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NATURE STUDY REVIEW [9 : 2— Feb., 1913 



Figure 4. — Roots growing from tlie trunks of cottonwood trees and 

 exposed by migration of the dune, (b'uller. ) 



and steep leeward slopes. Since the lee slope is protected from 

 the wind it will l)e just as steep as loose sand can stand. This 

 shape is represented in miniature b\ the wind ripples frequently 

 seen on a sandy surface (Fig. 3). 



If a dune acquires a protective covering of vegetation it 

 will stop traveling and become stable. But when for any reason 

 plant life ceases to protect it, or man carelessly cuts into it, the 

 wind soon attacks the exposed i)art and dunc-dcstnicfioii and 



