XXXIV.

THE MONT CENIS TUNNEL.

MOUNTAIN CHAINS BETWEEN NATIONS.—MONT CENIS.—CROSSING THE ALPS.—THE GREAT ALPINE TUNNEL.—LAYING OUT THE WORK.—THE ARC AND DORA.—DIFFICULTIES.—THE SURVEYS.—PENETRATING THE MOUNTAIN.—COMPLETION OF THE WORK.—THE CHANNEL TUNNEL.—ITS COST.—COST OF TUNNELS IN VARIOUS COUNTRIES. 510