Page:Africa by Élisée Reclus, Volume 4.djvu/123

 unable to complete the work of erosion required to form normal river beds. Hence after the heavy rains a large quantity of the precipitated water lodges in little reservoirs without any outflow, closed basins which often run dry through evaporation or infiltration before the next downpour. According to the season

these depressions are consequently either shallow lagoons in which the hunter dare not venture, or almost equally dangerous muddy quagmires, or lastly dry and arid plains. Some with porous beds are clothed with vegetation after the fresh water has evaporated, and these are the vleys of the Dutch explorers. Others, with impenetrable argillaceus beds, are more arid in summer than the relatively elevated surrounding plains, and these are known as salt-pans from the white saline efflorescences left on the surface after the rain water has evaporated.