Acceleration of erosion above geologic norms

Introduction —Soil‐erosion as a term refers to the acceleration under certain conditions of a process which is older than sedimentary rocks. The water‐cycle of evaporation, precipitation, and runoff has been the most active agent in degrading major land‐surfaces throughout the long record of geologic time. Wind has in arid regions of lesser extent played an important and often a dominant part; but flowing water, armed with abrasive materials fragmented from rock by weathering processes, has tirelessly and endlessly cut its way into uplifted rock‐formations, and created erosional potentials within drainage‐areas. Flowing water has at the same time swept the products of denudation and erosion with equal persistence toward the sea. Products of erosion have undergone a wide vicissitude of movements and depositions before finding their place finally in sedimentary beds. They may have been deposited many times on the way as shoal banks and as alluvium on flood‐plains and in alley‐fills, later to be moved stage by stage further seaward. Closed basins of inland continental regions have been the scenes of lesser cycles of denudation, erosion, and deposition, in which occur special conditions of importance in hydrology and dynamics of stream‐action. As a geologic process, erosion is as old as rain‐storms, but may be accelerated in soils by baring surfaces of pristine mantles of vegetation by man and his agencies.