ites.

In all the S. African mines the diamonds are not only crystals of
various weights from fractions of a carat to 150 carats, but also
occur as microscopic crystals disseminated through the blue ground. In
spite of this, however, the average yield in the profitable mines is
only from 0.2 carat to 0.6 carat per load of 1600 lb., or on an
average about 1-1/2 grs. per ton. The annual output of diamonds from
the De Beers mines was valued in 1906 at nearly L5,000,000; the value
per carat ranging from about 35s. to 70s.

[Illustration: SECTION OF KIMBERLEY MINE LOOKING EAST

From Gardner Williams's _Diamond Mines of South Africa_. FIG. 8.]

Pipes similar to those which surround Kimberley have been found in
other parts of S. Africa. One of the best known is that of
Jagersfontein, which was really the first of the dry diggings
(discovered in 1870). This large mine is near Fauresmith and 80 m. to
the south of Kimberley. In 1905 the year's production from the Orange
River Colony mines was more than 320,000 carats, valued at L938,000.
But by far the largest of all the pipes hitherto discovered is the
Premier mine in the Transvaal, about 300 m. to the east of Kimberley.
This was discovered in 1902 and occupies an area of about 75 acres. In
1906 it was being worked as a shallow open mine; but the description
of the Kimberley methods given above is applicable to the washing
plant at that time being introduced into the Premier mine upon a very
large scale. Comparatively few of the pipes which have been discovered
are at all rich in diamonds, and many are quite barren; some are
filled with "hard blue" which even if diamantiferous may be too
expensive to work.

The most competent S. African geologists believe all these remarkable
pipes to be connected with volcanic outbursts which occurred over the
whole of S. Africa during the Cretaceous period (after the deposition
of the Stormberg beds), and drilled these enormous craters through all
the later formations. With the true pipes are associated dykes and
fissures also filled with diamantiferous blue ground. It is only in
the more northerly part of the country that the pipes are filled with
blue ground (or "kimberlite"), and that they are diamantiferous; but
over a great part of Cape Colony have been discovered what are
probably similar pipes filled with agglomerates, breccias and tuffs,
and some with basic