For purposes of geologic study, deposits of manganese oxides may be considered in two groups, as follows: (1) those derived from more or less localized masses of carbonate or silicate materials, generally with more than 5 per cent. manganese, that seem to have no relation to the surface of the earth; and (2) those originally deposited near the surface as localized bodies of oxides. Under the first group are zones of carbonate or silicate rocks in contact with intrusive igneous rocks, such as are found in Brazil and India. These zones contain manganiferous carbonates (mixed with iron, lime, and magnesia); and silicates (spessartite or manganese garnet and piedmontite or manganese epidote and possibly rhodonite, or manganese pyroxene). By the weathering of such rocks, large bodies of high-grade oxides have been formed. Manganese also occurs in fissure veins or the adjacent wall rocks in regions that have been intruded by igneous rocks. The veins commonly contain rhodochrosite, manganiferous siderite, or rhodonite, associated with quartz and metallic sulphide minerals, including alabandite, the sulphide of manganese. Such veins are known in Philipsburg and Butte, Mont.; Silverton, Colo., and elsewhere. In such regions if the wall rocks adjacent to fissures are limestone or dolomite, they may be extensively replaced by manganiferous siderite or other carbonates which on weathering yield large bodies of manganese oxides, locally mixed with iron oxides. Such bodies are known at Leadville, Colo. The manganese existing in sediments, notably clayey, but in part carbonate, may migrate locally after the sediments are slightly buried and form zones of manganiferous carbonate and silicate concretions parallel to the bedding. Where, as in the Batesville district, Arkansas, these zones are exposed by erosion, the manganese is further concentrated as masses of oxides in residual clay. Metamorphic rocks, such as slates and schists, here and there, as in Spain, Newfoundland, California, and Washington, contain extensive lenses of rhodonite or other silicate with or without rhodochrosite, roughly parallel to the bedding. The origin of these lenses, which are generally rather remote from igneous intrusions, is obscure. Some are considered to be materials laid down during sedimentation, others are thought to represent concentrations effected during metamorphism when the sediments were deeply buried. In the second group mentioned above (manganese deposits first concentrated near the surface as oxides) are included extensive deposits of oxides interbedded with marine sediments, as in the Caucasus region, Russia. Others interbedded with volcanic material, tuffs and flows, are known in the Mediterranean region and in Chile. In India important beds of oxides are interbedded with quartzite and slate.