Hall: A gniess geological guide through the rocks of ages
Sunday, July 17, 2016
Aren’t the rocks in North Carolina good enough?
That was the question I had when I came across a NC home-school group traveling to West Virginia last month for a geology field trip.
The answer I got, from geologist Rob Greenberg of the Hawbridge School in Chapel Hill, conceded that the surface rocks in southeastern West Virginia and the surface rocks in western North Carolina are really not all that different from each other.
They were laid down in the same ancient seas from the same types of ancient marine dirt and debris, then deformed by the same brutal forces of continents slowly smashing together. If anything, the fossils in the North Carolina rocks are older.
But here in the 21st century, in the Holocene Epoch, a sunny day in West Virginia can be quite lovely, and I tagged along.
My own early experience with rocks had mainly been in trying to avoid them, or at least one, when sledding as a child in New York State. The same Appalachian rocks that ground West Virginia and North Carolina share a history with the Catskill Mountains, but in New York the now-gone glaciers left behind a mess of erratic rubble.
The profuse Catskill rocks are loathed by both gardeners and sledders bowled over by boulders. Our family garden sprouted nice broccolis and gniess breccias from the same packet of seeds. Out back we had a great sledding hill: long and steep and sometimes snow-covered into May, but it ended at a rock the size of a bus. OK, a small bus. Steering was not much of an option, so sledding was an act of tilt and terror.
Perhaps in West Virginia I could make peace with the rocks.
The group — it doesn’t have a name; I stumbled upon it when Googling “geology field trips” — originated with home-schoolers, but has evolved into a clast of rock hounds and geophiles accompanying the occasional youngster. Exploration has taken them all over the state and beyond, observing road cuts and stream cuts and ancient flood streams, piecing together the history of a place from the scars of the soil.
This trip, which included three of us from Greenville, was to examine the large folded mountains leading westward from Minnehaha Springs, W.Va., to the Greenbrier River, and farther west to the Alleghany Front, using rock hammers and chisels and magnifying lenses to peer into the past.
The Appalachian Mountain folds, Greenberg explained, are continental wrinkles squeezed up as the ancient North American continent collided with the ancient African continent 450 million years ago. Like a stack of newspapers squeezed edge toward edge, rock layers that had lain flat at the bottom of those long-ago seas buckled, leaving a dramatic fold in the storyline. The wrinkles are visible from above in a Google Maps satellite image, and from the side, at road cuts and streams.
The landforms in Greenville, by contrast, are relatively young. Layers of beaches and mountain runoff lie atop ancient bedrock that was gently squeezed 250 million years ago into small folds a thousand feet below the topsoil, folds so small they don’t break the surface in a road cut or river bend.
In West Virginia, shale that formed beneath the oceans in a time when the dry land was still barren accumulated shell and coral and, later, leaf fossils, many of which were identified by geologist Mary Watson, a rock star from Central Carolina Community College.
At a time 200 million years before the dinosaurs, she said, the climate was different and the configuration of the continents was different and the living species were different, but the processes of earthquakes and volcanoes and floods and erosion were the same as now, here in the Holocene, here in West Virginia and back home in North Carolina.
Timing is important, even on geological scales. Had we ventured out just a week later, we would have seen geologic processes at their worst. Five days after our exploration, the Greenbrier River, along whose banks and tributaries we had looked for evidence of multi-million-year-old floods, flooded again from a 10-inch deluge of rain that flashed down the mountain folds and killed 24 people, here, in the twenty-first century, in the Holocene Epoch.
Joy Moses-Hall teaches physics and astronomy at Pitt Community College. She has a PhD in oceanography and is the author of the novel Wretched Refuge.