 These are most common at inclines.Sleds, axles scraping the soil between wheel ruts, locked wheels skidding downhill and heavy weights dragged over the ground to brake the carts' descents would all continue eroding the surface down to the bedrock, if any, which then forms a natural pavement.When it rains, the mud and debris in an inclined hollow way tend to be washed down the channel, slowly flushing it out and leaving banks on either side where hedgerows may develop and collect more material.