In context, the description is negative, degrading. The "black fellows" are seen as "grotesque" and uncivilized. None-the-less, Marlow also describes their presence as comforting. Unlike Marlow, these men knew the landscape and the lay of the land. They were experienced. This would soon change, however, with other observations and an announcement by someone on board, that the men were enemies. Other negative descriptions include;
All their meager breasts panted together, the violently dilated nostrils quivered, the eyes stared stonily uphill. They passed me within six inches, without a glance, with that complete, deathlike indifference of unhappy savages.
Sandbanks, marshes, forests, savages,—precious little to eat fit for a civilized man, nothing but Thames water to drink. No Falernian wine here, no going ashore. Here and there a military camp lost in a wilderness, like a needle in a bundle of hay—cold, fog, tempests, disease, exile, and death,—death skulking in the air, in the water, in the bush.
'What a frightful row,' he said. He crossed the room gently to look at the sick man, and returning, said to me, 'He does not hear.' 'What! Dead?' I asked, startled. 'No, not yet,' he answered, with great composure. Then, alluding with a toss of the head to the tumult in the station-yard, 'When one has got to make correct entries, one comes to hate those savages—hate them to the death.'
And between whiles I had to look after the savage who was fireman. He was an improved specimen; he could fire up a vertical boiler. He was there below me, and, upon my word, to look at him was as edifying as seeing a dog in a parody of breeches and a feather hat, walking on his hind-legs. A few months of training had done for that really fine chap.