After walking a distance of about half a mile, the inspecting party arrived at the scene of the “frightful accident,” about which so much alarm had been spread. All that was visible was a certain unevenness of the ground, which had been forced up by the invert under it giving way; thus the ballast had been loosened, the drain running along the centre of the road had been displaced, and small pools of water stood about. But the whole of the walls and the roof were still as perfect as at any other part of the tunnel. [Picture: Entrance to the Summit Tunnel, Littleborough] The engineer explained the cause of the accident; the blue shale, he said, through which the excavation passed at that point, was considered so hard and firm, as to render it unnecessary to build the invert very strong there. But shale is always a deceptive material. Subjected to the influence of the atmosphere, it gives but a treacherous support. In this case, falling away like quicklime, it had left the lip of the invert alone to support the pressure of the arch above, and hence its springing inwards and upwards. Mr. Stephenson directed the attention of the visitors to the completeness of the arch overhead, where not the slightest fracture or yielding could be detected. Speaking of the work, in the course of the same day, he said, “I will stake my character and my head, if that tunnel ever give way, so as to cause danger to any of the public passing through it. Taking it as a whole, I don’t think there is such another piece of work in the world. It is the greatest work that has yet been done of this kind, and there has been less repairing than is usual,—though an engineer might well be beaten in his calculations, for he cannot beforehand see into those little fractured parts of the earth he may meet with.” As Stephenson had promised, the invert was put in; and the tunnel was made perfectly safe. The construction of this subterranean road employed the labour of above a thousand men for nearly four years. Besides excavating the arch out of a solid rock, they used 23,000,000 of bricks, and 8000 tons of Roman cement in the building of the tunnel. Thirteen stationary engines, and about 100 horses, were also employed in drawing the earth and stone out of the shafts. Its entire length is 2869 yards, or nearly 1¾ mile—exceeding the famous Kilsby Tunnel by 471 yards. The Midland Railway was a favourite line of Mr. Stephenson’s for several reasons. It passed through a rich mining district, in which it opened up many valuable coalfields, and it formed part of the great main line of communication between London and Edinburgh. The Act was obtained in 1836, and the first ground was broken in February, 1837.