A System of intrusions of the type now known as cone-sheets was first definitely recognized and mapped by Harker in the Cuillin district of Skye, and was described by him in the Geological Survey memoir issued in 1904. The members of the complex were simply designated “inclined sheets,” but they incline inwards towards a common centre from north, west, south, and south-east. When the Scottish Survey undertook the mapping of Mull, in the years preceding the war, two further series of centrally inclined intrusions were soon recognized. Owing to the number of these sheets, and consequent liability to confusion, individual members can seldom be traced very far, or shown to have arcuate curvature. But the systems as a whole sweep round centres in continuous curves. In one case the curve was originally closed, though it has been somewhat interrupted by later intrusions. In the other case the main body of sheets only forms a horse-shoe. Nevertheless the term cone-sheets, which was here applied to these intrusions by Professor Bailey, is extremely appropriate.