As they approached they saw that it was undoubtedly the work of human hands. It was shaped like a pyramid, and on either side stretched level land, covered with a dense growth of forest or underbrush.
“There are steps leading to the top!” cried Bob, who had gone around to the far side of the artificial hill. The others joined him and saw him ascending a rude flight of stairs made of stones set into the side of the mound.
“Better go slow,” advised Jerry. “No telling what’s up there.”
“Let me look for relics!” exclaimed the professor, and he hurried past Bob. “I’m sure there must be lots of them in this place.”
Bob stood aside while Jerry, who, as usual, assumed the leadership when there was a hint of danger, took the rifle. Then he started to follow the professor.
Jerry had not taken half a dozen steps when he trod on a loose stone. He nearly fell backward but recovered himself by an effort. In doing so, however, he leaned too far to one side. The next instant he had fallen and slid to the bottom of the mound.
The hammer of the gun came in contact with a stone or stick, and the weapon was discharged with a loud report. Fortunately the muzzle was pointed upward, and the bullet endangered no one.
“Are you hurt?” cried Ned and Bob, hurrying to Jerry’s aid.
They noticed that his face was white and drawn.
“I’m—afraid so,” he murmured, clenching his teeth to keep back a murmur of pain.