RECLAMATION OF THE SOIL. 33 



On the whole the cases mentioned under I and c 

 occur but sparingly. 



5. Fixation of Shifting Sands. 



Sand of a fine grain without a sufficient quantity of 

 binding material, such as clay or humus, is liable to 

 be blown about, and to become moving or shifting 

 sand, which overspreads adjoining lands. If the supply 

 is kept up, these shifting masses of sand form regular 

 waves which proceed at a certain rate in the same 

 direction as that of the prevailing wind. Shifting 

 sands are most prevalent along sea shores, but also 

 occur inland. In either case, but especially near the 

 sea, they are capable of forming considerable accumu- 

 lations of sand, reaching a height of 200 feet and 

 even more, which are called dunes. Before such areas 

 can be brought under wood, it is necessary to fix them, 

 so as to allow trees to spring up and lay hold of the soil 

 permanently. 



a. Coast Dimes. 



Along the sea coast the waves constantly throw up 

 sand, which after drying is carried inland by air cur- 

 rents, forming a series of ridges and valleys, in many 

 cases, though not necessarily, parallel to the sea shore. 

 These sand hills move steadily forward, being replaced 

 behind by fresh sand thrown up by the sea. The rate 

 of progress varies considerably according to circum- 

 stances. On the west coast of France it is said to be 

 about 14 feet a year, but as the process has gone on for 

 a long period of time, an enormous area comprising 

 millions of acres has become covered with sand. The 



VOL. II. D 



