proved
that the levels were too near one another, and that galleries driven
full size from the offsets were difficult to maintain and unsafe for
the workmen.
The
heavy expense of sinking vertical shafts and driving tunnels through
the hard rock surrounding the mine had led to the adoption of inclined
shafts in order to reach the blue ground more quickly ; but, for
several reasons, these inclines were not adapted for the prosecution of
deep underground works. The chief defects may be briefly summarized.
They were difficult to maintain, as they were sunk obliquely through
the horizontal strata of the shale, which frequently gave way and
crushed the shaft timbers. Secondly, being inclined to the horizon (De
Beers 560, and Kimberley Standard Shaft 320) and situated not far from the margins of the mines, they soon reached blue ground,
