FORMATION OF THE DIAMOND 125
On
the 1000-foot level of Kimberley mine a tunnel driven in the quartzite
outside the margin of the mine shows several dvkes of similar rock.
Wherever these dykes exist there is a considerable quantity of water at
the junction of the dykes and quartzite.
There
was a large mass of country rock in De Beers mine, which in the upper
levels covered several claims, or approximately an area of 3000 square
feet. It continued down to a depth of about 750 feet. It was an olivine
diabase, and was the same as the amygdaloidal rock, except that it was
filled with numerous veins of zeolites. The " Island," as it is called,
was a gigantic horse of country rock embedded in blue ground, and has
disappeared in depth. Islands of the same rock appeared in the
Kimberley mine near the surface and at a depth of 1200 feet, and near
the surface in Dutoitspan, Bultfontein, and Premier mines, where they
have been left standing as the blue ground which surrounded them has
been removed, and form huge islands in a sea of blue ground, which are
locally known as Mount Ararats.
Floating
shale appeared at or near the surface of the mines and covered many
claims. This was originally volcanic mud, and it contained no diamonds.
It gradually became smaller in depth, and has disappeared in the lower
levels.
In
the early descriptions of the mines fossil wood and plants are reported
to have been found in the blue ground. I am of the opinion that these
came either from the shale surrounding the craters, which was
constantly falling into the open mines, or from the pieces of shale
which became embedded in the blue ground at the time the craters were
filled. The only fossils which have been found in the mines since they
have been under my management are the fish which are shown in the
illustration on page 126. They are embedded in sandstone which was
found on the 185-foot level of Premier mine.1
The
surface shales and basalt surrounding the pipes are called reef, and
the masses of shale and igneous rocks, scattered through the blue
ground in the upper levels of the mines, are commonly spoken of as
floating reef.
1 A fossil lizard has since been found, see illustration, p. i 18. See Appendix VII,
