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322 THE DIAMOND MINES OF SOUTH AFRICA
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level.
At Kimberley mine nine levels are being worked, from the 1840-foot to
the 2160-foot level inclusive. The galleries are not supported in any
way by timbers, but all tunnels in soft blue
ground are timbered with sets of two props and a cap of round timber, and are covÂered with inch and a half lagging.
Soft
blue ground is drilled with long jumper drills sharpÂened at both ends.
In hard blue ground, drills and single-hand hammers are used. The
native workers become very skilful in both methods of drilling, and do
quite as much work as white men would do under similar conditions.
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