and a clause in the Act that should the North Midland Railway fail to build its line, the Manchester and Leeds Railway would have the power to do so. The Manchester and Leeds Railway Act was given Royal Assent on 4 July 1836. Authorised share capital was £1,300,000. An Act on 5 May 1837 authorised changes to the route. Tunnels Work on the section from Manchester to Littleborough began on 18 August 1837, and on the Summit Tunnel the following year. The tunnel proved much more expensive than planned, and took longer to complete. It was nearly finished in December 1839 when a portion of the invert failed, allowing the side walls to move by three-quarters of an inch, requiring them to be rebuilt. Stephenson explained the failure by saying The blue shale 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... 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. At the time of its completion it was the longest railway tunnel in the world, at 2,885 yd. The brickwork varies from five to ten rings in thickness. The total cost of Summit Tunnel was £251,000. There was a problem at Charlestown Tunnel, between Eastwood and Hebden Bridge. The ground consisted of loose, sandy earth which gave trouble from the start. On 8 June 1840 it was reported that the masonry inside the tunnel was collapsing and eventually, after much further consideration, the tunnel was abandoned and the line built round the hill at ground level on curves of 12 to 15 chains radius. Early track Whishaw wrote in 1842, "The [track] gauge is 4 feet 9 inches, in order to allow of an inch play on either side for the wheels of the locomotives and carriages. The rails are of the single parallel form... They are in 15-feet lengths, having 3-feet bearings..." The track consisted of T-section rails, 5 in deep with heads in wide and in deep, weighing 56 lb per yard, secured in chairs 10 in by 5 in by means of a -in diameter ball and key fitted into grooves in each side of the stem of the rail.