Mountfield Gypsum Mine 1876-1993. Gypsum seams first discovered in the 1870s during the sinking of the Sub-Wealden Borehole, ostensibly a scientific project. The gypsum occurs as several seams in the Jurassic Purbeck beds, two of which are substantial enough to merit extraction. Original access was by vertical shaft, replaced by inclined drift in the 20th century. Several working methods employed over the long history of the mine. Sussex gypsum production is now concentrated at Brightling Mine (2008). More information: "Kent and East Sussex Underground" publ. KURG. See www.kurg.org.uk