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
Kilsby Tunnel presence of large amounts of quicksand; trial borings into the hill had not revealed any quicksand in the vicinity, but Stephenson had already made efforts to avoid any such an encounter being made. However, similar problems had previously been encountered during the construction of the nearby Blisworth tunnel on the Grand Union Canal only a few decades earlier. The problems that were posed by the quicksand, which was eventually revealed to be quite prevalent at tunnel level, were so severe that some considerations were allegedly made towards the abandonment of the shaft and restarting work afresh elsewhere; the resulting stress