However, later in the day it seemed as if their particular camp had petered out. There were ruins there—a broken-down wall, a dry well and a bit of eroded bas-relief lying on its side. Burl's father looked at him thoughtfully. The tall, sandy-haired youth was sitting astraddle a pile of dust, methodically sifting it through a wide-mesh strainer. A large pile of sifted sand gave evidence of the length of his efforts, and one broken bit of clay was the only result he had obtained.
Two of the Indian guides sat patiently in the shade, watching them. One was digging slowly, turning up more dirt to be sifted.
"I think we've had enough here," said the elder Denning. "Burl, you can knock off. Tomorrow we'll pull up stakes and see what is in the next valley. We'll try to follow that old Inca road over the mountains. I don't believe anyone has ever penetrated there—and the airplane surveys indicated some evidence of human dwellings."
Burl nodded, and set the sifter down. He'd learned to curb his natural energies for the exacting tasks required of serious scientific research. "Okay," he said, "I was hoping you'd move on soon, Dad. This looked like a washout from the first. I'd say this place was sacked and ruined even before the Incas fell."
The older man nodded. "I suppose so. Well, let's wash up and see what's for supper."
They went down to the icy mountain stream to wash the dirt from their hands. "It's been a nice day," Burl commented. "In spite of the Sun being out steadily, it wasn't hot at all. Cooler than yesterday."
Mark Denning looked up at the sky and the Sun lowering toward the horizon. "There must have been some volcanic dust in the heavens," he said. "The Sun's been a bit dimmed, have you noticed?"
Burl squinted his eyes against the glare. "Wasn't any eruption around here. Maybe in Ecuador?"
His father shrugged. "Could have been thousands of miles away," was his slow reply. "Volcanic dust travels around the world, just as radioactive dust permeated the atmosphere from atomic testings. They say that the dust from the great Krakatoa explosion remained in the atmosphere for three years before the last of it settled."
When they had finished supper and the Sun was casting its last red rays over the rapidly purpling landscape, Burl got out the expedition radio, set up its antenna, plugged in its compact atomic battery, and tried to get the news from Lima. All he got was static.