Passage: On the train, Adam and Vadoma, who have set fire to the upcoming trestle, attack Lincoln, Sturges, and Johnson. During the fight, in which Speed is killed, Adam learns that the train holds only rocks. Lincoln reveals that Speed's betrayal was a ruse to lure Adam into a trap. Lincoln uses his silver watch and chain as a knuckle duster and kills Adam with it, and the three escape the train before it explodes. Meanwhile, Mary and Harriet Tubman have transported the silver to Gettysburg via the Underground Railroad.

Question: What did Harriet move through the Underground Railroad?
silver