Wayne's face: symbol
Wayne's face, which Cassandra sees all over, is an incredibly powerful symbol of her unresolved grief over the disappearance of her brother, Wayne. Because she never dealt with the disappearance of her brother many years prior, Cassandra was still actively grieving the death of her brother.
New Family
The new family that Cassandra's father starts is another important symbol of how he deals with the loss of his beloved son. Although destructive and unnecessarily cruel, Cassandra's father abandoning his old family and start a new one is how he decides to grieve the loss of his son.
Guilt
The Furrows is an allegory about guilt and how destructive it is. In the novel, Cassandra is wracked with guilt over her brother's guilt. She is told by her parents that she was the one responsible for his disappearance (and likely death), even though she was not responsible. She lives her live consumed with guilt, unable to escape it. This kind of guilt, the book argues, is deeply unhealthy and should be avoided whenever possible.
The Accident
The accident which causes Wayne to disappear is symbolic of childhood innocence, desire to have fun, and of childhood naivete. Adults would not have been in the situation that caused the accident that resulted in Wayne's disappearance; because Cassandra and Wayne were children that were innocent and naïve, though, the accident occurred.
