[101]. Account of some remarkable Ancient Ruins recently discovered in the Highlands. In a series of Letters by John Williams, mineral engineer. Edinburgh, 1777.
[102]. Proc. Soc. Antiq. Scot., vol. ix. p. 396, vol. x. p. 70, vol. xi. p. 298, and vol. xii. p. 13.
[103]. Archœological Journal, vol. xxxvii. p. 227.
[104]. Proc. Soc. Antiq. Scot., vol. iv. p. 350. A section and elevation of the rampart showing the oak-beams in position are given in Plate IX. of the same volume.
[105]. Memoire sur les ouvrages de fortification des Oppidum Gaulois de Murcens, d’Uxellodunum et d’Impernal situes dans le department du Lot. Congrès Archeologique de France, xli. session. Paris, 1875, p. 427.
[106]. The late Mr. Ramsay, Director of the Geological Survey, records a circumstance which has an obvious bearing on the question of the possibility of such vitrifaction. Near Barnsley, in Yorkshire, the country affords no good material for road-metal the sandstones made from the debris of granitic gneiss pounding up rapidly under cart-wheels. "To obviate this defect the following process is adopted:—The stone being quarried in small slabs and fragments is built in a pile about 30 feet square and 12 or 14 feet high, somewhat loosely; and while the building is in progress brushwood is mingled with the stones, but not in any great quantity. Two thin layers of coal about 3 inches thick, at equal distances, are interstratified with the sandstones, and a third layer is strewn over the top. At the bottom, facing the prevalent wind, an opening about 2 feet high is left, something like the mouth of an oven. Into this brushwood and a little coal is put and lighted. The fire slowly spreads through the whole pile and continues burning for about six weeks. After cooling, the stack is pulled down, and the stones are found to be vitrified. I examined them carefully. Slabs originally flat had become bent and contorted, and stones originally separate glazed together in the process of vitrifaction."—Proc. Soc. Antiq. Scot., vol. viii. p. 150.
[107]. Proc. Soc. Antiq. Scot., vol. ii. p. 95, and vol. ix. p. 379.
[108]. Ibid., vol. viii. p. 20.
[109]. Proc. Soc. Antiq. Scot., vol. v. p. 304.
[110]. Described by Dr. Arthur Mitchell, Proc. Soc. Antiq. Scot., vol. iv. p. 436.