Yorg led Thor to a great circular building with walls of glass, where sunlight fused across a tile floor, making the room alive with light. A girl with long yellow hair turned from a group at the end of the chamber. She screamed her delight. "Thor! Peter, Slag, it's Thor!" Their delight chased the worry from their eyes and faces for a few moments, as they shook his hand and pounded his shoulders. Peter Gordon said, "Jolly good to have you back, old man. But I'm afraid even having you here won't do any good. The androids have us surrounded. You say they are bringing Aava in the urns. Looks as though it's all over." "Not yet," Thor growled, and told them of the Discoverer, and the astral voyage they had made. Gordon wrinkled furrowed brows. "Can't see what good knowing that is, you know. It--" "Think, man. I'm not too good at chemistry, but there are clues and hints all over this planet. Most of it is sand, rolling mile after mile. Even the red grasslands have sandy beds. And the rocks. There is almost as much rock as sand. What do you and the robots build your cities of? Clay! What jewels are embedded in the cave where Aava dwells? Opal, onyx, carnelian, jasper! "Aava lives in a circle of pure quartz. Look!" * * * * * Thor put his hand in his pocket, drew out tiny green flecks of crystal, "I got this by scraping the urn where Aava appeared to his androids in the temple. It's glass! Something in Aava's nature was hardened by oxygen, and the sand in the substance of the urn turned into glass! "When the Discoverer took me out into space and back in Time, when I saw the worlds of this space-realm created, one thing struck me. I watched Aava and his planet evolve from an empty void, saw the planet grow and take form. "Gordon, I saw no fern forests, no great jungles of vegetation whose rotting and sinking into peat bogs gave us coal. Coal is carbon. And there were no petroleum wells, and petroleum is a compound of hydrocarbons." Gordon rubbed his chin, frowning. "It's all jolly interesting, old man." Thor waved a hand. "Can't you see? It all argues just one thing. No coal, no oil. No forms of carbon at all. Just quartz, sand, onyx, jasper, clay, carnelian, opal, rock--all forms of silicon. "Aava is silicate life, where we are carbon life!" The Englishman whistled low. Thor went on, "Silicon is almost as ingenious as carbon. Both have a valence of six. Both unite with other substances to form various compounds. But, just as life with carbon structure cannot stand its own refuse--the carbon dioxide that we exhale when we breathe, so life with a silicate base cannot stand its own refuse--silicon dioxide--or _sand_!" "Afraid I'm rather stupid, old man. Not following you very well."