acrid smoke and foul air built up. Chimneys were built in the shafts, with fires at their base to try to remove the foul air. The construction contract was awarded to Charles Jones, who managed to build about one third of it, but then had financial difficulties, and so other contractors were engaged to work on smaller sections. Difficulties during construction included different strata. Great Oolite (solid limestone) has water permeable fissure which led to rock falls and spring formation and, during dry periods, the water leaking out of the canal. In areas where the tunnel went through Fuller's Earth clay it had to be lined with brick. When the Fuller's Earth expanded this could lead to roof falls and pushed up the base of the tunnel reducing the depth of water for the boats passing through it. The tunnel was opened on 20 April 1789, after five years of construction. It has no towpath; boats were propelled through the tunnel by legging. There were some defects in the workmanship, causing closure for ten weeks' repairs after a year. Further attempts to repair and stabilise the walls included the insertion of oak beams at the base to stop the sides of the tunnel moving inwards as the clay expanded and, in 1904, a concrete lining to some sections. It was superseded as the longest canal tunnel in England in 1811 by the Huddersfield Narrow Canal's Standedge Tunnel, at long, afterwards lengthened, that remains the highest, longest and deepest instance in Britain – which only accommodates . Strood Tunnel on the Thames and Medway Canal was when it opened in 1824, but was interrupted six years later by a short section to create a passing basin. The last commercial traffic passed through the tunnel in 1911 and in 1916 further roof falls occurred. The whole canal was abandoned by 1933. The tunnel was passable until at least 1966, but is now blocked by roof collapses over several hundred yards, mainly in sections where the ground is fuller's earth. Restoration is proposed by the Cotswold Canals Trust as part of their project to re-open a direct route between Thames and Severn. The trust has operated tourist boat trips into the tunnel in winter months. The Sapperton railway tunnel, on the Golden Valley Line, follows a similar route under the 'Cotswold Edge'. There have been proposals to pump water from the River Severn