BASE-LEVEL OF EOLIAN EROSION 
CHARLES R. KEYES 
The recognition of a land-level coinciding very nearly with that 
of the surface of the sea, but below which stream-corrasion cannot 
go, is a concept which has had such a potent influence in molding 
opinion concerning land-sculpturing and its evolution that any excep- 
tion or modification is yet to receive general approval. That the 
generalization is not of universal application recent observations afford 
many proofs. Notwithstanding the fact that Powell’s Law of the 
Base-Level of Erosion’ had its inception in the arid land, later con- 
siderations show that it is really strictly referable only to countries 
enjoying climatic conditions of normal humidity. 
Vast areas of the globe there are where, it must be conceded, the 
effects of stream-corrasion are necessarily very impotent or practically 
nil. ‘These are the great arid tracts, or deserts, where the annual 
rainfall is less than ten inches, nearly all of which sinks into a porous 
and thirsty soil and never appears in the réle of stream-water. In 
such regions, as it has been recently shown,” erosion and shaping of 
the land forms are chiefly accomplished by wind-scour, or deflation. 
The great vigor with which general eolian erosion may operate, 
when moisture does not interfere, is indicated by the recent estimates 
that on the soft rock-belts eolative effects are ten times greater than 
they would be on the same rocks in a humid land, although on the 
harder rock-masses the rate is scarcely one-tenth so much. 
In the general leveling and lowering of the surface of a country 
notably elevated and fully exposed to the influences of an arid climate, 
one of the most remarkable results is that the plain is the characteristic 
and dominant feature from the very beginning of a geographic cycle; 
while in a humid climate the plain only becomes notably developed 
in the very last stage. Eolian erosion in a dry country may thus be 
« Expl. Colorado River of the West (1875), p- 207. 
2 Bull. Geol. Soc. America, XIX (1908), 81; also, Journal of Geology, XVII 
(1909), 31- 
3 Journal of Geography, VII (1908), 33. 
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