When Marlow talks of London being a dark place, the theme of civilization versus savagery comes into play. Marlow's aunt believes he is an emissary of light, being sent into the darkness. Marlow sees this darkness through the placing of heads on poles, for a man named Kurtz. All of this makes Marlow change his inner feelings of himself, which relates to the theme of the journey of the inner self. Marlow talks of when …showed first 75 words of 1345 total…

…showed last 75 words of 1345 total…threes", dark and light and civilization versus savagery. All of these themes lead to the understanding that Marlow's voyage into the deepness of the Congo, is symbolic of the journey he had to take into the deepest side of himself. He successfully battled with his savage side, and came out a changed man. It just shows that no matter hoe perfect something seems to be, there is always a heart of darkness deep within somewhere.