The origin and significance of mushroom stones in lowland karst regions

'Mushroom stones', or 'wave stones', are limestone erratics or protruding bedrock that shows signs of erosion or dissolution suggestive of prolonged exposure to standing water. Fifty-three stones in the central lowlands of Ireland were recorded in a systematic fashion, with accurate lip-height measurements taken for more than half the stones using GPS (Global Positioning System) equipment. The heights of their erosional lips are discussed with reference to estimated pre-bog water tables, lake fluctuations and other possible explanations for this phenomenon. The results suggest that the erosion of the stones now found in the bogs of County Offaly cannot be attributed to erosion by a single large lake as previously speculated, whereas the notching of stones in and around wetlands and lakes in Roscommon and Clare is likely to be due largely to flooding and winter water levels.