The effects of rock type and structure are also simplified. The Devonian sandstone are often flat-lying and divided into cuboidal blocks of various sizes by bedding planes and joints. Marine erosion attacks an ancient but simple masonry, allowing classic models of cliff evolution to be tested.
As elsewhere in Scotland, elements of the more sheltered part of the Orkney coastline are inherited from the period before the last ice sheet. The firths are products of many phases of glacial erosion and the shore platforms that edge them often pass below till left by the last ice sheet.