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
Dudley Tunnel the tunnel pass through a dolerite known locally as Rowley Rag; and through Coal Measures rocks. The Netherton Tunnel follows a parallel route 1½ miles to the south east; it is much larger and has twin towpaths running through it. It was built to ease congestion in the Dudley Tunnel. Dudley Tunnel Dudley Tunnel is a canal tunnel on the Dudley Canal Line No 1, England. At about long, it is now the second longest canal tunnel on the UK canal network today. (Standedge Tunnel is the longest, at , and the Higham and Strood tunnel is now rail only).