Rocking stone

Rocking stones (also known as logan stones or logans) are large stones that are so finely balanced that the application of just a small force causes them to rock. Typically, rocking stones are residual corestones formed initially by spheroidal weathering and have later been exposed by erosion or glacial erratics left by retreating glaciers. Natural rocking stones are found throughout the world. A few rocking stones might be man-made megaliths.

The word "logan" is probably derived from the word "log", which in an English dialect means to rock. In fact, in some parts of the UK, rocking stones or logan stones are called logging stones. The word "log" might be connected with the Danish word logre, which means to "wag a tail".

Some have suggested that the word "logan" comes from a Cornish expression for the movement that someone makes when inebriated.Davies Gilbert writes:

Such stones are common in Britain and other places around the world. For example, in Galicia, rocking stones are called pedras de abalar

Pliny the Elder (23–79) wrote about a rock near Harpasa (in Caria, Asia Minor) that could be moved with a finger, but could not be dislodged with a thrust of the whole body.Ptolemy (circa 90–168) wrote about the Gygonian rock, which he claimed could be moved by pushing on it with the stalk of an asphodel, but could not be removed by any force.

There are stones in Iona called na clachan-bràth, within the precincts of a burial ground, and placed on the pedestal of a cross, and have been according to Pennant, the supports of a tomb.

A massive 90– to 95-ton glacial erratic boulder near Halifax, Nova Scotia can still be rocked with a lever, but used to move quite easily, before a band of sailors from the nearby Halifax garrison rocked it into a more stable configuration in the 1890s, and before its base was worn down by excessive rocking in the 1980s and '90s when a park was developed around it at Kidston Lake, in the Spryfield area of the municipality. It used to be a popular picnic destination; in Victorian times, people would travel from Halifax, climb upon it and spread their lunches, while enjoying the sensation of rocking gently while seated upon the huge rock.

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