Deprived of the support of the hard blue ground, the walls of the mine tended to collapse, and additional trouble was caused by the underground water that percolated into the mine. By the end of 1883 the floor of the Kimberley mine was almost entirely covered by falls of ‘reef’ (Plate XVIII), as the surrounding rocks are termed, the depth then being about 400 feet (122 m.). In the De Beers mine, in spite of the precaution taken to prevent falls of reef by cutting the walls of the mine back in terraces, falls occurred continuously in 1884, and by 1887, at a depth of 350 feet (107 m.), all attempts at open working had to be abandoned. In the Dutoitspan mine buttresses of blue ground were left, which held back the reef for some years, but ultimately the mine became unsafe, and in March 1886 a disastrous fall took place, in which eighteen miners—eight white men and ten Kafirs—lost their lives. The Bultfontein mine was worked to the great depth of 500 feet (152 m.), but falls occurred in 1889 and put an end to open working. In all cases, therefore, the ultimate end was the same: the floor of the mine became covered with a mass of worthless reef, which rendered mining from above ground dangerous, and, indeed, impossible except at prohibitive cost. It was then clearly necessary to effect access to the diamond-bearing ground by means of shafts sunk at a sufficient distance from the mine to remove any fear of falls of reef. For such schemes co-operative working was absolutely essential. Plate XIX illustrates the desolate character of the Kimberley mine above ground and the vastness of the yawning pit, which is over 1000 feet (300 m.) in depth. [Illustration: _PLATE XIX_ KIMBERLEY MINE AT THE PRESENT DAY] [Illustration: _PLATE XX_ WESSELTON (_open_) MINE] A certain amount of linking up of claims had already taken place, but, although many men must have seen that the complete amalgamation of the interests in each mine was imperative, two men alone had the capacity to bring their ideas to fruition. C. J. Rhodes was the principal agent in the formation in April 1880 of the De Beers Mining Company, which rapidly absorbed the remaining claims in the mine, and was re-formed in 1887 as the De Beers Consolidated Mining Company. Meantime, Barnett Isaacs, better known by the cognomen Barnato, which had been adopted by his