Page:Walker (1888) The Severn Tunnel.djvu/283

170 I have stated before that there were about 1,500 ‘lengths’ in the whole tunnel, and under the river the tunnel is straight for about 2¾ miles; and though these separate lengths were put in from more than forty different ‘break-ups,’ connected by small headings, it is impossible to detect any deviation from the straight line upon the work that has been executed.

At 5.4 the pumping-shaft, about 45 feet to the south of the tunnel, was built from the bottom, from a centre point given by Mr. Schenk, which was set out from the tunnel through a small heading, and proved to be perfectly true with the shaft as set out from above; but the following was the most extraordinary piece of ‘setting out’ executed by Mr. Schenk: The original pumping-shaft at Sudbrook had been tubbed with iron, and three large pumps were fixed in it. When the 5-feet barrel-drain was completed to the new shaft, a heading on a sharp irregular curve was driven, and the bottom of the Iron Pit was excavated, with a roof of about 10 feet of rock between it and the bottom of the pumps, the pumps being constantly at work. A careful survey was made from the 5-feet barrel to find the centre of the Iron Pit. A point was fixed by Mr. Schenk, the lower part of the shaft built; and when a hole was broken through the roof into the Iron Pit, the point given did not vary one inch from the true centre-line of the shaft.

Mr. J. H. Simpson, who was chief of the