Second Manassas

Abstract

The outcomes of the Battles of Second Manassas and Gettysburg could not be more dissimilar, but the geology underlying the two battlegrounds is remarkably comparable. Union General Pope’s defeat can be directly tied to geology in a number of ways. On the largest strategic scale, his army failed to hold Thoroughfare Gap, the critical pathway through the Blue Ridge Mountains that allowed Confederate General Lee to unite the two branches of his army. On a tactical level, geology benefited the Confederate Army as Thomas Jackson arranged his divisions behind an unfinished railroad grade along the base of an igneous intrusion. This diabase ridge provided both an anchor for his stubborn defense and, when members of his “Stonewall Brigade” ran out of ammunition, projectiles for throwing.

The Battle of Gettysburg witnessed repeated incomplete or unsuccessful attacks by the Confederate Army across sedimentary rocks towards Union defenders on diabase ridges. During the Battle of Second Manassas this situation was exactly reversed, with Union General Pope ordering repeated and disjointed attacks by his infantry across gently rolling sedimentary plains towards Stonewall Jackson’s infantry positioned along a harder and higher diabase ridge.

“Boys, give ‘em the rocks”

—Infantryman of the famous Stonewall Brigade, upon running out of ammunition