GEOLOGY OF THE MONT CENTS TUNNEL. 
349 
tent. As this corresponds to about 40,000 cubic feet of space, 
some idea may be formed of the nature of the largest of the 
fissures ; and as the water was very quickly drained off, it is 
evident that no open communication could exist with any other 
fissure, or with the surface. There has been no seasonal 
change in the quantity of water entering at either end. The 
pressure of the water in the cavities reached was sufficient to 
throw a jet forwards into the tunnel to a distance of as much 
as 20 feet, this lasting in one or two cases for some hours. No 
exact record seems to have been made of these fissures. When 
examined, the largest of them was not more than from four to 
six inches, and they do not appear to have extended with any 
regularity even across the tunnel. The largest of these water- 
containing fissures was reached in 1861, not very long after the 
commencement of active perforation. Another, of some im- 
portance, was cut in 1867, when the middle had nearly been 
reached. Both of these were on the Italian side. Others have been 
cut on the French side, differing little in the circumstances, 
but generally smaller. The contact of rocks of very different 
nature does not seem to have been marked by the presence of 
springs, nor did the limestones on the French side, though of 
considerable extent, yield more water than the compact schists 
on the Italian side. The temperature of the water varied con- 
siderably. That of the largest spring, reached in 1861, was 
64°; that of the next largest, reached in 1867, was 79°. 
The water in the clefts on the French side was between 60° 
and 62°. The waters, on being roughly analysed, were found 
to contain oxide of iron, sulphate of lime, and sulphate of mag- 
nesia. As crystals of dolomite have been found, and there are 
large deposits of gypsum, no surprise can be felt at this result. 
It is important, however, to notice, that even at the distance 
of midway in the tunnel, and with so large a depth of rock 
above, the waters are not in any sense thermal, and do not pro- 
ceed from deep sources. The result is that which would take 
place of necessity, if water percolating from above should find 
an outlet in the interior after a long and probably very slow 
course. 
On the whole, then, the conclusion arrived at from the 
observations made in the tunnel tend to show that geological 
speculations as to the existence of free currents of water in the 
earth’s interior, and especially of heated water as connected 
with metamorphic action, are not altogether correct. At a 
depth of 5,000 feet the temperature of water in the earth’s 
interior should, according to these views, be very high, and the 
quantity of water should be large. Considering the large size 
of the excavation, and its great length, much more water than 
40,000 gallons per day might be expected to come in, and the 
