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