The portion of the great iceberg that was visible consisted of a good many square miles of hills and valleys of ice, with the two more important eminences standing close together near the middle of the vast field. It was so huge that its movement (and bergs are always in motion) could not be observed at all. It seemed as immovable as the island of Iceland itself, yet Captain Olaf Karofsen was positive that it had drifted a good many miles southward during the two weeks since his schooner had been wrecked on one of the outer reefs of the berg. As the _Winged Arrow_ swooped lower, and Tom Swift drove it around the entire outer edge of the iceberg, the schooner captain tried to mark the spot where the _Kalrye_ had struck and sunk and the spot where the lifeboat had been smashed. There was not a scrap of either wreck to be seen. The changing surface of the ice offered no certain mark of any party of castaways having been upon it. The seaplane circumnavigated the huge berg twice with the same result. The hearts of Tom and Ned failed them. They feared that the disaster had been wholly tragic, after all. But Captain Karofsen would not give up hope. He pointed out that his five sailors were all seasoned men, used to the Arctic, and of wide experience. First of all, he said, they would have saved the boat, cut it up with the boat axes, and transported it and the provisions to some sheltered place on the berg. “There be hunderts of caves—yes? Many, many places for to hide and keep varm. Iceland men don’t gif up so easy, Misder Swift.” It was plain to be seen that there were many valleys and sheltered dens in the middle of the berg into which the crew of the seaplane could not see. The flying boat might pass back and forth over the iceberg a hundred times and not be spied by the castaways if they were thus holed up. “But we do not even see any smoke,” said Ned. “If they had a fire——” “They would be careful with their fuel,” interrupted Tom. “We might hang around up here for a couple of days and miss seeing anything of them if they are there——” “A wise ‘if,’” interrupted Ned. “Unless they come out to hunt food——” “Hoh!” cried Ned again. “Dig potatoes, I suppose?” “Don’t be foolish!” commanded Tom. “There are seals and bears, and Captain Karofsen says that both Mr. Damon and Mr. Nestor had rifles.” “That’s right,” agreed Ned. “I did not think of that.” “So,” concluded Tom firmly, “I am going to descend into that middle valley——” “Not between those two peaks, Tom?” cried his friend. “That is a bad hole to get out of.” “I mean the valley just beyond. See! Look close.” He managed the controls so that the great flying boat headed in between the tall pinnacles of ice. As they rushed into the narrow valley between the greenish-white walls of ice, they found the cleft much deeper than they had at first supposed. There was an unexpected draught through the passage, too.