What are quotes that show peacefulness in A Separate Peace?

I would say that the best place to look for quotes about peace and peacefulness is in chapter 1. It's during this chapter that readers are introduced to both Finny and Gene, and we see how good of friends they are. For example, I would use the following quote.  

"It's you, pal," Finny said to me at last, "just you and me." He and I started back across the fields, preceding the others like two...

I would say that the best place to look for quotes about peace and peacefulness is in chapter 1. It's during this chapter that readers are introduced to both Finny and Gene, and we see how good of friends they are. For example, I would use the following quote.  

"It's you, pal," Finny said to me at last, "just you and me." He and I started back across the fields, preceding the others like two seigneurs.

We were the best of friends at that moment. 

The quote clearly shows that Gene and Finny get along quite well. This kind of peaceful relationship doesn't last long in the novel. Soon after, Gene begins competing against Finny in a way that ultimately destroys the relationship. 

The first chapter also contains some descriptive paragraphs about what the school looks like. Gene intermixes a few pieces of dark foreshadowing in the beginning sections, but there are some paragraphs that give readers an impression that Devon is a very peaceful and beautiful campus. 

Devon is sometimes considered the most beautiful school in New England, and even on this dismal afternoon its power was asserted. It is the beauty of small areas of order—a large yard, a group of trees, three similar dormitories, a circle of old houses—living together in contentious harmony.

A bit before that paragraph, Gene tells his readers that he is wandering around the beautiful campus with nothing to distract him. That sounds incredibly peaceful.  

It was early afternoon and the grounds and buildings were deserted, since everyone was at sports. There was nothing to distract me as I made my way across a wide yard, called the Far Commons, and up to a building as red brick and balanced as the other major buildings, but with a large cupola and a bell and a clock and Latin over the doorway—the First Academy Building.