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
Pennsylvania Canal Tunnel but that canal never reached its expected western end, and the tunnel's main use was to allow overflow from the canal to enter the Monongahela. Only one or two canal boats ever went through the tunnel and lock. The tunnel was made obsolete by the arrival of the Pennsylvania Railroad in 1852. The canal tunnel was uncovered during the construction of the U.S. Steel Tower in 1967, and later during the construction of the subway system, which used part of the tunnel on the south side. Pennsylvania Canal Tunnel The Pennsylvania Canal Tunnel was the Pittsburgh terminus of the Pennsylvania