tailieunhanh - Encyclopedia of Global Resources part 102

Encyclopedia of Global Resources part 102 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 938 Placer deposits Global Resources mizing the yield per hectare of wooded land. He built a strong . Forest Service financed in part by the sale of mature timber. He actively opposed the institution of national parks to be used for recreation considering them a waste of natural resources. After leaving the . Forest Service Pinchot became active in the Progressive Party founded by supporters of Theodore Roosevelt. Pinchot became chief forester of Pennsylvania in 1920 and he campaigned for and won election as governor of Pennsylvania in 1923 and again in 1931. Donald R Franceschetti See also Conservation Forest management Forest Service . Leopold Aldo Roosevelt Theodore. Placer deposits Categories Geological processes and formations mineral and other nonliving resources Placer deposits are mechanical concentrations of debris weathered out of rocks. Commonly economically important minerals have higher densities so they are concentrated as the lighter-density minerals are winnowed out by the action of water or wind. Background Placer deposits are found throughout the world wherever the mechanisms of concentration water and wind have been active and the resulting concentrates have not been redispersed by later processes. The best known types of placers occur in river channels and in beach sediments. The weathering and erosion of rocks release particles of varying size shape and density. Soluble materials are dissolved and removed in surface water or groundwater. Some minerals such as feldspars are hydrated and converted into clay minerals which being soft small and of low density are relatively readily removed in suspension. Quartz SiO2 common in many kinds of rocks generally weathers out as roughly equant grains that because of their hardness and insolubility wash into streams and rivers where they are moved by rolling bouncing and pushing along toward the oceans. The abundance of quartz and its resistance to mechanical and chemical weathering results in its