directions for each one that it led eastward. Realizing this, the explorers lifted the helicopter and began checking as close to the cliffs as Lampert dared at higher levels. In this way they worked back toward the camp site. Once again it was Mitsuitei who first spotted something of major interest.

"Found another city, Take?" asked Sulewayo at the other's call.

"Not exactly. It's—well, I guess it's really a system of those joints you keep talking about. Still, it looks awfully regular." He sounded a little wistful.

"It does." The paleontologist nodded slowly. "As you say, it's probably a joint system. Also, it's probably full of volcanic ash, if my eyes don't deceive me. Rob, what's the chance of a landing on one of the shelves? There are at least three formations accessible on foot from that point; and I could get some more tuff samples to make or break your peace of mind, while I was doing my own work."

Lampert examined the area carefully. Like Earth's Grand Canyon, this one receded from time to time in shelves where softer layers of rock had worn further back, or the orogenic processes had paused to give the river a longer bite at that level. The cracks Mitsuitei had seen formed a neat crisscross pattern on the top of one of the shelves. Some of them betrayed their nature by emerging from its vertical face. It was admittedly an unusually small-scale joint pattern, at least for this mountain system, and might well contain readable evidence of the forces which had shaped the area.

However, they had only one helicopter. Lampert slowly shook his head in negation.

"I'm afraid not, Ndomi. Your shelves may be big enough, but they're not level enough. I'd have to make a swinging landing, and I'm not that good a pilot."

"Well, how about letting me down on the ladder? We have a hundred feet of that, so you could be up above the next shelf while I went down. You'd have plenty of blade clearance. That next level goes back a couple of hundred feet."

"That might be all right." Lampert spoke hesitantly. "You certainly have the right to risk your own neck on the climb if you want to. We won't try it tonight, though. I'd like to check with String on the advisability of your being there alone. The place looks pretty hard to reach for anything that doesn't fly, and I don't know of any really dangerous flying things on this world; but we'd still better check."

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