Abstract This Memoir presents a detailed account of one of the most critical and interesting parts of the Lewisian complex of NW Scotland; a detached fragment of a supercontinent made up of Laurentia, Siberia and Baltica, which existed at the end of the early Proterozoic period. The Gairloch area, together with neighbouring Loch Maree, is the only part of the mainland Lewisian outcrop where Palaeoproterozoic supracrustal rocks (the Loch Maree Group] and their relationships to the Archaean basement can be studied, and has been the subject of a considerable amount of research, spanning a period of more than forty years. The Loch Maree Group represents an amalgamation of oceanic, trench, and arc assemblages with continental basement, and forms part of a Palaeoproterozoic collisional orogen stretching from Labrador through South Greenland to Scandinavia. The author is Emeritus Professor of Tectonic Geology at Keele University, England, and has studied the structural geology of Precambrian terrains in many parts of the world. He has mapped the area covered by the Memoir in detail, at a scale of 1:10 000, and has an intimate knowledge of the geology, acquired over many years.