Saturday, December 15, 2012

Stories rocks tell

I went for a hike at the Mohonk Preserve yesterday since I had no final exams scheduled (it was the day the English department did all of their group finals).  One of my courses, Physical Geology had finished the day before and was already graded so it was nice to be able to take advantage of the relatively nice day here in the Hudson Valley (mid-40s and sunny - not bad for mid-December).

For those familiar with the Preserve, I hiked up from Clove Chapel to Copes Lookout and back.  Not sure of the mileage, but it's a 1,000 foot or so elevation gain which makes for a little exercise.  On the way, I was thinking how one of the goals of my geology courses is to teach students how to see (that's why field trips are so important in geology).

This for example:

To most people, it's just a rock sitting in the woods.  Kids usually like rocks like this because they're fun to climb up and sit on the top.  To a geologist, however, it's a glacial erratic.  An out-of-place rock.  How did this boulder come to be sitting atop the bedrock out here in the woods?  No one placed it here.  Geologists know that this rock was once entrained within glacial ice during the last ice age and dumped here when the ice melted.

While hiking up the bedrock ledges, some people might notice that the rock, in places, is smooth and polished making for slippery footing when wet or icy.

Geologists, however, see glacial polishing and striations.  The rock was polished and scratched, not by ice, but by the rocks and sediment picked up and trapped within the glacial ice as it relentlessly slid southward during the great Pleistocene ice age.

Similarly, these little fractures would probably go unnoticed by most people walking past them on the trail.

But a geologist like me would utter "chatter marks" and get out their camera to snap a picture envisioning, in their mind's eye, a larger rock at the bottom of the glaciers skipping and chipping along the bedrock as the ice rode over it so many years ago.

When you take a geology course, those gray rocks start catching your eyes and telling stories.

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