One of the most curious stone implements of frequent occurrence in the northern islands is what the Shetlanders style a Pech's knife. They have already been referred to as partially resembling the lunar flint knives of Norway and Denmark. But in the Scottish examples the semicircular edge is sharp, while the straight side is thickened like the back of a common knife. Others are oval, or irregular in form, and brought to an edge round the whole circumference. One of the latter, in the Scottish Antiquarian Museum, formed of thin laminæ of madreporite, was found at one of the burghs or round towers of Shetland. It measures 4½ by 4 inches, and does not exceed, in greatest thickness, the tenth of an inch. Similar implements, in the collection of the London Antiquaries at Somerset House, are mentioned by Mr. Albert Way,[157] as probably the ancient stone instruments transmitted to Sir Joseph Banks by Mr. Scott of Lerwick, in Shetland, and communicated to the Society, March 9, 1820. Sixteen were found by a man digging peats in the parish of Walls, Shetland, placed regularly on an horizontal line, and overlapping each other like slates upon the roof of a house, each stone standing at an angle of 45°. They lay at a depth of about six feet in the peat moss, and the line of stones ran east and west, with the upper edge towards the east. A considerable number of implements, mostly of the same class, were found on the clay under the ancient mosses of Blair-Drummond and Meiklewood. Some of them are composed of slate, and others of a compact green stone. They are from four to six inches long, flat, and well polished. There were also along with them a number of stone celts and axe heads, mostly made of the same hard green stone. In the Scottish collection is a knife of an entirely different form, made of light grey flint, which was found, along with a stone celt of unusual shape, within the area of a "Druidical circle," in Strachur parish, Argyleshire. Two others, recently discovered in ploughing a field in the neighbourhood of Largo, Fifeshire, totally differ from any of the numerous examples found in Denmark or Sweden. They are bent back at the point, finished with great care, have a fine edge, and appear to have been attached to bone or wooden handles. Another example, somewhat resembling these, was found in cutting a drain on the Pentland Hills, near Edinburgh, and though simpler, is also peculiar, and apparently unique in form. On showing it recently to an East-Lothian farmer, he remarked that he had frequently seen such things turned up by the plough, but had never thought them worth the trouble of lifting.