On the northern declivity of Cockburn Law, in Berwickshire, there is a natural platform projecting from the shoulder of the hill over the valley of the Whitadder water, about 250 feet above the bed of the stream. On this platform there is an irregularly oval enclosure (Fig. [171]), the outlines of which are formed by the remains of two parallel earthworks and an outside ditch. The space thus enclosed is occupied by the remains of various smaller enclosures, some circular and others irregular in form. They are nearly all so ruined that nothing can be made of their details. But the principal structure within the enclosure is still capable of such examination as will suffice to determine its typical relationship with the Brochs of the extreme north. It is circular, consisting of a wall 17 feet thick, enclosing an area of 56 feet in diameter. In the thickness of this wall are two elongated oval-shaped chambers, one of which is 33 feet long and 7 feet wide, the other 23 feet long and 7 feet wide. In 1793 the roofs were still on them, and it was then seen that they were covered with a rude vaulting of overlapping masonry. Both these chambers open to the inner area. The only access to this area from the outside is the main doorway, which passes straight through the wall, and is flanked by a guard-chamber constructed in the thickness of the wall on either side. To the left of the doorway are the remains of the staircase, with an elongated chamber opposite the foot of the stair. No remains of galleries exist owing to the absence of the whole upper part of the structure, but the presence of the stair implies that they once existed. The masonry is massive in character (Fig. [172]), and the structure is also remarkable for its great size, being three times the width of Mousa and twice that of the Glenelg Brochs. But its features of form and character, and all the arrangements of its details, so far as they now exist, are those of the typical Broch structure; and, taken together, they form a group of features and arrangements which do not exist in any other type of structure.
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.
Figs. 173, 174.—Ground plan and section of elevation of doorway in Broch at Torwood, Stirlingshire. (Drawn by J. Romilly Allen.)
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.
These three examples are all that are known on the mainland of Scotland south of the Caledonian valley. A few years ago they were mere grass-covered hillocks, indistinguishable from many others that are yet to be seen in various quarters of the same wide district of country. It is impossible to say how many of these unexamined mounds, which exist abundantly in the valleys of the Forth and Teith for instance, may be of similar character. But it is possible to say that where three have been found without being specially looked for, the probability is that more will be found when they are looked for. The present position of our knowledge is that there are three examples south of the Caledonian valley, but if I were to conclude that these three are all that exist in that wide region I should be drawing from my ignorance of the actual facts a conclusion which could only be drawn from complete knowledge obtained by exhaustive investigation.