At Creevagh in County Offaly, a mound that was logged as a possible cairn, the kind of stone-heaped monument typically raised over a burial or to mark territory, appears on closer inspection to be nothing more than a natural glacial hillock, shaped not by human hands but by the slow drama of retreating ice.

The mound came to attention during a 1987 survey of the Clonmacnoise area carried out by McDonald, and was duly entered into the record as a cairn. When the Archaeological Inventory of County Offaly was published in 1997, however, the entry noted that no archaeological features were actually visible on the surface. What had caught a surveyor's eye as a potentially significant rise in the landscape was most likely a drumlin or similar glacial landform, the kind of rounded, elongated mound that ice-age glaciers left scattered across the Irish midlands as they deposited their loads of debris. The area around Clonmacnoise is particularly rich in such landforms, the Shannon floodplain punctuated by low hills that can, from a distance, read convincingly as man-made.

There is something instructive in this ambiguity. The Irish landscape contains so many genuine prehistoric monuments, ring forts, passage tombs, standing stones, that surveyors working quickly across large areas can find the natural and the manmade difficult to distinguish. A hillock in the right spot, with the right profile, earns a second look. At Creevagh, that second look appears to have found geology rather than prehistory.