The longest railway tunnel in France is that of La Nerthe on the Paris, Lyons and Mediterranean Railway, between Avignon and Marseilles. It is 4,638 metres (5,101 yards). It cost £90. 10s. per metre. Its shafts vary in depth from 65 to 623 feet.[131] There are twenty-four of these shafts, which are not over the centre of the tunnel, but about 30 feet on one side. They communicate with it by lateral galleries 10 feet wide, and as high as the tunnel itself. The shafts are all circular, about 10 feet wide, and have all been left open. The gradient from one end to the centre is 1 in 500—10½ feet in the mile. It then falls to the other entrance at the rate of 1 in 1,000. The tunnel of Blaisy on the same line, near Dijon, is 4,100 metres (4,510 yards). It cost £77 per metre. It had twenty shafts during construction, of which ten are now closed. Nine of the shafts are from 515 to 643 feet below the surface. They are not over the tunnel, but about 32 feet on one side, and connected to it by lateral galleries. The Credo Tunnel on the Geneva Branch of the same line 3,949 metres (4,344 yards), £65. 12s. per metre. There are several other long railway tunnels in France. That of Rilly near Rheims, is 3,500 metres long. There were nine shafts during construction, of which four were closed when the railway was opened. Although lined with masonry throughout, the thickness being 20 inches in compact chalk, and 32 inches in that which was seamy, the cost was only £28. 15s. per yard. Hommarting Tunnel (_Chemin de Fer de l’Est_), is 2,780 metres long, Pissy Poville, 2,400 metres; Tarare is a very long one but we are not sure of its exact extent. The Tunnel of Arschwiller, on the _Chemin de Fer de l’Est_, is 2,678 metres, and is close to the tunnel of the canal from the Marne to the Rhine, named on the previous page the Tunnel of Manvages. In fact, where they enter the mountain they are at the same level, and a double arched entrance—the intervening pier being only 22 feet thick, and the arches precisely similar—receives them both. The canal tunnel was completed before that for the railway, which latter diverges from the line of the former at the rate of 26 feet in 1,000, so that at the end of the railway tunnel it is 60 feet from that of the canal. The canal then makes a bend and presently crosses _over_ the railway tunnel, as it has a descending gradient of 1 in 200, and at what may be called its diverged entrance, it is 44 feet below the level of the canal. The railway tunnel took nearly eight years to construct at a cost of £38. 10s. per metre forward. There is also a large number of tunnels from 500 to 1,500 metres long. The price per metre forward varies nearly as much as in England, its maximum being £95, that of Batignolles, near Paris, on the _Chemin de Fer de l’Ouest_, a short one, only 333 metres (366 yards); minimum £30, that of Terre Noire 1,641 metres, on the Paris, Lyons and Mediterranean.