Limitations of the Problem
In humid regions of bold relief underlain by rocks susceptible of chemical decomposition, the hills at the stage of geomorphic maturity become rounded in profile and in contour and the slopes are mantled with soil. As geomorphic development proceeds from this stage the convexity of the hilltops becomes progressively flatter, while the contours tend to approximate more closely to the circle.2 If, within the region, there be areas of rock not susceptible of decay, such as pure quartzite, these areas present, in contrast to the rest of the region, steep slopes which recede under erosion without diminution of acclivity beyond a certain minimum which is determined by the size of the spauls shed by mechanical disintegration. These permanently steep slopes differ from receding mountain fronts in the desert in that they do not tend to become so effectively buried by rising alluvial embankment.3 In this way . . .