"Ugh!" grunted the professor; "a nasty place, this."
"For that reason we should be more anxious to get Jack and Joe out of it," said Van.
He had scarcely spoken when the smothered report of a revolver was heard from a point directly ahead of them.
Feeling that they had come upon their two friends, they made a rush forward.
But the next instant they were checked by a huge bowlder.
They came to a halt, completely nonplused.
"Why, here is the way," said the doctor, suddenly, holding his torch to the left as he spoke.
Sure enough, a continuance of the passage was disclosed!
"Well," observed our hero, "I'll fire off my revolver to let them know we are coming, and then we will go on."
Pointing the weapon in the air, he pulled the trigger.