The southern portion of the oasis is the only area where sand and wind can be said to be of any actual benefit to the inhabitants, but in this area, owing to the broad plains of alluvial clay, the suspended material consists to a very great extent of fine argillaceous particles. At many of the wells in the Dakhakhin and Beris districts the cultivators encourage the gradual deposition on their fields of the sand and clay-dust borne by the northerly winds. The mixture forms an excellent loam, and an annual dressing of the material is regarded as desirable, and even necessary, on account of its value as a fertilizer. The result of this gradual deposition of wind-borne material has been that the cultivated terraces have in many cases attained to such elevations that the discharges of the wells have suffered very considerable diminution, owing to the increased height of the outlets. To the west of the villages of Maks and Beris the great belt of sand has already enveloped a number of wells, and appears to be still encroaching—as the individual dunes follow their normal course in a direction slightly east of south—on the area occupied by the existing cultivated lands. Fortunately there are still extensive tracts of cultivable land comparatively free from accumulations of drift sand, and doubtless the inhabitants, when driven by the irresistible forces of Nature from the localities they now occupy, will again, as they have so frequently been compelled to do in the past, migrate to pastures new. CHAPTER XV SOME ECONOMICAL ASPECTS OF THE OASIS The Staple Crops of the Oasis — Rice the Summer Crop in Northern Kharga — The Value of Rice in the Reclamation of Land — The Date Harvest — Conditions under which the Date-Palm flourishes — Varieties — Propagation — The Doum-Palm — Lucerne — Its Value in Land-Reclamation — The Vine — Oranges and Other Fruits — The Wadi Molûk — Earthy Minerals — The Ancient Alum Mines — The Phosphatic Deposits.