These diamond-mines are of two kinds : they are known by
the name of "river diggings," existing in deposits of gravel containing agate and jasper pebbles ; and "dry diggings," in rocks
not disintegrated. The bed of the Vaal, as well as the drift on
its banks, says Morton, is made up of agate, jasper, chalcedony
pebbles, and quartz crystals, with diamonds interspersed.
Judging from the appearance of these gems found in the
gravel, it is thought they must have travelled far and perhaps been subject to glacial action.
The mines called the "dry diggings" are found in what is
called the Karoo formation, a conglomerate occupying an
extensive plateau, elevated some five thousand feet and spread
over a territory covering two hundred thousand square miles.
The diamond was not, probably, formed in the place where it
was discovered, but is an accidental constituent of the puddingstone. Fragments of the broken crystals, as well as entire
pebbles, are scattered with remarkable regularity throughout
the mass, but are never found near one another. It is mentioned as a rare occurrence that a diamond geode was brought
to light during the mining at the Cape.
The soil directly below the surface is described as chalky,
and interspersed with nodules enclosing diamonds. Under the
chalk rests a yellowish mass, containing more of the precious
substance, but the richest harvest is gathered from the conglomerate called by the miners " blue stuff," found at a depth
of fifty or sixty feet, and often inclosing topaz, zircon, jasper,
agate, opal, and other precious stones. A claim comprising
three hundred square feet of this conglomerate has been estimated worth from five thousand to forty thousand dollars,
— the difference of price varying according to circumstances.
At a place called Du Toit's Pan, twenty-five miles from the
"river diggings," the mines, covering many acres, have yielded
