It was underwater that the story of animals with backbones - our ancestors - was getting underway. It's in the quarries of Caithness in Scotland where they can be found. A live brown trout of today is very similar to the fossil - but younger, by 400 million years. Further north, in Orkney, the same lake sediments are preserved as flat as the day they were laid down. Because they split easily they are ideal for the building and paving stone much sought after by classy architects... or by collectors of exquisite finds.