The tunnel through the Alps at present being pierced to connect the railway system of France and Italy, has acquired the title of the "Mont Cenis Tunnel;" but its real position and direction have very little in common with that well-known Alpine pass. On examining a chart of the district which has been selected for this important undertaking, we shall observe that the main chain of the Cottian Alps extends in a direction very nearly East and West, and that this portion of it is bounded on either side by two roughly parallel valleys. On the North we have the valley of the Arc, and on the South the valley of the Dora Ripari, or, more strictly speaking, the valley of Rochemolles, a branch of the Dora. The Arc, flowing from East to West, descends from Lanslebourg to Modane, and from thence, after joining the Isere, empties itself into the Rhone above Valence. The torrent Rochemolles, on the other hand, flowing from West to East, unites itself with the Dora Ripari at Oulx, descends through a narrow and winding valley to Susa, and thence along the plain to Turin. The postal road, leaving St. Michel, mounts the valley of the Arc as far as Lanslebourg, then turns suddenly to the South, passes the heights of the Mont Cenis, and reaches Susa by a very steep descent. On mounting the valley of the Arc, and stopping about eighteen miles West of Mont Cenis, and a mile and a half below the Alpine village of Modane, we arrive at a place called Fourneaux. Here, at about three hundred feet above the level of the main road, is the Northern entrance of the tunnel; the Southern entrance is at the picturesque village of Bardonnêche, situated at about twenty miles West of Susa, in the valley of Rochemolles.