bedrock. Solid rock that has been unaffected by the processes of weathering. continental drift. The very slow movement of the continents on their underlying plates. See also plate tectonics. mineral. A naturally occurring, inorganic substance. It can be in the form of a chemical element or a compound which has a distinctive chemical composition and therefore predictable chemical properties. Examples of minerals are bauxite, diamond, gold, tin, and salt. ore. A natural mineral aggregate, especially one that is mined to extract minerals. plate tectonics. The theory that the Earth's surface is made up of huge plates that have moved very slowly during geological history, and continue to move, thus changing the position of continent and oceans. The plates are about 100 kilometres thick and move at a rate of about 1-12 centimetres per year. (See also continental drift.) water table. The top level of water in the ground that occupies spaces in rock or soil and lies above a layer of impermeable (non-porous) rock. When the water table rises about ground level a spring, lake or wetland is formed.
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Posted July 1998.
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