Brochs in having their entrances opening to the enclosed space and not directly opening into the passage, this structure has more affinities with the stone cashels than with the Brochs. Like them it adapts its form to the space in which it is situated, and like them it consists of a simple rampart with cells in the thickness of the wall. The wall is low, and of no great strength, and like the wall of a cashel is merely meant to add to the defensibility of a naturally defensive position. The special peculiarities of this defensive construction are, that it is a dry-built structure which is not a Broch but a cashel, and that it is situated on an island in a loch and rendered accessible by a causeway. The island is of natural formation, and has been thus utilised, because of its suitability for defensive purposes. ----- Footnote 93: Described in Low’s _Tour in Orkney and Shetland_, 1774 (Kirkwall, 1879), p. 177; and by Dr. Arthur Mitchell in the _Proceedings of the Society of Antiquaries of Scotland_, vol. xv. p. 304. ----- Such instances of the adaptation of natural islands in lochs as places of strength by constructing defensive buildings of stone upon them are not uncommon, although it rarely happens that the form and characteristics of the buildings themselves are so clearly traceable. But there is another variety of defensive construction which is more frequently found in similar positions. It possesses the additional peculiarity of being either wholly or partially constructed of wood.