This memoir presents a descriptive account and 1:20,000 coloured map 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 supacrustal 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.