A sharp horn projected from its mouth, and its gleaming eyes flashed like balls of fire.
With an ugly snort the queer creature started for the rock upon which the pair stood.
"I guess I had better shoot him," said Jack. "He might be able to jump up here."
Leveling his rifle at one of the animal's eyes, he pulled the trigger.
The bullet was true to its mark, and the next instant the beast was rolling upon the ground in the throes of death.
"That was a good shot," observed Joe, in an admiring tone. "But, look! there comes another!"
Sure enough, another of the beasts emerged from the passage; but that was not all. Another, and still another followed.
It was at this state of affairs that the two heard the muttered sound of a pistol shot.
"Our friends are coming to our rescue," exclaimed Jack. "Now, then, we have got to kill off these things at once, so they will not be attacked by them before they reach us."