The river was no longer thundering through the underground passage, and as the sudden silence following the stopping of engines on a passenger steamer will awaken every sleeper even more quickly than the roaring of a gale, so this lull in the tremendous din aroused Venning.
"What is the matter?" he asked, starting up.
"The river has stopped."
They sat straining their ears for the swift roar of the waters, but out of the slumbering depths below there came only the regular splash and tinkle of the falling drops.
"I don't understand it," muttered the Hunter.
"I do," said Venning, with a shout. "Hassan has blocked up the mouth of the canon."
"Nonsense, boy; how could he?"
"Look out of the loophole."
Mr. Hume put his face to the hole. "The water has risen, I think, from the noise."
"You remember what Muata said about the drowning of the valley? Well, that is what is happening. The Arab has blocked the mouth by blasting a mass of rock which overhung the river. That's what!"