Adapted from the successful BBC Radio 3 series, Cornerstones explores how different rock types give rise to their own distinct flora and fauna, and even affect the food we eat. Some of the authors express a sense of awe in the face of the abyss of time that is locked into the lie of the land, a sense that jostles up against our own fleeting encounters with it. For example, Sara Maitland tries to grasp the extraordinary journey through space and time that's been undertaken by Lewisian gneiss, one of the most ancient of rocks found in the UK, while Alan Garner captures the ways in which flint has enabled and accompanied human evolution, ever since our ancestors walked out of Africa with it, stone in hand.