il.

"There is but one thing we can do," said Jack.

"What is that?" asked Harry, anxiously.

"Break through that wall and get into the mosque; that's the only side
of the building which isn't surrounded."

"But it is impossible to pierce such a wall as that," said Harry.

"We'll try, at all events," Jack responded. "Come, boys," he added,
"one last desperate effort, and we'll baffle 'em yet."

The waiter and diver understood in a minute.

Hurriedly they collected the tools--pickaxes, crowbars, chisels, and
hammers--and they all set to work on the masonry.

But their momentary hopes soon subsided.

The mortar had, in the course of ages, become even harder than the
stone itself.

It was impossible to make any impression upon it.

When they saw this, disappointment was depicted upon every countenance.

Jack flung down, in sheer despair, the chisel with which he had
attempted to break the mortar.

As the implement fell upon the stones of the courtyard, Thyra's quick
ear noticed the peculiar sound.

"It is hollow beneath here," she exclaimed, eagerly.

Again testing the floor in the same way, they became convinced that she
was right.

There were probably vaults beneath this courtyard, and this stone
concealed the entrance to them.

Animated by this fresh hope, the party now worked away, and in a few
minutes had lifted the ponderous flagstone.

A flight of rude steps, leading down into utter darkness, was
discovered.

"As I thought," cried Jack, "these are vaults; we may baffle them after
all. Bogey, run down immediately and see what they are like."

Bogey hesitated not a moment, but skipped down the rude steps and
disappeared.

The others waited his return with great anxiety.

At this moment, a shout of triumph was raised by their enemies outside.

It signified that the cannon had been brought, and that the attack
would soon recommence.

The hope of escape was still of the very slightest.

In a few moments Bogey returned.

"Well?" asked Jack.

"All cellars, massa, goin' along--oh, miles and miles under de earth,
all dark, 'cepting a bit of light that comes here and there through
little holes in de roof. Plenty of room to hide all of us, sar. Oh,
golly, won't de nasty Turks go mad?"

"Hurrah! down you go immediately," said Jack. "Now then, ladies first.
Harry, I commend Thyra to your care. Take her down."

"I can not, will not leave you, dear Jack," she cried, desperately
clinging to ou