Marian understood, and her admiration for Phi grew. He had found the trail of the men who had crossed the Straits before them. He had put Rover on that trail. Rover could not fail to follow. The trail was fresh, only seven hours old. Rover could have followed one as many days old.
"Good old Rover," Marian murmured, "good old Rover, a white man's dog."
All at once a question came to her mind. They had been obliged to go several miles north to pick up the trail. This was due to the movement of the floe. This movement still continued. It was carrying them still farther to the north. The Diomede Islands, halfway station of the Straits, were small; they offered a goal only two or three miles in length. If they were carried much farther north, would they not miss the islands?
She confided her fears to Phi.
"I thought of that," he smiled. "There is a little danger of that, but not much, I guess. You see, I'll try to time our rate of travel, and figure out as closely as I can when we have covered the eighteen miles that should bring us even with the islands. Then, too, old Rover will be losing the trail about that time. When that bearded friend of yours and his guide leave the floe to go upon the solid shore ice of the islands, the floe is going to keep right on moving north. That breaks the trail, see? When we strike the end of that trail we can go due south and hit the islands. If the air is at all clear, we can see them. It's a clumsy arrangement, but better than going it without a trail."
Marian did "see," but this did not entirely still the wild beating of her heart as she leaped a yawning chasm between giant up-ended cakes of ice, or felt her way cautiously across a strip of newly-formed ice that bent under her weight as if it were made of rubber.
It was with a strange, wild thrill that she realized they were far out over the conquered sea. Hundreds of feet below was the bed of Bering Straits. Above that bed a wild, swirling current of frigid salt water raced.
Once, as they were about to cross a stretch of new ice, Phi threw himself flat and hacked a hole through the ice. Water bubbled up, while Marian caught the wild surging rush of the current.
For a second her knees trembled, her face blanched. Phi saw and smiled.
"Never fear," he exclaimed; "we'll make it all right. And when you get back home you'll have a story to tell that will make Eliza's crossing on the ice seem like a picnic party crossing a trout stream on stepping-stones."