A long exploration level conceived by the Chief lead mining agent for the W B Lead Mines, Thomas Sopwith.
Begun in 1855, the level was driven simultaneously from the adit mouth in Allendale Town and from four shafts sunk at Studdon Dene, Holmes Linn, Sipton and Breckon Hill.
There were two objectives for the undertaking, exploring the unknown ground between Allendale and Allenheads and providing a deep drainage adit for the extensive Allenheads workings.
Some veins were cut in the adit Esp's and Four Fathom Veins at Sipton and the St Peter's Vein being the most productive of them. The level was designed to connect to the bottom of the Gin Hill Shaft at Allenheads but economic conditions changed considerably during the course of its construction and it never attained its full length, stopping after 4.68 miles in 1903.