fog. I was able to see only a few inches ahead of me for hours. Then, abruptly the trail grew clearer. Until, at last I was moving in the shadowless, unearthly mist over hard-packed snow, following the clearly marked footprints of a girl's sandals.

Then they vanished without warning, those prints, and I stood hesitant, staring around. I could see nothing, but a brighter glow in the misty canopy overhead marked the sun's position.

I knelt and brushed away the snow with my hands, hoping to undo the wind's concealing work. But I found no more footprints. Finally I took my bearings as well as I could and ploughed ahead in the general direction the girl had been traveling.

My compass told me I was heading due north.

The fog was a living, sentient thing now, secretive, shrouding the secret that lay beyond its gray wall.

Suddenly I was conscious of a change. An electric tingle coursed through my body. Abruptly the fog-wall brightened. Dimly, as through a translucent pane, I could make out vague images ahead of me.

I began to move toward the images—and suddenly the fog was gone!

Before me lay a valley. Blue-white moss carpeted it except where reddish boulders broke the blueness. Here and there were trees—at least I assumed they were trees, despite their unfamiliar outline. They were like banyans, having dozens of trunks narrow as bamboo. Blue-leafed, they stood like immense bird-cages on the pallid moss. The fog closed in behind the valley and above it. It was like being in a huge sun-lit cavern.

I turned my head, saw a gray wall behind me. Beneath my feet the snow was melting and running in tiny, trickling rivulets among the moss. The air was warm and stimulating as wine.

A strange and abrupt change. Impossibly strange! I walked toward one of the trees, stopped at a reddish boulder to examine it. And surprise caught at my throat. It was an artifact—a crumbling ruin, the remnant of an ancient structure whose original appearance I could not fathom. The stone seemed iron-hard. There were traces of inscription on it, but eroded to illegibility. And I never did learn the history of those enigmatic ruins.... They did not originate on Earth.

There was no sign of the native girl, and the resilient moss retained no tracks. I stood there, staring around, wondering what to do now. I was tense with excitement. But there was little to see. Just that valley covering perhaps a half-mile before the fog closed in around it.

Beyond that—I did not know what lay beyond that.

I went on, into the valley, eyeing my surroundings curiously in the shadowless light that filtered through the shifting roof of fog. Foolishly, I expected to discover Incan artifacts. The crumbled red stones should have warned me. They were, I think, harder than metal, yet they had been here long enough for the elements to erode them into featureless shards. Had they been of earthly origin they would have antedated Mankind—antedated even the Neanderthaler man.

Curious how our minds are conditioned to run in anthropomorphic lines. I was, though I did not know it, walking through a land that had its beginnings outside the known universe. The blue trees hinted at that. The crimson ruins told me that clearly. The atmospheric conditions—the fog, the warmth high up in the Cordilleras—were certainly not natural. Yet I thought the explanation lay in some geological warp, volcanic activity, subterranean gas-vents....

My vision reached a half-mile, no farther. As I went on, the misty horizon receded. The valley was larger than I had imagined. It was like Elysium, where the shades of dead men stroll in the Garden of Proserpine. Streamlets ran through the blue moss at intervals, chill as death from the snowy plains hidden in the fog. "A sleepy world of streams...."

The ruins altered in appearance as I went on. The red blocks were still present, but there were now also remnants of other structures, made by a different culture, I thought.

The blue trees grew more