Late Tertiary faulting, footwall uplift and topography in western Ireland Michael Badley Petroleum Geology of Ireland’s Offshore Basins, Geological Society, London, Special Publication No. 188, 2001, p. 201-207. Abstract: The Erriff Fault in south Mayo, Ireland, is a rare example within the British Isles and Ireland of a sizeable onshore fault (normal displacement >500m) at which a correlatable stratigraphic horizon is preserved in both the footwall and the hanging wall. That this displacement probably accumulated during Late Tertiary time makes the Erriff Fault (and other similar faults in the area) all the more interesting. Structural forward modelling indicates that the footwall uplift and the hanging-wall subsidence accompanying faulting, followed by further isostatic uplift following glacial erosion during the Pleistocene glaciations, exercised a fundamental control on the overall form of present-day topography in western Ireland.