The layers of red and honey-coloured sandstone that make up the cliffs are between 380 and 370 million years old and date from the Devonian Period, when Scotland lay south of the equator and was part of a huge desert continent. The rocks that formed on this ancient landmass are traditionally known as the Old Red Sandstone. In Devonian times the area including modern-day Orkney, Shetland and north-east mainland Scotland was part of a large depression known as the Orcadian Basin. The rocks that formed in this basin, on desert plains and in lakes, salt flats, dunes and rivers, are preserved today in Orkney to dramatic effect. Scottish Geology Trust