Dayas of the Moroccan Sahara and Other Arid Regions

Five types of calcareous hollow occurring in arid areas are defined. One of these, the daya, was studied in detail and the findings recorded. A world geographical distribution of different dayas is given with quantitative data on surface features and type. Six dayas occurring in the Moroccan Sahara were investigated and field data are given on topography, soils, drainage and vegetation. Physical and chemical analyses of soil samples from dayas and their surrounding hamadas suggest that three processes are involved in their formation: lateral inwash, solution and deflation. Clay minerals, determined on a range of soil samples, showed major quantities of illite, traces of montmorillonite and the presence of calcite. Dayas in the Moroccan region are often cultivated for cereals, mainly barley, and for stubble grazing. The Berber tribesmen cultivate them after good rains and the yields obtained are about two-thirds of those obtained in the irrigated plots of the Oued Ziz. The grain is not marketed but consumed by nomads.