Recently I have been getting interested in geology. This started because around here there are a lot of big chunks of rock that, unlike the extrudant granite, seem to sit on the ground, rather than rise out of it. I was told they were called “Erratic Boulders”, which seemed an enchanting concept to me. I liked the idea of these huge stones ambling eccentrically about the moor; it turns out of course that they do no such thing – glaciers pushed them, like chess pieces, along the surface of unrelated formations. But this got me thinking about rocks moving, changing, being remade by sedimentation, metamorphosis and the death of undersea microorganisms. And then I learned that the bedrock of the Isle of Lewis and part of the West Coast of Scotland originally emerged from the