eyes was a fissure whence emanated a wailing and a foul odor. Hundreds of short, clawed legs slithered on the rocks under a long sinuous body. Then it seemed to leap into the air again. Webs grew taut between the legs, strumming as they caught a strong uphill wind. Again it turned to the attack, and missed them. This time Forepaugh was ready for it. He shot at it with his flash pistol.

othing happened. The fog made accurate shooting impossible, and the gun lacked its former power. The web serpent continued to course back and forth over their heads.

"Guess we'd better run for it," Forepaugh murmured.

"Go 'head!"

They cautiously left their places of concealment. Instantly the serpent was down again, persistent if inaccurate. It struck the place of their first concealment and missed them.

"Run!"

They extended their weary muscles to the utmost, but it was soon apparent that they could not escape long. A rock wall in their path saved them.

"Hole!" the Martian gasped.

Forepaugh followed him into the rocky cleft. There was a strong draft of dry air, and it would have been next to impossible to hold the Martian back, so Forepaugh allowed him to lead on toward the source of the draft. As long as it led into the mountains he didn't care.

The natural passageway was untenanted. Evidently its coolness and dryness made it untenable for most of Inra's humidity and heat loving life. Yet the floor was so smooth that it must have been artificially leveled. Faint illumination was provided by the rocks themselves. They appeared to be covered by some microscopic phosphorescent vegetation.

After hundreds of twists and turns and interminable straight galleries the cleft turned more sharply upward, and they had a period of stiff climbing. They must have gone several miles and climbed at least 20,000 feet. The air became noticeably thin, which only exhilarated Gunga, but slowed the Earth man down. But at last they came to the end of the cleft. They could go no further, but above them, at least 500 feet higher, they saw a round patch of sky, miraculously bright blue sky!

"A pipe!" Forepaugh cried.

He had often heard of these mysterious, almost fabulous structures sometimes reported by passing travelers. Straight and true, smooth as glass and apparently immune to the elements, they had been occasionally seen standing on the very tops of the highest mountains—seen for a few moments only before they were hidden again by the clouds. Were they observatories of some ancient race, placed thus to pierce the mysteries of outer space? They would find out.