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  • Lower limit of erosion of the land's surface by running water. Controlled locally and temporarily by the water level of stream mouths emptying into lakes, or more generally and semi-permanently by the level of the ocean (mean sea level).
  • The solid rock (sedimentary, igneous, or metamorphic) that underlies the unconsolidated (non-indurated) surface materials (for example, soil, sand, gravel, glacial till, etc.).
  • The suite of mostly crystalline igneous and/or metamorphic rocks that generally underlies the sedimentary rock sequence.
  • A topographic or structural low area that generally receives thicker deposits of sediments than adjacent areas; the low areas tend to sink more readily, partly because of the weight of the thicker sediments; the term also denotes an area of relatively deep water adjacent to shallow-water shelf areas.
  • Bed
    A naturally occurring layer of earth material of relatively greater horizontal than vertical extent that is characterized by physical properties different from those of overlying and underlying materials. It also is the ground upon which any body of water rests or has rested, or the land covered by the waters of a stream, lake, or ocean; the bottom of a stream channel.
  • A drainageway eroded into the solid bedrock beneath the surface materials. It may be completely filled with unconsolidated (non-indurated) materials and hidden from view.
  • A calcarenite containing abundant fossils or fossil fragments.
  • A low-gradient, low-volume stream flowing through an intricate network of interlacing shallow channels that repeatedly merge and divide, and are separated from each other by branch islands or channel bars. Such a stream may be incapable of carrying all of its load. Most streams that receive more sediment load than they can carry become braided.
  • The Burlington Limestone is named for the city of Burlington, Des Moines County, Iowa, where the formation is well exposed and about 70 feet thick. In Illinois, the Burlington extends from Henderson County in the northwest across a roughly triangular area southward to Jackson County and eastward to Iroquois County. Good outcrops are found in the Mississippi River bluffs from Quincy, Adams County, to near Alton, Madison County. In the vicinity of Quincy the lower 25 feet is relatively pure and is quarried as the "Quincy Lime." In the southern area the Burlington and the overlying Keokuk can be distinguished only by their fossils and are generally referred to as the Burlington-Keokuk Limestone.