The title of chapter 10 is "The Shell and the Glasses." The title foreshadows that the conch shell and Piggy's glasses will somehow become important during the chapter.
The reader does not have to wait long to find out what is important about the conch shell in this chapter. Rather, the reader finds out that the conch shell has actually ceased to be important.
“What we going to do?” Piggy nodded at the conch. “You could—”
“Call an assembly?” Ralph laughed sharply as he said the word and Piggy frowned.
“You’re still chief.”
Ralph laughed again.
Piggy is still clinging to the notion that Ralph is chief and that the conch shell is evidence of his position of power. Ralph laughs, because he realizes how naive a view that is. Ralph knows that he is no longer the chief. Ralph realizes that the conch shell is no longer symbolic of anything. It is merely an object.
The importance of the glasses doesn't reveal itself until the final sentences of the chapter.
The chief led then, trotting steadily, exulting in his achievement. He was a chief now in truth; and he made stabbing motions with his spear. From his left hand dangled Piggy’s broken glasses.
Jack and his boys attacked Ralph's group in the middle of the night and stole Piggy's glasses. The loss of the glasses with the emptiness of the conch shell shows the reader that all of the power is now with Jack and his tribe. The conch is meaningless, and the only power that Ralph still had (the ability to make fire) is now gone.