86 THE GREAT DIAMONDS OF THE WORLD.
well
ascertained that these diamonds were originally developed in an igneous
matrix belonging probably to that large series of eruptive rocks which
have burst further through the Karoo strata at so many points in South
Africa. In the dry diggings the stones are possibly found almost in
their original positions. Those which reward the digger in the river
beds have probably been washed down by running water, and there are
superficial deposits here and there in which ice has been the means of
transportation. Such, at least are the various hypotheses which have
been put forward in explanation of the somewhat singular distribution
of the diamonds at the Cape.
Hardly
a dozen years have past since these new fields were discovered. During
that time the yield of fine stones has been enormous. The first notable
one was the " Dudley," the next the " Stewart." The latter gem is the
only one which takes precedence in size of the Du Toit I. Although many
of the Cape diamonds are " straw coloured," a very fair proportion are
of the first water, bearing comparison with some of the finest gems of
Brazil and the Indies. Even the yellowish ones are of a peculiar
delicacy of tint which is very attractive in a well cut stone. It has
been estimated that 20 per cent, of the Cape stones are of the finest
quality, 15 of the second, and 20 of the third, the remainder being
what is technically called " bort." It is as well to add that all
diamonds which are not sufficiently pure for cutting are classed under
the term " bort." They are crushed into powder, which is used for
grinding diamonds, and also in the engraving of gems of exceptional
hardness.
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