Faint sounds of the life of the city came to their ears. A swarm of monoplanes roared past just beneath them. The streets were crowded with rapidly moving vehicles, the roof-tops with air-craft. Then suddenly the scene darkened; a deep rumbling came from the sea. As they watched in fascinated wonder, a great chasm opened up through the heart of the city. Tall buildings swayed and crumbled, falling into heaps of twisted metal and crushed masonry and burying hundreds of the populace in their fall. The confusion was indescribable, the uproar terrific, and within the space of a very few minutes the entire city was a mass of ruins, fully half of the wrecked area having been swallowed up by the heaving waters of the ocean. * * * * * Phaestra stifled a sob. "Thus it began," she stated. "Trovus was first--the city you just saw--then came three more of the cities of the western coast in rapid succession. Computations of the scientists showed that the upheaval was widespread and that the entire continent was to be engulfed in a very short time. The exodus began, but it was too late, and only a few hundred people were able to escape the continent before it was finally destroyed. The ocean became the tomb of two hundred millions. The handful of survivors reached the coast of what is now North America. But the rigors of the climate proved severe and more than three-quarters of them perished within a few days after their planes landed. Then the rest took to the caves along the shore, and for a while were safe." She manipulated the controls once more and there was a quick shift to another coast, a rugged, wave-beaten shore. Closer they drew until they observed a lofty palisade that extended for miles along the barren waterfront. They saw a fire atop this elevation and active men and women at various tasks within the narrow circle of its warmth. A cave mouth opened at the brink of the precipice near the spot they occupied. Then came a repetition of the upheaval at Trovus. The ocean rushed in and beat against the cliff with such ferocity that its spray was tossed hundreds of feet in the air. The earth shook and the group of people around the fire made a hasty retreat to the mouth of the cave. The sky darkened and the winds howled with demoniac fury. Quake after quake rent the rugged cliffs: huge sections toppled into the angry waters. Then a great tidal wave swept in and covered everything, cliffs, cave mouths and all. Nought remained where they had been but the seething waters. * * * * * "But some escaped!" exulted Phaestra, "and these discovered Theros. Though many miles of the eastern seaboard of your United States were submerged and the coastline entirely altered, these few were saved. Their cave connected with a long passage, a tunnel that led into the bowels of the earth. With the outer entrance blocked by the upheaval they had no alternative save to continue downward."