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 flaming liquid, but with dark crystal water. And on the bottom of that lake, clearly visible from the elevation upon which we stood, was a city! * * * * * A city below the water! The buildings were upright cylinders in groups of two or three, of dozens, even of hundreds. For miles, the bottom of the great lake was covered with them. They were all of crystal, azure-blue, brilliant as cylinders turned from immense sapphires. They were vividly visible beneath the transparent water. Not one of them broke the surface. Through the clear black water we saw moving hundreds, thousands of the giant crabs. The crawled over the hard, pebbled bottom of the lake, or swam between the crystal cylinders of the city. They were huge as the one we had seen, with red shells, great ominous looking stalked eyes, luminous green tentacular antennae and knobbed claws on forelimbs. "Looks as if we've run on something to write home about," Ray muttered in amazement. "A whole city of them! A whole world! No wonder they could build that cone-mountain for a lighting plant!" "When they got to knocking down airplanes with that heat-ray," he speculated, "they were probably surprised to find that other animals had developed intelligence." "Do you suppose those mushroom things are good to eat?" "We can try and see--if the crabs don't get us first with a heat-ray. I'm hungry enough to try anything!" Again we cautiously advanced. The river of light fell over a sheer precipice, but we found a metal ladder spiked to the rock, with rungs as inconveniently far apart as those in the shaft. It was five hundred feet, I suppose, to the bottom; it took us many minutes to descend. At last we stepped off in a little rocky clearing. The forest of brilliant mushrooms rose about us, great fleshy stalks of gold and graceful fringes of black and scarlet about them, with flattened heads of purple. We started eagerly across toward the fungoid forest. I had visions of tearing off great pieces of soft, golden flesh and filling my aching stomach with it. We were stopped by a sharp, poignantly eager human cry.