Inscriptions including the names of two children Henry Young and John Clark dating to the 18th century have been found in Grebe Swallet, an old mine at Charterhouse, reopened in 1982 by Dr. W.I. Stanton and his digging team. In February 2015 investigations at the Somerset Record Office produced background information from which it has been possible to gain an insight into the graffiti. Henry and John were both small boys when they were in Grebe Swallet, and could possibly have been accompanied by their fathers, John Young and Jeremiah Clark.