In Lord of the Flies, how are Simon's and Piggy's deaths foreshadowed?

In Lord of the Flies, the struggle to maintain order in the face of a ruthless and unrestrained instinct, most obvious in Jack and Roger, is almost too much for Ralph and Piggy to overcome. All of the boys are British schoolboys, stranded on an island with no "grown ups." Even Jack, at first, acknowledges that there are certain expectations of them all because "we're not savages..." (Ch 2), and with Ralph, whose father is a Navy commander, to lead them, they will have shelter and a signal fire.

However, Jack soon begins to forget about the rescue, as he becomes more in-tune with his surroundings. In chapter 3, he says, "Rescue? Yes, of course! All the same, I'd like to catch a pig first." Jack has an "opaque, mad look" in his eyes and it is apparently not the first time Ralph has noticed it. At this stage, the reader is increasingly sensing that all is not well and that Jack has a different agenda in organizing his "hunters."

Interestingly, Roger only really starts to emerge from chapter 4 which is significant because it is the chapter where Jack and his hunters paint their faces. Roger can begin to emerge. His presence scares the "littleuns" as he kicks over their sandcastles and scatters stones. He waits alone and furtive; watching some of the "littluns," already his "unsociable remoteness" is turning into "something forbidding." Roger is becoming all too relaxed in his new surroundings as "the taboo of the old life," which still restrains him, starts to lose its grip because on the island "civilization...was in ruins." He can throw stones in Henry's direction unnoticed and even Jack does not perceive the "darker shadow" that will eventually consume Roger. The reader becomes uneasy, beginning to realize that Roger is capable of far more than throwing stones and missing Henry. It doesn't take long for Jack to also begin transforming from a civilized school boy into an "awesome stranger," whose "laughter became a bloodthirsty snarling," also in chapter 4.  

Piggy and Simon are representative of the intellectual and spiritual sides of human nature. Without Piggy's sense of reason, the boys, and especially Ralph, would have been unable to maintain any kind of order. The breaking of Piggy's glasses is significant because not only does it affect Piggy but it represents the gradual breaking down of law. Piggy's death is foreshadowed through this slow, almost unnoticed, eroding of values: from Piggy feeling uneasy around Jack and playing with his glasses in the first chapter to Roger throwing the stones at Henry, to Jack's disregard for Piggy and the value of his glasses and finally Piggy clutching the conch moments before his death.

Simon's death is foreshadowed when, in chapter one, he and Ralph become a "happy, heaving pile in the under-dusk." Everything is still new and exciting and Ralph expresses himself by pushing Simon, a seemingly boyish, harmless prank. The boys cannot envision what will eventually happen. Jack's triumph at killing the sow and placing its head on a stick and Roger's disrespect and brutality also foreshadow the point when Simon, anxious to expose the beast for what it is, becomes the victim of the tribe's frenzied attack, epitomizing for them the beast itself.