The Alien Intelligence by Jack Williamson

The sun dropped beneath the rim, and the purple dusk began to thicken and to creep over the valley floor. I took up my precious equipment, and Melvar and I walked off through the red brush in the direction of the mountain. The vast strange buildings of the city of gems were still glowing with soft color, and the cold, bright surface of the Silver Lake flashed often into sight beyond the rolling eminences. Presently we came to a well-worn path through the crimson scrub, but I saw nothing to indicate that anyone had thought of paving or improving it. But the Astranians did not seem to have much energy for any kind of public work. Their material civilization appeared to be on a rather low scale. In fact they supplied their wants in the way of food entirely with the abundant fruit of the red bushes. As I had guessed from the girl's remarks, they did not even have the use of fire. Indeed the great physical and mental development of the race and the splendid city in which it lived was strangely contrasted with their absolute lack of scientific knowledge.

Our pace was hastened by thoughts of the terrors that night would bring, and perhaps because of them, we walked nearer one another, and presently we were hurrying along, hand in hand. About us the purple night deepened and, beyond the argent brilliance of the Silver Sea, the strange evil of the night gathered itself for the attack.