In Lord of the Flies chapter1 who identifies island as a part Coral Reef?

In William Golding's novel "Lord of the Flies", it is Ralph, the main protagonist, who identifies the island as a part of a coral reef. After Jack's group sets fire on Simon's shelter on the beach and creates destruction among the boys' shelter Ralph points to the mountaintop and says " We can all see now that we are on the mountain, we can see what is going to happen."