34 A MANUAL OF FORESTRY. 



further progress of the evil has been checked only in 

 comparatively recent times, by operations Avhich it is 

 useful to describe shortly in this place. 

 The measures which must be taken are : 



(1.) Cutting off a further supply of sand from the 



sea; 

 (2.) Fixing the sand temporarily, so as to allow sowing 



or planting ; 

 (3.) Growing a crop of trees and bushes, which will 



permanently fix the sand ; 

 (4.) Maintaining permanently a crop of trees and 



shrubs. 



The first of these four measures is based on the fact 

 that, although air currents are capable of moving the 

 sand along level and gently sloping ground, they cannot 

 lift it above a certain height. Hence it is necessary at 

 a moderate distance (100 300 feet) from high- water 

 level to form an artificial hill, which is high enough to 

 arrest the forward movement of the sand, and this is done 

 by the construction of an artificial dune, generally called 

 the " littoral dune." With this object in view a con- 

 tinuous line of paling is erected, consisting of planks 

 about 6 feet long by 6 inches wide, 1 inch thick, 

 and pointed at the lower end. The planks are in- 

 serted into the ground to about half their length, 

 an inch apart, the direction of the line being parallel 

 to the coast. Against this fence the sand is deposited, 

 a certain portion being forced through the interstices 

 and coming to rest in the comparatively quiet air 

 immediately behind the paling. As soon as the ac- 

 cumulation of sand approaches the upper ends of the 



