He and Jack now swam down the Guadalquivir, pushing before them a very large barrel, denominated a tun, which had been tarred black and laden with a long piece of heavy chain so that only a hand’s breadth extended above the surface. A circle of ox-hide was stretched over the top like a drum-head to prevent water from spilling in and sinking it altogether. Meanwhile the galleot backed water, fighting the river’s current, and began to spin round in mid-channel so that it was pointed upstream. But it was consumed in the darkness, from Jack’s and Dappa’s point of view, before it had half-completed that maneuver.