CARBONATE ROCKS AND CIVIL WAR INFANTRY TACTICS: CASE STUDIES FROM CIVIL WAR BATTLEFIELDS PRESERVED BY THE NATIONAL PARK SERVICE

The National Park Service conserves more than fifty Civil War sites where the relationship between geology, terrain, and tactics can be studied. The most researched of these locales, from a geological perspective, is Gettysburg National Military Park, and only the fighting around Manassas occurred on a similar combination of sedimentary rocks and igneous intrusions. Nevertheless, carbonate rocks underlie more battlefields than any other type of rock. Carbonates are found at ~40% of the 25 largest battlefields (defined by casualties) and its influence on the combat is underappreciated. The NPS manages multiple battlefields underlain by limestones and dolostones, including Antietam, Cedar Creek, Chickamauga, Monocacy, and Stones River.

The influence of carbonate geology on tactics is largely dependent on spatial scale. On the smallest scale, the local outcrops that form karrens at Stones River produced limestone trenches that were an ideal defensive position for an infantry company. On a larger geographical scale at Antietam, the consistent weathering of the Conococheague limestone produced relatively flat terrain that aided the Confederate defense during the morning phase of the battle. During the fighting in the afternoon, however, the rolling hills created by the differential weathering of the Elsbrook Formation concealed the Union infantry advancing towards the famous sunken road. On the largest scale, such as at Chickamauga or Franklin, carbonate rocks favored defense -- hard dolostones and limestones enriched with chert produced topographic ridges that were ideal positions for infantry and artillery.

Limestone was also a “force-multiplier” for both infantry and artillery on defense. Military theorists at the time recognized that inexperienced citizen-soldiers were more likely to stand and fight if provided natural cover such as karrens. Artillery was often positioned at the crest of carbonate ridges or on undulating terrain so that the gentle slope of the landscape would allow for the ricocheting of solid shot. When fired at approaching infantry a single spherical round or canister could kill multiple soldiers as it grazed across the ground. Whether providing natural cover for a single soldier or improving terminal ballistics for a single battery, limestone improved defensive effectiveness.