some amphibious creature," replied Herbert.

"An alligator, perhaps," said the reporter.

"I do not think so," replied Harding. "Alligators are only met with in
regions less elevated in latitude."

Meanwhile Top had returned at his master's call, and had regained the
shore: but he could not stay quiet; he plunged in among the tall grass,
and guided by instinct, he appeared to follow some invisible being which
was slipping along under the surface of the water. However the water
was calm; not a ripple disturbed its surface. Several times the settlers
stopped on the bank, and observed it attentively. Nothing appeared.
There was some mystery there.

The engineer was puzzled.

"Let us pursue this exploration to the end," said he.

Half an hour after they had all arrived at the southeast angle of the
lake, on Prospect Heights. At this point the examination of the banks of
the lake was considered finished, and yet the engineer had not been able
to discover how and where the waters were discharged. "There is no doubt
this overflow exists," he repeated, "and since it is not visible it must
go through the granite cliff at the west!"

"But what importance do you attach to knowing that, my dear Cyrus?"
asked Gideon Spilett.

"Considerable importance," replied the engineer; "for if it flows
through the cliff there is probably some cavity, which it would be easy
to render habitable after turning away the water."

"But is it not possible, captain, that the water flows away at the
bottom of the lake," said Herbert, "and that it reaches the sea by some
subterranean passage?"

"That might be," replied the engineer, "and should it be so we shall be
obliged to build our house ourselves, since nature has not done it for
us."

The colonists were about to begin to traverse the plateau to return to
the Chimneys, when Top gave new signs of agitation. He barked with fury,
and before his master could restrain him, he had plunged a second time
into the lake.

All ran towards the bank. The dog was already more than twenty feet off,
and Cyrus was calling him back, when an enormous head emerged from the
water, which did not appear to be deep in that place.

Herbert recognized directly the species of amphibian to which the
tapering head, with large eyes, and adorned with long silky mustaches,
belonged.

"A lamantin!" he cried.

It was not a lamantin, but one of that species of the order of
cetaceans, which bear the name of the "dug