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. Name 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". Davies Gilbert suggested that the word "logan" comes from a Cornish expression for the movement that someone makes when inebriated: It may be observed that I have always used the words Loging Rock for the celebrated stone at Trereen Dinas. Much learned research seems to have been idly expended on the supposed name, "Logan Rock." To log is a verb in general use throughout Cornwall for vibrating or rolling like a drunken man, and is frequently heard in provincial pronunciation for tug, characteristic of the modem present participle. The Loging Rock is, therefore, strictly descriptive of its peculiar motion. Examples of rocking stones 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 can be moved with one finger, but that also resists a push made with the whole body." Ptolemy (circa 90–168) wrote about the Gygonian rock, which he wrote "can only be moved with an asphodel and remains immovable by 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