Koku was overturned. He fell sprawling, with the broken handle still clutched in his mighty grip. The bear reared, plucking at the staff that impaled it. It stood taller than Captain Karofsen, or even Koku. It was a drab-white polar bear of fierce aspect, and its rumbling growls reverberated from the walls of ice, making a deafening clamor. The schooner captain started forward, rifle raised, and in a moment flame darted from the muzzle of his weapon. The bear was hit—indeed, the captain could not have missed it—but it was not yet dead and fell back into the darkness of the cave. They all advanced, holding their guns ready for another attack. Even Koku scrambled up and came on, brandishing his broken staff. It was fortunate indeed that the three young fellows and their two gigantic companions followed the wounded bear so closely. Scarcely had the echoing explosion of Captain Karofsen’s rifle died away when a mightier report sounded over their heads. Everybody halted, appalled. The peril of the wounded bear was forgotten. White-faced and motionless, they stared at one another. They all knew that something of vastly greater menace had occurred. The explosion above was the breaking away of some overhanging shelf of ice. It came sliding and bursting down the face of the cliff and in half a minute was dumped with a terrific shock directly in the mouth of this cave which they had entered. Powdered ice almost smothered the party for a few moments. Such light as there had been outside the cave in the cañon was snuffed out. The avalanche crowded the cave’s entrance and made the five explorers prisoners with a suddenness that stunned them all. While from ahead, in the pitch darkness, came again the challenge of the wounded bear. It was by no means _hors-de-combat_. The wounded brute was full of fight. And to fire again in hope of killing the bear might bring the very roof of the ice cave down upon their heads! CHAPTER XXI A SILVER LINING The intense darkness inside the cave made the event a serious one. The wounded polar bear might charge among them at any moment, and as they were all dressed in furs it would be difficult to distinguish each other from the bear. The bear uttered another terrific roar and charged from the back of the cave. Koku’s war cry was almost as savage, and, knocking the others right and left, he sprang between his beloved master and the wild beast. Tom, however, did not lose his self-possession. He was a little slow in getting it out, but he produced in time a flashlight, and the ray of it revealed the glaring eyes, the open, dripping jaws, and the blood-bedabbled breast of the big polar bear. The blinding ray of electric light confused the animal and Koku reached him with several terrific whacks with the staff of his spear.