We are on an island we are surrounded by a coral reef
Jack Ralph and some of the other boys enter the jungle to attempt to reach the top of the mountain to see if they really are on an island
As they climb up the mountain they find a boulder that is loose, they push it off the hill and it crashes into the valley below leaving a dent
When ontop of the mountain Ralph says "Thats a reef, a coral reef, I have see pictures like that!" pg. 29 With then seeing this reef the boys come to the realization that they are indeed on an island.
After they see that they are on an island Jack sees the quickest way back to the platform and they head back to tell the others.
While walking the boys all agree that they are hungry, so when Jack spots a pig stuck in the creepers, he pulls out a knife and tries to kill it, but he doesn't stab it and it is able to escape
After the encounter with the pig, the boys head back to the platform, without stopping this time, to tell the others of what they have seen