Page:Popular Science Monthly Volume 74.djvu/24

20

the barren waste of popular fancy. Vast tracts of it are certain to be reclaimed to the uses of mankind. Some of it is doubtless to become the most eagerly sought of all estates. Its beauties and its treasures are only beginning to be understood. Even scientists have only commenced to turn their attention seriously to the make-up, features and resources of the so-called desert regions.

The idea of a base-level of erosion, lying but slightly above tide, but below which stream-corrasion can not go, has done for geography what the principle of evolution has accomplished for biology. It is, in fact, the evolutionary principle applied to land sculpture. This theory of Powell's is justly regarded as one of the three grand deductions which geology of the century just past has bequeathed to science. Conceived midst the arid regions of the West, its widest influence has been in the moister countries of the earth.