The sulphur salt dome in Louisiana is a typical Gulf Coast salt dome, but is exceptional in its small area, about 75 acres, in the very great thickness of the cap, about 1,000 feet, and in the richness of its deposit of native sulphur. The cap is composed of anhydrite and a mantle-like mass of "lime" rock covering the top and flanks of the anhydrite. The sulphur is found as a secondary mineral in the transition zone between the "lime" rock and the anhydrite and has probably been precipitated from hydrogen sulphide or metallic sulphides in solution. After a long history of vain expensive attempts to mine the sulphur, the Frasch process was perfected, by which the sulphur is melted in place and pumped in liquid form to the surface. The total production to date has been abou 9,000,000 tons of sulphur with a gross value of $150,000,000. Small amounts of heavy oil were encountered in the early sulphur wells, but not in commercial quantity. The flanks have not been well tested for oil.