296 A FOREST TOUR AMONG THE DUNES OF GASCONY. 
rolled, inland by slow degrees; and as fresh ones are formed near 
the sea, which are in their turn moved onwards, it follows that, in 
the course of time, the whole surface of the plain has become 
covered with sand-hills for a distance of several miles from the 
coast. The rate at which the sand thus advances is very variable. 
Sometimes, during many months, there is no perceptible encroach- 
ment, while at others the movement is very rapid, amounting to 60 
or 70 ft. in the year; the average annual rate is said to be about 
14 ft. But the sand-hills do not move at an uniform rate of speed. 
Some, overtaking those in their front, become merged in them ; 
while they all undergo changes of height and form, so that the 
whole surface of the country is continually in motion, being turned 
over and over to a great depth, and under these conditions it is 
impossible to grow anything on it. The source of the evil lies at 
the sea beach ; and the first thing to do evidently is to stop fresh 
importations of sand ; while as regards the dunes already formed, it 
will be seen from what has been said, that the movement, at any 
particular time, is confined to the sand then at the surface, and if 
this can be fixed during the time necessary to enable a crop of 
herbs, shrubs, and young trees to be raised upon it, the movement 
of the entire mass will have been arrested. 
We rode from St Eulalie, through the forests, to the coast near 
Mimizan-les-Bains, where M. Lamarque explained to us that the 
system by which this is accomplished consists in promoting the 
formation, by the wind, of an artificial dune, close to the sea, and, 
generally speaking, parallel to it at high tide. This mound absorbs 
the fresh importations of sand ; while, under its shelter, sowings are 
made, which, extending gradually inland in parallel bands, fix and 
consolidate the surface of the naturally formed sand-hills ; ultimately 
the artificial dune is itself planted with trees, and the evil is then 
cured for so long a time as care is taken to maintain the works, 
which are commenced as follows :— 
At a distance of about 165 yards from high-water mark, a 
wattled fence 40 in. high is erected, the pickets being driven 20 in. 
into the sand. This serves to arrest the sand, which is heaped up 
on the seaward side, a portion of it filtering through the wattles. 
After a time the fence is overtopped, and the sand, blown up the 
outer face, forms a steep slope on the other side. A second 
wattled fence is then erected, about 6} ft. behind the first, and the 
space between the two becoming filled up, and a mound rising over 
it, the sand which falls over stands at a high angle against the 
