Clay Cross Tunnel

Clay Cross Tunnel is a tunnel on the former North Midland Railway line near Clay Cross in Derbyshire, England, now part of the Midland Main Line.
Construction.
It was designed by George Stephenson with an estimate of £96,000 for construction. The tenders for the work were issued by the North Midland Railway in December 1836. The contractors appointed were Messrs. Hardy, Copeland and Cropper of Watford for the sum of £105,400 (). The tunnel was to be wide and high with a bed of broken stone at the base deep to form the rail bed. The tunnel was to be arched completely round with brickwork laid in Roman cement deep in the roof and walls, and deep in the floor. Approximately 15 million bricks were required for the tunnel lining. The greatest depth below the surface was about .
Construction began on 2 February 1837 when the first sod was turned for the sinking of the ventilation shaft in the centre of the tunnel. The boring of the tunnel was not straightforward, eventually costing £140,000 (equivalent to £ in ), instead of the expected £98,000 (equivalent to £ in ), with the loss of fifteen lives.
It was reported in August 1839 that the tunnel excavation was completed, and the last brick was expected to be laid within a few days, but in fact was not completed until 18 December 1839.
Description.
It begins at the former Derbyshire summit of the line, also the highest point of the whole line, just after the old Stretton railway station. Situated at the watershed of the rivers Amber and Rother. Clay Cross is directly above it and there are ventilation shafts in Market Street (around which the council have placed seats) and High Street (some above the line).
Until the building of the tunnel, no deep prospecting for minerals had been carried out. The discovery of coal and iron led to George Stephenson moving to Tapton House, near Chesterfield. With a group of others, he bought a tract of land north of the tunnel and set up a company, George Stephenson and Co., later renamed the Clay Cross Company.
The northern portal is a magnificent Moorish design and is now Grade II listed. The south portal is also Grade II listed 
Clay Cross railway station was at the northern end, where the line was met by that from the Erewash Valley.
The tunnel saw one of the first uses of the absolute block signalling system, maybe after a narrow escape on the south bound inaugural run. The train was heavier than expected and a pilot engine was provided at the rear. This was detached at the entrance to the tunnel, but halfway through the train came to a halt, and someone had to walk back for the pilot, to the consternation of the passengers. Stephenson had been shown the system by its inventor William Fothergill Cooke supported by Wheatstone of the Wheatstone bridge fame. This was the forerunner of the Midland Railway's system.