Of course, the cupidity and curiosity of the explorers were aroused.

Not one but had a keen desire to know what the meaning of the light was. So after a few moments Randall said:

“That beats me! What is it?”

“Give it up,” said Wendel.

“We ought to investigate it. Eh, Frank?”

“That’s what we’re here for,” replied the young inventor.

He stepped into the coracle. It would hold three easily.

A moment later they were boldly sallying forth upon the waters of the underground lake. Frank, however, was very careful to keep his bearings, leaving the lantern to mark the spot they had just left.

Wendel and Randall used the paddles, while Frank steered. Thus they made their way over the underground waters.

They were placid, even dead, for there was no breeze to ripple their surface.

But there was another power, and it was felt before the voyagers were half across.

Suddenly the coracle began to wabble and turn. Randall and the sailors pulled harder at the paddles.

But it did no good. The little craft began to rock most violently.

“What in the deuce is the matter?” asked Randall, excitedly. “What ails the boat?”

“I think the waves are rising in the lake,” said Wendel. “Yes, there is really some commotion under us, mates.”

“Right!” cried Frank, as he balanced the coracle. “Keep steady, or we’ll be over.”

It seemed as if the boat had become a boiling cauldron.

The water foamed and surged and pitched until the three voyagers were certain that they would go to the bottom.

But they did not.

A distant, sullen, booming sound was heard, like rumbling thunder. Then there was a muffled explosion, a hissing cloud of steam surged across the lake, and then all became quiet again.

The coracle rested safely once more upon the placid waters.

Then the voyagers collected their wits. Light from the electric lantern yet shone obliquely across the little craft, and in the water Frank saw some small objects floating.

He put his hand over the thwarts and picked up one.

It was cold and slimy and slid out of his hand into the bottom of the boat.

“What’s that?” cried Randall.

“A fish!” ejaculated Frank. “The water is alive with them. Something has killed them.”

This was true.

The surface of the lake was covered with the dead fish. Surely some internal convulsion had taken place.

The red fire at the other end of the lake could now be seen plainer than ever.

It was like looking into a veritable Hades, or through the yawning jaws of a red-hot furnace. The voyagers gazed wonder-struck at it.

Then they paddled on slowly.

“Shall we go ahead, mates?” asked Wendel.

“Why not?” ejaculated Randall.

“Nothing, only if another whirl of the waters took place again like that we might have to swim.”

“I am willing to risk it,” said Randall, looking at Frank.

“It will probably not occur again,” declared the young inventor.

“Then we will go ahead.”

“Yes.”

Randall and the sailor gave way at the paddles. The coracle sped on and every moment drew nearer the fiery furnace.

Then it was seen that the cavern here enlarged into a mighty, yawning pit, which was filled with smoke and flames, and from which arose fearful fumes.

It was evidently a volcano.

A gallery ran from the lake shore to this pit and divided the two by about fifty feet of solid rock. The heat of the furnace was intense.

But the voyagers did not hesitate to draw the coracle up on the shore and walk over to the fiery pit.

It covered fully an acre. High above it was a funnel-like shaft. All in that instant Frank guessed the truth.

“By Jove!” he exclaimed, “I know where we are!”

“Eh!” exclaimed Randall.

“We are in the volcano!”

“The volcano?”

“Yes.”

“Impossible!”

“Not so! If you remember, we have traveled a good ways underground, and it has carried us without a doubt under the plateaus and straight into the heart of the mountain. Probably this is only one of half a hundred or more internal craters.”

The logic of this assumption was at once obvious.

Certainly in no other way could this crater of fire be explained. For a time the three men were silent.

They studied the strange scene awhile, then Randall said:

“Well, Frank, what shall we do about it?”

“Follow me,” said the young inventor.

Frank led the way around the gallery. It trended upward, and soon shot off at right angles into a serpentine course beyond the wall of the pit of fire.

It was as if this corkscrew-like passage had been bored for just such a purpose as it was now used. Frank led the way.

It was like ascending a winding stair in a tower. But before they had gone far Randall asked:

“Where are we going, Frank?”

“To follow this passage to its end,” was the reply.

“Where do you think it will end?”

“I don’t know. It may come out on top of the volcano.”

“But—is there no danger of losing our way?”

“I think not.”

“And if we come out on top of the mountain, shall we return this way?”

“We shall see.”

As they advanced now, the situation became one filled with terrors.

It was as if they were in a literal pandemonium. All sorts of strange sounds were about them.

There was a rumble of thunder, the gurgle of molten liquid and the hiss of steam. Then terrific explosions came with fearful echoes through the cavernous depths.

It was sufficient to strike fear into a strong man’s bosom. For a time even Frank Reade, Jr., himself was a trifle daunted.

“Is it quite safe, Frank?” asked Randall, with some apprehension. “Suppose a stream of lava should come tearing down this passage?”

“It would cook us,” said Frank, imperturbably, “but we won’t anticipate that.”

“Ugh!” exclaimed Wendel, “I think we’d better get out of here as soon as possible!”

“And so we will,” declared Frank, “but this is a watercourse. I don’t believe we need fear lava. We ought to be near the summit.”

But they toiled on for another hour. Then, however, they emerged into the open air.

The transition was for a moment surprising. Even the semi-gloom of the Antarctic night was dazzling.

But they were high in the air, and a mighty panorama of country lay before their gaze.

To the northward, shrouded in dull gloom, was the barrier of ice and snow; to the south, the Polar Continent, in its green hue.

To the east, the great pass, and west, the line of mighty craters, which belched at intervals their fiery contents a thousand feet into the air.

It was a spectacle which literally appalled the adventurers. They were truly on a new continent in an unexplored world.

Then Randall exclaimed:

“How is it, Frank? Shall we stay here long?”

“No,” replied Frank. “I have accomplished my object. Let us now return to the Scorcher.”

Randall was about to re-enter the downward passage, but Frank cried:

“Not that way!”

“What?”

“We will not return that way.”

“Why not?”

“It is too far, and too perilous. We can just slide down the mountain side here easier.”

“But we left the electric lantern on the shore of that lake——”

“Hang the lantern,” cried Frank. “We’ll let it stay there. We’ll not go back for it now, at least.”

“All right,” cried Randall, “I’m more than agreeable. Let’s slide on down.”

And down the crater side they proceeded to travel. Leaping from rock to rock they went rapidly down.

Soon the plateau below was reached. Then they saw the Scorcher dimly in the distance down the valley.

It was quite a long tramp down over the steeps to where the machine was. Barney and Pomp were not in sight.

When the three explorers reached the Scorcher after threading their way among the ruins they were surprised to find the two jokers missing.

What had become of them?

The truth was, they had gone upon a little exploring expedition of their own.

When Frank and his companions disappeared in the old ruin, the Celt turned a handspring on the pavement, and cried:

“Be me sowl, naygur, phwat do yez say av we have a little exploration av our own?”

“I’se wif yo’, I’sh. Wha’ am we gwine fo’ to explore?”

“The whole town, yez ignoramus! Shure, it’s loikely we may foind some valuable relics ourselves. Thin Misther Frank will be afther thankin’ us fer thim!”

Pomp hesitated.

“Wha’ do yo’ fink ob leavin’ de Scorcher?” he asked.

“Shure, that will be all roight. Don’t yez have no fears about that, at all, at all!”

“A’right, I go yo’ I’sh. Jes’ yo’ lead de way an’ I follers on!”

“Which it’s proper yez should, considerin’ me superior advantages.” declared Barney, in his puffiest way. “Do yez see that big heap av sthone down yonder?”

“Yes.”

“Well, I believe that’s some koind av a ruined temple or the loikes, an’ we’ll thry that first off!”

“A’right, I’sh. Yo’ go ahead.”

In a few moments they were among the ruins of a huge building, which Barney said might have been a temple.

They passed among a heap of fallen pillars, and just as the others had done found a descending stairway.