Blisworth Limestone Formation today in the seas off the Bahamas (Kirkaldy p. 59). Much of it also contains marine shells, notably of oyster. Subsequently, the site was submerged less deeply so that the overlying Blisworth Clay was deposited in brackish conditions. (Gallois p. 20) The stratum is known as Blisworth Limestone because it was first studied at Blisworth in Northamptonshire when the Blisworth tunnel was being dug for what is now called the Grand Union Canal. The tunnel finally opened in 1805. Blisworth limestone is a generally thin but widely spread deposit in eastern England. It becomes thicker as one progresses southward from
Butterley Tunnel Butterley Tunnel Butterley Tunnel is a one and three quarter mile long canal tunnel on the Cromford Canal below Ripley, in Derbyshire, England, opened to traffic in 1794. Along with Butterley Works blast furnaces, part of the canal tunnel and its underground wharf were declared a scheduled monument in 2013. The tunnel was 2,966 yard (2712m) long, wide at water level, and from water to soffit (depending on the water level). At the time of building it was the third longest canal tunnel in the World after Sapperton and Dudley. Thirty-three shafts were sunk during construction with the workings dewatered