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
Chirk Tunnel Chirk Tunnel Chirk Tunnel is a canal tunnel near Chirk, Wales. It lies on the Llangollen Canal, immediately northwards of the Chirk Aqueduct. It is long and has a complete towpath inside. The tunnel is designed for a single standard narrowboat, so passing is not possible. The tunnel is straight enough to be able to see if a boat is already inside the tunnel (boats are required to show a light). Northbound boats must maintain power and momentum in order to push through, due to the shallow, narrow nature of the canal in the tunnel (such that water has little