The remarkable cluster of monolithic groups and earth-works at Stennis in Orkney, includes a variety of sepulchral mounds, probably belonging to very different periods. Scattered around the great circle, or Ring of Broidgar, as it is commonly called, there are many tumuli differing considerably in size and form, but all known to the peasants under the general title of the Knowes of Broidgar. The dimensions of some of the largest of these were taken, during the recent Admiralty Survey, by Lieutenant F. W. L. Thomas, R.N., the intelligent officer in command, to whom I am indebted for the use of valuable notes of observations on the antiquities of Orkney:-- "The most remarkable tumulus, which is of elliptical shape, stands at the shore of the north or fresh-water loch. It measures one hundred and twelve feet long by sixty-six feet broad. The level ridge on the top measures twenty-two feet in length, and its height is nearly the same. It has been greatly destroyed by excavators at some former period. Near to it is a small standing stone. No other tumulus of this shape exists in Orkney. A large conoid tumulus, fifty feet in radius and twenty-eight feet in height, stands to the westward of the great circle, also pillaged at some former time; and in the same neighbourhood are ten smaller tumuli of various dimensions. Five of these are of equal size: radius six feet, height three feet, and only from two to three feet apart; four of them in a line." Besides these, there stands, at a short distance to the northward of the elliptical tumulus, and near the shore, another large earth-work of peculiar form, which can hardly be more definitely described than by comparing it to a colossal plum-cake. It rises perpendicularly five feet, and is nearly flat on the top, assuming the form of a greatly depressed cone, the apex of which is nine feet high. The radius of the whole measures thirty-one feet. This mound, however, is most probably not sepulchral, but rather the platform on which a building of wood had been reared, though its present symmetrical form may render this doubtful. The Ring of Bookan, in the same neighbourhood, appears to be a similar platform, but it is inclosed with an earthen vallum, and exhibits abundant traces of ruined works on its irregular area. Various other, though less regular mounds, of this character, occur in Orkney. The burgh of Culswick is represented as having stood on such a platform, the shape of which nearly corresponded with that of Stennis when drawn in 1774, but the materials of this venerable ruin have since furnished a quarry for the neighbouring cottars.[51] It is exceedingly doubtful if the larger tumuli in the neighbourhood of the great circle of Stennis would now repay the labour of exploring them. They exhibit, as has been observed, abundant traces of former investigation; and there is good reason to believe that most, if not all of them, have already been spoiled of their historic contents.