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
Riqueval Tunnel Riqueval Tunnel The Riqueval Tunnel is a -long tunnel on the St Quentin Canal, close to the commune of Bellicourt, in the department of Aisne, France. It connects Bellicourt with Bony. It was constructed as part of the St Quentin Canal between 1801 and 1810, on the orders of Napoleon. The tunnel remains in use, and can be traversed using a chain boat. Along with the Mauvages tunnel, on the Marne–Rhine Canal, it is one of the last locations in the world where a system of chain towing is still in operation. It was the longest tunnel in the world