Almost before our friends could retreat into the cave which now sheltered the Red Cloud, the attacking natives opened fire. Fortunately they only had old-fashioned, muzzle-loading muskets, and, as their aim was none of the best, there was comparatively little danger. The bullets, however, did sing through the fast- gathering darkness with a vicious sound, and struck the heavy sides and sloping front of the ice cave with a disconcerting "ping!"

"I don't hear Andy or his father firing!" called Tom, as he and the others returned the fire of the savage Indians. "I could tell their guns by the sharper reports. The Fogers carry repeating rifles, and they're fine ones, if they're anything like the one we took from Andy, Ned."

"That's right," agreed Tom's chum, "I don't believe Andy or his father dare fire. They're afraid to, and they're putting the poor ignorant natives up to it. Probably they hired them to try to drive us away."

This, as they afterward learned, was exactly the case.

The battle, if such it could be called, was kept up. There was about a hundred natives, all of whom had guns, and, though they were slow to load, there were enough weapons to keep up a constant fusilade. On their part, Tom and the others fired at first over the heads of the natives, for they did not want to kill any of the deluded men. Later, though, when they saw the rush keeping up, they fired at their legs, and disabled several of the Eskimos, the electric gun proving very effective.

It was now quite dark, and the firing slackened. From their position in the cave, Tom and the others could command the hole where the gold was, and, as they saw several natives sneaking up to it the young inventor and Ned, both of whom were good shots, aimed to have the bullets strike the ice close to where the Indians were.

This sort of shooting was enough, and the natives scurried away. Then Tom hit on the plan of playing the searchlight on the spot, and this effectually prevented an unseen attack. It seemed to discourage the enemy, too for they did not venture into that powerful glow of light.

"They won't do anything more until morning," declared Abe. "Then we'll have it hot an' heavy, though, I'm afeered. Well, we'll have t' make th' best of it!"

They took turns standing guard that night, but no attack was made. The fact of the Fogers coming back with the band of Indians told Tom, more plainly than words, how desperately his enemies would do battle with them. Anxiously they waited for the morning.

Several times in the night Mr. Parker was seen roaming about uneasily, though it was not his turn to be on guard. Finally Tom asked him what was the matter, and if he could not sleep.

"It isn't that," answered the scientist, "but I am worried about the ice. I can detect a slight but peculiar movement by means of some of my scientific instruments. I am alarmed about it. I fear something is going to happen."

But Tom was too worried about the outcome of the fight he knew would be renewed on the next day, to think much about the ice movement. He thought it would only be some scientific phenomena that would amount to little.

With the first streak of the late dawn, the gold-seekers were up, and partook of a hot breakfast, with strong coffee which Mr. Damon brewed. Tom took an observation from the mouth of the cave. The searchlight was still dimly glowing, and it did not disclose anything. Tom turned it off. He thought he saw a movement among the ranks of the enemy, who had camped just beyond the gold hole.

"I guess they're coming!" cried the lad. "Get ready for them!"

The adventurers caught up their guns, and hurried to the entrance of the cave. Mr. Parker lingered behind, and was observed to be narrowly scanning the walls of the cavern.

"Come on, Parker, my dear man!" begged Mr. Damon. "We are in grave danger, and we need your help. Bless my life insurance policy! but I never was in such a state as this."

"We may soon be in a worse one," was the answer of the gloomy scientist.

"What do you mean?" asked Mr. Damon, but he hurried on without waiting for a reply.

Suddenly, from without the cave came a series of fierce yells. It was the battle-cry of the Indians. At the same moment there sounded a fusillade of guns.

"The battle is beginning!" cried Tom Swift, grimly. He held his electric gun, though he had not used it very much in the previous attack, preferring to save it for a time of more need.

As the defenders of the cave reached the entrance they saw the body of natives rushing forward. They were almost at the gold hole, with Andy Foger and his father discreetly behind the first row of Eskimos, when, with a suddenness that was startling, there sounded throughout the whole valley a weird sound!

It was like the wailing of some giant--the sighing of some mighty wind. At the same time the air suddenly became dark, and then there came a violent snow squall, shutting out instantly the sight of the advancing natives. Tom and the others could not see five feet beyond the cave.

"This will delay the attack," murmured Ned, "They can't see to come at us."

Mr. Parker came running up from the interior of the cave. On his face there was a look of alarm.

"We must leave here at once!" he cried.

"Leave here?" repeated Tom. "Why must we? The enemy are out there! We'd run right into them!"

"It must be done!" insisted the scientist. "We must leave the cave at once!"

"What for?" cried Mr. Damon.

"Because the movement of the ice that I predicted, has begun. It is much more rapid than I supposed it would be. In a short time this cave and all the others will be crushed flat!"

"Crushed flat!" gasped Tom.

"Yes, the caves of ice are being destroyed! Hark! You can hear them snapping!"

They all listened. Above the roar of the storm could be made out the noise of crushing, grinding ice-sounds like cannon being fired, as the great masses of frozen crystal snapped like frail planks.

"The ice caves are being destroyed by an upheaval of nature!" went on Mr. Parker. "This one will soon go! The walls are bulging now! We must get out!"

"But the natives! They will kill us!" cried Mr. Damon. "Bless my soul! what a trying position to be in."

"I guess the natives are as bad off as we are," suggested Ned. "They're not firing, and I can hear cries of alarm, I think they're running away."

There was a lull in the snow flurry, and the white curtain seemed to lift for a moment. The gold-seekers had a glimpse of the natives in full retreat, with the Fogers--father and son--racing panic-stricken after them. Tom could also see a big cave, just beyond the gold hole, collapse and crumble to pieces like a house of cards.

"We have no time to lose!" Mr. Parker warned them. "The roof of this cave is slowly coming down. The sides are collapsing! We must get out!"

"Then wheel out the airship!" cried Tom. "We must save that! We needn't fear the natives, now!"

The young inventor hurried to the Red Cloud calling to Ned and the others. They hastened to his side. It was an easy matter to move the airship along on the wheels. It neared the opening of the cave. The rumbling, roaring, grinding sound of the ice increased.

"Why--why!" cried Tom in surprise and alarm, as the craft neared the mouth of the ice cavern, "we can't get it out--the opening is too small! Yet it came in easily enough!"

"The cave is collapsing--growing smaller every moment!" cried Mr. Parker. "We have only time to save our lives! Run out!"

"And leave the airship? Never!" yelled Tom.

"You must! You can't save that and your life!"

"Get axes and make the opening bigger!" suggested Ned, who, like his chum, could not bear to think of the destruction of the beautiful craft.

"No time! No time!" shouted Mr. Parker, frantically, "We must get out! Save what you can from the ship--the gold--some supplies--the guns--some food--save what you can!"

Then ensued a wild effort to get from the doomed craft what they could--what they would need if they were to save their lives in that cold and desolate country. Food, some blankets--their guns--as much of the gold as they could hastily gather together--their weapons and some ammunition--all this was carried from the cabin outside the cave. The entrance was rapidly growing smaller. The roof was already pressing down on the gas-bag.

Tom gave one last look at his fine craft. There were tears in his eyes. He started into the cabin for something he had forgotten. Mr. Parker grabbed him by the arm.

"Don't go in!" he cried hoarsely. "The cave will collapse in another instant!" He rushed with Tom out of the cavern, and not a moment too soon. The others were already outside.

Then with a rush and a roar, with a sound like a great explosion, with a rending, grinding and booming as the great pieces of ice collapsed one against the other, the big ice cave settled in, as does some great building when the walls are weakened!

Down crashed the roof of the ice cave! Down upon the Red Cloud, burying out of sight, forever, under thousands of tons of ice and snow, the craft which was the pride of Tom Swift's heart! It was the end of the airship!

Tom felt a moisture of tears in his eyes as he stood there in the midst of the snowstorm.