_Fort Lough_ occupies nearly the centre of an extensive bog on the right-hand side of one of the roads leading from St. Johnstown to Burt on Lough Swilly. It is described as about one mile long, and a quarter wide, but was formerly of much greater extent. There was a tradition that formerly a castle erected in the centre of this lake had been submerged by the neglect of a girl in not carefully _re_-covering a fairy fountain in the vaults, and consequently the waters burst forth in a raging torrent! After drainage operations, when the level of the lough subsided, marks of an island became visible in the centre, and by degrees stonework was observed rising above the surface, proving that the subaquatic castle was not altogether mere visionary fiction. These walls were found supporting a deposit of peat.[202] COUNTY FERMANAGH. [Illustration: Plate XLI. ELEVATION, PLAN, SECTION AND DETAILS OF THE BALLYDOOLOUGH CRANNOG, Co. FERMANAGH. W.F. Wakeman, 1870.] _Ballydoolough_ (_the place of the dark lake_) is five miles distant from the town of Enniskillen; the expanse of water covers not more than twenty-four acres, and even during times of flood never exceeds twenty feet in depth; at the bottom could be discerned remains of a primæval forest. In June, 1870, from the effect either of drainage or of long-continued drought, a small island became apparent, on which were found fragments of fictile ware, and this led to a careful examination being made. Near the centre was an oaken beam, fifteen feet seven inches long, having evidently formed portion of one side of the lower framework of a dwelling. It was grooved throughout its entire length (plate XLI., No. 7), and had two holes--measuring nine inches by six--that were plainly intended for the reception of upright posts, to which the sheeting or side-boards of the structure were attached. Several oaken slabs, grooved at the sides (plate XLI., No. 9), were discovered in close proximity buried in the sand and mud. Upon clearing the foundation, the framework of the house was shown to be composed of well-squared beams of oak, grooved for the reception of planks, and mortised for the insertion of uprights, the angles dovetailed together, and fastened with wooden pins. The beam forming the eastern foundation of the house rested upon two blocks of dressed oak that projected from it at a right-angle to a distance of seven feet (plate XLI., No. 2), and this foundation may perhaps have supported a landing-stage. The lowest timbers of house and projecting beams were secured in position externally and internally by a row of wooden pegs, or small stakes, which enclosed the entire foundation, and rested against it on the exterior (on the plan these are indicated by a dotted line); the south-western angle of the house was strengthened by a flat block (No. 6). Of the upper work of the edifice no description can be attempted, though several dressed boards (Nos. 4, 5, 8, 9, 10, 13, on a scale of ⅛