Geology of Castle Rock, Auchmithie, Angus
Positioned close to a fragment of raised beach and gravel storm beaches, the promontory of Castle Rock dominates the southern end of the shore by the harbour. The 30 metre headland cliffs near the harbour are composed of the Lower Devonian Auchmithie Conglomerate Member, which started to form around 400 million years ago. A close inspection of the rocks shows that the conglomerate is interbedded with thin layers of red sandstone, with limestone pellets also having been observed. The rocks that form Castle Rock were laid down during the Devonian Period when Scotland lay south of the equator and probably in the desert belt. At that time, the climate was hot, arid, and characterised by heavy rain, which caused flash floods on a wide scale. Huge temporal rivers carved through the landscape and left deposits of sand, gravel, cobbles, and boulders. The sand became the red sandstone beds of the Arbroath Sandstone Member while the cobbles became the conglomerate beds of the Arbroath Conglomerate Member. The clasts making up the Auchmithie Conglomerate were formed of well-rounded, fine- to coarse-grained material, which is mainly quartzite but does contain other varieties of stone, including differently coloured jaspers. Auchmithie lies within the Whiting Ness to Ethie Haven SSSI.
When Robert Burns and William Nicol were on Auchmithie Beach, they would have been aware of Castle Rock, as it is an imposing promontory with sheer cliffs that dominates the southern end of Auchmithie Bay. If the tide had permitted them to round the seaward tip of Castle Rock into the bay beyond, they would have found it to contain a dramatic landscape with towering rock faces of conglomerate, caves, and a natural arch. However, anyone with local knowledge, such as a boatman, would have known that this bay is a place where they could be cut off by a rising tide. As the travellers were, no doubt, eager to start their sightseeing trip along the coast, it is unlikely that they would have taken the time to venture into that bay in person. However, from their vantage point in the boat, they would have been able to see the bay and its features as they sailed along the coast.