Closely related to the replacement deposits are the contact metamorphic deposits, the fifth type. These only recently have begun to be of commercial importance, but promise to be among the greatest, if not the greatest, producers of this country and possibly of other countries. They are of the familiar kind--limestones or limey rocks which have been invaded by granites bringing large quantities of watery or gaseous solutions of silicon, iron, aluminum and magnesium, with less chlorine, fluorine, potash and sulphur, and, in this case, tungsten. In the Great Basin broad areas of limestone, extending from northwestern Utah to the Sierra Nevadas and around their southern extremity, have been thus intruded and metamorphosed. Some large deposits of scheelite have already been exploited in the region and others remain to be worked. Similar deposits occur in Korea, Japan and Tasmania, and probably exist, though as yet undiscovered, in China, the Malay Peninsula and other countries. The tungsten mineral in such deposits is invariably scheelite. Placers, the sixth type, are formed from all grades of deposits, but their value depends largely on local conditions. They are both residual and fluviatile deposits and have been large producers of tungsten minerals, especially of wolframite. A very large proportion of the Burmese output has been from semi-residual and stream placers, and the Chinese output in 1918, the largest ever made by any country in one year, was almost wholly from placers. GEOGRAPHICAL DISTRIBUTION The distribution of tungsten ores is far from being as wide as the distribution of the granitic rocks, and some regions with large areas of granite have almost no tungsten minerals. Among such regions are the Scandinavian peninsula, large stretches of Canada, the eastern United States, and Brazil.