Weekly Gem #50 Have a gneiss day
Location: This 'hidden gem' is about half a mile southeast of Huntersville, WV, on the south side of highway 39 (see Clue Me! map). Some people take it for granite ... but anyone worth their basalt will appreciate the amazing sequence of events that created this formation, and made it visible. Consider the history of our interestingly shaped rock:
It started as sand piled up around 450 million years ago. Maybe it was a nice beach, where some sea scorpions would hang out. The sand was gradually buried and compressed until it first became sandstone (with individual grains) and eventually was far enough underground that the heat changed sandstone to quartzite (has an interlocked crystal structure, that is much harder than sandstone).
Time passes. Continents drift. Chunks of the earth's crust swoop in from the southeast, pushing with incredible force into this area. Oh look! Here comes Africa!
Africa arrived about 200 million years after the sea scorpions moved on. In fact, the Atlas Mountains in Morocco are second cousins, twice removed, having originated in the same location as the Appalachians (see how they attach in this map of Pangaea).
Africa stayed for a good while, then drifted east. The Devils Backbone remained well underground for another 200 million years, until the Appalachian mountains rose again (the previous mountain ranges that formed here, as high as the Himalayas, were eroded away, leaving a flat plain). Roughly 50 million years ago, the entire area lifted.
Presumably because of millions of years of pressure from the Southeast, the hard quartzite got stacked and pressed into perpendicular rows, running roughly NE to SW. As the geology lifted, hard metamorphic rocks, like quartzite and gneiss, were left behind and softer rocks eroded away. Zoom out on the map, using satellite view, and you can see the ridges formed by the metamorphic rock, separated by valleys where softer rock used to lie. These run from central Pennsylvania to Birmingham, Alabama. Notice the massive curves where entire sections of crust bent while they were deep enough underground to behave like taffy. Then it all lifted at the same time (geologically speaking), and those curves remained.
Now, the last piece of the puzzle. The only reason we see this particular rock is that there was some sort of a weak spot way back when. Knapp creek mostly runs 'with the grain' of the Appalachians, but at this spot it runs 'across the grain.' 50 million years ago it found a crack, cut across the quartzite, and has been carving away ever since. This is one of the few naturally occurring east to west slices across an Appalachian mountain ridge, and it's this slice across the ridge that allows us to see the Devil's Backbone.
For those who weren't attuned to these amazing facts at first, we'll just chalk it up to experience, and let them start with a clean slate.
Here's the hidden gem entry from our Clue Me! map.
All bent out of shape.
Devil's Backbone (Huntersville Anticline)
Why It's Interesting
This is a great example of how rocks can bend. This rock was folded as the mountains formed. Have a gneiss day!