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AGRONOMY 



soils. These have been transported by wind. Sand 

 dunes are familiar examples. Less well known, though more 

 important, are the deposits of wind-blown materials known as 

 loess that cover large areas in China, Europe, and parts of the 

 Middle West. Loess is composed of particles much finer than 

 sand grains and makes very fertile soils. Parts of Iowa and 

 Kansas are covered with loess to the depth of hundreds of feet. 



Photograph by A. B. Klugh 



FIG. 13. A sand dune captured by vegetation 



Volcanic soils. As the name indicates, these are formed of 

 the ashes and dust thrown out by volcanoes. They are rare 

 in the United States except in the Far West, but in other 

 countries are often encountered. After weathering, they form 

 very fertile soils. Much of the land cultivated in the Hawaiian 

 Islands is of this type. 



Colluvial soils. These have been formed by gravity acting 

 upon the pieces of rock quarried from the cliffs by changes of 

 temperature and freezing water. Good illustrations are found 



