On the search for the beast the day after Samneric see it in the dark, Ralph, Jack, and a party of biguns head out to explore the only place on the island that Jack and his hunters have never been. He describes it as "the tailend part, where the rocks are all piled up. ... The rock makes a sort of bridge. There's only one way up." When they get there, Ralph, as chief, knows he must be the first to cross the ledge to get to the "castle," as they have named the area.
In the description of this scene, there is a significant amount of foreshadowing of Chapter 11, when Ralph and Piggy confront Jack's tribe at Castle Rock. The "one flat rock" below where the the water comes up and "boiled over the table rock with a roar" is the "square red rock" onto which Piggy falls after the boulder hits him.
The cave and the trickle of spring water are mentioned. Then Jack notices the rocking boulder and says, "Shove a palm trunk under that and if an enemy came— ... One heave ... and—wheee—!" This foreshadows how Roger will murder Piggy.
Although Ralph hates the place and calls it "rotten," Jack thinks it "would make a wizard fort." The other boys come up and start rolling rocks down into the sea. That the boys all like the place while Ralph points out that "there's no food here ... and no shelter [and] not much fresh water" foreshadows that Jack and the other boys will camp there, leaving Ralph an outcast. For now, however, Ralph commands the boys to leave, reminding them of the importance of the signal, and saying, "Are you all off your rockers?" That question foreshadows the soon-coming state of affairs where all the boys will lose their minds, so to speak, in their descent into savagery.