The deposits of the useful minerals & rocks; their origin, form, and content . f Reef Reef Series. The Main Reef Series is known for more than 80 km. along the the outcrop the mines become deeper as they go farther south, thoseat the outcrop being described as the outcrop mines, and those to thesouth as the deep-level mines. Among the latter, some in 1911 hadalready reached a depth of 1200 m., while others have been projected toa depth of 1800 metres. The gold content of the Witwatersrand conglomerates varies consider-ably at different levels. In the nei
The deposits of the useful minerals & rocks; their origin, form, and content . f Reef Reef Series. The Main Reef Series is known for more than 80 km. along the the outcrop the mines become deeper as they go farther south, thoseat the outcrop being described as the outcrop mines, and those to thesouth as the deep-level mines. Among the latter, some in 1911 hadalready reached a depth of 1200 m., while others have been projected toa depth of 1800 metres. The gold content of the Witwatersrand conglomerates varies consider-ably at different levels. In the neighbourhood of the surface, at adepth of d,bout 30-70 m., it is sometimes very high, such richness beingdue to cementation ; the Main Reef Leader where first worked yieldedat times as much as 6 ounces per ton, while from the Jumpers, specimensfrom the neighbourhood of the outcrop were so encrusted with fine goldthat assays of 600 ounces per ton were obtained. This cementation goldis completely crystalline, showing under the microscope well-definedVOL. II 2t 1156 OKE-DEPOSITS. Fig. 452.—Map of the Witwatersrand showing the outcrop of the banket reefs aud THE AUKIFEKOUS CONGLOMEEATES 1157
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