The boys explained to him that it was a new type of car that they were trying out for the first time and then Dick helped the scientist lift his bicycle into the tonneau.  He would have helped him with his weighty load of specimens, but the professor refused to be parted from them.  As they started off again he sat with the bag firmly gripped between his knees, as if afraid someone would separate him from it.

The professor lived with a spinster sister to whom his specimens were the bane of her life.  As the car rolled swiftly along, he occupied his time by peeping into the bag at frequent intervals to see that none of the specimens, by some freak of nature, flew out.

All at once he reached forward and clutched Jack by the shoulder.

“Stop!  My dear young friend, please stop at once!”

“What’s the matter?” asked Jack, slowing down at the urgent summons.

“Look!  Look there at that rock!”

To Jack the rock in question was just an ordinary bit of stone in a wall fencing in a pasture in which some cattle were grazing.  But evidently the professor thought otherwise.

“It’s a fine specimen of green granite,” he exclaimed.  “I must have it.  How did such a fine piece ever come to be placed in a common wall?”

The car having now been brought to a stop, he leaped nimbly out, clutching his geological hammer in one hand and his precious sack of specimens in the other.  He rushed up to the wall and stood for a minute with his head on one side, like an inquisitive bird.

“Too bad.  That stone’s a large flat one and goes right through the center of the wall,” he mused.  “The wall must come down.”

And then, to the boys’ consternation, he began demolishing the wall, pulling down the stones and throwing them right and left.

“Professor, you’ll get in trouble,” warned Dick in alarm.  “Those cattle will get out.  The farmer will be after us.”

But the professor paid not the slightest attention.  Taking off his coat, he resumed his operations with even greater vigor than before.  The cattle in the field eyed him curiously.  Then they began to move toward him.  In front of the rest of the herd was a big black-and-white animal with sharp horns and big, thick neck.

It gave a sudden bellow and then rushed straight at the considerable gap the man of science had made in the stone fence.

“It’s a bull!” yelled Dick suddenly.  “Run, professor!  Run or he’ll toss you!”

With lowered horns the bull rushed down upon the unconscious scientist at locomotive speed.  But the professor was oblivious to everything else but uncovering the odd-looking green stone embedded in the heart of the wall.

The boys shouted to him but he didn’t hear them.  On rushed the bull, bellowing, charging, ready to annihilate the scientist.

“Run!” yelled the boys at the top of their lungs.  “Run!”

But the professor, with his precious bag in one hand and his hammer in the other, stood staring at the advancing bull through his thick glasses as if the maddened creature had been some sort of new and interesting specimen.