It seems fairly obvious that sandstone is made of sand. What's 'fairly obvious' isn't always the case (as one example, the continents are not immovably fixed in their places, and stones do fall from the sky). However, in this case it is; and here are lake bed ripples of 350 million years ago, preserved in the Old Red Sandstone. But before that, what's the sand itself made of? In many cases, out of the erosion of earlier sandstone... This insight led James Hutton to the first realisation of the enormous age of the Earth.

West of the Ness at Stromness, Orkney Mainland, with view across to Hoy

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