NOTES ON THE FIXING OF THE DUNES. 251 



deposited in the form of an inclined plane sloping 

 very gradually seawards. Some of it passes through 

 the spaces left between the planks, and serves as 

 a sort of backing, thus increasing their stability. 

 When the sand reaches the top of the paling, and 

 begins to cover it, the latter is raised by means of a 

 lever with hooks. In this manner the littoral dune 

 rises higher. This increase in height must be ren- 

 dered as gradual as possible, otherwise the dune 

 might be washed away by the sea. 



To give the dune more stability, a tight-bound 

 fence is erected behind the paling. Stakes six feet 

 four inches in length are driven twenty inches into 

 the sand, and the wattling is at first carried only up 

 to a yard above the ground. The wattling is con- 

 tinued upwards as the dune rises. When the dune 

 reaches the top of the stakes, another fence of the 

 same kind is put up, for the old fence obviously 

 cannot be raised like the paling. 



The whole is at length fixed by planting over with 

 the Psamma arenaria in tufts of five or six plants 

 twenty inches apart. This grass possesses this im- 

 portant property, that, as the sand covers it, its 

 stalk grows higher and developes numerous adven- 

 titious roots, which form a veritable network. An 

 acre requires 120 bundles of this plant, weighing 

 twenty-two Ibs. each, besides five Ibs. of seeds. The 

 first thing done is to sow the seed broadcast, the 

 operation of planting and the going to and fro of the 

 labourers being enough to press them into the ground. 



A running foot of paling costs about eightpence. 

 It lasts on an average five years, when the planks are 



