The Devil of Colonialism

In paragraphs 3 and 4

Readers accompany the protagonist during his first visit and can now notice the presence of human beings. They are introduced as a group of 6 people, depicted from top to bottom. Then details are added hinting at their different anatomical parts. That description is paired with details about physical appearance and movements.

The natives are not defined at first blush (Conrad uses here the same method used for machinery). They are first a group of 6 men, they cannot be considered enemies, they become criminals, then unhappy savages and black shapes.

In paragraphs 1 and 2

Natural elements, used to describe the place in which the protagonist is moving around, are continuously contrasted with expressions referring to the exploitation of nature.

To these elements Conrad adds words connected to machinery to describe a process of decay. In the first paragraph the readers can only infer the machinery present in the scenery (a continuous noise). Then an abandoned boiler is introduced and immediately afterwards a railway-truck bearing the features of  a wounded animal. Finally the decay is overtly described (pieces of decaying machinery, a stack of rusty rails).