The landscape of Orkney has been shaped over thousands, if not millions of years. The Devonian flagstones are the building blocks for landforms on the islands. The processes which operate today to break down and erode the rocks are very different from those of the Ice Age when intense cold gripped the land and ice sheets periodically advanced to cover Orkney. The ocean penetrates the land, with storm waves undermining the great cliffs and the calmer waves of the firths carrying and depositing sand and gravel on beaches and bars. Most recently, people have started to modify and even create new landforms. The land persists but the form changes, oft times ever so slowly, but sometimes in a single, stormy, rain-drenched day.