page_title: Mushroom stones
hierarchical_section_title: Mushroom stones
caption_attribution_description: The base of the ‘wavestone’ at Gortlecka (Plate 1) was winter-flooded by Lough Gealáin (pH 8.2) when the photograph was taken, and the horizontal surface of the water contrasts strongly with the sloping and undulating lip. The lake water pH and lip shape both signify that formation cannot have occurred in the lake. Instead, the sharply-defined lip marks the former level of the (undulating) soil surface, below which solution by soil water (pH 6.0) occurred.
context_page_description: Mushroom stones, or mushroom rocks, in Ireland are limestone boulders undercut by past weathering regimes. These rocks take the form of solitary sentinels of limestone which still bear the unmistakable marks of long-continued erosion by ice, soil or lapping waves at the edge of lakes which have since vanished or retreated. These stones are sometimes shaped like mushrooms, others have an overhang facing in just one direction, but all are notched and undercut in such a fashion as to suggest prolonged exposure to standing water at some time in the past. The mushroom-shaped stones are produced where the notching forms a fairly even circle around the stone.
  Where a limestone boulder stands at the edge of a lake so that it is partly covered by water, the underwater part weathers more rapidly than the part above water because it is subject to more constant corrosion by water, accentuated by the abrasive lapping action of waves. If this continues for a long time the upper part will be undercut, and the stone will assume a very distinctive form which is frequently mushroom-like. Much more rarely the same process can be seen in limestone bedrock.
context_section_description: Mushroom stones, or mushroom rocks, in Ireland are limestone boulders undercut by past weathering regimes. These rocks take the form of solitary sentinels of limestone which still bear the unmistakable marks of long-continued erosion by ice, soil or lapping waves at the edge of lakes which have since vanished or retreated. These stones are sometimes shaped like mushrooms, others have an overhang facing in just one direction, but all are notched and undercut in such a fashion as to suggest prolonged exposure to standing water at some time in the past. The mushroom-shaped stones are produced where the notching forms a fairly even circle around the stone.
  Where a limestone boulder stands at the edge of a lake so that it is partly covered by water, the underwater part weathers more rapidly than the part above water because it is subject to more constant corrosion by water, accentuated by the abrasive lapping action of waves. If this continues for a long time the upper part will be undercut, and the stone will assume a very distinctive form which is frequently mushroom-like. Much more rarely the same process can be seen in limestone bedrock. Many mushroom stones have a second minor ‘lip’ below the main one, suggesting that the drop in water level which isolated the stones from the lake's edge took place in two stages.
caption: Plate 1,‘Wavestone’ at Gortlecka, R32011 94965, The Burren, Co. Clare.
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