ing this are deep-red ferruginous slates 4000 ft. thick, in the middle of which is a conspicuously contorted bed made of hard ferruginous quartzites and crystalline iron ore. Above these comes a further band of quartzite, the Hospital Hill Quartzite, 1400 ft. thick, and above this the Government Reef Series, also composed of deep-red ferruginous slates, with three bands of quartz pelpbles, the Coronation Reef, the Government Reef Leader, and the Government Reef. These and the final bed of soft red slates, the "Red Bar", are some 6000 ft. thick. On the Red Bar rest the Upper Witwatersrand Beds, some 8000 ft. of quartzites with banket reefs. At the base are the Main Reef Series, consisting of usually four or five beds of banket, separated by quartzite; the North Reef and the Main Reef are low-grade ore, but above the last is the Main Reef Leader, which is the chief source of the gold on the Rand. Its thickness varies from 6 in. to as many feet, and is very variable, sometimes running with the Main Reef, at others separated by several feet of quartzite. The middle Reef and South Reef are low-grade bankets. Following the Main Reef there are some 1500 ft. of quartzite, and then comes a large number of small pebble reefs, called the Bird and Livingstone Series. Then follow some 1200 ft. of quartzites arid slates with the Kimberley Reef Series on top. This last series consists of over a hundred bands of pebbles arranged in parallel position in quartzite, the whole running to some 1800 ft. This whole system of Reefs (see fig. 52 at p. 94) runs for some 40 ml. east and west of Johannesburg, and from it more than 30 million sterling is extracted in a year. The beds dip steeply at the surface to the south, and in the deeper mines they flatten out and are supposed to come up again in a simple
