As he waded out at first on shelving sand he laughed, and shouted, and jumped, and suddenly, as he stepped, his foot went over the edge of the deep hole; his spear, as he tried to save himself with it, touched nothing, so that it was only by good fortune that he recovered his balance. Once now and then in the autumn, when the water was very low, dried up by the long summer heats, this hole was visible and nearly empty, and the stream fell over a cataract into it, boiling and bubbling, and digging it deeper. But now, as the water had only just begun to recede, it was full, so that the stream ran slow, held back and checked by their sea. This hollow was quite ten feet deep, sheer descent, but you could not see it, for the shore seemed to slope as shallow as possible. Mark was much frightened, and sat down on the root to put on his shoes and stockings. Bevis took the spear, and going to the edge, and leaning over and feeling the bottom with it, he could find the hole, where the spear slipped and touched nothing, about two yards out. “It is a horrid place,” he said. “How should I have got you out? I wish we could swim.” “So do I,” said Mark. “And they will never let us go out in a boat by ourselves--I mean in a ship to the Unknown Island--till we can.” “No; that they won’t,” said Bevis. “We must begin to swim directly. My papa will show me, and I will show you. But how should I have got you out if you had fallen? Let me see; there’s a gate up there.” “It is so heavy,” said Mark. “You could not drag it down, and fling it in quick enough. If we had the raft up here.” “Ah, yes. There is a pole loose there--that would have done.” He pointed to some railings that crossed the stream. The rails were nailed, but there was a pole at the side, only thrust into the bushes. “I could have pulled that out and held it to you.” Mark had now got his shoes on, and they started again, looking for a bridge to cross the stream, and continue their journey round the New Sea. As they could not see any they determined to cross by the railings, which they did without much trouble, holding to the top bar, and putting their feet on the second, which was about three inches over the water. The stream ran deep and slow; it was dark, because it was in shadow, for the trees hung over from each side. Bevis, who was first, stopped in the middle and looked up it. There was a thick hedge and trees each side, and a great deal of fern on the banks. It was straight for a good way, so that they could see some distance till the boughs hid the rest. “I should like to go up there,” said Mark. “Some day, if we can get a boat under these rails, let us go up it.” “So we will,” said Bevis. “It is proper to explore a river. But what river is this?” “Is it the Congo?” said Mark. “O! no. The Congo is not near this sea at all. Perhaps it’s the Amazon.”