From Devon by W. G. Hoskins:

"Manganese was first found in Devon at Upton Pyne, about 1770. This mine, with two smaller mines in the same lode in Newton St. Cyres, supplied the whole country for many years. Manganese was used at first in the manufacture of Egyptian ware in the Potteries, and in purifying glass. Its later use in bleaching led to a considerable increase in output, some 2000 - 3,000 tons being shipped annually from Exeter in the early years of the 19th century.

When the older mines failed, new deposits were found in the hills west of Exeter - at Ashton, Doddiscombsleigh and Christow - and  about 1815 other deposits were found in West Devon, chiefly around Milton Abbot, Coryton and Maristow. By the end of the 19th century only the Milton Abbot mines were working, on a small scale. The old manganese workings now produce yellow ochre. (1954)"

To visit Andrew Westcott's interesting site with its detailed information on Doddiscombsleigh's manganese mines plus photographs, click on this link:

http://myweb.tiscali.co.uk/andyspatch/manganese.htm