How Geology Influenced the American Civil War

According to an article published in Geosphere, the Civil War – particularly the key battle at Gettysburg – was influenced by rock formations.

Geosphere is the journal of the Geological Society of America. The article details how rock formations were one of the deciding factors at Gettysburg where Union forces stopped the Confederate advance, leading to the eventual Union victory.

Scott P. Hippensteel, an associate professor of earth sciences at the University of North Carolina at Charlotte, analyzed the geology at Gettysburg. A mixture of harder diabase and softer sedimentary rocks that produced features like Cemetery Hill and Little Round Top. These features gave the Union army strong defensive positions.

The terrain of a battlefield is a major factor in its outcome. Many Generals throughout history have sought to use the terrain to help them and their army achieve victory. It was essential that a battle was fought on a terrain that sought the army. In the American Civil War, this was also the case.

On the other hand, the carbonates, such as limestone and dolostones that formed the battlefields like Antietam allowed the Confederate forces to repel the Union army in September of 1862. They were able to use natural features for defence.

“On many battlefields, outcropping limestone proved beneficial for attacking troops,” Hippensteel writes. “Differential weathering within carbonate formations produced rolling terrain that limited the range and effectiveness of both artillery and small arms.”

An example of the second instance was the “Sunken Road” at Antietam. There, 2,600 Confederate troops held off 5,500 Union troops for three and a half hours due to the terrain. The Union forces eventually pushed through but they took heavy losses. The Confederates were adept at using the land’s geological features for their own advantage.

Other battlefields with similar features include Stones River, Chickamauga, Franklin, Nashville and Monocacy, a battle in July of 1864 where the Union forces stopped a Confederate attack on Washington, D.C.

Hippensteel analyzed data of wartime casualties to find the rock formations that were most beneficial to defenders. In his analysis, he found that ground underlain by limestones and dolostones had a somewhat higher casualty rate (14%) than those defending over non-carbonate rocks or unconsolidated sediments, which had a 12% casualty rate.

“This suggests, in a limited manner, that the local smaller-scale defensive advantages provided by limestone, such as karrens, were not as important as the regional-scale advantages for attacking troops, including rolling terrain or forest cover,” he writes.

Ian Harvey

Ian Harvey is one of the authors writing for WAR HISTORY ONLINE