Be Kind to Rocks Week

by Carl Strang

St. James Farm Forest Preserve has a scattering of stones, large and small, in its forests and open areas. Some of these are chunks of local Silurian dolomite bedrock that were gouged out by the most recent continental glacier. Others are glacial erratics, stones likewise left by the glacier but picked up by it where the bedrock was different. These generally source back to Canada. Though much of the glacier’s Lake Michigan Lobe route followed that lake bed, the bedrock there is a soft shale that the ice ground to clay, with occasional surviving pieces up to a couple inches across, but nothing that could be called a boulder.

Recently my eye was caught by a trailside erratic split by the temperature changes that the seasons bring.

This appears to be a rock type known as gneiss, which started out as granite but was subjected to stresses that altered its structure into a banded pattern. Such bedrock is common around the east end of Lake Superior, where our glacial lobe exited Canada.

This appears to be a rock type known as gneiss, which started out as granite but was subjected to stresses that altered its structure into a banded pattern. Such bedrock is common around the east end of Lake Superior, where our glacial lobe exited Canada.

There was no indication that the rock had been struck by anything to create the break. Freezing and thawing were sufficient. I photographed the rock and left it as is. A week later, passing that way again, I saw that someone had replaced the fragment.

Gravity works, and the pieces were fitted precisely, so a human agent is indicated.

Gravity works, and the pieces were fitted precisely, so a human agent is indicated.

So, what motivation are we tracking here? Was it simply a matter of orderliness? Or, did someone want to make sure that the fragment did not become someone’s souvenir? Or, was this putting-back-together an act of kindness to the rock? I am reminded of one of the most widespread traditional stories west of the Mississippi River, with every Native American tribe having at least one version, in which an animated rock teaches Coyote (or his trickster equivalent, depending on the version) a lesson of respect.

 

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1 Comment

  1. April 26, 2016 at 10:10 pm

    Thanks for this post. I’m going to have to read about gneiss now. I did not know the term or that this is how the banding was formed.


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