150 years ago this week the Rock Island Line departed from Chicago on its maiden voyage. Over the next 50 years, the Rock Island Line would extend through 14 states and play a big role in the settlement of the West. Then it would inspire a song that would travel around the world. A documentary airing today at noon traces the history of the railroad and the song and how they fit into the story of America. In this excerpt, reporter Jim Bickal tells how the song was first discovered in a southern prison.