246 THE DIAMOND MINES OF SOUTH AFRICA the life of these shafts must be very short. Preparation was therefore made for future work by sinking shafts outside the margin of the open mine, and at sufficient distance from it to insure them against any probable caving of the surface ground in their vicinity. Vertical shafts were sunk by the Central and French companies, and tunnels driven from them. The plan of Kimberley mine, 1883, shows these tunnels.
	Before describing the subsequent application of engineering science to underground mining, it is desirable to trace the prog­ress of the other mines on the fields to the period in develop­ment reached by the leader. The claim-owners in De Beers mine profited greatly by the object lessons given in the opening of the great pit of Kimberley. For the first twelve years after the discovery of the mines, the Kimberley mine ran far ahead of the others from the superiority of its yield for some distance below the surface. The fatal error of the neglect of the claim-