136 ELEMENTARY GEOLOGY 
the path of sand-laden winds. In the arts, sand is 
violently thrown against glass by a blast of air, chip- 
ping it and producing ground glass. Nature acts in 
the same way on a more moderate scale. On the sandy 
island of Monomoy, on the southern side of Cape Cod, 
Massachusetts, the glass in the fishermen’s cottages has 
been made into ground glass, by the constant chipping 
Fic. 65. 
Section in wind-blown sand at Bermuda, showing the layers set at various angles. 
which it has received from the sand that is driven by 
the fierce ocean winds. It takes years to do this, but 
it bears witness to the power of the sand as an agent 
of erosion. 
So also in parts of the West, where sand is constantly 
moving, it-is smoothing and polishing the rocks by its 
continual action. Cliffs that are exposed to the wind 
are also eaten back and etched by it; and we often 
