Then on a sudden instinctive hunch I turned to Snow. "Got a lipstick in that handbag of yours?"
She looked at me blankly, but nodded, and produced the slim metal tube for my inspection.
I took it from her fingers, slipped off the cap, and twirled up a half-inch of the glossy red wax. "Now let's see if I'm right about this wall," I said, and made a streaking motion across the rough surface with the lipstick.
The end of the wax cylinder came away a bit disturbed by its apparent contact with the surface before us, but the wall held no trace, no mark, not even a smudge. I saw the little curls of sheared-off wax falling down the face of the wall to the floor of the tunnel.
I handed the lipstick back to a bewildered Snow.
"Just as I thought," I said. "That, honey, is the rock known as parabolite. The toughest, most impervious substance in the solar system. Nothing marks it, scratches it, or even budges it. We couldn't get past here with an intercontinental size collapser!"
"But Jery, look!" Snow cried, pointing at the wall. I looked. The flat wall of parabolite, the impervious mineral, was going slowly concave in the center. I took hold of Snow by the shoulders, and pulled her back from that rapidly deepening hemisphere, expecting—I don't know what I was expecting. But I was scared speechless.
The thing bulged back away from us until its diameter was equal to that of the tunnel itself, and then, before my hypnotized gaze, the deepest section of the ruddy mineral gaped, like a hole suddenly pricked in the side of a bubble. The remainder of the parabolite wrenched violently away from the opening, leaving us a clear gateway into—
Into a vast chamber of eye-disturbing metal, that shifted and shimmered in some mind-chilling fashion that made me want to turn and run with Snow back down that black tunnel behind us.
"Come in, Jery Delvin," said the voice of an ancient Martian.