“We go now,” said Mafumu. “Hurryup, hurryup.”
The boys squeezed themselves on to the rocky ledge. If they had slipped into the great torrent of water that poured out, that would have been the end of them. But they were careful to hold on to bits of jutting-out rock, so as not to fall. The ledge was damp and slippery. The air was full of fine spray. It was queer to be squeezing by a great river that became a waterfall two or three feet away from them!
The rocky ledge ran right into the mountain, keeping a foot or two above the level of the deep hidden river. The boys made their way along it. Soon they had left behind the thunder of the waterfall, and the mountain seemed strangely silent. Just below them, to their left, ran the underground river, silent and swift.
“It’s dark, Mafumu,” said Jack, shivering. It was not only dark, but cold. No sunshine ever came up the secret river! But soon a queer light showed from the roof and walls of the river tunnel.
It shone green and blue. Mafumu thought it was very odd, but Jack knew that it was only the strange light called phosphorescence. He was glad of its pale gleam, for now they could see more or less where they were going.
We shan’t fall down into the river now and be swept out into the waterfall,” he thought. “My goodness, Mafumu was clever to think there might be a way into the mountain, where the river came out and made a fall! I should never have thought of that in a hundred years! Wouldn’t it be marvellous if we could rescue everyone!”
After a long crawl along the ledge the tunnel opened out into a series of caves, some large, some small. The boys marvelled at some of them, for the walls were agleam with queer bright stones. Mafumu did not like them.
“The walls have eyes that look at Mafumu,” he whispered to Jack. Jack laughed — but he soon stopped, for his laugh echoed round and round the caves, and rumbled into the heart of the mountain and came back to him like a hundred giant-laughs, very queer and horrible.
On through the river-caves went the two boys, silent and rather frightened now. Then they came to what seemed a complete stop
“Mafumu! The river is in a tunnel here, and the roof almost touches the top of the water!” said Jack in dismay, “We can’t get any further.”