Old Man of Hoy

The UK's most famous sea-stack is made of Old Red Sandstone. This is a desert sandstone similar to the New Red, but formed 100 million years earlier, when the UK was passing through the hot, dry zone south (rather than north) of the Equator. But the Orkney Islands are formed of sand that washing out of the desert into a great inland sea, Lake Orkadie. The seabed layers hide unusual and intriguing fossil fishes, some of the very first animals with bones and ancestors, as it happens, of us. But these level layers formed in the bed of a great river system.

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