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Platteville Limestone
The Platteville Limestone is the Ordivician limestone formation in the sedimentary sequence characteristic of the upper Midwestern United States. It overlies the thin Glenwood Shale, which overlies the thick Saint Peter Sandstone.〔Mossler, J. and Benson, S., 1995, 1999, 2006, (Fossil Collecting in the Twin Cities Area ). Minnesota at a Glance: Minnesota Geological Survey: University of Minnesota.〕 It is shot through with dolomitic mottles in an anastomose pattern; this dolotimization occurred after deposition but prior to the development of joints in the rock.
This difficult-to-erode unit forms the cap of Saint Anthony Falls and the Mississippi River bluffs in most of the Twin Cities area. Sea life was abundant during the Ordivician Period and a large number of marine fossils including corals, bryozoans, brachiopods, clams, snails, cephalopods, and trilobites can be found in the limestone sediments at several areas in the Twin Cities and along the Mississippi River at Minnehaha Falls park and elsewhere.〔〔ftp://mgssun6.mngs.umn.edu/pub2/mnglance/Mn_Precambrian.pdf〕〔http://www.sciencebuzz.org/blog/collecting-fossils-minnesota〕
==Building material==
Many early stone buildings in Minnesota were constructed with this material, which often was quarried at the site.〔(Ancient Tropical Sea ) Minnesota historical society〕 It can often be seen in older neighborhoods as the foundation for a building or a retaining wall. A notable existing example is the Nicollet Island Inn in Minneapolis.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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