On the basis of new evidence, the Moine rocks SE of the Great Glen Fault are differentiated into two major units: the Central Highland Division, represented by a gneissose assemblage of about 1000 km2 extent, and the Grampian Division, a younger and more extensive sequence of less deformed metasediments which is separated from the gneisses by a tectonic break, the Grampian Slide. Since the 2 Divisions have greatly differing tectonometamorphic histories, they are believed to correspond respectively to a basement complex and a cover sequence. The discovery of a suite of syntectonic Precambrian pegmatites (c. 718 ± 19 Ma) equivalent in age to the Morarian pegmatites of Morar and Knoydart, permits the separation of Precambrian from Caledonian orogenic events.

The Central Highland division is considered to be an eastward extension of the high-grade rocks which in part form the Glenfinnan Division W of the Great Glen Fault, widely held to be of Grenvillian age, whilst the Grampian Division is interpreted as early post-Grenvillian sediments affected first by a limited Morarian orogenic event, and subsequently by the Caledonian orogeny.

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