The geology of the battlefield and surrounding areas played an important role in the complexity and outcome of the battle. Geologist Stephen W. Henderson from Oxford College of Emory University in Georgia will explore the geology of the Battle of Chickamauga on Friday, April 5, at the Geological Society of America’s North-Central Section and Southeastern Section Joint Meeting in Lexington, Kentucky.
The Appalachian Mountains in the area are composed of limestone, sandstone, and shale sedimentary rocks with different abilities to erode. Some formed valleys and others formed ridges. To engage in a military campaign, one had to maneuver troops around these ridges while looking for passes or gaps to get through.
“What I’ve found is that when the Union army moved south after they captured Chattanooga, they started pursuing the Confederate forces under the command of General Braxton Bragg into a place in Georgia called McLemore’s Cove which is a plunging anticline,” Henderson explained. It’s formed by a rather nonresistant combination of dolostone and limestone. It opens to the north and it’s closed to the south, where the resistant sandstones of Lookout and Pigeon Mountains come together. What Bragg did was to try and trap the Union army in the cove by using the geology essentially.”
But that didn’t work. The Union troops, which had been split into three wings, got wind of the plot and were able to come together near Chickamauga, to the north of McLemore’s Cove where the valley is broader. The Confederates tried unsuccessfully to drive the Union troops back down into McLemore’s Cove where it would have been easier to defeat them.
“Within the battlefield there are six different Ordovician rock formations, various dolostones and limestones. It turns out that the higher ground was high because of variations in the rock type, ” Henderson explained. “The topographic crest where the Union Army had stationed themselves was limestone which had chert in it and it was the chert that caused it to be higher topographically. So the Union line occupied a rather subtle high ground. Militarily, it’s the high ground that should have made a difference because the Confederates would have to go up hill. The battle raged for two days.”
The second day of battle was September 20, 1863. The Union troops were outnumbered but they held the strategic position on the high ground. However, when Rosencrans mistakenly moved some of his men out of their battle line, he created a gap that the Confederates were able to break through.
“The Confederates couldn’t believe their good luck. That was the major breakthrough of the entire war and it was totally due to an error,” Henderson said. “Part of the Union Army retreated to Chattanooga. General George Thomas rallied the remaining Union forces and made a stand on Snodgrass Hill, composed of a resistant dolostone with chert in it. He managed to save the army from 25 separate Confederate attacks and then successfully escaped to Chattanooga. For his stand on Snodgrass Hill, Thomas was forever afterwards called the “Rock of Chickamauga.”
By Kara LeBeau, GSA Staff Writer
Stephen W. Henderson
Dept. of Geology
Oxford College of Emory University
Oxford GA 30054 USA
Abstract available at: http://gsa.confex.com/gsa/2002NC/finalprogram/abstract_32291.htm
Geological Society of America
Southeastern Section and North-Central Section Joint Meeting
April 3-5, 2002
Hyatt Regency Hotel and Lexington Civic Center
For information and assistance during the meeting, please see the media assistant at the GSA registration table or call 859-253-1234.