The Moinian assemblage is composed mainly of metamorphosed arenaceous and argillaceous sedimentary rocks but includes a minor proportion of calcareous or dolomitic beds. Psammitic granulite and pelitic schist occur typically in thick successions. Correlation of at least part of the Moine rocks with the Torridonian generally is accepted as a working hypothesis, suggesting that Moine deposition began 800-850 m.y. ago. The upper part of the Moine succession and the lower part of the Dalradian together might represent the Scandinavian Sparagmite Formation. Thus the Moinian assemblage may comprise both pre-Eocambrian and Eocambrian rocks.

The Moine rocks of Scotland are separated into two large geographic divisions--the Northern Highlands and the Grampian Highlands--by the Great Glen fault. The Northern Highlands can be subdivided into three areas: western Inverness-shire, Ross-shire, and Sutherland. In western Inverness-shire, the mapping of minor rock types has proved useful in detailed lithologic work. On a broad scale, the oldest Moine rocks (Morar division) are confined to the west, adjacent to the Lewisian rocks of the foreland, and are succeeded eastward by the younger Glenfinnan and Loch Eil divisions. The Central Highland Granulite is probably the youngest unit of the Moine rocks.

A major difficulty in interpreting the regional structure of the Moinian assemblages is the contrast between radiometric dates and the maximum dates of folding episodes established by stratigraphic considerations. Three major tectonic events are known to have affected the Moine rocks. They apparently were deformed and metamorphosed during a long period beginning in the late Precambrian and continuing possibly until Early Devonian time, at least in the central part of the orogenic belt.