An abrupt break of slope- shows how, even in the winter, the chalk is a really "dry" land- very porous rock, very thin soil above it. "Dry Valleys" are thought to have formed in glacial and periglacial times when the rock would ahve been frozen, so water flowed on the surface. (NB, much of the Chalk lands in Britain are south of the last major ice sheet, so you cannot really see any particularly glacial features.) Anyway, the trees seem to like it in the bottom there, even if they don't grow on the top.
