This is a group of eight outliers of Namurian strata on the hills around Lough Allen straddling counties Leitrim, Roscommon, Sligo and Cavan. The three largest outliers, on Kilronan, Altagowlan (Spion Kop) and Sliabh an Iarainn, to the east and west of the lough, carry workable bituminous coals.
In the Arigna area there are five coal seams varying from 12 to 36 inches in thickness. The seams have a very shallow dip and could be worked from adits driven at various points along their outcrops. From the lowest upwards they were, Lower Crow Coal, the Middle Crow Coal, the Upper Crow Coal, the Main Coal and the Top Coal. The latter two are now worked out.
The Main Coal was discovered on Kilronan in 1765 and was initially mined as fuel for iron smelting furnaces. Between then and 1990 some 25 collieries were worked.
- Irish maps viewer
- Connacht District Report
- Arigna Mining Experience
- NMRS online mapping of the collieries of the British Isles