In A Separate Peace, what is the point of the rivers being described as they are?
The two rivers in the book are described in symbolic ways. The Devon School sits between two rivers, the Devon and the the Naguamsett. The Devon is described as a place of fun, and it is the river into which Phineas leaps from his canoe. Later, it is the place in which the boys jump from a tall branch into the water and where Phineas has his accident.
The other river, the Naguamsett, is a saline river whose movements are mysterious. Gene describes it in the following way: "its movements were governed by unimaginable factors like the Gulf Stream, the Polar Ice Cap, and the moon." The boys do not use this river, which runs to the ocean. This second river, unlike the freshwater Devon, is not an idyllic place; it is a river fringed with muck and seaweed.
These two rivers represent boyhood (the Devon) and adulthood (the Naguamsett). The Devon is a seemingly innocent place in which Finny frolics until he experiences his fall. The other river, which is connected to the wider world and which also straddles the school, represents the less idyllic nature of adulthood. When Gene destroys the innocent nature of the boys' experiences on the Devon by shaking a tree branch and causing Finny to fall into the river, he moves from boyhood into adulthood. The idyllic nature of the Devon then ends forever for him.
The author is using the rivers as symbols. The Devon River, in Gene's mind, is fondly remembered. It is the river into which he and Finny jumped many times during the halcyon summer before they were drawn into the war. It is significant that the Devon is a freshwater river, as it represents for Gene a time of innocence and freedom, when he and his companions were still boys, too young to be considered as fodder for war. The Devon is the river of the carefree summer, and even after Finny's accident, it does not lose its appea.; it is symbolic of serenity, and a time of peace.
In contrast, the Naguamsett River is "an ugly, marshy, saline river." It is influenced by the forces of the world outside of the sanctuary of Devon School, like "the Gulf Stream, the Polar Ice Cap, and the moon." The Naguamsett does not have the pristine and untouched insulation of its counterpart, the Devon River. Dark and forbidding, it is a symbol of the war, and the outside world gone mad.
The Devon River may represent the pureness of Finny while the Naguamsett may represent the Gene's heart which is full of hatred.
Also, after having pushed Finny, Gene never sets foot in the Devon. it is almost like he is sinful, and simply can't do it.
But, without any intentions, he does end up in the Naguamsett after his fight with Quackenbush. This is almost like his baptism into his sinful and guiltful life.