Geology Assignment: Structural geology
Gettysburg NMP (1895):
• https://www.dcnr.state.pa.us/cs/groups/public/documents/document/dcnr_014596.pdf
• https://blogs.scientificamerican.com/history-of-geology/geology-and-generals-howgeology-influenced-the-gettysburg-campaign-part-i/
• https://blogs.scientificamerican.com/history-of-geology/geology-and-generals-howgeology-influenced-the-battle-of-gettysburg-part-ii/
Chickamauga and Chattanooga NMP (1890):
• https://www.nature.nps.gov/geology/inventory/publications/s_summaries/CHCH_gri_scoping_summary_2009-0805.pdf
1. "Trafficability" is a military term meaning the ability of an army to move soldiers, supplies and equipment safely and easily through an area. The town of Gettysburg has good trafficability. Examine a map showing the Gettysburg area and its roads in 1863 (either the Pennsylvania Department of Conservation and Natural Resources pamphlet or the Scientific American blog will have it); how many roads lead into Gettysburg? Use Google Maps or a similar site to examine Gettysburg today; how many numbered roads (federal, state and county routes) lead into Gettysburg? How important was Gettysburg as a hub of transportation in the 1860s?
2. The Great Valley, the Blue Ridge and the Piedmont (in fact, all of the Appalachians from Georgia to Maine) were all tilted by the same massive tectonic event that happened about 400 million years ago. What was this event, and what type of plate tectonic boundary did it
occur along?
3. What type of rocks were found in the Great Valley (the Cumberland/Hagerstown/ Shenandoah valleys), and what do these rocks have to do with why the Great Valley is there? (Hint: the geologic definition of the word "incompetent" may help)
4. Gettysburg is sited within the Gettysburg-Newark basin. What tectonic event (occurring about 220 to 200 million years ago) occurred to create this and other similar basins (such as the Culpeper basin to the south)? Along what type of plate tectonic boundary did this event occur?
5. Cashtown Gap, through which the Confederate Army of Northern Virginia advanced on Gettysburg, is a wind gap, similar to what you saw in the previous week. Yet this particular gap is much more straight and level than other wind gaps through the Blue Ridge - what other geological phenomenon influenced the formation of Cashtown Gap?
6. Diabase is the rock in the Gettysburg area that plays a major role in the ultimate Union Army victory. What type of rock is diabase? How "competent" is this rock? How and where in the Earth did the diabase form in the first place?
7. Both the pamphlet and the blog were written for the general public (that is, interested people with no particular background in geology). Which do you think conveyed the connection between the geology of the area and the historical events better? Why?
8. By contrast, the National Park Service itself publishes "Geologic Resources Inventory" documents as part of their organization's mission. In that document for the Chickamauga and Chattanooga NMP (see link above, especially pages 12 and 13), how effectively are the geology and Civil War history of the area tied together?
9. Did the same tectonic event in question 2 that affected the Gettysburg area also occur in the Chickamauga-Chattanooga area? What is the evidence for this event in this area? Hint: note the phrase "Alleghanian orogeny" - what's an "orogeny"?
10. Four new terms appear in the text of the Chickamauga and Chattanooga NMP Geologic Resources Inventory: anticline, syncline, décollement and thrust fault. Search all of these terms at the same time, and find an image (or, more probably, two images) that illustrate what these terms are. Sketch it (or them) as well as you can below, labeling each of the terms to the proper part of the sketch. Why do all of these images have to be crosssections?