This is superstitious name given to triangular flints, Belemnites, which are found in many countries, particularly Scotland. These stones were thought to have been shot by elves and fatal to cattle when hitting them. The cure was to touch the cattle with the stone with which they had been hit and to give them a drink of water in which the arrow had been dipped in. Other cases recorded even state an Irish bishop was shot at by an evil spirit; the stone was made by the Devil himself helped by attending imps who roughhew them, while the Archfiend finished them himself. Other legends have it that such stones were made and used by Scottish witches. Similar tales circulated in Italy, Africa, and Turkey. A.G.H.
Spence, Lewis. An Encyclopaedia of Occultism. New York. University Books. 1968. p. 139