88 



PHYSICAL GEOLOGY 



of the eruption of Krakatoa in 1883, it was carried repeatedly 

 around the earth in diminishing amount, its progress being re- 

 corded by the brilliant sunsets which it occasioned. It has, 

 indeed, been suggested that every place upon the surface of 

 the earth may possibly have dust brought by the wind from 

 every other place upon the land. 



Much wind-transported material settles upon the oceans. 

 The aggregate effect of wind transportation is therefore to 

 lower the lands and to raise the ocean floors, and this has been 

 the case since the continents and oceans were formed. Al- 

 though the result is insignificant within any short period, it is 

 doubtless important in the long ages. 



Fine material is carried higher and farther by the wind 

 than coarse material, and it settles upon the surface more 

 evenly, rarely forming surface fea- 

 tures. Sand, on the other hand, is 

 rolled and dragged along the ground, 

 or lifted but a few feet above it, and 

 therefore encounters many obstacles, 

 such as trees, fences, buildings, and 

 the like, about which it may lodge 

 to form hills or mounds. 



FIG. 76. Telegraph pole 

 near Palm Springs Sta- 

 tion, southern Califor- 

 nia, deeply cut by wind- 

 driven sand . The stones 

 have been placed about 

 the bottom of the pole 

 to protect it so far as 

 possible from the sand. 

 (Mendenhall, U.S. Geol. 

 Surv.) 



ABRASION 



How accomplished. Wind of itself 

 can do little or nothing in the way of 

 wearing solid rocks, but the sand par- 

 ticles it often carries serve as effective 

 tools which cut and wear the surfaces 

 against which they are driven. The 

 wearing power of wind-blown sand 

 may be illustrated in various ways. 



It is shown by the artificial sand 

 blast, a process in which glass is etched by sand driven against 

 it with force. The glass in car windows has been destroyed 



