The Geology of Vermont

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geologic time

An example of Sedimentary Rock on the shores of Lake Champlain



            Before you learn about the way Vermont looks today, you should know about some of the geological forces that helped to shape the landscape.  The subject of geology is the scientific study of the Earth, its origins and evolution, the materials that make it up, and the processes that act on it. 


    To understand how and why parts of Vermont are different, you should first know the three basic rock types.  These types are igneous, sedimentary, and metamorphic rocks.


            Igneous rock is formed when magma, or molten rock, cools and hardens.  This cooling can take place at the surface of the earth or below the surface.  Granite is a good example of igneous rock.


            As rocks are exposed to rain, frost and wind, they begin to wear down.  This process is known as erosion.  Particles of rock, called sediments, are often carried by the flow of water, wind and ice.  Sediments can be sand, silt or pebbles.  As these particles settle they form layers of deposits.  Over time, tremendous pressure compacts and changes the particles to form sedimentary rock.  Limestone is a sedimentary rock that is very common around Lake Champlain.  Red sandstone, also a sedimentary rock, is common near Burlington.


            Rocks buried deep in the earth are exposed to intense heat and pressure.  The heat and pressure will change, or metamorphose, rock into a new form.  We call this type metamorphic rock.  Marble is the metamorphic form of limestone.  Slate is formed when layers of shale or mudstone are exposed to heat and pressure to form rock.


            Remember that geologic time is very long.  Many of these processes occur over thousands or millions of years.


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Exercise on the Rock Cycle

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