"It's one of the many islets with which this sea is strewn. For ships a mere reef, for us an immense cavern. I discovered it by chance, and chance served me well."

"But couldn't someone enter through the mouth of its crater?"

"No more than I could exit through it. You can climb about 100 feet up the inner base of this mountain, but then the walls overhang, they lean too far in to be scaled."

"I can see, captain, that nature is your obedient servant, any time or any place. You're safe on this lake, and nobody else can visit its waters. But what's the purpose of this refuge? The Nautilus doesn't need a harbor."

"No, professor, but it needs electricity to run, batteries to generate its electricity, sodium to feed its batteries, coal to make its sodium, and coalfields from which to dig its coal. Now then, right at this spot the sea covers entire forests that sank underwater in prehistoric times; today, turned to stone, transformed into carbon fuel, they offer me inexhaustible coal mines."

"So, captain, your men practice the trade of miners here?"

"Precisely. These mines extend under the waves like the coalfields at Newcastle. Here, dressed in diving suits, pick and mattock in hand, my men go out and dig this carbon fuel for which I don't need a single mine on land. When I burn this combustible to produce sodium, the smoke escaping from the mountain's crater gives it the appearance of a still-active volcano."

"And will we see your companions at work?"

"No, at least not this time, because I'm eager to continue our underwater tour of the world. Accordingly, I'll rest content with drawing on my reserve stock of sodium. We'll stay here long enough to load it on board, in other words, a single workday, then we'll resume our voyage. So, Professor Aronnax, if you'd like to explore this cavern and circle its lagoon, seize the day."

I thanked the captain and went to look for my two companions, who hadn't yet left their cabin. I invited them to follow me, not telling them where we were.

They climbed onto the platform. Conseil, whom nothing could startle, saw it as a perfectly natural thing to fall asleep under the waves and wake up under a mountain. But Ned Land had no idea in his head other than to see if this cavern offered some way out.

After breakfast near ten o'clock, we went down onto the embankment.

"So here we are, back on shore," Conseil said.

"I'd hardly call this shore," the Canadian replied. "And besides, we aren't on it but under it."

A sandy beach unfolded before us, measuring 500 feet at its widest point between the waters of the lake and the foot of the mountain's walls. Via this strand you could easily circle the lake. But the base of these high walls consisted of broken soil over which there lay picturesque piles of volcanic blocks and enormous pumice stones. All these crumbling masses were covered with an enamel polished by the action of underground fires, and they glistened under the stream of electric light from our beacon. Stirred up by our footsteps, the mica-rich dust on this beach flew into the air like a cloud of sparks.

The ground rose appreciably as it moved away from the sand flats by the waves, and we soon arrived at some long, winding gradients, genuinely steep paths that allowed us to climb little by little; but we had to tread cautiously in the midst of pudding stones that weren't cemented together, and our feet kept skidding on glassy trachyte, made of feldspar and quartz crystals.

The volcanic nature of this enormous pit was apparent all around us. I ventured to comment on it to my companions.

"Can you picture," I asked them, "what this funnel must have been like when it was filled with boiling lava, and the level of that incandescent liquid rose right to the mountain's mouth, like cast iron up the insides of a furnace?"

"I can picture it perfectly," Conseil replied. "But will master tell me why this huge smelter suspended operations, and how it is that an oven was replaced by the tranquil waters of a lake?"

"In all likelihood, Conseil, because some convulsion created an opening below the surface of the ocean, the opening that serves as a passageway for the Nautilus.