All these unpleasantnesses were sharply accentuated by the darkness, which fell upon us like a pall; for now the stars began to be obscured by great black clouds that came sweeping in from seaward, while the increasing roar and swish in the boughs overhead seemed to indicate that the wind was freshening.  Progress was difficult enough, under such conditions, while we were traversing solid ground and had no special need to pick our footsteps; how would it be, I wondered, when it came to our re-crossing the belt of mangroves and mud that lay between us and the gig?  Then, to add still further to our difficulties, the dank, heavy, pestilential fog that rises from the tropical African rivers at nightfall began to gather about us, and in a few minutes, from being bathed in perspiration from our exertions, we were chilled to the bone, with our teeth chattering to such an extent that we could scarcely articulate an intelligible word.