At length, when they had been journeying up the river in leisurely fashion for about three weeks, meeting with no adventure worthy of record, on a certain hot and steamy afternoon, when the boat, under sail, was doing little more than barely stem the current, they gradually became aware of a low, faint roar, at first scarcely distinguishable above the rustle of the wind in the trees aloft and the buzzing hum of the innumerable insects which swarmed in the forest and hovered in clouds over the surface of the water. But as the boat continued to creep upstream the roar gradually increased in intensity, until at length, as they rounded a bend and entered another reach of the river which extended practically straight for nearly three miles ahead of them, they saw, at a distance of about a mile, a long stretch of foaming, tumbling water, rushing headlong down through a rocky gorge, about three hundred yards wide, over what was evidently a rocky bed, for the brown heads of several rocks were seen protruding above the leaping water in the channel. Rapids! with a fall of nearly thirty feet in about half a mile. This was a formidable obstacle indeed, for it did not seem possible that they could get the boat through them; and if they should be obliged to abandon her, what would then happen? Obviously they would be obliged to walk the rest of the distance--or to build another boat, or canoe, above the rapids; and it was difficult to say which was the more distasteful alternative of the two. Walking, probably, for although their belongings were few and by no means cumbersome to carry, the forest was so dense that, as they had already proved by experience, it was scarcely possible to travel a hundred feet without being faced by the necessity to cut their way. "Well," said practical Dick, after they had sat staring at the beautiful but tantalising scene for full five minutes, "it's no use meeting trouble halfway, or wondering how we are going to get across the bridge until we come to it; let's push on and get as close up as we can; then we'll get ashore, walk up along, and have a look at the place. Perhaps when we come to it, it will not look so bad as it does from here."