fig.
12) with their ascending and descending buckets disappeared, and with
it the cosmopolitan crowd of busy miners working like ants at the
bottom of the pit. In place of all this, the visitor to Kimberley
encounters at the edge of the town only a huge crater, silent and
apparently deserted, with no visible sign of the great mining
operations which are conducted nearly half a mile below the surface.
The aspect of the Kimberley pit in 1906 is shown in fig. 13 of Plate
II., which may be compared with the section of fig. 8.

In fig. 13, Plate II., the sequence of the basalt, shale and melaphyre
is clearly visible on the sides of the pit; and fig. 8 shows how the
crater or "pipe" of blue ground has penetrated these rocks and also
the underlying quartzite. The workings at De Beers had extended into
the still more deeply seated granite in 1906. Figure 9, Plate I.,
shows the top of the De Beers' crater with basalt overlying the shale.
Figure 8 also explains the modern system of mining introduced by
Gardner Williams. A vertical shaft is sunk in the vicinity of the
mine, and from this horizontal tunnels are driven into the pipe at
different levels separated by intervals of 40 ft. Through the blue
ground itself on each level a series of parallel tunnels about 120 ft.
apart are driven to the opposite side of the pipe, and at right angles
to these, and 36 ft. apart, another series of tunnels. When the
tunnels reach the side of the mine they are opened upwards and
sideways so as to form a large chamber, and the overlying mass of blue
ground and debris is allowed to settle down and fill up the gallery.
On each level this process is carried somewhat farther back than on
the level below (fig. 8); material is thus continually withdrawn from
one side of the mine and extracted by means of the rock shaft on the
opposite side, while the superincumbent debris is continually sinking,
and is allowed to fall deeper on the side farthest from the shaft as
the blue ground is withdrawn from beneath it. In 1905 the main shaft
had been sunk to a depth of 2600 ft. at the Kimberley mine.

For the extraction and treatment of the blue ground the De Beers
Company in its great winding and washing plant employs labour-saving
machinery on a gigantic scale. The ground is transferred in trucks to
the shaft where it is automatically tipped into skips holding 96 cubic
ft. (six truck loads