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  • Any rock derived from pre-existing rocks by mineralogical, chemical, and structural changes, essentially in the solid state, in response to marked changes in temperature, pressure, shearing stress, and chemical environment at depth in Earth's crust (for example, gneisses, schists, marbles, quartzites, etc.).
  • Said of an igneous rock composed chiefly of one or more ferromagnesian, dark-colored minerals in its mode; also, said of those minerals. The term was proposed by Cross, et al. to replace the term femag, which they did not consider to be euphonious. Etymol: a mnemonic term derived from magnesium + ferric + ic. It is the complement of felsic.
  • Naturally occurring molten rock material generated within Earth and capable of intrusion into surrounding rocks or extrusion onto the Earth's surface. When extruded on the surface it is called lava. The material from which igneous rocks form through cooling, crystallization, and related processes.
  • The Maquoketa Shale Group is Ordovician in age, with green to blue shale with limestone and dolomite beds in lower portion. The group has been eroded over part of northern Illinois, but underlies most of the rest of the state.
  • One of a series of somewhat regular, sharp, sinuous curves, bends, loops, or turns produced by a stream, particularly in its lower course where it swings from side to side across its valley bottom.
  • Crescent-shaped, swales and gentle ridges along a river's flood plain that mark the positions of abandoned part of a meandering river's channel. They are generally filled in with sediments and vegetation and are most easily seen in aerial photographs.
  • An era of geologic time, from the end of the Paleozoic to the beginning of the Cenozoic, or from about 248 to about 65 million years ago.
  • A naturally formed chemical element or compound having a definite chemical composition, an ordered internal arrangement of its atoms, and characteristic crystal form and physical properties.
  • A period of the Paleozoic era (after the Devonian and before the Pennsylvanian), thought to have covered the span of time between 354 and 323 million years ago; also, the corresponding system of rocks. It is named after the Mississippi River valley, where rocks of this age are well exposed. It is the approximate equivalent of the Lower Carboniferous of European usage.
  • A local steeping of an otherwise uniform gentle dip.
  • (a) A piece of unfractured bedrock, generally more than a few meters across. (b) A large upstanding mass of rock
  • A mound, ridge, or other distinct accumulation of glacial drift, predominantly till, deposited in a variety of topographic landforms that are independent of control by the surface on which the drift lies. (see also End Moraine)
  • The scientific study of form, and of the structures and development that influence form; term used in most sciences.
  • Cambrian sandstone with with a few thin red shale beds.