When the sea was even higher
All the Clyde islands have a more or less complete fringe of flat ground round them. Much of the road round Arran, for example, runs along this flat area, which lies only a few metres above sea level. It may be only a few metres wide or a broad plain, and is commonly backed by cliffs. This is a feature called a raised beach and dates back about 6,000 years to a time when the sea was higher than it is at present. This is because the world sea level rises and falls with the increase and decrease in the size of ice caps during ice ages and also because the land ‘rebounds’ slowly after the weight of ice is removed. These changes are still happening, so the islands are still rising out of the sea!
This raised beach exactly mirrors the present beach, but at a higher level. Right at the end of the Ice Age the sea was up to about 30 metres higher than it is now, and there are deposits and features at several heights up to this level, particularly where there were broad estuaries like those behind Brodick, Loch Ranza and Lamlash. There are sand and shingle beach deposits, wave-cut platforms in rock, sea-stacks, and cliffs with sea-caves at different levels.
The Shiskine valley was once a broad estuary and Torr Righ was an island. Indeed, at the end of the Ice Age, Bute was three islands, at least at high tide when the sea flooded the valleys between Kames Bay and Ettrick Bay in the north and between Rothesay Bay and Scalpsie Bay including Loch Fad and Loch Quien the south.
Sea-stacks vary in shape depending on the rock. Lion Rock and Diel's Dyke on Great Cumbrae are narrow ridges formed by large dolerite dykes. In contrast The Haystack on Bute is round because it is formed out of a uniform conglomerate.