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      Loess
      Loess is a fine grained deposit of wind-blown dust composed of angular unweathered grains of quartz, feldspar, and other minerals that are unconsolidated, but usually held together by calcerous cement.  Loess has a porosity often near 60%.  Deposits blanket hills and valleys downwind of glacial outwash and provide a source supply of fine sediment.  It is easy to dig into and has the peculiar ability to stand as a vertical cliff without slumping.

      During the glacial periods, the rivers that drained what now the mid-western United States transported and deposited vast amounts of glacial outwash.  Later, wind eroded silt and clay from the floodplains of the rivers and blanketed large areas of the midwest with the loess.  Loess is responsible for much of the region's agricultural focus and productivity, both in the past and today.

      Major loess deposits in the United States
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