A geographical position, not unlike that which condemns the plains along the western foot of the Peruvian and Bolivian Andes to perpetual aridity, renders also the greater part of tropical and sub-tropical Southern Africa subject to severe droughts, and in general to great scarcity of rain. For the emanations of the Indian Ocean, which the easterly winds carry towards that continent, and which, if equally distributed over the whole surface, would render it capable of bearing the richest productions of the torrid zone, are mostly deposited on the eastern slopes of the mountain-chains, which, under various denominations, traverse eastern South Africa from north to south; and when the moving mass of air, having crossed their highest elevations, reaches the great heated inland plains, the ascending warmth of that hot dry surface gives it greater power of retaining its remaining moisture, and few showers can be given to the central and western lands. Thus, while the sea-board gorges of the eastern zone are clad with gigantic forests, and an annual supply of rain there keeps a large number of streams perpetually flowing, Damara Land, the Namaqua country, and the Kalahari, are almost constantly deprived of moving water. * * * * * From these general remarks it might be imagined that regions so scantily supplied with one of the prime necessaries of life could be nothing but a dead and naked waste; yet, strange to say, even the great Kalahari, extending from the Orange river in the south, lat. 29°, to Lake Ngami in the north, lat. 21°, and from about 24° E. long. to near the west coast, has been called a desert simply because it contains no flowing streams and very little water in wells; as, far from being destitute of vegetable or animal life, it is covered with grass and a great variety of creeping plants, interspersed with large patches of bushes and even trees. In general, the soil is a light-coloured, soft sand; but the beds of the ancient rivers contain much alluvial soil, and, as that is baked hard by the burning sun, rain-water stands in pools in some of them for several months in the year. The abundance of vegetation on so unpromising a soil may partly be explained by the geological formation of the country; for as the basin-shape prevails over large tracks, and as the strata on the slopes where most of the rain falls dip in towards the centre, they probably guide water beneath the plains, which are but ill-supplied with moisture from the clouds.