Suddenly there came a dull rumbling and the cave was jarred by a shock. Then it grew as black as night.
“That struck somewhere!” cried Jerry.
“And near here!” exclaimed Broswick. “I’m afraid it was too close for comfort.”
“Are we in any danger?” asked Professor Snodgrass, calmly.
Broswick had groped his way forward. He seemed to be fumbling in the darkness at the mouth of the cave.
“What’s happened?” shouted Nestor.
“A rock has fallen and closed the mouth of the cavern!” cried the hunter.