"You should have been able to figure that out," was the response. "When the ice thaws it increases the volume of water under the ice. The edges are frozen solid to the land, the middle is more or less elastic, and so of course the sides stay solid and the middle heaves up. In warmer climates, it is the edge that thaws out first, but up here the rivers, strictly speaking, do not thaw free, the ice is forced from them by the spring floods. It is strictly a break-up rather than a thaw, although it gets warm thereafter very rapidly."
"It certainly does," replied Roger, mopping his forehead. "It's hot enough now, and this is only the middle of May; while two weeks ago it was snowing like Billy O."
On May 18th the ice broke, moved down about a mile and jammed, and a few hours later broke again, finally clearing from the upper reaches of the Jack River on the 19th. Rivers was delighted at the opportunity to get out so soon, as he had feared it might be as late as the first week in June before he could get away.
"I think, Doughty," he said to Roger, "that we can count easily now on accomplishing what we set out to do, and probably get into the Arctic Ocean in good time for an early return."
"That is, barring accidents," put in the topographer.
"We will make up our minds not to have any," replied the chief of the party.
The following morning, therefore, the canoes being all packed, the party bade good-by to the little camp on Broad Pass, where they had spent so many quiet, uneventful days, and plunged into the grinding forced march that was to occupy every waking moment for so many months to come. The stern reality of Alaskan work became potent to Roger before they had been half an hour on the trail. The Jack River, though swollen by the spring currents, had worn an erratic bed, and was filled with bars on which the canoes stranded. Then there was nought to do but wade into the snow-fed stream, with large chunks of ice roaring down at him, and the chill of the water such as to make the boy gasp and turn everything black before his eyes, while his legs became numb and hurt cruelly. But he gritted his teeth and buckled to it, well aware that the other members of the party were watching him, awaiting a sign of weakening.
The entire morning was spent wading, helping the canoes over a series of small bars with a fairly steep gradient, but the work was slow, and Rivers seized eagerly any chance to increase the pace. Shortly after the midday halt, a reach fairly free from obstacles presented itself, and the party climbed into the boats and shot down the stream. Although Roger had not done any canoe work since he had been on the Survey, he was brought up beside a stream and had handled a paddle nearly all his life, and his delight was great when he found that he had not lost the knack. Not only was he quite at home in a few moments, but he found that his toughness and maturer strength told in every stroke. Harry, the Indian, who was in the stern, nodded approvingly, after ten minutes' work.
