Ray picked up a block
of black lava that lay beneath his hand and hurled it silently and
swiftly. It crashed splinteringly on the rocks far beyond the
creature, on the other side of the stream of light.

In fascination I watched the monster as it paused as if astonished.
The glittering compound eyes twisted about on their stalks, and the
long shining green tentacles wavered questioningly. Then the knobbed
limbs snapped the white metal tube to a level position. A metallic
click came from it.

And a ray of red light, vivid and intense, burst from the tube. It
flashed across the river of fire. With a dull, thudding burst it
struck the rocks where the stone had fallen. It must have been a ray
of concentrated heat. Rocks beneath it flashed into sudden
incandescence, splintered and cracked, flowed in molten streams.

* * * * *

In a moment the intensely brilliant ruby ray flashed off. The rocks in
the circle where it had struck faded to a dull red and then to
blackness, still cracking and crumbling.

To my intense relief, the monstrous crab lumbered on.

"That," Ray whispered, "is what got Major Meriden's airplane wing."

When we could hear its scraping progress no longer, we climbed up from
behind our boulder and continued cautiously down the cavern, beside
the rushing luminous river. In half a mile we came to a bend. Rounding
it, we gazed upon a remarkable sight.

We looked into a huge cavity in the heart of the earth. A vast
underground plain lay before us, with the black lava of the roof
arching above it. It must have been miles across, though we had no way
to measure it, and it stretched down into dim hazy distance. Its level
was hundreds of feet below us.

At our feet the glistening river of fire plunged down again in a
magnificent flaming fall. Below, its luminous liquid was spread out in
rivers and lakes and canals, over all the vast plain. The channels ran
through an amazing jungle. It was a forest of fungus, of mushroom
things with great fleshy stalks and spreading circular tops. But they
were not the sickly white and yellow of ordinary mushrooms, but were
of brilliant colors, bright green, flaming scarlet, gold and
purple-blue. Huge brilliant yellow stalks, fringed with crimson and
black, lifted mauve tops thirty feet or more. It was a veritable
forest of flame-bright fungus.

In the center of this weirdly forested subterranean plain was a great
lake, filled, not with the