"How?"

"Look this way a bit," I said, showing towards the west, on the horizon, a black spot across the white plain.

It was six o'clock in the morning. The sun had risen. But it could not be found in the surprisingly polished air. And not a breath of air, not a breath. Suddenly one of the camels called. An enormous antelope had just come in sight, and had stopped in its flight, terrified, racing the wall of rock. It stayed there at a little distance from us, dazed, trembling on its slender legs.

Bou-Djema had rejoined us.

"When the legs of the mohor tremble it is because the firmament is shaken," he muttered.

"A storm?"

"Yes, a storm."

"And you find that alarming?"

I did not answer immediately. I was exchanging several brief words with Bou-Djema, who was occupied in soothing the camels which were giving signs of being restive.

Morhange repeated his question. I shrugged my shoulders.