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.