At Berriane, one of the M’Zab cities, there are over 30,000 palms of a superior sort, watered from over 400 wells. The surroundings of this oasis are extremely desertic and a casual survey of the route between this place and Ghardaia, 44 kilometers distant, reveals almost no vegetation. Here the calcareous plain of Cretaceous origin, the Chebka, is even more eroded than in the portion farther to the north, and the valleys are wider. The soil is a fine clay without an admixture of sand. It is only in the most favorable places, along the washes, that plants are to be found, and here are _Deverra chlorantha_, _Anabasis articulata_, _Gymnocarpon fruticosum_, _Artemisia herba-alba_, _Ononis angustissima_, _Linaria fruticosa_, _Antirrhinum ramosissima_, and _Haloxylon articulatum_ (Massart, _loc. cit._). _Peganum harmala_ occurs very sparingly by the roadside. The habits and the habitats of certain of the above-mentioned species will be described in greater detail later in this paper. =GHARDAIA.= The Ghardaia region can be characterized as a vast plain, broken to the north by low, irregularly disposed mountains, and stretching for a great distance to the south and southeast with a fairly monotonous surface, diversified only by oueds, chotts, or occasional dunes, which may be the size of small mountains. Thus on the one hand one finds the fairly diversified and stony Chebka and on the other the hamada, which has been aptly described by Brunhes[18] as “le désert par excellence, la vrai désert . . . les grandes plaques pierreuses indéfinies des hamadas!” The leading oued of this region is the M’Zab, which extends for about 270 kilometers in a direction south of east across the southern part of the Chebka. It takes its origin about 80 kilometers west of Ghardaia and extends to the vicinity of Ouargla, where it debouches on the Ouargla plain. At Ghardaia the oued lies in a valley, with abrupt sides, which is sunk about 60 meters below the surrounding plain and which at this place is about 3 kilometers in width. (See fig. 16.) There are four main tributaries of this oued, all of which join it from the north or the Chebka side. The valley of the M’Zab becomes more and more shallow as one proceeds eastward and at last lies but little below the general level of the country. Like the other deeper valleys of the Chebka, the M’Zab Valley represents the work of erosion by water at an earlier geological epoch, when the great terraces were formed. The filling of the eroded valleys has perhaps taken place during the long arid period since that time and has probably proceeded very slowly. It appears to be uncertain how long the M’Zab has been inhabited by man, or, more accurately, by the race now dwelling there;[19] but it has probably been not less than nine centuries.[20]