GEOLOGY OF THE MONT CENIS TUNNEL. 
353 
taking, and the difficulties anticipated in obtaining fresh air, 
rendered it to a certain extent a hazardous and speculative 
matter at one time ; but the successful adaptation of the ap- 
paratus for boring, by machinery driven by compressed air and 
carried into the tunnel in such a manner as to be ultimately 
applied by elastic tubes, completely settled all doubts, and 
renders it as easy to bore for ten miles, retaining good ventila- 
tion, as it had previously been to drive a level for a hundred 
yards. The geological and physical questions involved were 
not, however, at first considered, and have been to some extent 
neglected ; but specimens of the rocks cut through have been 
preserved from the first, and two or three collections of this 
kind are available. One of these has been taken to Paris by 
Professor Sismonda, and forms the subject of a description by 
M. Elie de Beaumont, published in the Comptes-rendus of 
the Academie des Sciences for the 4th July last. Other but 
less complete collections, with many duplicates, exist in the 
offices of the resident engineers at Modana and Bardonneche 
respectively. Both are in the highest degree interesting, and 
an inspection of them has greatly assisted the author in pre- 
paring this article. He has also to express his acknowledge- 
ments to the engineers for their kindness in placing before 
him the results of such observations as they have made on the 
various subjects alluded to. 
It should be known that the present is a very favourable 
moment for examining the works and their geological results ; 
although the inside of the tunnel is not easily accessible, owing 
to the great activity with which the works there are being 
pushed. There is no cessation, night or day, from one year’s 
end to another, the only holidays in the year being on the 
occasion of the great festivals of the Church. To ensure the 
greatest activity and energy a premium is given to all hands 
employed in proportion to the rate of progress, and sometimes 
it has been found necessary to check the extreme eagerness to 
get on lest accidents should occur. The accidents hitherto 
have been very few and slight, and the general conduct of the 
works reflects the greatest credit on all concerned. The study 
of the rocks in the neighbourhood, and their comparison with 
the fragments brought out from the end of the tunnel, will 
afford ample occupation to the geologist for many days, and 
will not fail to render him familiar with some of the most 
interesting results of metamorphic action. The total absence 
of plutonic rock in the district near the tunnel will not fail 
also to attract his attention. 
The whole group of rocks alluded to in this article belong, 
as has been already pointed out, to the middle part of the 
secondary system, from the middle oolite to the Blunt ic inclu- 
VOL. IX. NO. XXXVII. A A 
