st of it. One hoof seemed to
hesitate, hanging in the air by itself. Then it was gone.

Jan turned desperately to avoid the spot and brought himself to a halt a
few feet beyond. The hair on the back of his neck felt prickly with fear
of the unknown. He returned cautiously to inspect the mysterious,
glistening square slab.

It was no more than four feet across each way. There was no way of
telling what its surface was like. About where its surface might be was
a soft carpet of glistening, cool force that seemed neither solid nor
fluid. It was something like the surface of a glowing ember in a dying
fire, smoothed out flat and spread with uniformity over an area of
sixteen square feet.

Jan's eyes pulled away from this fascinating thing and turned to survey
what had first caused him to break his pace in surprise. A short
distance away a skeleton of twisted and sheered off steel girders hinted
at what had once been a bridge across a deep gash in the rolling
terrain. On the other side was what had once been a huge city of
sky-scrapers, though Jan had never heard of such a thing and did not
know that that was what it had been.

[Illustration: Nothing was visible in the mysterious plate, yet a man
had gone into it!]

With a frown of uneasiness he dismissed the ruins of the city and the
bridge and turned to the mysteriously glowing square once more. The deer
had vanished over it. Therefore it must have something to do with the
vanishing of the deer. Since he had chased the deer so far, it would be
foolish to turn away without investigating. The deer might still be
there somewhere.

Jan's face lit up with an idea. He looked around until he spied a rock
about as big as a fist. He came back with it and stood thoughtfully near
the edge of the mysterious square. Then he tossed it with just enough
force to carry it across. When it reached a point above the edge of the
square it vanished. Jan waited, but it didn't land on the other side. It
had simply ceased to exist!

Jan looked thoughtful for a moment. He turned and went back to the patch
of blackberry bushes. Taking his long slim blade from its deerskin
scabbard he cut a long, tough stick, trimming the younger shoots away.
With this he returned to the calmly glistening, mysterious slab.

Ready to drop his hold on the stick at the first sign of the unusual, he
thrust it part way into the area where things vanished. The end of the
stick disappeared. There was no sign of an