Page:Popular Science Monthly Volume 82.djvu/479

Rh thin and gravelless; and all surface materials are transported. There is almost total absence of distinct waterways in the broad valleys. None of these relief characters bespeak of water-action of any kind. They all bear testimony of some erosive agency other than the one with which most of us are most familiar. Water can not do such geologic work. It seems to be a great advance in earth-study to be able at last to account satisfactorily for the formation of all those wonderful expressions on the face of the desert that have been so long so manifestly little understood or misinterpreted.

As in the case of ordinary general erosion, there are involved the three major processes of rock-weathering, transportation of rock-waste, and deposition of sediments, so in eolation there are the three corresponding phases termed insolation, deflation and aeroposition. Rock weathering in the desert is peculiar in that there is practically no chemical decay going on at the surface. The destruction of rock-masses is accomplished by means of a process known as insolation—a constant flaking-off of rock fragments due to the great diurnal range of temperature so prevalent in dry climates.

The movement and exportation of fine rock-waste through deflation