Although the island is described as majestic and beautiful, there are elements from the very first paragraph of the chapter that lend an aura of sinisterness and dark foreshadowing. In the opening lines, the author says,
"...the long scar smashed into the jungle was a bath of heat....a bird, a vision of red and yellow, flashed upwards with a witch-like cry..."
The words "witch-like" in particular seem to hint at the presence of evil.
Later, in the latter part of the chapter, the boys are uplifted by "a kind of glamour...spread over them and the scene," but that glamour is soon tempered, when
"...toward the end of the afternoon, the mirages were settling a little. They found the end of the island, quite distinct, and not magicked out of shape or sense...there was a jumble...some unknown force had wrenched and shattered (the) cubes (of rock) so that they lay askew...the darkness under the trees...the forest minutely vibrated."
Beneath the outward beauty of the island, there lies a subtle, threatening force. Things are not as they seem.
As the boys continue on through the forest, there are further hints of this dark undertow. The author says,
"The creepers were as thick as their thighs and left little but tunnels for further penetration,"
"...the forest further down shook as with the passage of an enraged monster..."
"...the forest stirred, roared, flailed."