During the lesson observe students for active participation in group discussions and activities. Monitor and provide feedback for the following in order to foster student understanding of the significance of the geologic terrain in the outcome of the battle:

• Students are connecting the defensive positions on the battle field with significant geological features.

• Students are working appropriately in groups.

• Geologic histories and the group discussions surrounding the creation of them are relevant to the lecture.

• Strategies for the narrative and presentation are appropriately structured and tasks are fairly distributed among the group members.

Start the lesson with a narrative of the Battle of Gettysburg (S-8-4-1_Battle of Gettysburg Overview.doc). Allow students to ask questions and, if necessary, hold a short discussion on the impact the battle had on the Civil War.

“Today we’re going to investigate how geology influenced the Battle of Gettysburg. What do we know about the Battle of Gettysburg?” Facilitate a short class discussion. “So, the Battle of Gettysburg was…” Integrate student comments with a short history of the battle and a look at the map (S-8-4-1_Battle of Gettysburg.doc and S-8-4_Map of the Battle of Gettysburg.doc).

“The Battle of Gettysburg can be viewed from a geological perspective as well. The Union army was defending its position along ridges and hills in the battlefield area. The Confederate army was trying to drive the Union army out. How do you think the Earth’s surface influenced the battle?” Facilitate a brief class discussion.

Project the Gettysburg battlefield sketch map. “This is a sketch map of the Gettysburg battlefield. Let’s look at the map legend to see what it tells us about the map.” Facilitate a short class discussion noting the Union position, the fishhook pattern of the Union position, the Confederate attacks, and the scale of the map. “Notice the hills and ridges in the area. Do you see the relationship between the Union position and the hills and ridges?” Yes, the position follows the terrain. “Why do you think the Union troops chose this position to defend?” Higher areas give a strategic advantage—easier to defend. Greater loss of troops attacking the higher areas. “How do you think these ridges and hills got here?” Facilitate a short class discussion of student ideas.

“The Union Fishhook follows the shape of an outcrop—a part of a rock unit at the surface of the Earth—of an igneous rock that formed during the separation of Pangaea millions of years ago. This rock unit is called the Gettysburg sill.” Show students a diagram of a sill (see S-8-4-1_Igneous Sill Diagram in the Resources folder). “When magma intrudes (forces its way in) between other rock layers and solidifies, the igneous rock layer formed is called a sill. The rock layers shown in red in this diagram illustrate examples of igneous sills. The Gettysburg sill formed when magma intruded—forced its way in between—layers of sedimentary rocks. The magma crystallized into an igneous rock called diabase, which looks similar to a dark granite.”

“Remember that some rocks are more resistant to weathering than other rocks. What does it mean to be more resistant to weathering?” The rock does not break down into smaller pieces as rapidly as other rocks in the same area. “How would this difference in resistance to weathering affect the terrain over geologic time?” Facilitate a class discussion of student ideas. “So, what I’m hearing is that …” In this case the diabase (igneous rock) is more resistant to weathering than the surrounding sedimentary rock layers. So the sedimentary rock layers weather back into sediments more quickly and are transported away (eroded) leaving the igneous rock behind as hills and ridges.

Group students. “Your job is to write a group narration of the geologic history of the Gettysburg battlefield, beginning just after the formation of the Gettysburg sill and ending with the Battle of Gettysburg. You need to include labeled diagrams to illustrate your history.”

Extension:

• For students needing further practice, they can create a 3-dimensional map of the battle field, highlighting union and confederate positions and significant geological features that influenced the battle.

• Students hypothesize and describe alternate battle tactics and outcomes if there had been no Gettysburg sill emplaced in the battlefield area. Students can create an alternative timeline of the battle reflecting the different geology.