The ground had risen, the groove had stayed level and gone underground.
Except that now it wasn't a groove. It was a round tunnel.
A hole.
A few paces farther on, I thumped the ground with my heel where the hole ought to be. The dirt crumbled, and there was the little dark tunnel, running straight in both directions.
I walked on, the ground falling away gradually again. The entire process was repeated in reverse. A hairline appeared in the dirt—widened—became lips that drew slowly apart to reveal the neat straight four-inch groove—which shrank as slowly to a shallow line of the ground—and vanished.
I looked ahead of me. There was one low ridge of ground between me and the enormous boulders. A neat four-inch semicircle was bitten out of the very top of the ridge. In the house-sized boulder directly beyond was a four-inch hole.
Allenby winced and called the others when I came back and reported.
"The mystery deepens," he told them. He turned to me. "Lead on, Peters. You're temporary drill leader."
Thank God he didn't say Fall in.