(1) "I went to work the next day, turning, so to speak, my back on that station. (2) In that way only it seemed to me I could keep my hold on the redeeming facts of life. (3) Still, one must look about sometimes; and then I saw this station, these men strolling aimlessly about in the sunshine of the yard. (4) I asked myself sometimes what it all meant. (5) They wandered here and there with their absurd long staves in their hands, like a lot of faithless pilgrims bewitched inside a rotten fence. (6) The word 'ivory' rang in the air, was whispered, was sighed. (7) You would think they were praying to it. (8) A taint of imbecile rapacity blew through it all, like a whiff from some corpse. (9) By Jove! I've never seen anything so unreal in my life. (10) And outside, the silent wilderness surrounding this cleared speck on the earth struck me as something great and invincible, like evil or truth, waiting patiently for the passing away of this fantastic invasion. (11) "Oh, these months! Well, never mind. (12) Various things happened. (13) One evening a grass shed full of calico, cotton prints, beads, and I don't know what else, burst into a blaze so suddenly that you would have thought the earth had opened to let an avenging fire consume all that trash. (14) I was smoking my pipe quietly by my dismantled steamer, and saw them all cutting capers in the light, with their arms lifted high, when the stout man with moustaches came tearing down to the river, a tin pail in his hand, assured me that everybody was 'behaving splendidly, splendidly,' dipped about a quart of water and tore back again. (15) I noticed there was a hole in the bottom of his pail.

Sentences 12 and 13 ("Oh, these months! Well, never mind. Various things happened.") marks Marlow's shift to

a description of an event strictly to provide levity
an analysis of the station's current state of affairs
an anecdote to reveal the evil nature of the African jungle
an explanation of the risks involved in the ivory trade
a recollection of a singular event given as an example