It might have been supposed that the discharge of water was at this place, for the extremity of the lake was almost on a level with the edge of the plateau. But no signs of this were discovered, and the colonists continued to explore the bank, which, after a slight bend, descended parallel to the shore.

On this side the banks were less woody, but clumps of trees, here and there, added to the picturesqueness of the country. Lake Grant was viewed from thence in all its extent, and no breath disturbed the surface of its waters. Top, in beating the bushes, put up flocks of birds of different kinds, which Gideon Spilett and Herbert saluted with arrows. One was hit by the lad, and fell into some marshy grass. Top rushed forward, and brought a beautiful swimming bird, of a slate color, short beak, very developed frontal plate, and wings edged with white. It was a "coot," the size of a large partridge, belonging to the group of macrodactyls which form the transition between the order of wading birds and that of palmipeds. Sorry game, in truth, and its flavor is far from pleasant. But Top was not so particular in these things as his masters, and it was agreed that the coot should be for his supper.

The settlers were now following the eastern bank of the lake, and they would not be long in reaching the part which they already knew. The engineer was much surprised at not seeing any indication of the discharge of water. The reporter and the sailor talked with him, and he could not conceal his astonishment.

At this moment Top, who had been very quiet till then, gave signs of agitation. The intelligent animal went backwards and forwards on the shore, stopped suddenly, and looked at the water, one paw raised, as if he was pointing at some invisible game; then he barked furiously, and was suddenly silent.

Neither Cyrus Harding nor his companions had at first paid any attention to Top's behavior; but the dog's barking soon became so frequent that the engineer noticed it.

"What is there, Top?" he asked.

The dog bounded towards his master, seeming to be very uneasy, and then rushed again towards the bank. Then, all at once, he plunged into the lake.

"Here, Top!" cried Cyrus Harding, who did not like his dog to venture into the treacherous water.

"What's happening down there?" asked Pencroft, examining the surface of the lake.

"Top smells 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.