“What is it?  The wild man?” gasped Dick, looking round him in alarm.

“No, your boots, your boots; look at them!” cried the professor.

“Is there a snake on them?” cried Dick, preparing to jump up.

“Don’t move!  Don’t move for your life!” fairly screamed the dumpy little geologist, springing forward.  He fell on his knees at Dick’s boots as if they had been sacred, and with trembling fingers flaked off, into his left palm, some black mud which stuck to them.

Then he stood erect, his face aglow with triumph and enthusiasm such as the man of science rarely permitted himself.

“Gentlemen,” he said, with a flourish, “there is no reason to look further for the mineral-bearing ground.”

“You have found it?” choked out Jack.

“Yes.”

“Where?”

“On Dick Donovan’s boots.”

They looked at him as if they thought he had suddenly gone demented.  Dick examined his boots carefully as if he expected to see money plastered all over them.

The professor extended his palm.  In it lay the black earth he had scraped from Dick’s boots.  In it tiny particles glittered and gleamed like myriads of infinitesimal eyes.

“Z. 2.  X.,” said the professor in solemn tones, and he waved his hand down toward the black barren where the moist, unhealthy-looking bare patch lay quivering and sweltering in the sun.  A kind of haze hung above it, like a very thin fog.

“There it is,” he went on, “down there.  Waiting to be extracted from that black earth.  Look.”

He shook the black earth from his palm.  Where it had lain there was a red, irritated-looking patch.  The professor showed it.  It looked like a slight burn.

“Did that stuff do it?” asked Jack.

“Yes; and that’s almost as definite a proof as an analysis, of its intense radio activity.  You noticed that the sample that Zeb had was enclosed in a leaden tube.  That was the reason.  Such powerful stuff would inflict bad burns if not handled properly.”

“So that was why you made us include asbestos gloves and foot coverings and black goggles in the outfit?” cried Tom, who had been much puzzled over the reason for that part of the equipment.

“That was why,” said the professor, “and that also is the reason we brought along those lead containers.  Z. 2.  X. or its ally, radium, or in fact vanadium or any of the allied radio-active metals, would destroy any other sort of container.”

“Let’s go down now and start digging,” suggested impulsive Dick.

“Don’t venture out there till you are fully equipped for the job,” said the professor.  “Serious results might ensue.  In the meantime, I am going to analyze this sample in order to be doubly sure.”

Jack gave a deep sigh of relief.  After all, it was not a dream.  They had found the valuable earth.  It was now only a question of transportation.  His father’s fortunes were saved.  The radio-’phone would be rushed to perfection and placed on the market within a short time of their return home.