The Corbieres, a branch of the Pyrenees, run in a south-west and north-east direction along the southern district.
There is a continuous transition between the Senonian and Danian, proving that the Algerian region did not participate in the immersion which occurred in Provence and in the Corbieres of southern France during the Danian epoch.
The river skirts the northern spurs of the Corbieres, some distance below which it is joined by the Orbieu and the Cesse.
On the French side the central zone is followed by (1) the zone of Ariege, consisting of Lower Cretaceous and Jurassic beds, together with granitic masses; (2) the zone of the Petites Pyrenees, Upper Cretaceous and Eocene; and (3) the zone of the Corbieres, consisting of Eocene and Primary rocks.
The zone of the Corbieres has no equivalent in Spain, while in France there is no definite zone of Eocene like that of Aragon.