Cyrus Harding's project had succeeded, but, according to his usual habit he showed no satisfaction; with closed lips and a fixed look, he remained motionless. Herbert was in ecstasies, Neb bounded with joy, Pencroft nodded his great head, murmuring these words,--

"Come, our engineer gets on capitally!"

The nitro-glycerine had indeed acted powerfully. The opening which it had made was so large that the volume of water which escaped through this new outlet was at least treble that which before passed through the old one. The result was, that a short time after the operation the level of the lake would be lowered two feet, or more.

The settlers went to the Chimneys to take some pickaxes, iron-tipped spears, string made of fibers, flint and steel; they then returned to the plateau, Top accompanying them.

On the way the sailor could not help saying to the engineer,--

"Don't you think, captain, that by means of that charming liquid you have made, one could blow up the whole of our island?"

"Without any doubt, the island, continents, and the world itself," replied the engineer. "It is only a question of quantity."

"Then could you not use this nitro-glycerine for loading firearms?" asked the sailor.

"No, Pencroft; for it is too explosive a substance. But it would be easy to make some guncotton, or even ordinary powder, as we have azotic acid, saltpeter, sulphur, and coal. Unhappily, it is the guns which we have not got.

"Oh, captain," replied the sailor, "with a little determination--"

Pencroft had erased the word "impossible" from the dictionary of Lincoln Island.

The settlers, having arrived at Prospect Heights, went immediately towards that point of the lake near which was the old opening now uncovered. This outlet had now become practicable, since the water no longer rushed through it, and it would doubtless be easy to explore the interior.

In a few minutes the settlers had reached the lower point of the lake, and a glance showed them that the object had been attained.

In fact, in the side of the lake, and now above the surface of the water, appeared the long-looked-for opening. A narrow ridge, left bare by the retreat of the water, allowed them to approach it. This orifice was nearly twenty feet in width, but scarcely two in height. It was like the mouth of a drain at the edge of the pavement, and therefore did not offer an easy passage to the settlers; but Neb and Pencroft, taking their pickaxes, soon made it of a suitable height.

The engineer then approached, and found that the sides of the opening, in its upper part at least, had not a slope of more than from thirty to thirty-five degrees. It was therefore practicable, and, provided that the declivity did not increase, it would be easy to descend even to the level of the sea. If then, as was probable, some vast cavity existed in the interior of the granite, it might, perhaps, be of great use.

"Well, captain, what are we stopping for?" asked the sailor, impatient to enter the narrow passage. You see Top has got before us!"

"Very well," replied the engineer. "But we must see our way. Neb, go and cut some resinous branches."

Neb and Herbert ran to the edge of the lake, shaded with pines and other green trees, and soon returned with some branches, which they made into torches. The torches were lighted with flint and steel, and Cyrus Harding leading, the settlers ventured into the dark passage, which the overplus of the lake had formerly filled.

Contrary to what might have been supposed, the diameter of the passage increased as the explorers proceeded, so that they very soon were able to stand upright. The granite, worn by the water for an infinite time, was very slippery, and falls were to be dreaded. But the settlers were all attached to each other by a cord, as is frequently done in ascending mountains. Happily some projections of the granite, forming regular steps, made the descent less perilous. Drops, still hanging from the rocks, shone here and there under the light of the torches, and the explorers guessed that the sides were clothed with innumerable stalactites. The engineer examined this black granite. There was not a stratum, not a break in it. The mass was compact, and of an extremely close grain. The passage dated, then, from the very origin of the island. It was not the water which little by little had hollowed it. Pluto and not Neptune had bored it with his own hand, and on the wall traces of an eruptive work could be distinguished, which all the washing of the water had not been able totally to efface.

The settlers descended very slowly. They could not but feel a certain awe, in this venturing into these unknown depths, for the first time visited by human beings. They did not speak, but they thought; and the thought came to more than one, that some polypus or other gigantic cephalopod might inhabit the interior cavities, which were in communication with the sea. However, Top kept at the head of the little band, and they could rely on the sagacity of the dog, who would not fail to give the alarm if there was any need for it.

After having descended about a hundred feet, following a winding road, Harding who was walking on before, stopped, and his companions came up with him. The place where they had halted was wider, so as to form a cavern of moderate dimensions. Drops of water fell from the vault, but that did not prove that they oozed through the rock. They were simply the last traces left by the torrent which had so long thundered through this cavity, and the air there was pure though slightly damp, but producing no mephitic exhalation.

"Well, my dear Cyrus," said Gideon Spilett, "here is a very secure retreat, well hid in the depths of the rock, but it is, however, uninhabitable."

"Why uninhabitable?" asked the sailor.

"Because it is too small and too dark."

"Couldn't we enlarge it, hollow it out, make openings to let in light and air?" replied Pencroft, who now thought nothing impossible.

"Let us go on with our exploration," said Cyrus Harding. "Perhaps lower down, nature will have spared us this labor."

"We have only gone a third of the way," observed Herbert.

"Nearly a third," replied Harding, "for we have descended a hundred feet from the opening, and it is not impossible that a hundred feet farther down--"

"Where is Top?" asked Neb, interrupting his master.

They searched the cavern, but the dog was not there.

"Most likely he has gone on," said Pencroft.

"Let us join him," replied Harding.

The descent was continued. The engineer carefully observed all the deviations of the passage, and notwithstanding so many detours, he could easily have given an account of its general direction, which went towards the sea.

The settlers had gone some fifty feet farther, when their attention was attracted by distant sounds which came up from the depths. They stopped and listened. These sounds, carried through the passage as through an acoustic tube, came clearly to the ear.

"That is Top barking!" cried Herbert.

"Yes," replied Pencroft, "and our brave dog is barking furiously!"

"We have our iron-tipped spears," said Cyrus Harding. "Keep on your guard, and forward!"

"It is becoming more and more interesting," murmured Gideon Spilett in the sailor's ear, who nodded. Harding and his companions rushed to the help of their dog. Top's barking became more and more perceptible, and it seemed strangely fierce. Was he engaged in a struggle with some animal whose retreat he had disturbed? Without thinking of the danger to which they might be exposed, the explorers were now impelled by an irresistible curiosity, and in a few minutes, sixteen feet lower they rejoined Top.

There the passage ended in a vast and magnificent cavern.

Top was running backwards and forwards, barking furiously. Pencroft and Neb, waving their torches, threw the light into every crevice; and at the same time, Harding, Gideon Spilett, and Herbert, their spears raised, were ready for any emergency which might arise. The enormous cavern was empty. The settlers explored it in every direction. There was nothing there, not an animal, not a human being; and yet Top continued to bark. Neither caresses nor threats could make him be silent.

"There must be a place somewhere, by which the waters of the lake reached the sea," said the engineer.

"Of course," replied Pencroft, "and we must take care not to tumble into a hole."

"Go, Top, go!" cried Harding.

The dog, excited by his master's words, ran towards the extremity of the cavern, and there redoubled his barking.

They followed him, and by the light of the torches, perceived the mouth of a regular well in the granite. It was by this that the water escaped; and this time it was not an oblique and practicable passage, but a perpendicular well, into which it was impossible to venture.

The torches were held over the opening: nothing could be seen. Harding took a lighted branch, and threw it into the abyss. The blazing resin, whose illuminating power increased still more by the rapidity of its fall, lighted up the interior of the well, but yet nothing appeared. The flame then went out with a slight hiss, which showed that it had reached the water, that is to say, the level of the sea.

The engineer, calculating the time employed in its fall, was able to calculate the depth of the well, which was found to be about ninety feet.

The floor of the cavern must thus be situated ninety feet above the level of the sea.

"Here is our dwelling," said Cyrus Harding.

"But it was occupied by some creature," replied Gideon Spilett, whose curiosity was not yet satisfied.

"Well, the creature, amphibious or otherwise, has made off through this opening," replied the engineer, "and has left the place for us."

"Never mind," added the sailor, "I should like very much to be Top just for a quarter of an hour, for he doesn't bark for nothing!"

Cyrus Harding looked at his dog, and those of his companions who were near him might have heard him murmur these words,--

"Yes, I believe that Top knows more than we do about a great many things."

However, the wishes of the settlers were for the most part satisfied. Chance, aided by the marvelous sagacity of their leader, had done them great service. They had now at their disposal a vast cavern, the size of which could not be properly calculated by the feeble light of their torches, but it would certainly be easy to divide it into rooms, by means of brick partitions, or to use it, if not as a house, at least as a spacious apartment. The water which had left it could not return. The place was free.

Two difficulties remained; firstly, the possibility of lighting this excavation in the midst of solid rock; secondly, the necessity of rendering the means of access more easy. It was useless to think of lighting it from above, because of the enormous thickness of the granite which composed the ceiling; but perhaps the outer wall next the sea might be pierced. Cyrus Harding, during the descent, had roughly calculated its obliqueness, and consequently the length of the passage, and was therefore led to believe that the outer wall could not be very thick. If light was thus obtained, so would a means of access, for it would be as easy to pierce a door as windows, and to establish an exterior ladder.

Harding made known his ideas to his companions.

"Then, captain, let us set to work!" replied Pencroft. "I have my pickaxe, and I shall soon make my way through this wall. Where shall I strike?"

"Here," replied the engineer, showing the sturdy sailor a considerable recess in the side, which would much diminish the thickness.

Pencroft attacked the granite, and for half an hour, by the light of the torches, he made the splinters fly around him. Neb relieved him, then Spilett took Neb's place.

This work had lasted two hours, and they began to fear that at this spot the wall would not yield to the pickaxe, when at a last blow given by Gideon Spilett, the instrument, passing through the rock, fell outside.

"Hurrah! hurrah!" cried Pencroft.

The wall only measured there three feet in thickness.

Harding applied his eye to the aperture, which overlooked the ground from a height of eighty feet. Before him was extended the sea-coast, the islet, and beyond the open sea.

Floods of light entered by this hole, inundating the splendid cavern and producing a magic effect! On its left side it did not measure more than thirty feet in height and breadth, but on the right it was enormous, and its vaulted roof rose to a height of more than eighty feet.

In some places granite pillars, irregularly disposed, supported the vaulted roof, as those in the nave of a cathedral, here forming lateral piers, there elliptical arches, adorned with pointed moldings, losing themselves in dark bays, amid the fantastic arches of which glimpses could be caught in the shade, covered with a profusion of projections formed like so many pendants. This cavern was a picturesque mixture of all the styles of Byzantine, Roman, or Gothic architecture ever produced by the hand of man. And yet this was only the work of nature. She alone had hollowed this fairy Aihambra in a mass of granite.

The settlers were overwhelmed with admiration. Where they had only expected to find a narrow cavity, they had found a sort of marvelous palace, and Neb had taken off his hat, as if he had been transported into a temple!

Cries of admiration issued from every mouth. Hurrahs resounded, and the echo was repeated again and again till it died away in the dark naves.

"Ah, my friends!" exclaimed Cyrus Harding, "when we have lighted the interior of this place, and have arranged our rooms and storehouses in the left part, we shall still have this splendid cavern, which we will make our study and our museum!"

"And we will call it?--" asked Herbert.

"Granite House," replied Harding; a name which his companions again saluted with a cheer.

The torches were now almost consumed, and as they were obliged to return by the passage to reach the summit of the plateau, it was decided to put off the work necessary for the arrangement of their new dwelling till the next day.

Before departing, Cyrus Harding leaned once more over the dark well, which descended perpendicularly to the level of the sea. He listened attentively. No noise was heard, not even that of the water, which the undulations of the surge must sometimes agitate in its depths. A flaming branch was again thrown in. The sides of the well were lighted up for an instant, but as at the first time, nothing suspicious was seen.

If some marine monster had been surprised unawares by the retreat of the water, he would by this time have regained the sea by the subterranean passage, before the new opening had been offered to him.

Meanwhile, the engineer was standing motionless, his eyes fixed on the gulf, without uttering a word.

The sailor approached him, and touching his arm, "Captain!" said he.

"What do you want, my friend?" asked the engineer, as if he had returned from the land of dreams.

"The torches will soon go out."

"Forward!" replied Cyrus Harding.

The little band left the cavern and began to ascend through the dark passage. Top closed the rear, still growling every now and then. The ascent was painful enough. The settlers rested a few minutes in the upper grotto, which made a sort of landing-place halfway up the long granite staircase. Then they began to climb again.

Soon fresher air was felt. The drops of water, dried by evaporation, no longer sparkled on the walls. The flaring torches began to grow dim. The one which Neb carried went out, and if they did not wish to find their way in the dark, they must hasten.

This was done, and a little before four o'clock, at the moment when the sailor's torch went out in its turn, Cyrus Harding and his companions passed out of the passage.