"Have you any idea what caused the noise just then, Dick?" asked Crane; who, with characteristic imperturbability, had taken out his notebook and was making exact notes of all that transpired. "I imagine we cracked a few of his plates," replied Seaton with a laugh, as he held the Skylark in place a few hundred feet above the fleeing animal. Pitted for the first time in its life against an antagonist, who could both outfly and outfight it, the karlon redoubled its efforts and fled in a panic of fear. It flew back over the city of Kondalek, over the outlying country, and out over the ocean, still followed easily by the Skylark. As they neared the Mardonalian border, a fleet of warships rose to contest the entry of the monster. Seaton, not wishing to let the foe see the rejuvenated Skylark, jerked his captive high into the thin air. As soon as it was released, it headed for the ocean in an almost perpendicular dive, while Seaton focused an object-compass upon it. "Go to it, old top," he addressed the plunging monster. "We'll follow you clear to the bottom of the ocean if you go that far!" There was a mighty double splash as the karlon struck the water, closely followed by the Skylark. The girls gasped as the vessel plunged below the surface at such terrific speed, and seemed surprised that it had suffered no injury and that they had felt no jar. Seaton turned on the powerful searchlights and kept close enough so that he could see the monster through the transparent walls. Deeper and deeper the quarry dove, until it was plainly evident to the pursuers that it was just as much at home in the water as it was in the air. The beams of the lights revealed strange forms of life, among which were huge, staring-eyed fishes, which floundered about blindly in the unaccustomed glare. As the karlon bored still deeper, the living things became scarcer, but still occasional fleeting glimpses were obtained of the living nightmares which inhabited the oppressive depths of these strange seas. Continuing downward, the karlon plumbed the nethermost pit of the ocean and came to rest upon the bottom, stirring up a murk of ooze. "How deep are we, Mart?" "About four miles. I have read the pressure, but will have to calculate later exactly what depth it represents, from the gravity and density readings." As the animal showed no sign of leaving its retreat, Seaton pulled it out with the attractor and it broke for the surface. Rising through the water at full speed, it burst into the air and soared upward to such an incredible height that Seaton was amazed. "I wouldn't have believed that anything could fly in air this thin!" he exclaimed. "It is thin up here," assented Crane. "Less than three pounds to the square inch. I wonder how he does it?"