GREAT EROSION AL WORK OF WINDS 



475 



erally 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 ex- 

 pressions on the face of the deseit 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 corre- 

 sponding phases termed insolation, deflation and aeroposition. Kock- 

 weathering in the desert is peculiar in that there is practically no chem- 

 ical decay going on at the surface. The destruction of rock-masses is 

 accomplished by means of a process known as insolation — a constant 

 fiaking-off of rock fragments due to the great diurnal range of tem- 

 perature so prevalent in dry climates. 



The movement and exportation of fine rock-waste through deflation 



Fig. S. Desolate Main Street in Mexican Adobe Town in the Desert. 



