An example of irony can be seen from this passage because the descriptions and implications of the almighty nature contradicts to what is really happening. In fact, in reality it is the humans (European colonists) that are breaking down mentally and physically in the environment of Africa by exploiting the natural resources and the abusing the indigenous people. And the irony is here in this passage suggests that nature is more superior than human beings. Yet on the other hand, events from previous chapter foreshadows that nature might fight back against human. The vegetation growing through the skeletons of Fresleven who was a former executive of the Company symbolizes that mother nature takes vengeance and devours the ones that has done harm to it.
Recounting his story about his curiosity as a child, he refers to a "big river, that you could see on the map, resembling an immense snake uncoiled".In biblical times the snake created the evil in the story of Adam and Eve. Usually, when snakes are used in a literary context, they have a figurative meaning attached to it. The snakes serve to create a sense of foreboding - a sort of foreshadowing. The metaphor of the snake used upon the river makes the river seem ominous. He also describes himself as "a silly little bird". Birds get eaten by snakes. This could be foreshadowing again, saying that the river might devour some part of this "silly little bird".
Few parallels can be drawn from the idea of forest having both good and evil qualities to other parts in the story. First is the institution which Marlow applied his job earlier in the story. Although the institution possesses a white exterior, but the job it is doing inside is rather immoral and sinister. Secondly, although the European colonists might be well-dressed and wear a coat of “civilization” but they continue degenerating as their moralities are gradually getting consumed by greed, lust, and savagery. In contrast, the cannibals on board with Marlow may seem bestial but they have self restrain to overcome the instinct of hunger. Thus this implies that the bestial cannibals holds more humanity than the civilized Europeans. In addition, the fog that Marlow encounters while going up the river is a parallel comparison to the painting the Kurtz had drawn- a blindfolded African holding a torch. The painting symbolizes that the European is a guiding torch in the dark and the Africans are following Europeans' lead blindly. And in similar manner, the fog has blinded Marlow's sight on the river and the group of Europeans are just moving aimlessly since their paddler is dead. This is also ironic because the Europeans were "supposed" to be the beacon for the Africans and lead their way, but in this scene, the Europeans themselves are lost among the darkness and wilderness of Africa. These examples all contributes to the theme of exterior versus interior and that we must examine the interiors of things before we can make judgments because what seems to be real may most often be misleading.
Although Conrad's uses of most words and phrases in the portrayal of the nature evoke a dark atmosphere yet he deliberately asserted some traits of light and goodness within the lines to emphasizes that there are always two sides to a thing. Phrases such as “gloom of overshadowed distances”, “impenetrable forest”, “sluggish”, “unrestful”, and “noisy world” all have negative connotations which contributes to the idea of nature being vicious and devilish. But he also placed in phrases such as “brilliance of sunshine”and “ on 'silvery banks' hippos and alligator sunned themselves side by side” as an implication to that the seemingly sinister nature also provides comfort and goodness. This contradiction not only supports the theme of light versus dark but also the theme of exterior and interior which suggests that all things have two sides. Though the forest and the river might be portrayed as dark and sinister but we can still find good and light within the surroundings of darkness.
In conclusion, Conrad's use of jungle imagery strengthens and emphasizes the central ideas and themes of Heart of Darkness. The jungle imagery constructs the structure of the novel for it contains elements of light vs. Dark, human vs. nature and exterior vs. interior. These themes linked either linked directly or indirectly within the frame provided by the jungle imagery.