“Ah,” cried the Doctor, “this great slab of rock then must have slid down from the summit and shut off the mouth of the cave like a door. Poor fellows! What a dreadful time they must have spent in there!—Oh, if we only had some picks and shovels now!”
“Picks and shovels wouldn’t do much good,” said Polynesia. “Look at the size of the slab: a hundred feet high and as many broad. You would need an army for a week to make any impression on it.”
“I wonder how thick it is,” said the Doctor; and he picked up a big stone and banged it with all his might against the face of the rock. It made a hollow booming sound, like a giant drum. We all stood still listening while the echo of it died slowly away.
And then a cold shiver ran down my spine. For, from within the mountain, back came three answering knocks: Boom!... Boom!... Boom!
Wide-eyed we looked at one another as though the earth itself had spoken. And the solemn little silence that followed was broken by the Doctor.
“Thank Heaven,” he said in a hushed reverent voice, “some of them at least are alive!”