Taken from ucd.ie/envinst/envstud/mushroomstones/about02.html
In the townland of Clonkeen (in a field close to the road from Clonbullogue to Clonad House, in County Offaly) is a stone known as Finn Mac Cool’s stone. According to legend this is a stone which the mythical Irish giant tried to throw from the top of Croghan Hill at another giant standing on the Hill of Allen in the Kildare hills. The stone however fell short of its target in Clonkeen, where it was spotted by a dog as it rolled along the ground; the dog is said to have stopped it with its paw. A credulous eye can still make out the mark of a dog’s paw on one side of the stone and the giant’s hand on the other.