A very large glacial erratic that stones have been piled up to to form a cairn like structure. This stone dominates the landscape and is of the same stone type as the central stones at Miller's Grave. It is certain to be part of the ritual landscape of this moorland.
Robin Hood was believed to possess supernatural powers. In the parish of Halifax is an immense stone or rock, supposed to be a Druidical monument, there called Robin Hood's penny-stone, which he is said to have used to pitch with at a mark, for his amusement. There was likewise another of these stones of several tons weight, which the country people would say he threw off an adjoining hill with a spade, as he was digging.
From an 1832 Reader's Digest-esque miscellany called 'The Mirror of Literature, Amusement, and Instruction' by Reuben Percy and others - p205 (it's on Google Books).