Gettysburg: The Lay of the Land

Two Johns Hopkins experts examine the rocky terrain of Gettysburg and how it impacted the historic battle

For three days in the beginning of July 1863, two great armies met and clashed in the fields surrounding the township of Gettysburg in Adams County, Pennsylvania. Standing today atop the boulder-strewn, treeless plain known as Little Round Top on what is now the Gettysburg National Military Park, it’s easy to understand why historians assert that the battlefield’s unique topography – an eclectic mix of rolling fields, hills, and rocky protuberances – had a profound impact on the movements and strategies of both the Union and Confederate armies during this historical battle now considered the turning point of the American Civil War.

A Johns Hopkins geologist and an alumnus who conducts tours of the battlefield recently discussed how the outcome of this seminal event in American history – the Battle of Gettysburg – was literally shaped by subterranean magma and rifts that occurred thousands of years ago, when dinosaurs roamed the earth. (In fact, you can still see dinosaur footprints on some of the rocks.)

Bruce Marsh is a professor in the Morton K. Blaustein Department of Earth and Planetary Sciences in the Krieger School of Arts and Sciences. Informally known as Johns Hopkins’ own “Magma P.I.,” Marsh studies the physics and chemistry of the origin and evolution of magma, particularly in regard to the formation of continents. He has worked on volcanic and magmatic systems the world over, and presently has a considerable field program in the Dry Valley region of Antarctica. Each fall, Marsh – a Civil War history buff – takes students on a field trip to the Gettysburg battlefield to discuss the role that the geology of the area played in the battles there.

Guillermo Bosch graduated from Johns Hopkins in 1971 and now serves as a Licensed Battlefield Guide at the Gettysburg National Military Park. Though he practices law part time, shepherding visitors and schoolchildren through the battlefield’s highlights is his true avocation.