Iron ores are associated with many different classes of rocks--sedimentary, igneous, and metamorphic. Where associated with sedimentary rocks the ores may be the result of direct sedimentation or may be later replacements of sedimentary beds by magmatic or meteoric iron-bearing waters. Many iron-ore deposits associated with sedimentary rocks are formed by the enrichment of original iron-bearing beds, either by solution and transportation of iron compounds or by the removal of other associated mineral constituents. Among those important iron-ore deposits of sedimentary origin that have undergone little or no further enrichment since deposition, except perhaps directly at the surface, are the iron ores of the Clinton type of the eastern United States, the Wabana iron ores of Newfoundland, the “minette” ores of the Lorraine district in northern France, Luxemburg, and southern Germany, the oolitic siderite beds of the Cleveland district in northern England, and the hematite ores of Minas Geraes in Brazil. The most important of the sedimentary iron ores that are the result of further enrichment since deposition are those of the Lake Superior district in the United States. Iron ores associated with igneous rock are mostly of deep-seated origin, usually having been formed by solutions that accompanied or followed the intrusion of the rocks with which the ores are associated. These ores are of two main classes: (1) Those associated with siliceous igneous rocks; and (2) those associated with basic igneous rocks. The ores associated with siliceous igneous rocks consist either of hematite or, more commonly, magnetite. They occur in granite, syenite, and monzonite, and in gneiss derived from these by metamorphism. Many important ore deposits in different countries belong to this class, among them being the magnetite and hematite deposits of Swedish Lapland and of central Sweden, the magnetite bodies of the Adirondacks and northern New Jersey in the eastern United States, various magnetite and hematite bodies in California and elsewhere in the western United States, the mixed hematite and magnetite deposits of the south coast of Cuba, most of the iron-ore bodies of Chile, and the newly developed iron ores of Manchuria. As a class, the iron ores associated with siliceous igneous rocks rank next in importance to iron ores of sedimentary origin. Iron-ore deposits associated with basic igneous rocks are nearly all of a distinct type known as titaniferous magnetites. These ores consist of a mixture of magnetite and ilmenite in varying proportions, and therefore carry a variable amount of titanium. Many large ore deposits of this class are found in different parts of the world, among the larger ones being certain ore bodies in Wyoming, in the Adirondack region, and elsewhere in the United States, and several deposits in Norway and in northern and southern Sweden.