Wherever bridges have been built along the road, it was possible to see how very thin the topsoil was: gravel and heath sand for a hand’s breadth, common in the damp places and even more so in the dry, followed by clay often for as much as 4 feet. Between the sand and the clay there was a layer of gravel, and another at the bottom where the clay stopped. Water was flowing from the clay in particular and it was producing a deposit of slime. Could this be ochre?