Britain has several celebrated examples of this odd geological formation, otherwise called a rocking stone, which can be moved back and forth by applying varying amounts of force.
Logan stones were formed through selective weathering of layered rocks, a softer lower layer being worn away by wind, rain and frost until only a thin neck remained. This became understood only in the nineteenth century — before then many believed they had been constructed by the ancient Druids. Their weirdness has long given them supernatural associations and made them a focus for witchcraft. It was thought, for example, that the rocking stone near Nancledrea in Cornwall could only be moved at midnight when witches were abroad; people believed that if you touched it nine times at midnight, you turned into a witch. The one at Land’s End was said to have been put there by a giant who rocked himself to sleep on it.
Logan, as odd a word as the object it describes, has an origin that’s not well understood. It comes from the English dialect log that means to rock (in some parts of Britain the stones are called logging stones). We can’t go further with confidence, but the word may have a link with Danish logre, to wag the tail, which could suggest a Norse origin.