You might want to just pick one of the descriptions that Marlow gives us and not how through it Conrad, through the voice of Marlow, offers his own ironic view on colonialism. One of my favourite passages of this excellent novella is when Marlow is going round the coast of Africa and he comes across of man-of-war, anchored off the coast. This passage offers an intensely ironic view of progress in Africa.
Note the description we are given of this ship and its activity:
There wasn't even a shed there, and she was shelling the bush. It appears the French had one of their wars going on thereabouts. Her ensign drooped limp like a rag; the muzzles of the long six-inch guns stuck out all over the low hull; the greasy, slimy swell swung her up lazily and let her down, swaying her thin masts. In the empty immensity of earth, sky and water, there she was, incomprehensible, firing into a continent. Pop, would go one of the six-inch guns; a small flame would dart and vanish, a little white smoke would disappear, a tiny projectile would give a feeble screech--and nothign happened. Nothing could happen. There was a touch of insanity in the proceeding...
Note how the colonial endeavour is symbolised in this sight. There is a "touch of insanity" in the whole event as one man-of-war seeks to leave an impression on "a continent" with the "feeble shriek" of its guns. The futility of such a task is indicated by the repetition of "nothing happened." Note too the description of the ensign which is "limp like a rag." European nations are thus shown as trying to besiege a continent and leave their mark, but with absolute futility. As in this event, there is a touch of "insanity" about such an insane task. Note too the droll irony in the phrase "It appears that the French had one of their wars going on thereabouts." Such a general, non-specific phrase points towards the chaotic policy of colonialism.