"I _am_ serious, that is true, my boy. I see in this terrible heat the threat of a great and sudden change in this glacier. We must start as soon as the freeze comes on to-night, and travel as fast as we can toward the far end. Mr. Roebach knows the trail, I believe?" "I've been over it several times; but I must say that the glacier has sunk a whole lot since I was across it before," the oil man declared. "We can follow the wolves," said Andy Sudds, stoutly. "They knew their way out." "That is true, we will hope," Professor Henderson said. "For I must state that I believe our peril is very great." "How so, sir?" Jack queried. "We do not know how soon this glacier may move on." "Another earthquake?" cried Mark. "Oh, gollyation! I suttenly hopes not," wailed Wash. "No. I do not think we need apprehend any further seismic disturbance. Such gaseous trouble as there is in the heart of this island will find escape--if I do not mistake--through Mr. Roebach's oil well." "Then what is troubling you, sir?" queried the boys in chorus. "The knowledge I possess of the nature of glaciers leads me to fear this peril," replied the aged scientist. "Under the immediate conditions this vast river of ice may move forward at any moment." "Impossible, I tell you!" interrupted Phineas Roebach. "I tell you this is a 'dead' glacier. It has not been in motion for ages. I have seen the face of it at the lower end of this valley. There is only a small stream of water trickling from under it, and the forest has grown right up to the base of the ice wall." "And how big a stream do you suppose is flowing from beneath the glacier now, and working its way toward what was once the Arctic Ocean--or Beaufort Sea?" queried the professor. "Why--why---" "Exactly," concluded Mr. Henderson, sharply. "You had not thought of that. You see this vast amount of water pouring into yonder crevasse? Water cannot run up hill. It is bound to seek a lower level. It must force its way down the valley, beneath the glacier, and so stream out from beneath the ice at the far end. "Gradually this flow of water is going to wear away the ice--is going to loosen the entire glacier. And then, suddenly, with no warning at all, the field will plunge forward--break up, sink, grind itself to powder against these cliffs! And where will we be?" "My goodness gracious gollyation!" cried Washington White. "I wants to git out o' disher right away--me an' Buttsy is ready ter go ter onct, an' no mistake!" "What will you do--swim?" queried Jack, pointing to the river that was now washing the shore of the strip of soil on which they stood--a river which seemed to stretch the entire breadth of the glacier.