In consequence, they act as a shell of
armour, protecting land surfaces from denuda -
tional agents. Duricrusts that develop in low-lying
areas where surface and subsurface flows of water
converge may retard valley down-cutting to such
an extent that the surrounding higher regions
wear down faster than the valley floor, eventually
leading to inverted relief (Box 7.3). Where
duricrusts have been broken up by prolonged
erosion, fragments may persist on the surface,
carrying on their protective role. The gibber plains
of central Australia are an example of such longlasting
remnants of duricrusts and consist of
silcrete boulders strewn about the land surface.