ABSTRACT
True aridity mummifies a landscape by slowing down the rates of change just as the dry sand and desiccating air preserved Egyptians and Peruvians for the museums of the twentieth century. The traveller in the deserts of the Sahara, Arabia and Australia accustomed to the relief of the world's humid lands is stunned by the immensity of the vast plains which often extend unbroken to the horizon or are broken forcefully by steep slopes. Many of the processes of weathering, erosion and transport under these conditions are not yet fully understood although serious doubt has already been cast on some of the older explanations. Sand blast has almost the same effect as the artificial polishing of building stone, which by reducing the surface irregularities prevents the accumulation of moisture which form the seat of weathering attacks. The apparently flat plains of the great deserts turn out on investigation to be made up of gently sloping surfaces of erosion or deposition.
