Glacial erratics are fragments of
rock, often boulders like this one, that were eroded from the bedrock
at one place and transported to another place by a glacier.
Erratic boulders can be one of many different kinds of rock. This
particular boulder is the kind of metamorphic rock called gneiss (a
German word pronounced "nice"). It was eroded from somewhere in
Ontario, Canada, and deposited here in Richland County when the ice
carrying the boulder melted. Not only this boulder, but most of
the gravel, sand, silt, and clay that make up our "soil" was also
carried from locations north of Richland County by a glacier.
The responsible glacier was the Laurentide Ice Sheet that flowed from
Canada and at times covered most of Ohio (except part of the
Appalachian Plateau in the southeast part of Ohio) during the Great Ice
Age or Pleistocene Epoch (1.8 my to 10,000 years ago). It has
been estimated that the ice sheet might have been as much as a thousand
feet thick in central Ohio and probably more than two miles thick where
Hudson Bay is located.
-- David Nickey
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