#79 Rocking Around Charlottesville
This show originally aired on March 6, 2008 on “The Rivanna Rambler,” a weekly public affairs show airing every Thursday at 11:55 a.m. on WTJU 91.1 FM or wtju.net.
March 6, 2008
It’s a whirlwind geologic tour of the Virginia, and it all takes place within five square miles in Charlottesville. We’re a group of Rivanna Master Naturalists, standing before a rock outcrop that borders the rough boat launch into Ivy Creek just upstream of the Woodlands Road bridge. Tom Biggs, Professor of Geology at UVA, invites us to use the rock hammers he’s brought along, stepping forward himself to take a swing. A chunk of rock cleaves off, dropping into his practiced hand.
This is an outcrop of the Lovingston formation, a high grade metamorphic formation of foliated feldspars and granites that represent some of the oldest rocks in Virginia. It’s what geologists call the basement or foundation of Virginia, laid down when the first major mountain-building event called the Grenville orogeny took place some 1.2 billion years ago. We’re being encouraged by Tom to take a closer look, so we pull out our loops –those clever magnifying lenses that you flick open from their protective cases into the crook of your index finger.
Bringing lens to eye, and rock to lens, ,we look for the pattern of alignment that indicates it’s gneiss. Gneiss with a “g”. that is, the name for a type of metamorphic rock that generally has visible grains of feldspars, that group of silicates that predominantly makes up the crust of the Earth. There’s something about holding a rock in your hand and knowing it is literally as old as the hills that inspires an appropriate pause.
Tom has spread open a colorful map of the geology of Albemarle County, the most recent one available, published by Wilbur Nelson in 1962, and likely based on research done in the 50’s when plate tectonic theory was just emerging. Needless to say, it is out of date. It’s not that rocks have changed so much in the fifty odd years since that this map has been produced, but research by geologists has certainly rendered some of the theories about these rocks obsolete or, at least, questionable.
Each rock type – by formation - is given its own color, and this two-dimensional map shows the predominant type in a given location down to a depth of several thousand feet and in many cases much deeper. Cross sections along various transects enhance the story of the land, revealing the great folding anticlines and synclines that resulted from the major mountain building events on the east cost of North America. My three-dimensional visualization skills are not the best, so I keep referring to the variety of views and draw sketches in my book, hoping I’ll make better sense of it during my review later on. The repetition helps, and Tom is generous with his knowledge with us Master Naturalists-in-training.
As Master Naturalists, we’re joining a statewide corps of volunteers that is provides education, outreach, and service, extending the reach of the various state agencies. Like Master Gardeners, once trained and certified, we’re required to volunteer in the community by giving trainings, or helping in restoration work, or offering our time to citizen science projects. But for now, we’ve got a whole lot of information coming in with weekly class time and field trips with specialists like Tom, whose disclaimer is familiar, when he tells us, “In these three hours, you’ll be getting an overview of what I teach in a semester to my freshmen.” Fortunately, the study of natural history can be life long – and these classes are designed to impart basic information, but more importantly, to instill practices that will help us learn how to learn and to see and appreciate with new eyes our natural community.
This morning, we make four more stops around the city looking at distinct formations, ending up at the Forestry Building off of Fontaine Avenue, where a rock garden” hosts 49 good sized rocks from all over the state, all numbered and labeled. Something tells me I’ll be back to take a second look at these rocks as I piece together my understanding of the story in then rocks.