Before he could complete the thought there came a sudden dull reverberation from the swamp to eastward, a quivering of the ground beneath him, a rumbling thunder rapidly nearing him. In sudden panic he shrank back into the forest at the broad path's edge, and the next moment their appeared in the east along that path a mighty shape, thundering down the path toward him and dimly visible in the starlight. It was a brontosaur, he saw, bearing one of the dark lizard-shapes which rode at the base of its great neck, thundering down the path toward the west in giant, earth-shaking strides. Another followed it, and another, until four had passed, and then the thunder of their great tread died away in the west, as they galloped on toward Brinton. Rowan stared after them and then, as a sudden thought flared in his brain, he crept again from the sheltering trees and moved steadily eastward into the swamp, following the great path by which the brontosaurs had come. The path was beaten hard and flat, he found, and seemed to lead due eastward into the heart of the swamp. And as he followed it, as he crept onward, light came to his eyes from far ahead, a white brilliance which filtered faintly through the ranks of close-packed trees. Steadily Rowan crept on toward it, and then as its radiance began to strengthen he left the broad path and slipped again into the shelter of the forest, creeping forward ever more cautiously between the close-ranked trees and over the rotting, stagnant slime toward the source of the pallid light ahead. A dull roar of sound came to his ears as he went on, a whistling, shrieking clamor as of some great wind which raged ceaselessly, louder and louder as he neared it. Through the trees ahead he glimpsed a broad open space lit by the white radiance, and dropped to his knees, crawling silently on. At last he had crept to the very edge of the open space and lay crouched in the slime behind a great tree, peering tensely forward. Before him lay a great, flat mound of solid ground, elevated a few feet above the ooze of the swamp, roughly square in shape and fully one thousand feet across. It was quite bare and treeless, all vegetation upon it having apparently been sheared away, and was lit by a single globe of radiant white light suspended by a slender shaft of metal high above the great mound's surface. At the center of the broad, flat surface there yawned a tremendous pit which occupied half the mound's expanse, a vast circular shaft some hundreds of feet across whose smooth, perpendicular sides gleamed dully as though coated with metal. From where he crouched at the great mound's edge he could glimpse only the round mouth of the great shaft and a few feet of its downward-sinking sides, but he perceived that it was from this mighty pit that there roared upward the thunderous torrent of unceasing winds. Then his attention shifted from the great pit to the creatures grouped near its rim.