He led them into an elevator and it sank into the darkness. Steve remembered about the poisonous gases that crept about underground and it made him shiver to think about it.
Dr. Harding watched Bud hopping around uncomfortably inside his small space cage. “Do you remember, Mr. Shannon,” he asked over his suit radio, “when they used to use canary birds in mines to warn about leaking gas? The birds would notice it first and give the miners time to get out.”
“I’ve read about that, Dr. Harding,” said Mr. Shannon.
“Now we have automatic warning machines in the tunnels to do that,” the chief engineer told Sue and Steve.
Deeper and deeper below the soil of Callisto the elevator sank. At last the cage reached the bottom, and the riders found themselves in a large cavern. There were machines and men all about, working busily. Tracks led off into tunnels and ore cars were running on them. Some were going empty into the tunnels while others were coming out full of rock and gravel.
“The magna is separated from the rock in that big machine over there,” Dr. Harding explained. “Want to ride an ore car into one of the tunnels?”
“Sure!” Steve spoke up.
“The mine is air-conditioned,” the chief engineer said, “so we can take off our helmets.”
This done, Steve let Bud out of his cage. The little bird hopped up on his gloved finger, saying, “Rocket away!” several times. His two-word language seemed to do for everything.
One worker controlled all the cars at a main switch in the middle of the cavern. The Shannons and their guide climbed into an empty ore car and it rolled into a tunnel.