amphitheater debouched into a half dozen or more smaller corridors or openings; for a moment Captain Lane stood considering these silently, then he nodded toward that on their extreme left.

"Might as well go at it in orderly fashion. We'll try that one first. No, wait a minute!" He halted Tim, who had pressed obediently toward the corridor-mouth. "Try not to be a groundhog all your life, Mallory! You should know better than to stroll aimlessly around a place like this. A confounded labyrinth, that's what it is! If we got lost down here, we might spend the rest of our natural lives trying to find a way out."

He slipped his needle-gun from his bulger belt, let its scorching ray play for an instant on the rocky floor of the cavern. Hot rock bubbled, and a fresh, new groove shone sharply in the shape of an arrow.

"Every time we make a turn we'll do this. Then we can retrace our steps." Lane smiled sarcastically. "But a hot-and-cold engineer wouldn't think of a thing like that, I suppose?"

Tim made no reply. But he reproached himself secretly for not having considered this necessity; it did not make him feel much better that Dorothy, standing beside him, pressed his arm in mute encouragement.

The corridor was a short one, opening into another cavern like that which they had just quitted. Similar, but not quite the same. For as Lane played his light about the walls of this inner, deeper, chamber, all three adventurers gasped with the impact of sudden, breathtaking beauty. The ebon walls, warmed by the light, flashed into a glittering, scintilliscent miracle of loveliness; a galaxy of twinkling stars seemed to appear from nowhere and hang in dark space burning and gleaming.

"It—it's magnificent!" breathed the girl. "What is it, Daddy? Jewels? It looks like the fabulous caves of Ali Baba."

It was Tim who supplied the answer. "They're not jewels. Just nitre crystals protruding through a coating of black oxide of manganese. I've seen the same thing on Earth—in the Mammoth Cave of Kentucky."

And they moved on. Deeper and yet deeper into the Lethean depths, pausing from time to time to char a signpost for their retreat. Miracles without wonder they saw. Domes huge enough to house a spaceship, stalactites lowering like great, rough fangs from ceilings lost in dizzy heights, twin growths springing, oftimes without apparent reason, from the cavern floor—stalactites formed by centuries of slow lime dripping from the roof. And gigantic 

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