All climbed down through the rain to the level of the sea. There was now eight feet of the opening above the water. It was like the arch of a bridge, under which rushed the foaming water.

Leaning forward, the engineer saw a black object floating on the water. He drew it towards him. It was a boat, moored to some interior projection of the cave. This boat was iron-plated. Two oars lay at the bottom.

"Jump in!" said Harding.

In a moment the settlers were in the boat. Neb and Ayrton took the oars, Pencroft the rudder. Cyrus Harding in the bows, with the lantern, lighted the way.

The elliptical roof, under which the boat at first passed, suddenly rose; but the darkness was too deep, and the light of the lantern too slight, for either the extent, length, height, or depth of the cave to be ascertained. Solemn silence reigned in this basaltic cavern. Not a sound could penetrate into it, even the thunder peals could not pierce its thick sides.

Such immense caves exist in various parts of the world, natural crypts dating from the geological epoch of the globe. Some are filled by the sea; others contain entire lakes in their sides. Such is Fingal's Cave, in the island of Staffa, one of the Hebrides; such are the caves of Morgat, in the bay of Douarnenez, in Brittany, the caves of Bonifacio, in Corsica, those of Lyse-Fjord, in Norway; such are the immense Mammoth caverns in Kentucky, 500 feet in height, and more than twenty miles in length! In many parts of the globe, nature has excavated these caverns, and preserved them for the admiration of man.

Did the cavern which the settlers were now exploring extend to the center of the island? For a quarter of an hour the boat had been advancing, making detours, indicated to Pencroft by the engineer in short sentences, when all at once,--

"More to the right!" he commanded.

The boat, altering its course, came up alongside the right wall. The engineer wished to see if the wire still ran along the side.

The wire was there fastened to the rock.

"Forward!" said Harding.

And the two oars, plunging into the dark waters, urged the boat onwards.

On they went for another quarter of an hour, and a distance of half-a- mile must have been cleared from the mouth of the cave, when Harding's voice was again heard.

"Stop!" said he.

The boat stopped, and the colonists perceived a bright light illuminating the vast cavern, so deeply excavated in the bowels of the island, of which nothing had ever led them to suspect the existence.

At a height of a hundred feet rose the vaulted roof, supported on basalt shafts. Irregular arches, strange moldings, appeared on the columns erected by nature in thousands from the first epochs of the formation of the globe. The basalt pillars, fitted one into the other, measured from forty to fifty feet in height, and the water, calm in spite of the tumult outside, washed their base. The brilliant focus of light, pointed out by the engineer, touched every point of rocks, and flooded the walls with light.

By reflection the water reproduced the brilliant sparkles, so that the boat appeared to be floating between two glittering zones. They could not be mistaken in the nature of the irradiation thrown from the glowing nucleus, whose clear rays were shattered by all the angles, all the projections of the cavern. This light proceeded from an electric source, and its white color betrayed its origin. It was the sun of this cave, and it filled it entirely.

At a sign from Cyrus Harding the oars again plunged into the water, causing a regular shower of gems, and the boat was urged forward towards the light, which was now not more than half a cable's length distant.

At this place the breadth of the sheet of water measured nearly 350 feet, and beyond the dazzling center could be seen an enormous basaltic wall, blocking up any issue on that side. The cavern widened here considerably, the sea forming a little lake. But the roof, the side walls, the end cliff, all the prisms, all the peaks, were flooded with the electric fluid, so that the brilliancy belonged to them, and as if the light issued from them.