Upon reaching the Outer Station, Marlow is struck by the poverty and sickness of the people and land. Walking up a rocky path to the Station, he observes:

I came upon a boiler wallowing in the grass... an undersized railway-truck lying there on its back with its wheels in the air. One was off. The thing looked as dead as the carcass of some animal.
[...]
I avoided a vast artificial hole somebody had been digging on the slope, the purpose of which I found it impossible to divine. It wasn't a quarry or a sandpit, anyhow. It was just a hole.
(Conrad, Heart of Darkness, eNotes eText)

Although he is not yet fully aware of it, these things are remnants of previous expeditions, left to rot in the grass because they no longer matter. Because no one takes the time to clean up, the machinery lying in the grass takes on an organic texture, like an "animal carcass," and shows how little concern there is for human life or civilization. The hole in the ground, which serves no purpose, is another example of the malaise that infects people in the jungle; without a clear purpose, people are reduced to busywork with no goal in mind. Marlow doesn't understand why this "objectless" work is continuing, but since he is still mostly untainted by the jungle, he continues on his own mission.