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
Greywell Tunnel and so avoid the possibility of closure under the Railway and Canal Traffic Act 1888. Harmsworth, the last trader working on the canal, bought the canal in 1923, but only the lower section up to Woking was used. The tunnel was finally closed when part of the roof collapsed in 1932, after which the canal to the west, including Basingstoke Wharf, was sold. It was still possible for canoeists to get through the tunnel until the late 1950s, but the blockage is now total. The tunnel is of interest for its bat populations: it has more roosting bats than any