Abstract: The Moore Hill fault system in the central part of the Kentucky-Illinois fluorspar field is about 26 miles long. Fluorspar has been produced from a part nearly 5 miles long, and since mining began in 1899 this system has yielded more than 300,000 tons of fluorspar. Lead and zinc sulfides commonly are found in the ore, but only rarely do they occur in sufficient quantity to be worth recovering. The productive part of the fault system was mapped and the properties and principal mines described. The high-angle normal faults of the system cut limestones, sandstones, and shales of Mississippian age. Stratigraphic displacements range from less than a foot to as much as 550 feet. The fluorspar bodies are sporadically distributed in veins of calcite and fluorite along the faults.