In the largest of the towers of Dun Dornadilla, situ ated near the top of Loch Tongue, in Sutherland, the walls are 30 feet high; the outer circumference is about 150 feet; the diameter of the inner area is 27 feet, which leaves about 10 feet 6 inches for the thickness of the walls, including the passage ; in this passage there is a stair from the first to the second story.
The tower of Dunalaskiag, in the Dornoch Firth, is not situated upon any' promontory, but upon the side of a steep bank, opposite to the vitrified fort which occu pies the top of the conical hill of Criech. It stands about 50 feet above the level of the sea, and the view from it is rather confined. The present height, on the upper side next the public road, is about 11 feet; but on ac count of the steepness of the bank, the foundation of the lower side is about 7 or 8 feet under the level of that on the upper side. The form appears to be exactly circu lar; the diameter of the inner area is 31 feet; and the thickness of the walls, including the passage between them, is about 12 feet. On the inside of the inner wall, at about five feet above the present surface of the ground, there is a ledge or offset all round, of about one foot in breadth, which of course reduces the diameter, at this place, to 29 feet; but from this the face of the wall ta pers downward, so that at the surface of the ground the diameter is 31 feet. Below the level of this ledge there is only one opening; this is on the north cast side, and is 4 feet 9 inches high, 3 feet 2 inches wide at the bottom, and 2 feet 9 inches at the top. On each side of this open ing there is a jamb with a recess, as if to receive a door to be fastened on the inside; there are also holes, appa rently for wooden bars, at the back of the door imme diately within the jambs. On each hand, there is an opening like the entrance to a passage in the middle of the wall; the one is 1 foot 6 inches, and the other 2 feet wide, and 3 feet 6 inches high. Round the outer wall there is no other opening but this, but in the inner wall there are four openings placed immediately upon the aforesaid ledge, and opposite to each other; one just over the entrance doorway is 4 feet high and 3 feet wide, the others are partly broken down. In the passage between the walls there are steps of a stair; this passage is about 3 feet 3 inches in width at the entrance, but diminishes to about 18 inches near the upper part; the middle is 4 feet 6 inches in width, from the steps or lintelling over the head; the height is from 5 feet 9 inches to 6 feet. There have also been two other staircases between the walls. The masonry is composed of stones similar to those now lying in the immediate neighbourhood. They
are large, naturally well-shaped, and laid with great re gularity; but neither externally nor internally, is there any appearance of artificial dressing by means of a ham mer or other instrument. From the light to the passages in the middle of the walls, having, in all these structures, been procured from the inside area, it would appear that this never was covered at the top; and yet, in those northern countries, it is improbable that people could remain long thus exposed iu these open inclosures; it is equally improbable that the narrow staircases and pas sages could be employed as permanent dwellings. These buildings must therefore have been only signal towers, or very temporary places of refuge; or they may per haps have been employed for religious purposes ; but whatever were their original destination, it is sufficient, in the present enquiry, to know that they were all built in a regular manner without mortar.
During the 400 years in which the Romans possessed Britain, the modes of building were completely changed : the introduction of lime mortar was alone sufficient to form a new sera. The fortified ramparts constructed be tween the Forth and Clyde, and Newcastle and the Sol way Firth, were a school with which the northern moun taineers, from their constant efforts to destroy them, were, no doubt, quite familiar. The art of combining into one compact and comparatively impenetrable body, the smallest and most irregular stones, must have imme diately struck a people eager to seize any means of ob taining more perfect protection We accordingly find the vestiges of very old towers constructed in this manner upon insulated rocky promontories, along the whole of the sea coast of Scotland; also on the shores and islands of the numerous inland lochs; and in the passes and commanding stations of the mountains. They arc most usually single towers of three stories in height, but not unfrequently, in those reckoned royal residences, the buildings were of greater extent, as Inverlochy castle in Lochaber, which is a regular square, with round towers at the angles: or they consisted of one plain square only, as Balvarie, Elgin, and Duns, in Moray. In other places, in order to occupy the whole rocky or insulated site, they were of an irregular shape, as at Urquhart upon Lochness, and Dunstaffnage upon Loch Etive ; and Ruthven in Badenoch stood upon a neck of high ground projecting into a marshy plain, terminating in a conical mound, on which the castle was built; the area on the top was 100 yards by 30, the south wall 9 feet in thick ness, the other side was 4 feet ; there were two turrets at the northernmost angles. This was the seat of Comyn, Lord of Badenoch.