The next division, that which embraces the centre of the continent, can scarcely be called hilly, for what hills there are are very low.  It consists for the most part of extensive, slightly undulating plains.  There are no lofty mountains, but few springs, and still fewer flowing streams.  Rain is far from abundant, and droughts may be expected every few years.  Without artificial irrigation no European grain can be raised, and the inhabitants (Bechuanas), though evidently of the same stock, originally, with those already mentioned, and closely resembling them in being an agricultural as well as a pastoral people, are a comparatively timid race, and inferior to the Caffres in physical development.

The western division is still more level than the middle one, being rugged only near the coast.  It includes the great plain called the Kalahari Desert, which is remarkable for little water and very considerable vegetation.

The reason, probably, why so little rain falls on this extensive plain is that the prevailing winds of most of the interior country are easterly, with a little southing.  The moisture taken up by the atmosphere from the Indian Ocean is deposited on the eastern hilly slope; and when the moving mass of air reaches its greatest elevation, it is then on the verge of the great valley, or, as in the case of the Kalahari, the great heated inland plains; there, meeting with the rarefied air of that hot, dry surface, the ascending heat gives it greater capacity for retaining all its remaining humidity, and few showers can be given to the middle and western lands in consequence of the increased hygrometric power.

This is the same phenomenon, on a gigantic scale, as that which takes place on Table Mountain, at the Cape, in what is called the spreading of the “table-cloth”.  The southeast wind causes a mass of air, equal to the diameter of the mountain, suddenly to ascend at least three thousand feet; the dilatation produced by altitude, with its attendant cold, causes the immediate formation of a cloud on the summit; the water in the atmosphere becomes visible; successive masses of gliding-up and passing-over air cause the continual formation of clouds, but the top of the vapory mass, or “table-cloth”, is level, and seemingly motionless; on the lee side, however, the thick volumes of vapor curl over and descend, but when they reach the point below, where greater density and higher temperature impart enlarged capacity for carrying water, they entirely disappear.

Now if, instead of a hollow on the lee side of Table Mountain, we had an elevated heated plain, the clouds which curl over that side, and disappear as they do at present when a “southeaster” is blowing, might deposit some moisture on the windward ascent and top; but the heat would then impart the increased capacity the air now receives at the lower level in its descent to leeward, and, instead of an extended country with a flora of the ‘Disa grandiflora’, ‘gladiolus’, ‘rushes’, and ‘lichens’, which now appear on Table Mountain, we should have only the hardy vegetation of the Kalahari.