To think in this case was to act, and the boys did let out a couple of yells which brought the caretaker running back from the shaft.
The boys were listening for some answer to their shouts when he arrived, and so they paid little attention to his numerous questions.
"There is no time to lose," Canfield went on. "I'll go to the top at once and call an engineer and a couple of firemen. When you find the beat, take a trip down the main gangway here and stick your lights into all the cross-headings and chambers you see. But, above all," he continued, "don't fail to leave a light here at a shaft, and be careful that you never pass out of sight of it."
Canfield hastened away, climbing the ladders two rungs at a time, and soon disappeared into the little dot of light at the top.
The two boys searched patiently for the boat for a long time, but did not succeed in discovering it. At last, Will suggested that it might be in the mule stable and thither they went.
The boat was there, in excellent condition, and the boys soon had it swinging to and fro on the surface of the water which now lay several feet deep in the main gangway.
"Jerusalem!" exclaimed George, taking the depth of the water with an oar, "if the water is four feet deep here, how deep must it be at the middle of the dip?"
"About forty rods, I should think!" exaggerated Will.
The boys left a large searchlight at the shaft so situated that it looked straight down the passage they proposed following, and started away in the boat. The flashlights illuminated only a small portion of the underground place, but the boys could see some distance straight ahead.
Once they ceased rowing to listen, believing that they had heard calls from the darkness beyond. The sound was not repeated, and they were about to proceed when a sound which brought all their nervous energy into full swing reached their ears.