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Paleo Slide Set: The Ice Ages
Erratic, Baffin Island, Nunavut, Canada.
In 1837 Louis Agassiz presented his theory that ice had covered much of the northern hemisphere. He based his theory on an abundance of observations made in Scotland, northern England, Scandinavia, Switzerland, France, Italy and northern North America, but the idea was not widely accepted. One observation that Agassiz attempted to explain with his ice-age theory was the presence huge boulders scattered across the landscape. Often these boulders rested atop bedrock of a very different composition; metamorphic quartzite on top of sedimentary limestone, for example. Such boulders, called erratics, were often found several kilometers from any other bedrock of their type. Clearly, something had lifted these enormous boulders and carried them tremendous distances. Agassiz theorized that these boulders had been trapped in enormous, moving ice sheets. When the ice melted, the boulders were dropped many miles from their origin.

Photo Credits:
John T. Andrews
INSTAAR and Department of Geological Sciences, University of Colorado, Boulder.
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Last Modified: 12 October 2001

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