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 exception 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 considerations 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 r6le of stream-water. In such regions, as it has been recently shown,2 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 beginnihg of a geographic cycle; while in a humid climate the plain only becomes notably developed in the very last stage.3 Eolian erosion in a dry country may thus be