Timbering Tunnels.
thiough
this loose reef, and the blue ground, which has been cut off and buried
by debris, is taken out; but it is sometimes left for those working the
next level below to extract.
After
the first " cut" near the rock is worked out, another cut is made, and
in this manner the various levels are worked back, the upper level in
advance of the one below, forming terraces as shown in section on page
320. In De Beers mine there are now eleven levels on which work is
progressing, commencing at the depth of 1280 feet and extending down to
the 1720-foot
