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of the potency of wind-action in the general leveling and lowering of the country. Of late years others who have traversed this field have caught occasional glimpses of deflative activity. Spurr notes certain minor aspects of it in the intermont basins of Nevada. Davis mentions others in Utah and Arizona. Cross calls attention to some notable phenomena in the San Juan district of southwestern Colorado that he mainly ascribes to wind-action. Hill describes still other features in northern Mexico. Free summarizes the literature on the action of the wind in the formation of soils. In none of these records of observation is the great principle of regional eolation recognized or even suggested. Through all of them the influence of the idea of peneplanation by water is overpowering.

No phase of land-sculpturing by water explains the peculiarities of desert relief. Where in humid lands are there such vast and even surfaces as the intermont plains of arid regions? Where under conditions of moist climate do such lofty mountains stand out so isolated as in our southwestern country—ideal monadnocks only theoretically and faintly suggested elsewhere? Where but in a dry climate does entire absence of foothills characterize the mountain ranges? Towering desert eminences rise out of elimitable expanse of level plain as volcanic isles jut from the sea. Plain meets mountain as sharply as the strand-line of the ocean. The rock-floor of the desert is often a plain itself worn out on the beveled edges of the strata beneath. The remarkable plateau-plains clearly represent former plains-levels. The soil-mantle is