallen rock . , 
1. Upper member , consisting of schists, 
sandstones, and psammite with an- 
thracite, resting on a thick band of 
quartzite, corresponding to Oxford 
200 feet. 
420 feet. 
clay series 
2. Middle member. Gypsums, crystal- 
line, limestone, and calcareous schist, 
4,500 „ 
7,707 „ 
corresponding to lower oolites . , 
3. Lenccr member. Calcareous schist 
■with bands and strings of quartz and 
threads of limestone. Liassic and 
1,700 „ 
2,815 „ 
lihtetic series . . , , , 
17,500 „ 
29,151 „ 
23,900 
40,093 
