A group of barytes mines were flooded, but not obliterated, during the construction of the Cowgreen Reservoir in the 1960s. The main veins worked at the primary mine were the large Winterhush, Greenhush, and Isabella veins, which had been previously exploited in earlier superficial workings. Later development occurred through the Wrentnall Shaft, initiated by the Hedworth Barium Co., along with the company’s principal level.

The main period of working began in 1935 under the Anglo-Austral Mining Co., who deepened the shaft and drove levels both north and south of it at various horizons down to, and including, the Whin Sill. The sandy shale, known as whetstone, adjacent to the Whin Sill has undergone albitisation, and lime-silicates have formed in argillaceous parts of the limestone.

1859 Jacob Walton & Co. 1872-1881 J.H. Robinson & Co. 1892-1896 Teesdale Mineral Co. Ltd 1898 James C. Rollin 1899 Hedworth Barium Co. Ltd 1900-1909 James C. Rollin 1910-1921 Hedworth Barium Co. Ltd 1923-1929 George Hodsman & Sons Ltd 1930-1931