How does Marlow describe going up the river?

Marlow becomes somewhat delusional. River travel brings back the past—enlarging and distorting it until it becomes an uncontrollable paranoia that he is being watched. The telling of the tale takes on the tone of an epic quest that is larger than life. There is pregnant silence and a failing of the senses. Marlow appears to be traveling deeply into his own mind. His fanatic interest in the proper working of things is evident when he states that scraping a ship on the river bottom is "sinful." The religious language, which in another context might be humorous, demonstrates Marlow’s mounting panic. This paranoia in turn diminishes his sense of reality, leaving him searching for a sense of truth and stability. There is something primal about going up river which Marlow describes as the land of "darkness".