The last paragraph

The last paragraph in chapter four says they sat on the boarding house porch and saw the sun plunge in the same crack in the earth from which the night emerged. When you first read this you obviously notice that they are talking about how they were sitting on the porch watching the sunset. While watching the sunset it starts to disappear into the night. They use a metaphor in saying that the sun is disappearing to where the night arises. I honestly don't know if there is any other meaning than that, but I think its a pretty powerful metaphor.