 It includes the metawackes of the Oronsay Greywacke Formation, the sandstones of the Dun Gallain Grit Formation, the metasandstones and metamudstones of the Machrins Arkose, Kilchattan and Milbuie formations, the sandstones and phyllites of the Kiloran Flags Formation and the phyllitic semipelites and quartzites of the Staosnaig Phyllite Formation.In the far north at the north end of Traigh Ban is an outcrop of the orthogneiss of the Palaeoproterozoic age Rhinns Complex named from the larger outcrop on nearby Islay.Intrusive igneous rocks are represented by diorites and monzonites of the 'North Britain Siluro-Devonian Calc-Alkaline Dyke Suite' seen at Scalasaig and Balnahard.