It was extremely difficult to manage the _Snowbird_, for she answered to the levers so much more quickly than before. The air pressure on the craft was so slight that at the least touch she mounted upward like a scared quail! The speed of the aeroplane had to be reduced, too; they traveled scarcely forty miles an hour. On either hand as they winged their way over the great river of ice (it was quite four miles broad) sharp cliffs arose, guarding the glacier. These cliffs ranged from two hundred to a thousand feet high. The professor, at once interested in such a marvel of nature, begged Jack to reduce the speed even more. They merely floated above the cracked expanse of whitish-green ice for some minutes. "That's what the earthquakes did for it," said Phineas Roebach. "You see those crevasses--and some of 'em mighty deep? Well, they weren't here the last time I came this way." "She is in motion again, perhaps," suggested Professor Henderson. "It ain't been in motion for ages--or, so the Aleuts say," responded the oil hunter. "But there looks now to be some sagging forward. There is a crevasse splitting the glacier from wall to wall," proclaimed the scientist. "We'd never be able to sled over this trail in the world!" cried Mark. "How would you pass such a yawning gulf as that?" "It beats me what's happened here since I was across last," muttered Roebach, scratching his head in bewilderment. The yawning ice was right beneath the flying machine. It was a hundred yards across at the surface. They seemed to be looking down for five hundred feet, or more, into its greenish depths. Jack had turned the _Snowbird's_ prow and they were drifting toward the western cliffs which guarded the glacier. Here the rocky heights were at least seven hundred feet above the ice. Out of a crack in the high wall--from its eyrie without doubt--a huge female eagle suddenly shot down toward the drifting aeroplane. The flying machine seemed not to startle the great bird at all; it only angered her. Perhaps she had young up there in the cliff and she feared her hereditary enemy, Man, was coming on wings to deprive her of them. With a scream of rage the eagle dashed herself directly into the face of Jack, strapped to the operator's seat. For once Andy Sudds had not his rifle at hand; and, the attack was so unexpected, it is doubtful if he could have come to the rescue in season. With beak and claws the bird endeavored to tear at the youth's face. Jack jerked loose the transmitter and beat it to pieces over the bird, but without making her desist. Again and again the feathered creature darted in, claws expanded and beak snapping. With one talon she raked Jack's right arm and shredded the heavy coatsleeve, the sleeve beneath, and scratched his arm. The next instant her iron beak snapped upon his left hand. Jack Darrow was plucky, but the pain of the wound brought a scream to his lips. It was answered by the wild shrieks of the eagle.