“The brown current ran swiftly out of the heart of darkness, bearing us down towards the sea with twice the speed of our upward progress; and Kurtz’s life was running swiftly, too, ebbing, ebbing out of his heart into the sea of inexorable time. . . . I saw the time approaching when I would be left alone of the party of ‘unsound method.’”

This quote, which comes as the steamer begins its voyage back from the Inner Station in the third section of Part 3, with Kurtz and his ivory aboard, brings together the images of the river and the “heart of darkness” which it penetrates. The river is something that separates Marlow from the African interior: while on the river he is exterior to, even if completely surrounded by, the jungle. Furthermore, despite its “brown current,” the river inexorably brings him back to white civilization. The first sentence of this quote suggests that Marlow and Kurtz have been able to leave the “heart of darkness” behind, but Kurtz’s life seems to be receding along with the “darkness,” and Marlow, too, has been permanently scarred by it, since he is now ineradicably marked as being of Kurtz’s party. Thus, it seems that the “darkness” is in fact internalized, that it is part of some fundamental if ironic “unsoundness.”