It is important not to overlook some of the more subtle themes and meanings in the novel 'Lord of the Flies' by William Golding. There are indeed two sorts of 'concrete' ideas of fire on the island 1) the flare/beacon fire and 2) the 'forest fire' but there is another underlying fire theme that emanates from William Golding's themes of good, evil and christianity and the idea of man's fall from grace to primeval drives. In this context, the forest 'fire on the mountain' chapter title can refer to Hell - the hell the boys are creating for themselves through impatience, lack of care, impulsiveness, cruelty and so on. As the novel develops, we see them sink further and further into disorder, chaos and a hell of their own making. Vestiges of christianity such as their robes begin to fall away.
The second chapter in William Golding's novel, Lord of the Flies is named "Fire on the Mountain". In this chapter, Ralph stresses to the other boys the importance of being rescued. The boys agree that they need a fire in order to do this. Ralph suggests they go to the highest point of the island, on the top of the mountain, to start this fire. The boys start up the mountain and use Piggy's glasses to start a fire. In their excitement, however, the fire goes out. As they are arguing, Jack suggests that he and some of the other boys become hunters in order to gather meat for everyone to eat. Ralph agrees, and the boys do not realize that they set several trees aflame. The result is a huge, uncontrollable fire. The boys almost burn the entire mountain down, hence the reason for the chapter's title.