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."

It was not long after that, however, when even this daring boy's face
sobered. Old Rover, who had been following the trail unhesitatingly,
suddenly came to a halt. He turned to the right, sniffing the ice.
Then he turned to the left. After that he looked up into the face of
the boy, as if to say:

"Where's the trail gone?"

Phi examined the ice carefully.

"Been a sudden jam here," he muttered; "then the ice has slid along,
some north, some south. It has all happened since our friends passed
this way. You just wait here. I'll take Rover to the north and let
him pick up the trail. When I find it, I'll come back far enough to
call to you. May be to the south, though, but we'll soon see."

He disappeared around a giant ice-pile and, i