Thursday, August 1, 2013

Got Rocks

When we were searching for our retirement land, we had a list of prerequisites.  Since I was still employed, nearness to the job was at the top of that list.  My new found delight in piling field stones into walls mandated a generous supply of stones.  We found the last piece of an old farm that seemed to fill the bill.

Our gravel bank was likely opened to bury the remains of the barn that burned following a lightning strike more than half a century ago.  Before it was ours, town highway workers removed enough gravel each year to keep the face of the bank free of vegetation.  For the past two decades the only gravel removed was taken by me using hand tools.

How our gravel hill was left behind by the retreating glacier is a puzzle.  It is a rounded dome set in the middle of lower hummocky land.  Layers of fine black sand uncovered are not horizontal.  Most of what can be seen has tumbled down the slope so the actual layers remain hidden.  Fossils are common but exotic stones from far away are rare.

Our driveway needed more fill than could be hand shoveled from our bank.  Five miles upstream from us is home to a real gravel operation.  My interest in how these deposits were formed prompted an invitation from the owner to visit his site.  This location is near a long straight section of the Unadilla River.  This gravel was likely deposited in a depression between the remains of an ice tongue and the bedrock ridge.  Water trapped here allowed an occasionally gentle period of deposition.

This exposed face reveals horizontal layers of sand and clay.  Each must record different climate conditions that caused different volumes and speeds of meltwater.  The layer containing the rounded pebbles deserved closer examination but the exposed face is not stable.  My invitation to visit was based on the owner's belief that I was smart enough to stay out of trouble.  I love to visit this place, but I don't want to be buried here!

This area of New York State has not sparked much geologic study.  We lack the beautiful long lakes and waterfall filled glens that the glacier left behind to our north.  Our rivers are flat and muddy and our local stones are gray.  A metamorphic or igneous stone found here has been transported over great distance from its point of origin.  These exotics spark our interest.  We would like to know them by name and have some understanding of how they acquired their present form.  The pictured treasures were picked from the margins of the professionally operated gravel mine.

The white chunks pictured here are likely quartz while the rusty colored cement may be rich in iron.  The professional geologist that prepared the report to obtain state certification found some copper in the gravel.  Is it possible that this stone contains copper?

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