The Witwatersrand gold mines are a series of approximately forty gold mines situated in the Witwatersrand district of the Transvaal. The mining area runs roughly from east to west for a distance of about sixty miles. All the gold mines are what is known as ‘deep’ mines, the average working depth being well over 4,000 ft. below the surface. Some mines are considerably deeper, and a few are now working at a depth of approximately 7,000 ft. The Witwatersrand is situated at an elevation of between 5,000 to 6,000 ft. above sea-level.