No CrossRef data available.
Published online by Cambridge University Press: 26 July 2012
The Lewisian complex, which forms the continental basement to north-west Scotland, crops out on the Inner Hebridean islands of Rona, Raasay, Skye, Coll, Tiree, Iona and Islay. Upon this basement, four major rock successions were deposited before the Caledonian orogeny. The upper Precambrian Moine assemblage forms only a small area of metamorphosed rocks on Mull but the c. 790 m.y. (million year) old Torridonian sediments are found on Raasay, Scalpay. the Sleat of Skye, Soay and Rhum. The upper Precambrian to Cambrian Dal radian Supergroup dominates Islay, Jura, Gigha and the islands of the Firth of Lome whilst also forming a partial rim around the Tertiary Northern granite in Arran. Other Precambrian rocks of uncertain affinity are found on Islay, Oronsay, Colonsay and Iona. Cambro-Ordovician sediments are found on Skye where they have been partially metamorphosed by Tertiary intrusions.
South-east of the Moine thrust zone, the Precambrian and lower Palaeozoic rocks were deformed and metamorphosed during the late Cambrian to early Devonian Caledonian orogeny which resulted in the development of the Caledonian mountain chain. Subsequently, Scotland north-west of the Highland Boundary fault has tended to persist as a land area undergoing erosion with sedimentation restricted to peripheral areas now preserved around the present coast. Upper Palaeozoic rocks are therefore only well represented on Arran although Old Red Sandstone (Devonian) sediments are found in the Firth of Lome and a very small area of possible Permian rocks occurs on Islay.