The ground began to go down at about four and a half kilometres.
The road tilted, gently at first and then not gently, and the ridges on both sides fell away — and then they came over a lip and the whole thing opened out in front of them.
The old river was enormous.
It had been a real river once and it had been gone for a very long time. Half a mile across, sunk twenty metres below the level of the flats, with pale gravel and cracked grey mud running the whole width of it and slabs of bare stone standing up out of that where the current had scoured down to bedrock. Not one drop of water anywhere.
The banks on both sides were steep and eroded into a mess of shelves and undercuts and loose scree.
And in the middle of it, a stone crossing — old, heavy, built by people who had expected to come back — ran out from the near bank in a raised causeway of dressed blocks.
