Arthur’s Seat, the extinct volcano that rises above Edinburgh, looks like solid, permanent rock that has always stood exactly where it is.
This page contains affiliate links, which may earn us a small commission.
In reality, its shape tells the opposite story: what is highest today once lay far below the surface, while the lower ground around it used to be much higher.
The hill formed from a volcano active around 340 million years ago, during the Carboniferous period. Layers of lava, ash and volcanic rock built up and were later buried under thick beds of softer sedimentary rock. For hundreds of millions of years, this volcanic core sat hidden underground, with nothing to mark it out on the surface.
The transformation came much later, during the last Ice Age. A huge glacier moved eastward across the area, grinding down everything in its path. Soft sedimentary rock eroded quickly. The old volcanic rock, far harder and more resistant, wore away much more slowly.
Over time, the ice carved away the ground that once lay above and around it, leaving the volcanic core standing proud as a hill, with a long, gentle tail stretching to the east. Geologists call this a ‘crag and tail’ formation, the same shape seen next door at Salisbury Crags, and the process that also formed Castle Rock, on which Edinburgh Castle now stands.
In other words, Arthur’s Seat did not grow upward. It was exposed. Everything that once surrounded and covered it was simply stripped away, uncovering rock that had been buried long before the ice arrived. The summit visitors reach today is not something that grew tall. It is what remained when everything else was gone.