The linguistic features of Marlow's narrative are actually identified by the anonymous narrator himself quite close to the beginning of the story, when he introduces Marlow and tells the reader something very important about the way in which Marlow tells stories. Whereas other seamen tell stories very simply and in a direct fashion, Marlow takes a very different approach, as the following quote demonstrates:
The yarns of seamen have a direct simplicity, the whole meaning of which lies within the shell of a cracked nut. But Marlow was not typical... and to him the meaning of an episode was not inside like kernel but outside, enveloping the tale which brought it out only as a glow brings out a haze, in the likeness of one of these misty halos that sometimes are made visible by the spectral illumination of sunshine.
Marlow's narrative style is therefore defined not by a focus on the meaning of the story itself but the entire story and the way it is told. This is highly significant in the way that the narrative he relates has no simple and direct "meaning" or message, but is rather a complex, mutli-layered narrative with many possible meanings and interpretations. Marlow's story in this text can never be described as having a "direct simplicity," and the way in which Marlow only gradually reveals the motives and characters of some actions supports this. For example, he describes the way that his journey to Kurtz is halted inexplicably because he is not able to get the materials he needs to repair the boat, but only later does he reveal that the manager deliberately blocked the shipment of rivets in the hope that Kurtz would die in the interim. Marlow's narration is therefore full of ambiguities and mysteries, some of which are never resolved.