Whenever a river recovers after a flood, the soil that isn't covered is called silt.
If the movie is perhaps a documentary, then it is telling you factual information of actual events (includes pictures or pictures of actual documents or events); this makes it a primary source.
If the movie is based off of real events, has factual information, but also has added information to create a well-rounded plot, this makes it a secondary source.
The role that the Railroads played in the Southern Economy was that "They Shipped materials to Northern Markets" Their main goal was to ship crude materials.
