In the last light of day, looking round anxiously for early hunters, they drank hastily at the stream and started the climb up to their caves. They were still a hundred yards from the New Rock when the sound began.

It was barely audible, yet it stopped them dead, so that they stood paralyzed on the trail with their jaws hanging slackly. A simple, maddeningly repetitious vibration, it pulsed out from the crystal; and hypnotized all who came within its spell. For the first time – and the last, for three million years – the sound of drumming was heard in Africa.

The throbbing grew louder, more insistent. Presently the man-apes began to move forward, like sleepwalkers, toward the source of that compulsive sound. Sometimes they took little dancing steps, as their blood responded to rhythms that their descendants would not create for ages yet. Totally entranced, they gathered round the monolith, forgetting the hardships of the day, the perils of the approaching dusk, and the hunger in their bellies.

The drumming became louder, the night darker. And as the shadows lengthened and the light drained from the sky, the crystal began to glow.

First it lost its transparency, and became suffused with a pale, milky luminescence, Tantalizing, ill-defined phantoms moved across its surface and in its depths. They coalesced into bars of light and shadow, then formed intermeshing, spoked patterns that began slowly to rotate.

Faster and faster spun the wheels of light, and the throbbing of the drums accelerated with them. Now utterly hypnotized, the man-apes could only stare slack-jawed into this astonishing display of pyrotechnics. They had already forgotten the instincts of their forefathers and the lessons of a lifetime; not one of them, ordinarily, would have been so far from his cave, so late in the evening. For the surrounding brush was full of frozen shapes and staring eyes, as the creatures of the night suspended their business to see what would happen next.