Page:Popular Science Monthly Volume 81.djvu/241

Rh region of continual high wind and constant sand-storm. Nowhere else in the arid region of the southwest is wind-scour in active operation so advantageously viewed. Nowhere else in this country are deflative effects and desert-leveling so well displayed. Nowhere else in all the world is general lowering of an elevated country by the winds so strikingly presented. Few places there are on this continent where stream action as a general erosional power is so manifestly utterly impotent.

That this high, dry, almost waterless waste on the continental divide should owe its landscape features chiefly to the incessant blowing away of the dry pulverulent soils seems to need little argument in this place. In the case of a desert district where the rocks alternate in hard and soft strata a mesa capped by a more indurated layer might not always offer conclusive evidence in support of this contention. Against the mesas surfaced by lava-sheets of diverse ages such objections can not be raised.

The existence of desert mesas whose surfaces stand at many different levels throughout the broad belts of the less resistant rocks appears to furnish one of the strongest proofs of the eolic character of the regional erosional activities; since in situations of this kind not only are rainfall and water-action very deficient and wholly inadequate to produce the relief effects presented without the time-element be vastly and unreasonably prolonged, but conditions are such in many cases as absolutely to preclude the intervention of stream-work.