The diameter of this enormous pit was fully a thousand feet. The walls were smooth and appeared to be composed of a black, basaltic rock.
For a moment the vessel hovered motionless directly above the centre of the gaping void, then slowly she began to settle into the black chasm. Lower and lower she sank until as darkness enveloped us her lights were thrown on and in the dim halo of her own radiance the monster battleship dropped on and on down into what seemed to me must be the very bowels of Barsoom.
For quite half an hour we descended and then the shaft terminated abruptly in the dome of a mighty subterranean world. Below us rose and fell the billows of a buried sea. A phosphorescent radiance illuminated the scene. Thousands of ships dotted the bosom of the ocean. Little islands rose here and there to support the strange and colourless vegetation of this strange world.
Slowly and with majestic grace the battleship dropped until she rested on the water. Her great propellers had been drawn and housed during our descent of the shaft and in their place had been run out the smaller but more powerful water propellers. As these commenced to revolve the ship took up its journey once more, riding the new element as buoyantly and as safely as she had the air.
Phaidor and I were dumbfounded. Neither had either heard or dreamed that such a world existed beneath the surface of Barsoom.
Nearly all the vessels we saw were war craft. There were a few lighters and barges, but none of the great merchantmen such as ply the upper air between the cities of the outer world.
"Here is the harbour of the navy of the First Born," said a voice behind us, and turning we saw Xodar watching us with an amused smile on his lips.
"This sea," he continued, "is larger than Korus. It receives the waters of the lesser sea above it. To keep it from filling above a certain level we have four great pumping stations that force the oversupply back into the reservoirs far north from which the red men draw the water which irrigates their farm lands."
A new light burst on me with this explanation. The red men had always considered it a miracle that caused great columns of water to spurt from the solid rock of their reservoir sides to increase the supply of the precious liquid which is so scarce in the outer world of Mars.
Never had their learned men been able to fathom the secret of the source of this enormous volume of water. As ages passed they had simply come to accept it as a matter of course and ceased to question its origin.