d 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.

"Gracious! He's a goner!" groaned Dick.

CHAPTER III.

THE PROFESSOR'S DILEMMA.

But the professor was seen to suddenly dart, with an activity they
would hardly have expected in him, across the road. He was only in the
nick of time.

Almost opposite to the gap in the fence he had made was a tree with
low-hanging boughs. As the bull charged through the gap, right on his
heels, the professor, still with his bag, slung by its leather strap
across his shoulders, swung himself up into the lower limbs.

The boys set up a cheer.

"Good for you, professor!" cried Dick, as the bull, wit