96 Description of the Landes of Acquitania. 
very characteristic, ) Phalaris oryzoides, Isnardia palustris, Litorelia 
lacustris, Pilularia globulifera ; where there is a little water, the 
Conferva reticulata may be found. , 
These mares increase so much during some seasons, that their 
waters form running streams, which course down the very slight 
inclination of the Landes towards the sea. Meeting there with the 
sand-hills, they are arrested, and form ponds of greater or less 
extent, which are also supplied by spring waters, descending 
either as rivulets or small rivers. These lagune mostly empty 
their waters into the sea by a common outlet ; but this often changes 
its place, and is sometimes blocked up altogether, obliging the wa- 
ters to return to the bosom of the hills, and the size of the pond 
becomes greatly increased. One of the largest of these, the Etang 
of Orx, runs from north to south, (the general direction of the 
whole series, which is parallel to the line of the coast,) a distance 
of eight miles, upon one and a quarter of a mile wide, and a depth 
of from 15 to 18 feet towards the centre ; it covers with its waters 
8 to 9000 English acres of land, and, according to a report of Col. 
Bory St. Vincent, its waters are elevated about 15 feet above the 
level of the ordinary tides. 
The laguna of Hossegors is 9842 feet long, by 984 feet broad, 
and 9 feet deep ; it is bordered on the east by a chain of downs, 
from 1000 to 1300 feet of elevation ; on the west by other downs; 
which separate it from the ocean, and are clothed with vines half 
way up their acclivities. 
The laguna of Mouson is from 1 to 200 yards broad, and 26 feet 
deep. It discharges itself by a rivulet into the basin of Boucau : 
its name is derived from a tradition, according to which a Captain 
Mouson having a vessel in the laguna, then communicating with 
the sea by a navigable river, neglected, upon being informed of a 
sudden change in the sands, to make his escape, and his vessel was 
in consequence stranded. 
Between the 24th and the 27th of June 1802, several sand-hills 
in the ponds of Biscarosse, from 40 to 50 feet above the level of 
the pond, gave way beneath, for a length of 5 to 6000 feet, upon a — 
width of 300, and were reduced to a level with the water. The 
pine trees followed the motion of the sands ; but their roots were 
too much bared to enable them to draw sufficient moisture for their 
nourishment. The waters of the present pond, are only elevated 
about 12 feet above the level of low tides. 
The basin of Arcachon having two exits into the ocean, cannot 
be considered as a true laguna, though its origin may be traced to 
pretty nearly similar circumstances, with certain modifications con- 
nected with the inconstancy of the situation, and little fixity of the 
downs. It forms, in its present condition, an arm of the sea, near- 
ly 50 miles in circumference. Its entrances are the Passe du Nord 
and the Passe du Sud. Several pines, arranged in the form of a 
cone, and placed upon the downs, serve as guides to navigators 
entering the roads. These signals are termed balises. They are 
