"The paper describes those features of the Scardroy Lewisian mass, a sheet-like body of basement rocks thrust into the younger Moine series, which suggest that this mass was driven up through a thickness of several kilometres of Moinian rocks and inserted as a narrow wedge within the Moine succession. never penetrating the highest members of that succession. The relations of the Scardroy mass, to which most of the Lewisian outcrops of central Ross-shire belong, differ from those of the more westerly outcrops of Lewisian in the region of Glenelg where the basement rocks have been shown by the work of Clough and others to represent wedges lying between tightly-compressed synclines of Moinian rocks which form a more or less autochthonous cover. The connection between the two types of structure is discussed."