Page:Popular Science Monthly Volume 82.djvu/472

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S in the eighteenth century marine planation was one of the notable discoveries in earth-study, and as in the last century the theory of general peneplanation through stream-corrasion was one of the grander conceptions of the age, so the recognition of desert wind scour as the principal among erosional agencies seems destined to take its place among the first half-dozen great and novel thoughts which shall especially distinguish geologic science of the twentieth century. Under conditions of arid climate, by which more than one half of the land-surface of our globe is profoundly influenced, eolian erosion appears to become, as recently aptly stated, more potent than stream-corrasion, more constant than the washings of the rains, more extensive and persistent than the encroachments of the sea. Both as a sculpturing power and as a sedimentative agent the wind is thus in every way comparable to erosion and deposition by river and by ocean.

That it is possible for the universal disintegration of the rocks to go on by means of insolation instead of through ordinary chemical decay, that general and rapid exportation of rock-waste takes place through the agency of the winds instead of through the movement of waters, and that on the land deposition of wind-borne dusts in terranes