by Christianity. It seems therefore that, so far as our present knowledge will carry us towards a definite conclusion, the period of this peculiar type of structure will lie between the time of the general establishment of Christianity and the departure of the Romans from Scotland. ----- Footnote 116: Described by Lord Rosehill in _Proc. Soc. Antiq. Scot._, vol. viii. p. 105. Footnote 117: 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.