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
Bruce Tunnel stone, each with a decorative plaque of Pennant stone. Construction was begun in 1806 and finished in 1809. It is lined with English bond brickwork and has a wide bore to cope with the 'Newbury Barges' used on this canal. There is no towpath through the tunnel, so walkers and cyclists must walk across the top of the hill. When canal boats were still pulled by horses, the boatmen had to haul boats through the tunnel by hand, pulling on chains that ran along the inside walls. The tunnel is about northeast of Burbage village. To the north lies the