Landforms ancient and recent: The paradox

Very old etchforms of Cretaceous age or older (Pangaean surfaces) are prese rved in many parts of the world. Some have been exposed to the elements for periods of 10(8) years and their persistence poses problems per se. Moreov er, landforms are actively developing within or immediately adjacent to the se palaeosurface remnants. Unconsolidated materials, whether occurring as r egolith on palaeosurfaces or as deposits in valleys and basins,are readily eroded, but coherent rocks are resistant, particularly in well drained situ ations. A model involving unequal erosion and positive feedback provides op timal conditions for survival.