4 Description of the Landes of Acquitania. 
formed of the same sedimentary deposits, belonging to the tertiary 
or superior order, which cover the northern base of the Pyrenees, 
from the Bay of Biscay to the Mediterranean. For geognostical 
details, we refer to the excellent labours of the French geologists, * 
to which we have nothing to add; but their connection with the 
present state of the Landes, is an object of novel interest. . 
The circumscription of the tertiary formations, is formed by the 
chain of the Pyrenees on the one hand, and the schistose rocks of the 
Vendée on the other; but the limitation of the Landes occurs in 
the Alpine limestone to the south of the Adour, and in the cliffs of 
Parisian limestone which gradually approach to overhang the nor- 
thern banks of the Garonne. 
The new red sandstone, muschelkalk, quadersandstein, and lias, 
may all be traced to the south of the Adour, while the sandstone, 
oolitic series, and chalk, may be found to the north of the Gironde, 
The succeeding second arenaceous tertiary formation, or upper ma= 
rine deposit of the Landes, lies on Parisian limestone, plastic clay; 
and chalk. The Parisian limestone crops out to the north of the 
Garonne, from which it is, however, separated by the upper fresh 
water formation. When we consider the newness of these tracts, 
as deduced from their geognostic structure, are we not inclined to 
ask, whether their barrenness is not owing to that very circum- 
stance, inducing such a thinness of vegetable soil as to preclude the 
access of a variety of plants, as must originally have been much 
more the case over secondary arenaceous formations, which were 
never covered by a diluvial gravel or alluvial mud ? 
In the case of the Landes it is, however, certain that their steri< 
lity is in a great part owing to a hard and compact bed, (called alios 
in Acquitania,) of a dark-brown colour, from some inches to several 
feet in thickness, formed by a quartzose sand, bound by a cement, 
in which iron oftentimes exists in so great a quantity, that it can be 
extracted with great advantage, the bed lying at a few feet, and 
oftentimes only as many inches in depth beneath the surface. 
The soil of the Landes, every where sandy, does not consist of a 
mobile sand, but is bound down by plants and lichens, and black- 
ened a little by the presence of a small portion of vegetable matter. 
During four months of the year, these plains are partly covered 
with water, forming shallows (mares) of little depth, marked in 
the summer months only by a slight difference of vegetation, heaths 
especially never growing on these spots. These collections of water 
are sometimes so great as to give rise to strong streams, which work 
* La Perouse Fragments de la Mineralogie des Pyrenées, (Mem. de PAcade- 
mie de Thoulouse, Vol. III.) Palassou Memoire sur les atterissements formés 
des debris des Pyrenées, inserted in the “ Memoires pour servir a 1’ Histoire Na- 
turelle des Pyrenées, Pau 1815;” and D’Aubuisson “ Traité de Geognosie, 
t. ii.”’ Charpentier, in his elaborate work, has not described the tertiary forma- 
tions, but Boué, in the “‘ Annales des Sciences Naturelles,” has given sections of 
the territory from Bordeaux to Bayonne. 
