Francis Bacon

One of the things I've learned with doing 'xkcd' is that you sort of give people, 'Here's the thing, and here's the button you can press to get another thing.' Sometimes that can be more easy to digest than, 'Here's a long page of things.'

Topsoil is a place of digestion. It sucks and chews things into smaller pieces. When it's hungry, it turns grey and stony; when it's thirsty, it opens thousands of cracked lips. Subsoil is more skeletal: it doesn't digest.