Long ago Ireland was covered in woodland, and five great forests are traditionally said to have stood in Leitrim, with a 19th-century county survey stating- a hundred years ago almost the whole country was one continued, undivided forest, so that from Drumshanbo to Drumkeeran, a distance of nine or ten miles, one could travel the whole way from tree to tree by branches. Many of these great forests were denuded for the making of charcoal for iron works around Sliabh an Iarainn. Working of the county's rich deposits of iron ore began in the 15th century and continued until the mid 18th century. Coal mining became prominent in the 19th century to the east of Lough Allen at Sliabh an Iarainn and also to the west in Arigna, on the Roscommon border. The last coal mine closed in July 1990 and there is now a visitor centre. Sandstone was also quarried in the Glenfarne region.