130	PRECIOUS STONES.
	began to give trouble in the wet weather, its absence in the dry season being equally troublesome. These difficulties were overcome by the gradual combination of the workers, and finally the whole group passed into the hands of the De Beers Company, whose great capital has enabled work to be carried on in a scientific way. At present in the Kimberley mines the blue ground is worked by shafts sunk in the solid Karoo beds, from which levels run out to cut the pipe. The blue ground so obtained is laid out on depositing floors of large area; on these, the blue ground spread out to a depth of 30 inches or so, crumbles down under the influence of atmospheric changes, the process requiring from a few months to two years, the resistance of the material varying in different mines, and in different parts of the same mine even. Any material which does not soften under this treatment is disintegrated mechanically. The broken down material is next washed and concentrated in machines somewhat like the "buddies" and "jiggers" of metalliferous mines, advantage being taken of the higher specific gravity of the Diamond to separate it from the lighter minerals, though several of its associated minerals being of nearly as great, or in some cases greater, density, remain with it; from such the Diamond was till recently separated by hand, the washed gravel being fed on to a long shallow trough lined with zinc, and having a slight slope. The gravel reaching the table at the higher end along with a stream of water was moved along by the sorters standing at the side by means of small flat pieces of thin metal, and any gems picked out and placed in small dishes, according to their kind and quality. Great dexterity was shown in this sorting and a remarkable