A ball of fine-grained claystone, in the Perth Museum (Fig. 148), which is said to have been dredged up from the Tay, has its surface divided into four circular discs which scarcely project beyond the circular outline of the ball, and impinge upon each other. In one of the discs the ornament consists of projecting knobs, arranged in rows both ways by the channels between them crossing each other at right angles. The knobs rise from a square base, and are rounded at the summits. This is also the character of the prickly ornament of the hemispheres of the terminal bulbs of the penannular brooches of silver found at Skaill, to which the ornament on the disc of this stone ball has a distinct resemblance. The treatment of the segmental spaces between the discs is also seen in the example from Freelands, Glasterlaw (Fig. 144), and the simply incised ornament of the remaining discs occurs on two other balls (Figs. 149, 150), which have each but one of their discs ornamented. [Illustration: Fig. 149.—Ornamented Stone Ball found at Inverawe (2⅝ inches diameter).] [Illustration: Fig. 150.—Ornamented Stone Ball found at Loch Lochy (3 inches diameter).] [Illustration: Fig. 151.—Ornamented Stone Ball found in the Isle of Skye (2¾ inches in diameter).] An example from the island of Skye (Fig. 151) has its surface covered with small hemispherical protuberances. This variety is akin to another which has the whole surface studded with projections of a pyramidal form. Two balls of this latter variety (Figs. 152, 153) were found in one of the chambers of a curious composite structure, or group of structures, situated close to the shore on the south side of the Bay of Skaill, in the mainland of Orkney.[70] One of these (Fig. 152) has the central portion pierced with a hole. The perforation is roughly made, and considerably wider at its external orifices than in the centre, where it is less than half an inch in diameter. ----- Footnote 70: This structure, which was explored by Mr. William Watt, consisted of several sub-rectangular chambers with rounded corners, having small cell-like constructions opening off them. The chambers were arranged on both sides of a long winding passage. Their door-ways had checks for the doors, and bar-holes behind them. The largest chamber was about 20 feet square. From 6 to 8 feet of the height of the walls remained. They were dry-built, and converged towards the upper part as if to form beehive roofs. Hearths of square form, surrounded by flagstones on edge, were found in the floors. Many implements of stone and bone were found in the chambers, and a large accumulation of bones and horns of animals, among which those of the red-deer and the _Bos primigenius_ were abundant. Among the stone implements were several polished celts. The collection is preserved at Skaill House. -----