VITRIFIED FORTS  , the name given to certain

rude stone enclosures whose walls have been subjected in a greater or less degree to the action of fire . They are generally situated on hills offering strong defensive positions . Their form seems to have been determined by the contour of the flat summits which they enclose . The walls vary in size, a few being up-wards of 12 ft. high, and are so broad that they present the appearance of embankments . Weak parts of the defence are strengthened by double or triple walls, and occasionally vast lines of ramparts, composed of large blocks of unhewn and unvitrified stones, envelop the vitrified centre at some distance from it . No lime or cement has been found in any of these structures, all of them presenting the peculiarity of being more or less consolidated by the fusion of the rocks of which they are built . This fusion, which has been caused by the application of intense heat, is not equally complete in the various forts, or even in the walls of the same fort . In some cases the stones are only partially melted and calcined; in others their adjoining edges are fused so that they are firmly cemented together; in many instances pieces of rock are enveloped in a glassy enamel-like coating which binds them into a uniform whole; and at times, though rarely, the entire length of the wall presents one solid mass of vitreous substance . Since John Williams—one of the earliest of British geologists, and author of The Mineral Kingdom—first described these singular ruins in 1777, about fifty examples have been discovered in Scotland . The most remarkable are Dun Mac Uisneachain (Dun Macsnoichan), the ancient Beregonium, about 9 M . N.N.E. of Oban; Tap o' Noth, in Aberdeenshire; Craig Phadraic, or Phadrick, near Inverness; Dun Dhardhail (Dunjardil) in Glen Nevis; Knockfarrail, near Strathpeffer; Dun Creich, in Sutherland; Finhaven, near Aberlemno; Barryhill, in Perthshire; Laws, near Dundee; Dun Gall and Burnt Island, in Buteshire; Anwoth, in Kirkcudbright; and Cowdenknowes, in Berwickshire . Dun Mac Uisneachain is the largest in area, being 250 yds. long by 50 yds. broad .

In the Tap o' Noth the walls are about 8 ft. high and between 20 and 30 ft. thick . In Dun Mac Uisneachain, Barryhill and Laws the remains of small rectangular dwellings have been found . For a long

time it was supposed that these forts were peculiar to Scotland; but they are found also in Londonderry and Cavan, in Ireland; in Upper Lusatia, Bohemia, Silesia, Saxony and Thuringia; in the provinces on the Rhine, especially in the neighbourhood of the Nahe; in the Ucker Lake, in Brandenburg, where the walls are formed of burnt and smelted bricks; in Hungary; and in several places in France, such as Chateauvieux, Peran, La Courbe, Sainte Suzanne, Puy de Gaudy and Thauron . They have not been found in England or Wales . In some continental forts the vitrified walls are supported by masses of unvitrified stone built up on each side .