At last they came to an open space, where the trees ceased to grow and where the tracks of the bear were lost in a rocky way. Beyond them lay the canyon, which had been once the bed of a river. Only the waters of the spring rains lay in the hollows of the rocks that lined its bottom.

Here the Cave People halted, for they knew not which way the black bear had taken, nor how to follow her. As they separated to seek further for her tracks, no word was spoken. Only Strong Arm gave a low grunt of approval, as his comrades departed.

Then, in the silence of the old world, it came, the strange voice echoing down the great canyon, grunting in the tones of Strong Arm! The whole tribe heard it and they paused, motionless, while their eyes swept the canyon for him who had spoken. But they saw no one.

Silently they gathered together, with weapons raised. But the stillness remained unbroken. Then Strong Arm raised his voice in a soft “Wough!” And in his own tone, the Echo answered him, “Wough!”

It was very strange. The Cave People could not understand. But they forgot the black bear and sent their voices ringing down the great canyon. Came again the echo, in many tones, back to them.

Then a great chattering arose among them, and even as they spoke, the chatterings of many voices arose from the canyon.

“Wough-ee!” said the Cave People. And they gave a sign in the gesture language, for they thought the sounds were the voices of their enemies, the Hairy Folk.

With great caution they departed to the point whence the sounds had come. Not boldly, but by varied paths they made their way, slowly, concealing themselves behind the rocks and the trees as they progressed. Long they hunted, one and all, but no man they found, nor any signs of man, and they returned at length to the mouth of the great canyon.

Again their voices rang down the bed of the old river, this time defiantly. And the Echoes replied once more, challenging them. The Cave People grew angry and the search was continued, but they found no one. And they were compelled to return to their caves in the Hollow with hearts heavy with wrath against the Hairy Folk.

Often they returned to the great canyon, bearing their bone weapons. There they remained long in hiding, awaiting the advent of the enemy, till at last they learned no one was there. Then the mystery grew more strange, for no man could tell whence came the voices that replied to them.