Abstract
Synopsis: A group of alkaline basic igneous rocks in the eastern part of the Orkney Islands is described as seen in the field and petrographically. The rocks differ from the andesitic and calc-alkaline Old Red Sandstone igneous rocks of Shetland and the Scottish mainland. They show marked similarity to the Carboniferous teschenites and basanites of the Midland Valley of Scotland, but the Middle Old Red Sandstone age assigned to them in previous accounts is upheld.

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