Page:Popular Science Monthly Volume 41.djvu/474

458 1s. 6d., and the natives 3d., per carat. Nearly double these amounts are paid for stones found in the mines.

Mr. Gardner Williams, the eminent mining engineer who occupies the important post of general manager to the De Beers Company, was kind enough to accompany me all over the mines, and to explain in detail the method of operation. The De Beers and the Kimberley mines are probably the two biggest holes which greedy man has ever dug into the earth, the area of the former at the surface being thirteen acres, with a depth of 450 feet, the area and depth of the latter being even greater. These mines are no



longer worked from the surface, but from shafts sunk at some distance from the original holes, and penetrating to the blue ground by transverse drivings at depths varying from 500 to 1,200 feet. The blue ground, when extracted, is carried in small iron trucks to the "floors." "These are made by removing the bush and grass from a fairly level piece of ground; the land is then rolled and made as hard and as smooth as possible. These 'floors' are about 600 acres in extent. They are covered to the depth of about a foot with the blue ground, which for a time remains on them without much manipulation. The heat of the sun and