The ice of the polar sea is not an immovable surface.

Twenty-four hours--or even twelve hours--of strong wind, even in the depth of the coldest winter, will set the big floes grinding and twisting among themselves, crushing up into pressure ridges in one place, breaking into leads in another place.
Under normal conditions, however, this movement of the ice is not very great in a period of eight or ten days, so that a party starting back over an outward trail at the end of several days is able to knit together all faults and breaks in the trail that have occurred during that period by reason of the movement of the ice.
The second supporting party, starting back several days later from a point still farther on, knits together the broken ends of the trail of its own division; and when it comes upon the trail of the first supporting party, reunites such other breaks as have occurred since the first supporting party went over it on its way back to land.

So with the third and fourth supporting parties.
When I speak of knitting together breaks in the trail, I mean simply that the passage of the supporting party from that point where the trail was broken by the movement of the ice to the point where the trail went on again, some distance either to the east or west, would itself renew the broken trail, the passage of the men and dog teams packing down the ice and snow.

So that when the main party came back it would simply follow the track of the supporting party, and not have to scout for the trail.
As a result of this method of keeping the return trail continuously open, when the main party starts to return it has a continuous trail back to the land, which it can follow with from fifty to one hundred per cent.

greater speed than it was possible to make on the outward journey.
The reasons for this are obvious: no time is wasted in selecting and breaking a trail; the dogs are more energetic when following a beaten track and when on the road home; no time is wasted in making camp, the snow igloos built on the outward journey being reoccupied on the return journey.
[Illustration: TYPICAL TRAIL IN SOFT SNOW (LOOKING BACKWARD)] It must be understood that when each supporting party reached the land again, its work in regard to the polar dash was over.