Henry Alexander Miers,
1911 Encyclopædia Britannica
(1911)
“ In a very few years, however, the open pit mining was rendered impossible by the mud rushes, by the falls of the masses of barren rock known as “reef,” which were left standing in the mine, and by landslips from the sides, so that in 1883, when the pit had reached a depth of about 400 ft., mining in the Kimberley crater had become almost impossible. By 1889, in the whole group of mines, Kimberley, Dutoitspan, De Beers and Bultfontein, open pit working was practically abandoned. Meanwhile mining below the bottom of the pits by means of shafts and underground tunnels had been commenced ”
