ddle 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.

Why there should be so much vegetation on the Kalahari may be explained
by the geological formation of the country.