[Illustration: Fig. 172.—Masonry of Broch on Cockburn Law.]
On the highest elevation of the Torwood, in the parish of Dunipace in Stirlingshire, are the remains of a circular structure, excavated in 1864 by Colonel Joseph Dundas. Its appearance previous to its excavation was that of a conical hillock situated nearly on the verge of a precipitous crag, and enclosed on the accessible side by the remains of a double wall of fortification. After excavation it was found to be the ruin of a circular tower of uncemented masonry which, by the gradual dilapidation of its walls, had become a conical hillock of stones covered with grass and heather, and overgrown by a clump of large fir-trees. The structure, now cleared from the superincumbent mass of ruin, is a circular wall 15 feet thick, enclosing a central area of 35 feet in diameter. The entrance doorway has some of the massive lintels still upon it. It is about 7 feet high and 3 feet wide at the door-checks, behind which are the usual bar-holes (shown at A A in the ground plan and section, Figs. 173, 174). To the left of the doorway is the staircase, as usual in the thickness of the wall. The height of wall remaining is not sufficient to show any traces of the galleries, but the presence of the stair implies their former existence. There are no chambers in the thickness of the wall on the ground floor, but all the other features of the building are those of the typical Broch structure.
[Illustration: Figs. 173, 174.—Ground plan and section of elevation of doorway in Broch at Torwood, Stirlingshire. (Drawn by J. Romilly Allen.)]
[Illustration: Fig. 175.—Ground plan of the Broch of Coldoch, Perthshire. (From a Plan by Mr. Ballingall.)]
On the other side of the valley of the Forth, and farther west, at Coldoch, in Perthshire, a similar mound, covering the ruins of a circular tower of uncemented masonry, was excavated in 1870. The structure consists of a circular wall (as shown on the ground plan, Fig. 175) 17 feet thick, enclosing a central area of 30 feet in diameter. The doorway on the east side passes straight through the wall, and is three feet wide, with checks for the door about half-way through the thickness of the wall, and immediately behind them the usual bar-holes. To the left of the doorway is the staircase. No remains of the upper galleries exist, but the presence of the stair implies that they did exist. Opening from the central area are the entrances to three chambers in the thickness of the wall. They are nearly of a size, 8 feet long, 4 feet wide, and a little over 6 feet high. One still retains its roof, rudely vaulted with overlapping masonry. In this case also the group of features characteristic of the structure and its arrangements is such as can be found only in the typical structure of the Broch.