Upper Old Red Devonian Sandstone at Portmahomack

On the shore in Portmahomack Part 2

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The exposures of rock towards Tarbat Ness east of the small fishing village of Portmahomack are very interesting. The strata edging the Dornoch Firth date from the Upper Old Red Sandstone of the Devonian Period and comprise the Balnagown Group lying above the Strath Rory Group. The area is famous for fish fossils which unfortunately, I did not find.

The rock patterns and textures were fascinating though. They reveal the way that each layer or stratum varies in colour and texture dependent on the depositional environment for the sediments. The different layers have been eroded by the elements in varying ways, according to their hardness and the degree of exposure, giving rise to pits and hollows and smoothing the edges. And the rocks become covered by a range of organisms because of their seashore situation, from black biofilms which peel away in the drying sun, to colonising animals like limpets.

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