The Lewisian complex or Lewisian gneiss is a suite of Precambrian metamorphic rocks that outcrop in the northwestern part of Scotland, forming part of the Hebridean Terrane and the North Atlantic Craton. These rocks are of Archaean and Paleoproterozoic age, ranging from 3.0–1.7 billion years (Ga). They form the basement on which the Torridonian and Moine Supergroup sediments were deposited. The Lewisian consists mainly of granitic gneisses with a minor amount of supracrustal rocks. Rocks of the Lewisian complex were caught up in the Caledonian orogeny, appearing in the hanging walls of many of the thrust faults formed during the late stages of this tectonic event.
Outcrop of weathered Lewisian gneiss, 5 km NW of Lochinver
Undeformed Scourie dyke cutting Lewisian Gneiss, about 1.6 km west of Scourie
Scourie dykes (now foliated amphibolites) cutting grey gneiss of the Scourie complex, both deformed during the Laxfordian tectonic event and cut by later (unfoliated) granite veins - road cutting on the A838 just north of Laxford Bridge
Lewisian Gneiss - Rhiconich, Scotland
In geology, the term Torridonian is the informal name for the Torridonian Group, a series of Mesoproterozoic to Neoproterozoic arenaceous and argillaceous sedimentary rocks, which occur extensively in the Northwest Highlands of Scotland. The strata of the Torridonian Group are particularly well exposed in the district of upper Loch Torridon, a circumstance which suggested the name Torridon Sandstone, first applied to these rocks by James Nicol. Stratigraphically, they lie unconformably on gneisses of the Lewisian complex and their outcrop extent is restricted to the Hebridean Terrane.
Layers of Torridonian sandstone exposed near Diabaig
Slioch formed of Torridon Group sandstones lying on an irregular unconformity over Lewisian gneiss, seen in the middle and foreground around Loch Maree
Thick-bedded sandstones of the Stoer Group exposed on the Old Man of Stoer
Horizontally bedded sandstones of the Torridon Group, forming the Horns of Beinn Alligin