At the northern side, the slope down commences near the East India Dock entrance, and turns out of the East India Dock Road. The slope is fairly gradual—about one in thirty-four—and it passes under the Blackwall line of the Great Eastern Railway, and near to Poplar Station. The part of the tunnel near to this point—that is the part between the river and the open slope—was executed by what is called “cut and cover” work—that is, a huge trench was dug, then arched in and covered over. “Cut and cover” work also took place on the south side; and there, at the foot of an immense excavation ninety feet down, and with its sides held up by huge timbers, might have been seen a river of water which had drained in and was being pumped up quickly by powerful machinery. Not far distant, the shaft was being sunk for the staircase. In principle, the sinking of the shaft was conducted much as Brunel’s shaft at the Thames Tunnel, only it was built up of iron instead of brick. Imagine a big gasometer with a scaffold near the top, where men are busy building the walls higher and higher by adding on plate after plate of iron. On reaching the scaffold you find that there are two great cylinders of iron, one standing inside the other, and concrete is being filled in between them. Men also are down below digging out the earth which is being swung up in iron buckets; and as the soil is gradually removed, the immense double iron and concrete cylinder slowly sinks by its own weight. In this manner, the great shaft was sunk nearly ninety feet, and within it the staircase has been built, giving entrance for foot passengers, not far from the river. Thus, on either side are sloping entrances to the tunnel, and also, nearer the water, stairways of descent down great shafts. Engineers have also found their way beneath other great English rivers—the Severn and the Mersey. Much water had to be dealt with in the cutting of the Severn Tunnel. This important work, four and one-third miles long, was driven in some places forty-five feet under sandstone, and at the Salmon Pool—a hollow in the river bed—the tunnel was thirty feet under soil called trias marl. Much greater space, therefore, exists here between the tunnel and river than at Blackwall. But the river burst through. The work was begun in 1873, and completed in 1886.