This section is from the book "Ancient Legends, Mystic Charms, And Superstitions Of Ireland", by Jane Francesca Wilde. Also available from Amazon: Ancient Legends, Mystic Charms, And Superstitions Of Ireland.
Near the great mountain of Croagh-Patrick there is a lake called Clonvencagh, or the Lake of Revenge, to which evil-disposed persons used to resort in order to imprecate maledictions on their enemies. It was the custom also to erect monuments round the well by placing on end a long flagstone, and heaping round it a pyramid of sand in order to keep it fixed firmly in its place. Over these pillar-stones certain mystic rites were then performed by the pilgrims, and prayers were said which took the form of the most terrible imprecations. It was therefore with awe and terror that one man said of another, " He has been cursed by the stone."