What do the boys find at the top of the mountain and how do they react?

Jack claims he saw something bulge on the mountain. Since Jack seems for the first time somewhat afraid, Ralph agrees that they will look for it immediately. The boys see a rock-like hump and something like a great ape sitting asleep with its head between its knees. As soon as they see it, the boys run off, terrified.The boys think it is the beast and are scared.