The dusk came gliding into it long before the sun had set. The current ran smooth and swift, but a dumb immobility sat on the banks. The living trees, lashed together by the creepers and every living bush of the undergrowth, might have been changed into stone, even to the slenderest twig, to the lightest leaf.

This exert desribes the transition into the night, and in doing so sets a bleak mood upon the atmosphere of Marlow's situation.