Formation of Sedimentary Rocks Sedimentary rock is rock formed from the bits of rock or sediments that are deposited and compressed. When wind, water, or ice erodes the surface of a mountain or rock it slowly chips away at the surface. Those bits of rock or sediments that have been chipped away are blown by the wind or floated down the river by a current. The sediments being transported are knocked around so much that by the time they reach their destination all those tiny grains are round. Eventually the sediments are deposited in a river bed or valley where the current or wind can’t push it around anymore. When the sediments are deposited by a river a sedimentary rock will begin to form. The layer of water and the top layer of mud press the bottom layers tightly together to form sedimentary rocks (Ortleb & Cadice, 1986).
Sedimentary rocks are classified by the sediments the rock is made up of. It is not hard to identify different types of sedimentary rocks. The sedimentary rock sandstone consists of sand size particles, usually of quartz and feels very gritty. Conglomerate is a mixture of finely-rounded pebbles (usually quartz) and tiny fragments of sand held tightly together. Shale is fashioned from tiny molecules of quartz and clay minerals under pressure. The type of sedimentary rock that is produced depends on how much pressure is on it and how much water is around the rock. Different pressure and water result in different rocks. About seventy-five percent of the earth’s surface is covered by sedimentary rocks. They are always steadily being formed, because the earth’s surface is constantly being eroded by wind, water, and ice and sediments are continuously being deposited and compressed into sedimentary rocks.
Bibliography
Ortleb, E., & Cadice, R. (1986). Geology-Rocks and Minerals. Dayton: Milliken Publishing Company.
Rhodes, F. (1991). Geology. New York: St. Martin's Press.