For 200 years people have been fascinated by the exotic stones that turn up in fields or on beaches of Caithness and Orkney. The exotics do not belong on the Old Red Sandstones– they include crystalline igneous and metamorphic rocks and sedimentary sandstones, mudstones, and limestones that are younger than the Devonian. Although some beaches have exotic stones that were once the ballast of wrecked ships, most exotics are glacial erratics, eroded and carried by glacier ice and washed from the boulder clay. A map of the finds gives us clues as to which rocks were eroded by the ice and the directions of ice flow. It’s a complex picture. We have igneous and metamorphic rocks that are typical of the Banffshire coast, of which the green serpentinites are the most striking. We have lots of schist and gneiss from the Northern Highlands, including Inchbae augen gneiss, with its bright pink “eyes”. Intriguingly, there are a few reports of Cambrian quartzite, including the distinctive pipe rock with its Skolithos burrows. Intriguing, because the Cambrian outcrop lie on or beyond the main ice shed towards Ullapool. On the North Isles, we find erratics from south-west Norway – rhomb porphyry from the Oslo region, other porphyries from Dala in Sweden, and even one from the Aland Islands of Finland. That’s quite a journey – and it’s likely that part of the epic trip across the North Sea was hitched on icebergs.

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