A FOREST TOUR AMONG THE DUNES OF GASCONY. 295 
A special law relating to the dunes was enacted in 1810, its 
principal features being that the State can order the planting up of 
any area which, in the public interest, requires to be so dealt with ; 
and that when the land belongs to communes or private proprietors 
who cannot, or do not wish to undertake the work, the State can 
execute it, reimbursing itself, with interest, from the subsequent 
yield of the forest. As soon as the money has been recovered in 
this manner, the land is restored to the proprietors, who are bound 
to maintain the works in good order, and not to fell any trees 
without the sanction of the Forest Department. 
CONSTRUCTION OF THE WORKS. 
The dunes are formed by the combined action of the wind and 
sea. Each ebb tide leaves a quantity of sand, a portion of which 
dries before it is covered by the next flow, and it is then liable to 
be blown away by the wind. The individual sand-grains, which 
are not, generally speaking, either sufficiently large to resist the 
force of the strong westerly breezes that blow from the sea towards 
the low plain which bounds it, nor sufficiently small to be carried 
away in the air in the form of dust, are driven along the surface of 
the ground, rarely rising to a height of more than 13 or 2 feet 
above it, until they meet with some obstacle which arrests their 
course, and thus promotes the formation of a little mound. Up 
this succeeding sand-grains are propelled, and on reaching its 
summit they fall down the sheltered reverse slope at a steep angle. 
In this manner sand-hills or dunes, rising sometimes to a height of 
200 to 250 feet, are formed, the line of their crests being, generally 
speaking, perpendicular to the direction of the prevailing winds, 
that is, in the case of the tract between the Gironde and Bayonne, 
parallel to the general line of the sea-shore. This action is not 
completely regular. The formation of some of the dunes is com- 
menced close to the sea, while others have their origin at some 
distance from it; and fresh importations of sand either add to the 
bulk of those already existing, or, being blown through breaks in 
the chain, pass on till they encounter some other obstacle. But 
the sand-hills themselves are kept moving slowly landwards by the 
wind, which drives the upper layer of sand from the gently-sloping 
outer face up to the summit, whence it falls down the steep slope 
on the landward side, and this process being continued whenever 
there is enough wind to produce it, the dunes are moved, or rather 
