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
Shrewley Tunnel which crosses the tunnel; having crossed this the path then descends on another ramp to reach the southern portal. The interior of the tunnel is unusually wet and this has led to the creation of flowstone formations. The tunnel runs from the south-east to the north-west. From the northern portal, the canal is level for to the bottom of a flight of five locks at Knowle, which raise the level of the canal by . Kingswood Junction, which connects to the Stratford-upon-Avon Canal occurs about halfway along this stretch. To the south, the canal if level for around to Hatton