But such a gallery could only be driven in a horizontal direction, and would be a much longer business than the sinking of a shaft from above, for the masses flung down by the avalanche, although only sixty feet deep, covered a space more than five hundred feet in diameter. Of course the prisoners could not be aware of this fact, and if they should succeed in boring their horizontal gallery, it would be eight days at least before they could cut through the last layer of ice, and by that time they would be totally deprived of air, if not of food.

Nevertheless the Lieutenant carefully went over every portion of the accumulation himself, and listened intently for any sounds of subterranean digging, but he heard nothing.

On the return of day the men toiled with fresh energy, bucket after bucket was drawn to the surface of the shaft loaded with earth. The clumsy wooden props answered admirably in keeping the earth from filling in the pit, a few falls occurred, but they were rapidly checked, and no fresh misfortunes occurred throughout the day, except that the soldier Garry received a blow on the head from a falling block of ice. The wound was not however severe, and he would not leave his work.

At four o'clock the shaft was fifty feet deep altogether, having been sunk through twenty feet of ice and thirty of sand and earth.

It was at this depth that Mac-Nab had expected to reach the roof of the house, if it had resisted the pressure of the avalanche.

He was then at the bottom of the shaft, and his disappointment and dismay can be imagined when, on driving his pickaxe into the ground as far as it would go, it met with no resistance whatever.

Sabine was with him, and for a few moments he remained with his arms crossed, silently looking at his companion.

"No roof then?" inquired the hunter.

"Nothing whatever," replied the carpenter, "but let us work on, the roof has bent of course, but the floor of the loft cannot have given way. Another ten feet and we shall come to that floor, or else"--

Mac-Nab did not finish his sentence, and the two resumed their work with the strength of despair.

At six o'clock in the evening, another ten or twelve feet had been dug out.

Mac-Nab sounded again, nothing yet, his pick still sunk in the shifting earth, and flinging it from him, he buried his face in his hands and muttered-

"Poor things, poor things!" He then climbed to the opening of the shaft by means of the wood-work.

The Lieutenant and the Sergeant were together in greater anxiety than ever, and taking them aside, the carpenter told them of his dreadful disappointment.

"Then," observed Hobson, "the house must have been crushed by the avalanche, and the poor people in it"--

"No!" cried the head-carpenter with earnest conviction, "no, it cannot have been crushed, it must have resisted, strengthened as it was. It cannot-it cannot have been crushed!"

"Well, then, what has happened?" said the Lieutenant in a broken voice, his eyes filling with tears.

"Simply this," replied Mac Nab, "the house itself has remained intact, but the ground on which it was built must have sunk. The house has gone through the crust of ice which forma the foundation of the island. It has not been crushed, but engulfed, and the poor creatures in it"--

"Are drowned!" cried Long.

"Yes, Sergeant, drowned without a moment's notice-drowned like passengers on a foundered vessel!"

For some minutes the three men remained silent. Mac-Nab's idea was probably correct. Nothing was more likely than that the ice forming the foundation of the island had given way under such enormous pressure. The vertical props which supported the beams of the ceiling, and rested on those of the floor, had evidently aided the catastrophe by their weight, and the whole house had been engulfed.

"Well, Mac-Nab," said Hobson at last, "if we cannot find them alive"--

"We must recover their bodies," added the head carpenter.

"And with these words Mac-Nab, accompanied by the Lieutenant, went back to his work at the bottom of the shaft without a word to any of his comrades of the terrible form his anxiety had now assumed.