Concerning Rocks

Some years ago I had a passing interest in the abstract shapes and forms rocks can take. 

Recently I was out on the Aberdeenshire coast hunting photos with a friend, who, being impressed with the rocky coastline, wondered exactly where the Highland Boundary Fault emerged at its most north-eastern extremity.

After a bit of research (particularly exploring using the BGS‘s iGeology app), I tracked it to a small headland, Garron Point, beside the golf club outside Stonehaven.

From the outside it doesn’t look like much, but on closer inspection it is awesome.

There are actually two faults – a small one at the north-eastern end of Craigeven Bay corner with Garron Point, forming a small spur off the Highland Boundary Fault which clips the coastline from the town out to sea.

On the lowland side the bedrock is metabasalt, psammite and pelite (North Esk formation) – metamorphic bedrock formed around 461-485MYa in the Ordovician period. On the highland side is gritty psammite (Glen Lethnot grit formation) – around 541-1000MYa.

The fault itself can be tracked to a matter of a few feet – a view from beside one of the golf greens shows the junction of both faults, with a strip of incredibly deformed grey rock leading away some meters rather like a line of chewing-gum.

Some of the most impressive rock outcrops I know. Toward the top-right of the frame – those cliffs are tall, especially from below! – a small fault runs diagonally down to the spray of water and out the left side; from front to back, a line of deformed pale grey rock only a foot or two wide, twisted like chewing gum, marks the Highland Boundary Fault at its most narrow only metres away from its most north-eastern extremity on land, at Garron Point headland near Stonehaven. The gnarly shapes of psammite (metamorphosed medium-grained grey former sandstone) and micro-basalt are awesome.

My favourite image is an abstract closeup – purply-red microbasalt meeting gritty blue-green psammite in a spray of cracks and marbling lines.

Prints are available on my ShinyPhoto photo gallery: Under Pressure

Perhaps the clearest view into the workings of the Highland Boundary Fault I can think of. On the left, red-purple microbasalt (its fine cuboidal structure putting me in mind of streaky thick bacon); elsewhere the blue-green-grey of psammite and pelite, medium- to fine-grained metamorphosed former sandstones. All jumbled together with fine cracks and lines of marble hinting at the pressures involved.

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