3-034-641 - The Print Collector/Heritage Images

Plan and section of the Mont Cenis Tunnel, 1871. '...it will be perceived that the approach line to the Savoy mouth of the tunnel, shown at the left, makes a remarkable bend, passing up the valley of the Arc to Modane, then turning round and descending the same valley, parallel to its former course, to reach the mouth of the tunnel at Fourneau. This was needful to gain the requisite elevation, the tunnel being 400 ft. above the bottom of the valley, 150 ft. above the Mont Cenis road at Modane, and 8709 ft. above the sea level. Entering the tunnel, its level is found to rise with an average incline of 1 in 45, or 117 ft. 4 in. per mile...descending to the Italian side, the incline is very slight, about 1 in 2000, serving only to let the moisture run off the floor. The exact length is 7½ English miles and 242 yards...The transverse section displays the outline of the mountain mass, called Le Grand Vallon, through which the tunnel is pierced. The highest point of this mountain is 9600 ft. above the sea level...The dimensions of the tunnel, as excavated, are 25 ft. 3½ in. wide at the base; 26 ft, 2¾ in. at the broadest part, with a semicircular top; 24 ft. 7 in. high at the Modane end, but 11¾ in. higher at the Bardonnèche end'. From "Illustrated London News", 1871.