Besides the classes of iron ores already mentioned, widely distributed iron ores occur as residual products derived from the weathering of either igneous or sedimentary rocks. These ores have been formed by the concentration of iron-bearing materials originally disseminated through the rocks whose weathered products they now constitute. They are mainly in the form of limonite and occur either as large bodies of relatively pure ore or as aggregates of irregular masses of various sizes imbedded in clays. To this class belong the brown iron ores associated with clay in the Appalachian region of the United States, the limonite ores of parts of Russia, and similar ores in Korea. In this class should also be included the extensive limonite deposits derived from the weathering of serpentine which have recently been developed along the north coast of Cuba, as well as the lateritic iron-ore deposits found in many tropical countries. Limonite ores associated with clays have been smelted since early ages, owing to their accessibility and the ease with which they could be smelted by crude methods. They have, however, furnished a decidedly minor percentage of the world’s production of iron ore. GEOGRAPHICAL DISTRIBUTION The iron ore consumed by the world has been obtained principally from the four great iron-producing countries: United States, Germany, France and Great Britain. Other countries that yield important quantities of iron ore are, in the order of their importance: Spain, Russia, Sweden, Luxemburg, Austria-Hungary, Cuba, Newfoundland, and Algeria. The normal annual output in each one of these countries is more than one million tons. Minor amounts of iron ore are produced in many other countries. TABLE 11.--IRON-ORE OUTPUT OF PRINCIPAL PRODUCING COUNTRIES, 1910-1917, IN GROSS TONS[12]