The oldest strata, consisting of gypsiferous marls, are referred to the Muschelkalk and show an alternation of lagoon with marine conditions.
The gypsiferous and saliferous marls of Shellata, Suk Ahras and Ain Nussi have yielded Triassic fossils.
The Oligocene period consists of a marine phase confined to the littoral zone of Kabylia, and of a continental phase occupying vast areas composed of lacustrine, alluvial, gypsiferous marls, sandstones and conglomerates.
In this part of the country the Permian beds are largely red sandstone, often saliferous and gypsiferous.
Thus the lower Eocene has some lignite in the eastern Gulf region, while in Teias lignite and saliferous and gypsiferous sediments are found, though most of the system is marine and of shallow water origin.