1 December 2023

Friday fold: a Massanutten cross-section from a century ago

Posted by Callan Bentley

Happy Friday, friends!

Here’s an image I came across this week while searching for something else. It’s from a 1935 issue of The Virginia Teacher that describes the geology of the Massanutten mountain system for the benefit of students at James Madison University (then the State Teachers College at Harrisonburg) climbing the mountain on the weekends. The breezy article includes several illustrations, but I was particularly taken with this one, a modified reproduction of a 1929 sketch.

Here it is:

I’ve written a lot here about the geology of Massanutten, having lived in the depths of its differentially-eroded doubly-plunging synclinorium for 8 years. But this was the first time I’d seen this image. I like how it puts emphasis on the lower elevation of the Page Valley (right/east) relative to the Shenandoah Valley (left/west). I also note the overturned strata in the furthest east (right) position, something I’ve also documented on this blog.

The article accompanying the sketch describes the ridge forming layer as the Tuscarora (rather than the Massanutten Sandstone), which is out of vogue these days (but I think ultimately correct). In terms of interpretation and elucidation, one thing the article did really well was emphasize that though the entire Great Valley is a vast syncline in structure, and Massanutten Mountain is the deepest part of that structure, and those brings the youngest strata (Tuscarora/Massanutten) to the lowest level anywhere along the strike of that Great fold. Ironically, this results in the highest topographic elevations along the Great Valley, because of the Masscarora’s terrific resistance to weathering and erosion.

That Tuscanutten is really somethin’!