The Lewisian complex, formed before the deposition of the Torridonian sedimentary sequence, contains remnants of at least two sedimentary groups and shows evidence of polyphase deformation and metamorphism in at least three orogenic episodes--Scourian, Inverian, and Laxfordian--dated at about 2,600+ to 2,460 m.y. ago, 2,200 to ?2,000 m.y. ago, and 1,600 to 1,300 m.y. ago, respectively. The dominant foliation in a supracrustal assemblage of quartzo-feldspathic gneiss, hornblende schist, amphibolite, and distinctive sedimentary types, which occurs both in a northern belt (Rhiconich group) and a southern belt (Loch Maree Series), formed as the result of deformation early in the Laxfordian orogeny. The regional ESE-WNW trend of this banded sequence is controlled by major asym etric folds, such as the Strath Dionard antiform in the northern belt and the Tollie antiform and Letterewe synform in the southern belt. These large-scale structures were formed during a second deformational phase of the Laxfordian orogeny and deform the dominant foliation and banding. The central belt shows evidence of basement deformation during both the Laxfordian and Inverian orogenies, and the disposition of the structural elements was influenced by structures formed during the Scourian orogeny. These earlier-formed structures deform the lithologically layered, supracrustal Kylesku group, which includes metasedimentary relics. The dominant banding shown by the rocks of this group was formed coevally with granulite-facies metamorphism during an early deformational phase of the Scour an orogeny. The largest structure recognized in the central belt, the Kylesku fold, formed during a later (third) deformational phase of the Scourian orogeny.

The Laxfordian orogenic belt probably continues for a considerable distance west of the Outer Hebrides, and could join with the Elsonian orogenic belt in the Nain region of eastern Labrador. There is marked correspondence in the ages of other Precambrian orogenic episodes deduced to have occurred in Scotland and Canada.