304 GEOLOGICAL SURVEY OF NEW JERSEY. 
Plate XX VI 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 driven 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 arenaria).t ‘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. Gardes 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 dependeut 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 year book of the Department 
of Agriculture.) It is common on the Atlantic coast of both Europe and America. 
