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THE BOOK OF DIAMONDS
which
today are worth millions of dollars. These farms make up the important
part of the DeBeer's Consolidated Mines which controls ninety-five per
cent of the diamond output of the world.
These
mines on this land have been worked so thoroughly today that some of
them are 3,000 feet down in the ground and are kept from caving in only
by the greatest engineering knowledge.
The
five diamond mines or craters (of Kimberley) are all contained in a
circle three and one-half miles in diameter. They are irregularly
shaped round or oval pipes, extending vertically towards to an unknown
depth, retaining about the same diameter throughout. They are said to
be volcanic necks filled from below with a heterogeneous mixture of
fragments of the surrounding rocks, and of older rocks such as granite,
mingled and cemented with bluish-colored, hard clayey mass, in which
famous blue clay the imbedded diamonds are hidden.
The
diamond fields at Kimberley funnel their way up from a great depth in
the foundations of the earth crust, widening as they approach the
surface. There they vary from about 60 feet to a half-mile across.
There is a series of tunnels forty feet below each other in one of
these spans. At the top is that rotted yellow rock which hardens as you
go deeper until it passes into a hard, igneous rock called the blue
ground, or Kimberlite. After careful observations Dr. Stelzner and
others have reached the conclusion that the blue ground is of volcanic
origin and was forced up from below. There are no beds of sand and
gravel into
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