In reply to Mr. Barr's question, the ensign nodded. "The strain is already pretty strong," he said; "we don't want to force her too hard." Accordingly the inventor, utilizing the auto control device, cut down the speed till, instead of ploughing through the waves, the _Peacemaker_ skimmed over them. Unlike most submarines, which cannot do otherwise than plunge into heavy seas, the _Peacemaker's_ hull was so constructed that she rode the waves like a duck. After a while the sensation of heaving and falling began to get upon Mr. Barr's nerves. "I'm feeling a bit squeamish," he declared; "let's dive and get out of this." The ensign nodded and laughed. "Our friend Rob here is getting a bit pale, too," he said; "and as we don't want a sea-sick crew, maybe we had better seek the seclusion of Davy Jones' locker." An instant later the _Peacemaker_ was plunging downward. At a depth of twenty feet the angry motion of the waves was unfelt. In those dim depths all was as quiet and undisturbed as if the elements were at perfect peace above. Down, down dropped the submarine till her depth indicator showed that she was submerged five hundred fathoms. "The chart gives seven hundred hereabouts," commented Ensign Hargreaves, glancing at it; "so I guess we are safe for forty miles more before the floor of the ocean slopes upward. We must go up a bit higher then." The inventor nodded. "I understand," he said, and then, "we are now running at what speed?" The ensign turned to the speed indicator. "A trifle under twenty miles an hour," he said. Mr. Barr glanced at the clock before him, which was illuminated by a tiny shaded electric bulb. "I'll keep on this course at this speed for about two hours then," he determined. "That will be all right, I imagine," was the rejoinder, "but don't keep on too long. The bed of the sea, according to the chart, rises up very rapidly further on. It must be almost cliff-like in its sudden elevation." "I'll be on the lookout," the inventor assured him. Rob descended the ladder once more and reëntered the engine room to find out how Merritt was getting along. He found the young engineer seated on the leather lounge alongside the engines watching them lovingly. "Work smoothly, don't they?" he said. "They sure do," was the other's response; "smoothly as a Geneva watch." The boys sat chatting on various matters, and the time flew along rapidly till Rob suddenly looked at his watch. "Almost two hours. It's time we were rising," he said. "What do we want to rise for? It's deep enough here, isn't it?" "That's just it. The ensign says that the chart shows that a sort of submarine cliff looms up right ahead of us somewhere hereabouts." "Great ginger snaps! I thought the bottom of the sea was as level as a floor." "Not a bit of it. It's as full of mountainous regions and flat, depressed plains and valleys as the Rockies themselves." "Gee whiz! I'd hate to hit one of them. I----"