Geology Reference
In-Depth Information
of the piedmont and are of limited areal extent, whereas planation surfaces, in places rolling or
undulating, elsewhere flat and featureless, occupy huge areas (Mabbutt, 1966, 1978).
4.2.1
Rolling or undulating plains
A peneplain is a rolling or undulating erosional surface of low relief and of regional extent formed
by weathering, wash and river work. The broad interfluves are gently convex-upward in form.
According to Davis (1899, 1909), slopes are lowered once streams have achieved their initial major
incision and when maturity has been reached and passed. Divides are lowered more rapidly than
the streams are incised, and a surface of low relief is developed.
Though principally of erosional origin, flood plains due to deposition extend along the main
drainage lines. It is difficult to demonstrate the slope decline implied in the Davisian model though
several workers have produced statistical evidence which is consistent with the scheme.
(a)
(b)
Figure 4.1.
Rolling plains in granite (a) southwest of Western Australia. (b) Saldanha, northwestern Cape
Province, South Africa.
