THE SURFACE OF THE EARTH 



165 



at different places. In the Province of Shansi, China, 

 are deposits several hundred feet thick. Near Kan- 

 sas City, Missouri, there is a deposit at least thirty 

 feet thick. 



Sand is also carried by the wind, but since it is 

 heavier than dust, a 

 much stronger wind 

 is necessary for car- 

 rying it. Sand never 

 rises to any great 

 height, but is carried 

 near the earth. There 

 are many obstacles 

 on the earth to stop 

 it. Sand blown by a 

 strong Avind has con- 

 siderable cutting 

 force. For this rea- 

 son sand blasts are sometimes used for etching glass. 

 In the semi-arid regions of western United States, pro- 

 jecting rock cliffs are often carved into strange and 

 fantastic forms. The softer parts of the rock are cut 

 more rapidly so that the harder parts are left project- 

 ing. Even the hard rocks are not able to withstand 

 the long continued action of blown sand. 



Sand dunes. Mounds and ridges of wind-blown sand 

 are called dunes. In the dry parts of western United 

 States there are thousands of square miles where 

 dunes are abundant. On the east and south shores of 



Photograph by Detroit Publishing Co. 



FIG. 61. Balanced Rock, Colorado 

 Springs, Colorado. This rock has been 

 yut by wind-blown sand. 



