304 GEOLOGICAL SURVEY OF NEW JERSEY. 



Plate XXVI shows a church at Soulac which was buried by 

 the sand. 



The methods employed in fixing the dunes may be briefly 

 •described as follows : 



A littoral dune was constructed straight along the shore from 

 the mouth of the Gironde to Bayonne. This dune was the secret 

 of the success in the fixation of these shifting sands. It is simply 

 a bank of sand of certain dimensions, with a certain slope suited 

 to the condition of affairs. This protective, or littoral, dune 

 is formed as follows : a double fence is constructed of brush,* 

 or of palisades driveij in the sand. This stops the sand which 

 ■comes from the ocean. Soon a ridge of sand forms, equal in 

 height to the fence, A double fence is used, as it gives breadth 

 to the dune, and stops the sand which blows through the fence 

 on the ocean side. As soon as a ridge of sand is formed as high 

 as the fence, the old fence is pulled up, or a new one built on 

 top ; and so on, until a dune of the height desired is formed 

 artificially. The proper height of a protective dune is 33 feet. 

 It should slope 25° towards the sea, and may be 60° on the land 

 side. The dune must be at least 300 feet from high-water mark. 

 After the dune has reached the proper size, it is kept in shape 

 by the sea marram {Psamma arenarid).\ This peculiar plant, 

 called gourbet in France, is exclusively used for fixing the sand 

 on the littoral dune. It has long, much-divided rhizomes, and 

 will grow well only when covered with fresh sand. The dune 

 must always be kept in shape. If sand accumulates in any one 

 spot in undue amount, a draft is formed, which may end in a 

 breach of the littoral dune. Ga7'des cantonniers are stationed 

 along the dune, to watch it closely, and here and there on this 

 long, straight sand-bank groups of men and women may be seen 

 digging up the gourbet in places where it is too thick, and 

 planting it where needed. Constantly the dune is watched and 

 mended ; the forest, villages and fields in its lee are dependent 

 upon it, and it in turn is dependent upon the humble, but per- 

 sistent, gourbet. 



After the formation of the littoral dune comes the work of 



* This system of making a fence of brush is called Clayonage. 



^Psamma or Ammophila arenaria, beach or marram grass is the best known of the true sand- 

 binding grasses. (See Sand-binding Grasses, by F. Lamson-Scribner, in yeai; book of the Department 

 -of Agriculture.) It is common on the Atlantic coast of both Europe and America. 



