Sliabh an Iarainn, anglicized Slieve Anierin, is a mountain in County Leitrim, Ireland. It rises to 585 metres (1,919 ft) and lies east of Lough Allen and northeast of Drumshanbo. It is part of the Cuilcagh Mountains. The mountain was shaped by the southwestward movement of ice age glaciers over millions of years, the morainic drift heaping thousands of drumlins in the surrounding lowlands. Historically there were many iron ore deposits and ironworks in the area. Irish mythology associates the mountain with the Tuatha Dé Danann, particularly the smith god Goibniu. Sliabh an Iarainn is an important natural heritage site with exposed marine and coastal fauna of paleontological interest