390 



THE WORK OF THE ATMOSPHERE 



FIG. 258. Sand dunes, showing ridges caused by winds. 



sand hills are pushed rapidly onward and quickly engulf houses 

 and forests, bury railroad tracks, and destroy travelers. 



The shifting of sand and the formation of dunes can be 

 prevented by trees, shrubs, and grasses. Leaves and branches 



FIG. 259. Accumulation of sand about an object which breaks the 

 wind. 



shelter sand from the wind, and roots act as nets and hold the 

 sand firm. In Provincetown, Massachusetts, beach grass was 



