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masses buried in loose clay. Within, the rocks are much more 
compact. 
Next beyond tbe schists comes in a series of bluish and blackish- 
grey schistose rocks, alternating with quartz, and this extends not 
only to the end of the tunnel on the Italian side, but far beyond 
for a distance of several miles, as far as the Dora valley. Every- 
where these schists present the same general character, but they 
vary infinitely in matters of detail — such as hardness, colour, 
and texture. They are traversed by strings of steaschist, and 
quartz, and contain occasionally crystals of calcite, iron pyrites, 
and (though rarely) copper pyrites. Within the cutting there 
has been no discovery of any vein containing ore. Externally 
there are few special indications. Owing to the mixture of 
decomposing schist and hard, compact quartz, and the fact 
that the schist falls readily into shale, and from that into loose, 
powdery fragments, the mountains above where these rocks 
crop to the surface are singularly jagged and picturesque, and 
weather at an extremely rapid rate. At the surface they pre- 
sent little appearance of peculiar structure. Within the tunnel 
they are, as has been said, extremely interesting and varied, 
although the variations are strictly confined to matters of detail, 
and may be taken as the results of metamorphic action com- 
bined with enormous squeezing on stratified rocks, consisting of 
clay, sand, and some (though a comparatively small proportion) 
carbonate of lime. 
There seems to have been everywhere observed some trace 
of stratification, showing itself on a small scale by imperfect 
lamination, and on a large scale by the position of bands of 
quartz. The sand of the original rock would seem to have 
been partly converted into crystalline quartz, partly left in 
grains to form very compact gritstone. The various com- 
pounds of the clay have become converted into a greenish 
talcose rock, with very smooth, irregular faces, splitting irre- 
gularly, with many intervening cavities of little breadth, filled, 
or partly filled, with crystalline carbonate of lime, often deve- 
loped into beautiful crystals of various forms. Occasionally, 
but very rarely, these interstices were occupied by iron pyrites. 
Throughout the long distance (upwards of four miles) tunnelled 
through this rock no essential change seems to have taken 
place. It was easy to penetrate and not unsound, leaving 
ample time to brick in before any fall of the roof could take 
place. It was always dry, except when, on a very few occa- 
sions, small apertures were pierced containing water under 
pressure; but even then the quantity of water was not sufficient 
to cause trouble. The rock was close-grained and moderately 
tight, and blasts well in large blocks. Among the pieces re- 
moved by blasting are many measuring about a cubic yard. 
