With difficulty Waldo suppressed a shriek of dismay as he turned to plunge madly down the precipitous trail. The girl had not yet descended from the ledge above. She must have sensed what had happened, for as Waldo turned to fly she gave a little cry of terror. At the same instant the cave man leaped to his feet. But the girl's voice had touched something in the breast of Waldo Emerson which generations of disuse had almost atrophied, and for the first time in his life he did a brave and courageous thing. He could easily have escaped the cave man and reached the valley--alone; but at the first note of the young girl's cry he wheeled and scrambled back to the ledge to face the burly, primitive man, who could have crushed him with a single blow. Waldo Emerson no longer trembled. His nerves and muscles were very steady as he swung his cudgel in an arc that brought it crashing down upon the upraised guarding arm of the cave man. There was a snapping of bone beneath the blow, a scream of pain--the man staggered back, the girl sprang to Waldo's side from the ledge above, and hand in hand they turned and fled down the face of the cliff. From a dozen cave-mouths above issued a score of cave men, but the fleeing pair were half-way across the clearing before the slow-witted brutes were fully aware of what had happened. By the time they had taken up the pursuit Waldo and the girl had entered the forest. For a few yards the latter led Waldo straight into the shadows of the wood, then she turned abruptly toward the north, at right angles to the course they had been pursuing. She still clung to the young man's hand, nor did she slacken her speed the least after they had entered the darkness beneath the trees. She ran as surely and confidently through the impenetrable night of the forest as though the way had been lighted by flaming arcs; but Waldo was continually stumbling and falling. The sound of pursuit presently became fainter; it was apparent that the cave men had continued on straight into the wood; but the girl raced on with the panting Waldo for what seemed to the winded young man an eternity. Presently, however, they came to the banks of the little stream that had been visible from the caves. Here the girl fell into a walk, and a moment later dragged the Bostonian down a shelving bank into water that came above his knees. Up the bed of the stream she led him, sometimes floundering through holes so deep that they were entirely submerged. Waldo had never learned the vulgar art of swimming, so it was that he would have drowned but for the strong, brown hand of his companion, which dragged him, spluttering and coughing, through one awful hole after another, until, half-strangled and entirely panic-stricken, she hauled him safely upon a low, grassy bank at the foot of a rocky wall which formed one side of a gorge, through which the river boiled.