Described by Lord Rosehill in _Proc. Soc. Antiq. Scot._, vol. viii. p. 105.
This “diamond broaching” is very common in the reparations of the Roman wall and its stations between the Solway and the Tyne, while the stones used in Hadrian’s original erections are severely plain.—Dr. Bruce, in _Lapidarium Septentrionale_, p. 39.
The range of the type includes the whole eastern area of Scotland, stretching from Berwickshire on the south to the Shetland Isles. Its special form is so peculiar that it must be held to constitute a distinction sufficiently characteristic to separate the Scottish group from all other varieties of underground structures, and sufficiently constant to warrant us in assigning to it a specific value. There is an Irish group and a Cornish group of underground structures, but they do not generally present the special features of form which characterise the Scottish group. The Irish examples are usually associated with raths, thus resembling the specimen in the rath of Dunsinnane, which is the only one known of that special variety in Scotland. They are excavated in the area enclosed by the interior rampart of the rath, and consist of one or more chambers, sometimes circular or oval in plan but often rectangular, and connected together by low narrow passages. Sometimes the chambers are lined with masonry, and roofed by overlapping courses forming a rude dome-shaped vault; at other times they are simply excavated in the hard earth, while the passages and doorways are lined with stones. They thus differ considerably in form from the Scottish variety, and they differ also in being usually associated with raths or earthworks, while the Scottish structures are usually contiguous to the sites of overground habitations.
The general features of the Cornish group, on the other hand, are more allied to those of the Scottish area, inasmuch as they are often associated with clusters of overground habitations. One at Chapel Euny, in the parish of Saucreed, near Penzance, contiguous to the sites of four circular huts, is an underground gallery presenting features of remarkable similarity to that at Cairn Conan, in Forfarshire. The gallery, which is slightly curved, is about 60 feet in length, 6 feet wide, and from 6 to 7 feet high. A circular chamber, 16 feet in diameter, constructed of large granite blocks, each overlapping the one below it and thus forming a domed roof which must have been 10 or 12 feet high, was connected with the wider end of the gallery by a passage 10 feet long, opening off one side. Another small offset near the narrower end of the gallery, also about 10 feet long, slopes up to the surface, presenting an entrance doorway 2 feet 8 inches in height, with recesses on either side as if to retain a slab to close the doorway. The floors of the gallery and chamber were paved with flat stones, and provided with drains underneath the pavement. The relics found in the structure were whetstones; hammer-stones; spindle-whorls; several varieties of domestic pottery, red and black, mostly plain, but occasionally ornamented with markings made by a pointed instrument; an iron spear-head; and a fragment of the red lustrous ware commonly called Samian.[118] Another at Halligey, near Trelowarren, consists of a slightly-curved gallery 90 feet in length, from 3 to 5 feet in width, and about 6 feet high in the middle, becoming lower towards the extremities. It has a small rectangular chamber off one side at the farther end of the main gallery. The main gallery opens off the middle of the side of a shorter and wider gallery 28 feet in length, 5½ feet wide, and 6 feet high. At one end of this shorter gallery a narrow passage rises to the surface. The entrance passage is provided with checks for two doors, and the whole structure is strongly and substantially built and lintelled with large flags. On the surface there are traces of two embankments with an intervening ditch surrounding a large area within which there may have been a cluster of overground structures.[119]