Environmental historians . . . insist that we have got to go . . . down to the earth itself as an agent and presence in history. Here we will discover even more fundamental forces at work over time. And to appreciate those forces we must now and then get out of parliamentary chambers, out of birthing rooms and factories, get out of doors altogether, and ramble into fields, woods, and the open air. It is time we bought a good set of walking shoes, and we cannot avoid getting some mud on them.