Mrs. Weldon, then almost reached by the
water, had raised little Jack in her arms. All were stifling in this
narrow space. Their ears buzzed.

The lantern only threw a faint light.

"Is the cone, then, entirely under water?" murmured Dick Sand.

He must know; and, in order to know, he must pierce a third hole, at
the very top.

But it was asphyxia, it was immediate death, if the result of this
last attempt should prove fruitless. The air remaining inside would
escape through the upper sheet of water, and the water would fill the
whole cone.

"Mrs. Weldon," then said Dick Sand, "you know the situation. If we
delay, respirable air will fail us. If the third attempt fails, water
will fill all this space. Our only chance is that the summit of the
cone is above the level of the inundation. We must try this last
experiment. Are you willing?"

"Do it, Dick!" replied Mrs. Weldon.

At that moment the lantern went out in that medium already unfit for
combustion. Mrs. Weldon and her companions were plunged in the most
complete darkness.

Dick Sand was perched on Hercules's shoulders. The latter was hanging
on to one of the lateral cavities. Only his head was above the bed of
water.

Mrs. Weldon, Jack, and Cousin Benedict were in the last story of
cells.

Dick Sand scratched the wall, and his ramrod pierced the clay rapidly.
In this place the wall, being thicker and harder also, was more
difficult to penetrate. Dick Sand hastened, not without terrible
anxiety, for by this narrow opening either life was going to penetrate
with the air, or with the water it was death.

Suddenly a sharp hissing was heard. The compressed air escaped--but a
ray of daylight filtered through the wall. The water only rose eight
inches, and stopped, without Dick Sand being obliged to close the
hole. The equilibrium was established between the level within and
that outside. The summit of the cone emerged. Mrs. Weldon and her
companions were saved.

At once, after a frantic hurra, in which Hercules's thundering voice
prevailed, the cutlasses were put to work. The summit, quickly
attacked, gradually crumbled. The hole was enlarged, the pure air
entered in waves, and with it the first rays of the rising sun. The
top once taken off the cone, it would be easy to hoist themselves on
to its wall, and they would devise means of reaching some neighboring
height, above all inundations.

Dick Sand first mounted to the summit of the cone.

A cry es