A valley. Its length reached out before them to end some half mile away. Sides that might once have sloped evenly seemed weathered to a series of great steps, and an alternation of striations in black and white made a banding that encircled the entire oval. Each step was dead-black stone, each riser was snow-white marble; and the steps mounted up and up until they resembled the sides of a great bowl. In the center, like an altar for the worship of some wild, gargantuan god, was a stepped pyramid of the same startling black and white. Banded like the walls, it rose to half their height to finish in a capstone cut square and true. An altar, perhaps; an arena, beyond a doubt, or so it seemed to Chet. He was first to put the impression in words. "A stadium!" he marvelled; "an arena for the games of the gods!" "The gods," Diane breathed softly, "of a wild, lost world--" But Chet held to another thought. "Who--who built it?" he asked. "It's tremendous! There is nothing like it on Earth!" * * * * * Only Kreiss seemed oblivious to the weird beauty of the spectacle. To Professor Kreiss dolomite and black flint rock were dolomite and black flint; interesting specimens--a peculiar arrangement--but nature must be permitted her little vagaries. "Who built it?" He repeated Chet's question and gave a short laugh before answering in words. "The rains, Herr Bullard, and the winds of ages past. Yes, yes! A most remarkable example of erosion--most remarkable! I must return this way some time and give it my serious attention." Harkness had not spoken; he was shaking his head doubtfully at Kreiss' words. "I am inclined to agree with Chet," he said slowly. "But who could have built a gigantic work like this? Have there been former civilisations here?" He straightened up and shook himself free from the effects of the wild, barbaric scene. "And you needn't come back," he told Kreiss; "you can have a look now, to-night, by moonlight. We can't go on. I think we'll be safest on that big altar rock; nothing will get near us without our knowing." Chet felt Diane Delacouer's hand on his arm; her other hand was gripping at Harkness. The shiver that passed through her was plainly perceptible. "I'm afraid," she confessed in a half-whisper; "there's something about it: I do not like it. There is evil there--danger. We should not enter." Walt Harkness gently patted the hand that trembled on his arm. "I don't wonder that you are all shot to pieces," he assured her. "After last night, you've a right to be. But I really believe this is the safest spot we can find." * * * * *