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170
THE DIAMOND
and covers the stratum of diamondiferous material at the bottom. The water is carried up by a chain pump of bowls operated by hand, and the diamond-bearing earth is hoisted in baskets by a pulley to the surface. A hole in the wall of the pit near the bottom affords shelter for the overseers set to watch the miners. When prase is found in abundance it is regarded as a sure indication that the yield of diamonds will be more than ordinarily good.
A few miles northeast of Panna, the geological con­ditions are more favorable for mining. The overlying stratum is a firm rock of Rewah sandstone which permits considerable tunneling in the underlying diamond-bearing stratum, from the bottom of the pits.
These mines of the northern spur of the Panna group reaching toward Allahabad are all at some depth, except those at the extreme eastern end of it, where the diamond-bearing stratum is a sandstone conglomerate which crops out to the surface. To the south are two waterfalls which carry .diamondiferous material from the stratum situated above, to the valley of the Baghin river below, where the diamonds are collected from the sands.
There is a mine southwest of Panna, abandoned some years ago, though it is believed to contain many diamonds yet, which illustrates the first idea the African diamond miners had of the chimneys there, before they under­stood their volcanic nature. It lies in a great conical ba­sin in the sandstone, several hundred feet in diameter and about ioo feet deep. The basin is partially filled with a green mud covered by a deposit of calcareous tufa. It has been worked to about half the depth, and it is claimed that the yield increases with the depth.