GEOLOGY OF TIIE MONT CENIS TUNNEL. 
341 
Mont Frejus at a distance of nearly sixteen English miles west 
of the former road. Starting from Modana on the Savoy side, 
about ten miles higher up the valley than St. Michel (the pre- 
sent terminus of the main line), advantage is taken of the 
widening of the valley, and the railway is conducted by a 
zigzag up the side of the mountain into a small ravine to a 
height of 3,946 feet above the sea, being a rise of 346 feet 
from St. Michel, showing an average rise of thirty-five feet in a 
mile, or one in about 150. From this point a direct line 
through the mountain, drawn at right angles to the axis of the 
chain at that part, carries us under the Mont Frejus to an open 
part of the valley of Bardonneche, an important tributary of the 
Dora, emerging at a distance of 12,220 metres (13,365 yards), 
or about 7^ English miles. The direction of the tunnel is 
about NNW.-SSE. The railroad, after emerging from the tunnel, 
runs down the Bardonneche valley for another seven miles into 
the comparatively wide and open valley of the Dora, the ground 
being afterwards not particularly difficult for a railway, and 
much less liable than the upper part of the Arc valley to injury 
from floods and torrents. The road follows the course of the 
Dora without further divergence to Turin. 
It will be evident to the reader, from this account of its 
position, that the tunnel has been driven through the crest of 
the Alps, across what would at one time have been regarded as 
being almost inevitably an axis of elevation, and it would have 
been presumed that in the course of the work, the primitive 
granite, considered not long ago to form the nucleus of all 
great mountain chains, must be crossed under circumstances 
involving perhaps extreme mechanical difficulties, large and 
incessant incursions of water, hard, tough, and contorted 
rocks, and all those indications of convulsion and disturbance 
inseparable from such conditions. 
Fortunately the engineers who first projected this great work 
had not sufficient faith in the geological theories common 
then among the multitude, and not unsupported by very high 
authorities, to be frightened by the prospect of these proba- 
bilities. Perhaps they had not made acquaintance with them, 
and regarded the question as one of ordinary tunnelling through 
ordinary rock. At any rate they induced the Grovernment of 
Sardinia (at that time possessed of both sides of the Alps) to 
listen seriously to their suggestions, and support the work, 
which was commenced about twelve years ago under auspices 
favourable in some degree, but with a prospect of a very long, 
if not endless, work. According to the methods at first adopted, 
the excavation of the tunnel, although commenced at both 
ends together, could only proceed very slowly at first, and was 
likely to be delayed when the great distance from the entry 
