621 



CHAPTEE III. 



PROTECTION AGAINST SHIFTING SAND.* 



UNDER the term shifting sand is meant a fine-grained sand 

 containing so little clay or humus that when dry and the soil 

 is badly covered with vegetation, it is set in motion by the 

 wind and blown from place to place. Shifting sand is generally 

 found on the sea-coast, but also in the interior of countries. 

 As the productive forest area becomes rapidly reduced by the 

 spread of the sand, the evil must be promptly and vigorously 

 met. 



SECTION I. SAND DUNES. 



1. Description. 



Sand is thrown up by the waves along the sea-coast at high 

 tide, and becomes under certain circumstances heaped up into 

 hillocks, or dunes, and is then carried further into the interior 

 of the country. Vasselot de Eegne states that the grains of 

 sand on the Gascon coast are too large to be carried like dust 

 before the wind, but are rolled up the slope of a dune and fall 

 over its ridges, so that the dune naturally attains a slope of 

 about 25 towards the sea, whilst its slope inland is generally 

 steeper, and may attain 60. The sand is blown away from 

 the ridges or from any eminences in the dune, however slight 

 they may be, and is also carried through depressions made in 

 a ridge to the further side of the dune. Two forces are at 

 work on the sand the sea-breeze which prevails during day- 

 time and drives the sand inland, and the land-breeze by night, 

 which finds the sand firmer owing to the dew, and is not so 

 effectual in blowing it back as the sea-breeze is in blowing it 

 forward. 



* Wessely, Josef, " Der Europaische Flugsand u. seine Cultur." Wien, 1873. 

 " Notice sur les Dunes de la Coubre," par Vasselot de Regne. Paris, Imp. Nat., 

 1878. " La Dune Littorale," par C. Grandjean. " Revue des Eaux et Forets." 

 July December, 1887. Lehnpfuhl, " Dunenwanderung und Diinenwald " 

 (" Mundener Forstliche Heft," 2 Heft, 1892, p. 53). 



