are
situated, therefore, where vegetation is or has been extremely
luxurious. Some of these sections in this age, elevated and denuded of
soil, are almost barren, though the surface of the Karoos in South
Africa, consisting chiefly of ferruginous reddish sands and clays
which bake hard in time of drought, rests on a slaty rock which retains
the rain water and keeps alive the bulbous and other alkali plants
until the wet season transforms the country, with tropical rapidity, to
oceans of blossoms. A large part of the South African plateau lying
within the hills of the west coast, the Bokkeveldts in the South, and
the Drakenberg mountains which skirt it on the east coast and turning
westward form a northern interior frontier in the Transvaal south of
the Limpopo river, probably held at one time lacustrine basins
interspersed with great stretches of the rankest vegetation, which
deposited during the ages immense stores of carbonaceous material. If
by any means, vertical fissures were opened in such an area of the
earth's surface, there would be a great in-pouring of this material
into the cavities, sufficient one might think reasonably, to supply an
abundance of the carbon necessary to produce the very small proportion
diamonds constitute of the mass contained in the diamond chimneys.
As
stated, this high plateau of the diamond-bearing part of South Africa
appears to have been raised to its present elevation, from whatever
cause or by whatever means, either by one uplift, or by a gradual
exercise of force which did not break up and distort the trend of the
strata. In Brazil and elsewhere, the strata in which the diamondiferous
deposits occur are broken and often folded. In many places they are raised to a
