Sliabh an Iarainn (iron mountain), formerly Sliabh Comaicne (mountain of the conmaicne natives), is a large hill in County Leitrim, Ireland. Its present form evolved from the southwest movement of ice age glaciers over millions of years, the morainic drift heaping thousands of drumlins in the surrounding lowlands. Irish cultural folklore records strong association with the mythological Tuatha De Dannan. Sliabh an Iarainn is an important natural heritage site with exposed marine and coastal fauna of paleontological interest