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
Union Canal (Pennsylvania) closure in 1881. In April 1950, the Union Canal Tunnel was purchased by the Lebanon County Historical Society. The tunnel was placed on the National Register of Historic Places on October 1, 1974. It was designated a National Historic Civil Engineering Landmark in 1970. On April 19, 1994, the tunnel was designated a National Historic Landmark by the Secretary of the Interior Bruce Babbitt. The tunnel is open to visitors in the Union Canal Tunnel Park. A restored portion of the canal along Tulpehocken Creek is maintained by the Berks County Parks System at the Union Canal Towpath Park in