The Algerian Sahara was divided into four territories, officially named Tuggurt, Ghardaia, Ain Sefra and the Saharan Oases (Tuat, Gurara and Tidikelt).
South of that point the Saharan frontiers of Algeria, Tunisia and Tripoli remained undefined.
This depression is the termination of what is in all probability the bed of one of the dried-up Saharan rivers.
The area of the lake is shrinking owing to the progressive desiccation of the country, Saharan climate and conditions replacing those of the Sudan.
Besides these isolated posts Spain holds Rio de Oro, a stretch of the Saharan coast, and its hinterland lying between Morocco and French West Africa; the Muni River Settlements or Spanish Guinea, situated between French Congo and the German colony of Cameroon; Fernando P0, Annobon, Corisco and other islands in the Gulf of Guinea.
The central part, the Zab Mountains, is of lower elevation, the Saharan Atlas reaching its culminating point, Jebel Shellia (7611 ft.
The Saharan Atlas is essentially one chain, though known under different names: Jebel K'sur and Jebel Amur on the west, and Jebel Aures in the east.
By an exception rare in Saharan settlements, there are no defensive works save the fort containing the government offices, which the French have built on the south side of the town.
Near Bilma is a small circular oasis, kept green by a fine spring, but immediately to the south begins the most dreary part of the Saharan desert, over which the caravans travel for fifteen days without discovering the slightest trace of vegetable life.
Along the northern border of the protectorate this has resulted in the encroachment of the Saharan desert over once fertile districts.