Erosion of a thrust sheet that lies above a shallowly dipping fault commonly leaves an isolated remnant of the allochthon, a klippe, resting on the lower plate (Figure 6.4). (Klippe comes from a German word that means "cliff", reflecting the fact that most klippen in the Alps are bounded by cliffs.) A klippe indicates a minimum extent of the original thrust sheet, a window or fenster (Fenster is the German word from "window"), and expose an isolated area of the rocks that lie beneath the thrust (Figure 6.4). These rocks may be part of the autochthon or part of another underling thrust sheet.