There are geological aspects of just about every battle on land, including those of the American Civil War.
(J.T. Hannibal and K.R. Evans, Civil War and Cultural Geology of Southwestern Missouri, Part 1: The Geology of Wilson’s Creek Battlefield and the History of Stone Quarrying and Stone Use, in From Precambrian Rift Volcanoes to the Mississippian Shelf Margin: Geological Field Excursions in the Ozark Mountains, 2010 p. 45)
Even someone with only a passing knowledge of the Civil War is likely to know some portion of the litany of famous geological features of different battles, pivotal places on these battlefields which men struggled and died to attain or defend.
One of those famous geological features appears in the picture below, taken by Timothy O’Sullivan shortly after the Battle of Gettysburg in early July, 1863. It shows Union defensive positions on Little Round Top, located to the southeast of the town of Gettysburg, Pennsylvania (Big Round Top is in the distance). The success of Union forces in holding this rugged, steep hill on the left of the Union line during the battle was instrumental in the ultimate Union victory. (The source of the photo is the Library of Congress.)
According to Andrew Brown, in his short and absorbing Geology and the Gettysburg Campaign (Commonwealth of Pennsylvania, Department of Conservation and Natural Resources, Educational Series 5, 1962), Little Round Top is part of a diabase sill, an outcropping of rock that intruded perhaps 200 million years ago into the Triassic sandstone of the Gettysburg Formation. This diabase is described in a geologic map from the Pennsylvania Geological Survey (1980) as “dark gray, medium to coarse grained.” The material making up these diabase outcroppings is more resistant to erosion than the rock that was originally above it or surrounding it. As a result, the outcroppings stand above the plains that fall away on each side – hence their military importance. The Union forces occupied a fish hook-shaped position anchored at one end by Little Round Top; in effect, the entire line was on this diabase sill.
Brown's booklet outlines “the extent to which the movements of the two armies toward Gettysburg, and the battle itself, were influenced by the geology of the region in which the campaign was conducted.” (p. 1) These influences played out, not only in which features of the terrain on the battlefield were contested by soldiers, but also in how the armies moved across the Virginia, West Virginia, Maryland, and Pennsylvania landscapes, and why an encounter in the Gettysburg basin became increasingly likely.
The geology of the land exerts its influence in another deadly way when bedrock lies fully or nearly exposed. The defenses in the photo above consist largely of some extant walls of piled rock and diabase boulders. This was the largely the only protection on Little Round Top and for much of the Union position. As a result, casualties were dramatically greater for the Union defenders of this higher ground than was the case in most other battles in which forces defended elevated positions. Why didn’t the soldiers use trenching tools and erect more substantial defenses? As Brown explains, “The resistant diabase sill is so close to the surface that it was impossible for the soldiers to ‘dig in,’ . . . . “ (p. 13)
As will be evident shortly, that brutal influence of geology is a natural segue to the Battle of Wilson’s Creek, getting us closer to the genesis of this posting. The battle took place on a rolling Missouri landscape of the western Ozarks, captured in the newspaper illustration below showing Union General Nathaniel Lyon leading a charge of the First Iowa Regiment. A key feature of the battlefield, a ridge that would become known as Bloody Hill, is what I think is seen in the background. (The immediate source of this image is the Library of Congress and was copied from Frank Leslie’s Illustrated Newspaper.)
In the early morning of August 10, 1861, General Lyon, tired of waiting for reinforcements to counter a growing Confederate threat to Missouri, took the fight to a numerically superior enemy commanded by Generals Benjamin McCulloch and Sterling Price camped along Wilsons Creek. Lyon marched from Springfield and launched a surprise attack from the north. With their initial success, Lyon’s men occupied the ridge that, over a four-hour period, would earn its new name. But Lyon’s advance faltered on that exposed ridge in the face of artillery fire, triggering a vicious struggle for control of Bloody Hill. The other component of Lyon’s plan, an attack by Union Colonel Franz Sigel from the south, failed. Then Lyon fell, the first Union General to be killed in combat in the war. The battle ended with the defeated Federal troops retreating to Springfield.
As for the geology of the event, the bedrock for much of the most contested portion of the battlefield is Lower Mississippian limestones of the Keokuk and Burlington Formation. The 1987 geologic map for the area published by the U.S. Geological Survey describes these limestones as “light-gray to medium gray, coarse- to fine-crystalline, massive-bedded, crinoidal limestone.” That last adjective confirms the expectation we have of limestones – there are fossils here.
This is also a karst landscape in which water has eroded the underlying limestone bedrock, creating such features as sinkholes and rocky protuberances. This would directly affect the ebb and flow of the battle. And geology extended here a gory hand similar to the one that was offered two years later at Gettysburg. As Hannibal and Evans write,
The terrain, since it was developed on karst, was also uneven in places in what was at the time a fairly open area. Glades [open areas with limestone bedrock very near the surface] . . . affected the battle, most critically at the knob that would become known as Bloody Hill. The shallow depth to bedrock would also have an effect on the ability to dig entrenchments and gave an advantage to artillery. (emphasis added, p. 46)I have an image of many artillery shells and bullets hitting expanses of limestone at or near the surface of Bloody Hill and elsewhere on the battlefield. With what result? Flying fragments of rock and metal, ricocheting bullets, and deformed spent bullets?
Earlier in this decade, the Midwest Archeological Center, part of the U.S. National Park Service undertook an archeological inventory of the Wilson’s Creek Battlefield. This involved using metal detectors, as well as visual inspections, to identify and collect artifacts from the battle in as systematic a fashion as possible over as much of the battlefield as was accessible. The effort, headed up by historical archaeologist Douglas Scott, resulted in an in-depth report published in 2008, entitled “The Fire Upon Us Was Terrific:” Battlefield Archeology of Wilson’s Creek National Battlefield, Missouri (Technical Report No. 109)
Among the kinds of bullets recovered were .69 caliber spherical balls; these bullets were made of soft lead. One of the 154 fired spherical balls found is the inspiration for this posting. Scott’s report notes, in passing, that
One impacted ball retains an interesting impact scar that of a tiny fossil shell where it struck a piece of limestone. (p. 40; the photo below, copied from the report, suggests what the authors saw)
In describing the Battle of Wilson’s Creek, I drew on Scott’s “The Fire Upon Us Was Terrific” and, among several books, Michael Weeks’ The Complete Civil War Road Trip Guide (2009), a surprisingly detailed treatment of the events at many Civil War sites.