PRINCIPLES OF AGRICULTURAL CHEMISTRY 



heaped by the wind into wave-like hills called dunes. Dunes 

 whose sands are not fixed by vegetation, travel slowly with the 

 wind, and they may invade and destroy forests and fields, and 

 bury villages beneath their slowly advancing waves. River 

 deposits on flood plains are often worked over by the winds dur- 

 ing summer droughts, and much of the silt is caught and held by 

 the forests and grassy fields bordering on the area. 



Wind-blown materials may aid in the formation of soils even 

 in humid regions. Thus, Hall 1 relates that a beach composed of 

 coarse rocks (shingle) was found in years to have accumulated 

 a few inches of a black powder, probably borne there by the 

 wind. 



Soils from Oceanic Deposits. The more important oceanic 

 deposits from which soils are derived are sands and sandstones, 



AfudandC/ays Limestone Sand 



Fig. 22. Present distribution of deposits in the Atlantic near 

 the United States. 



muds, shales, and other consolidated sediments, and limestone 

 deposits. The material of the oceanic deposits comes from the 

 wear and tear of the waves on the shore, and from the waste 

 1 The Soil, p. 10. 



