There occurred a sudden sharp tremor of the rocks about them; then the stones beneath their feet seemed to heave up and down. Their little universe was being turned topsy-turvy, it seemed to them.
At the first tremor, the Pony Rider Boys were thrown prone upon their faces on the rocky floor, partially stunned by the sudden shock. A distant boom, like the report of a cannon sounded in their ears, then all at once a terrifying rending of the rocks about them, accompanied by loud crashes.
"Are you all right?" shouted Mr. Phipps after the deadening effect of the shock had passed.
"I'm all right," returned Ned Rector. "Can't anything kill me now.
I'm proof against bullets, wrecks and earthquakes."
"Was that an earthquake?" questioned Walter weakly.
"Dynamite. The red car exploded when it was wrecked," explained the mining engineer. "That was what I feared. Is Master Tad hurt?"
"No, he's all right, I guess," answered Tad for himself. "All the lights have gone out. Can't we turn them on again?"
"I'm afraid not. The wires undoubtedly have been torn and twisted apart in many places. There will be no more light in this drift for some time to come, I reckon."
"Think anyone was killed?" asked Walter apprehensively.
"Oh, no. There was no one near the explosion, except ourselves, and luckily we are safe and sound. I'll try the telephone."