“Break through? Why, you don’t think it is hollow under here?”
“I should rather believe that there was a stony crust hardened by cooling, and that a very short distance beneath us the rocks are all molten.”
“But all these great stones lying about don’t break through. Let’s go a little way down.”
“Don’t be rash then. Will you come, Instow?”
“Oh yes, if it’s safe. Let’s go cautiously.”
Just then the sailors, who had had to pack up and carry the camping-out necessaries, appeared at the edge, and waited there watching the little party as they slowly descended toward the shimmering pool, threading their way in and out among the blocks of lava and pumice which lay in their road.
Sir John led, with Jack close beside him, and the doctor and Ned followed a little way behind, to their right. But they had not descended a hundred yards before Sir John stopped short.
“No farther!” he said. “The heat is getting intense, and overpowering gases are escaping from the ashes. We must go back, Jack.”
“I suppose so,” said the lad unwillingly. “We don’t see the pool any the better for being here either. Oh, look at that!”
There was no need to call attention, for all were startled by a sudden report, and a glow of heat swept past their faces as a huge fountain of fire suddenly played up some sixty or seventy feet like a geyser, and fell back with a heavy splash, lower and lower, still playing till there was only a slight eminence, as if bubbling in the middle of the pool. Then it was perfectly level again, and a cloud of white smoke floated away.