Don't know why it's called the Sack stone , there's another in Lincolnshire , the top of which is said to resemble an opened sack . If you take the South road to Little Glenshee you get to drive through the ford ,or walk across the bridge. Just round the sharp bend after the ford there is room for a couple of cars to park. Take the track heading North follow it until it forks , just after a mile , the leave it going due east . The stone is unmissable at 3M x 2M . what is odd though is that there is a bit of a view to the South but all other directions are quite limited being in a wee corrie.
Major Mercer was further informed of the site of a monolith called in the district "The Sack Stone," which he at once went to see. From his notes I gather that this is a great smoothed boulder, having one side flat and the other rounded, both with deep longitudinal glacial grooves. It stands about 9 feet 6 inches in height, is 6 feet in breadth and about 3 feet thick near the base, from which it increases to about 4 feet near the upper part.
Its position, as far as could be ascertained from the map, is about three-quarters of a mile N.E. of Creag na Criche, near the 1000-foot contour-line, and on the north side of the burn that divides Tullybeagles from Tullybelton, on the slope of the hill near the latter place. Anderson, the old keeper, said that the current tradition - doubtless, to account for the name - was that some one had brought this Sack Stone in a bag and left it there! If this is a residue of some early legend telling of the Stone being "dropped out of the apron of a witch," it is still one more instance of the folk-lore of Standing Stones.
From 'Report on Stone Circles in Perthshire' by Fred Coles, in PSAS v45 (1910-11).