"And you are surprised at this total absence of springs?" he said.

"Doubtless--I am very uneasy on the point. We have certainly not enough water to last us five days."

"Be quite easy on that matter," continued my uncle. "I answer for it we shall find plenty of water--in fact, far more than we shall want."

"But when?"

"When we once get through this crust of lava. How can you expect springs to force their way through these solid stone walls?"

"But what is there to prove that this concrete ma.s.s of lava does not extend to the centre of the earth? I don't think we have as yet done much in a vertical way."

"What puts that into your head, my boy?" asked my uncle mildly.

"Well, it appears to me that if we had descended very far below the level of the sea--we should find it rather hotter than we have."

"According to your system," said my uncle; "but what does the thermometer say?"

"Scarcely fifteen degrees by Reaumur, which is only an increase of nine since our departure."

"Well, and what conclusion does that bring you to?" inquired the Professor.

"The deduction I draw from this is very simple. According to the most exact observations, the augmentation of the temperature of the interior of the earth is one degree for every hundred feet. But certain local causes may considerably modify this figure. Thus at Yakoust in Siberia, it has been remarked that the heat increases a degree every thirty-six feet. The difference evidently depends on the conductibility of certain rocks. In the neighborhood of an extinct volcano, it has been remarked that the elevation of temperature was only one degree in every five-and-twenty feet. Let us, then, go upon this calculation--which is the most favorable--and calculate."

"Calculate away, my boy."

"Nothing easier," said I, pulling out my notebook and pencil. "Nine times one hundred and twenty-five feet make a depth of eleven hundred and twenty-five feet."

"Archimedes could not have spoken more geometrically."

"Well?"

"Well, according to my observations, we are at least ten thousand feet below the level of the sea."

"Can it be possible?"

"Either my calculation is correct, or there is no truth in figures."

The calculations of the Professor were perfectly correct. We were already six thousand feet deeper down in the bowels of the earth than anyone had ever been before. The lowest known depth to which man had hitherto penetrated was in the mines of Kitzbuhel, in the Tirol, and those of Wurttemberg.

The temperature, which should have been eighty-one, was in this place only fifteen. This was a matter for serious consideration.

CHAPTER 16

THE EASTERN TUNNEL

The next day was Tuesday, the 30th of June--and at six o'clock in the morning we resumed our journey.

We still continued to follow the gallery of lava, a perfect natural pathway, as easy of descent as some of those inclined planes which, in very old German houses, serve the purpose of staircases. This went on until seventeen minutes past twelve, the precise instant at which we rejoined Hans, who, having been somewhat in advance, had suddenly stopped.

"At last," cried my uncle, "we have reached the end of the shaft."

I looked wonderingly about me. We were in the centre of four cross paths--somber and narrow tunnels. The question now arose as to which it was wise to take; and this of itself was no small difficulty.

My uncle, who did not wish to appear to have any hesitation about the matter before myself or the guide, at once made up his mind. He pointed quietly to the eastern tunnel; and, without delay, we entered within its gloomy recesses.

Besides, had he entertained any feeling of hesitation it might have been prolonged indefinitely, for there was no indication by which to determine on a choice. It was absolutely necessary to trust to chance and good fortune!

The descent of this obscure and narrow gallery was very gradual and winding. Sometimes we gazed through a succession of arches, its course very like the aisles of a Gothic cathedral. The great artistic sculptors and builders of the Middle Ages might have here completed their studies with advantage. Many most beautiful and suggestive ideas of architectural beauty would have been discovered by them. After pa.s.sing through this phase of the cavernous way, we suddenly came, about a mile farther on, upon a square system of arch, adopted by the early Romans, projecting from the solid rock, and keeping up the weight of the roof.

Suddenly we would come upon a series of low subterranean tunnels which looked like beaver holes, or the work of foxes--through whose narrow and winding ways we had literally to crawl!

The heat still remained at quite a supportable degree. With an involuntary shudder, I reflected on what the heat must have been when the volcano of Sneffels was pouring its smoke, flames, and streams of boiling lava--all of which must have come up by the road we were now following. I could imagine the torrents of hot seething stone darting on, bubbling up with accompaniments of smoke, steam, and sulphurous stench!

"Only to think of the consequences," I mused, "if the old volcano were once more to set to work."

I did not communicate these rather unpleasant reflections to my uncle.

He not only would not have understood them, but would have been intensely disgusted. His only idea was to go ahead. He walked, he slid, he clambered over piles of fragments, he rolled down heaps of broken lava, with an earnestness and conviction it was impossible not to admire.

At six o'clock in the evening, after a very wearisome journey, but one not so fatiguing as before, we had made six miles towards the southward, but had not gone more than a mile downwards.

My uncle, as usual, gave the signal to halt. We ate our meal in thoughtful silence, and then retired to sleep.

Our arrangements for the night were very primitive and simple. A traveling rug, in which each rolled himself, was all our bedding. We had no necessity to fear cold or any unpleasant visit. Travelers who bury themselves in the wilds and depths of the African desert, who seek profit and pleasure in the forests of the New World, are compelled to take it in turn to watch during the hours of sleep; but in this region of the earth absolute solitude and complete security reigned supreme.

We had nothing to fear either from savages or from wild beasts.

After a night's sweet repose, we awoke fresh and ready for action. There being nothing to detain us, we started on our journey. We continued to burrow through the lava tunnel as before. It was impossible to make out through what soil we were making way. The tunnel, moreover, instead of going down into the bowels of the earth, became absolutely horizontal.

I even thought, after some examination, that we were actually tending upwards. About ten o'clock in the day this state of things became so clear that, finding the change very fatiguing, I was obliged to slacken my pace and finally come to a halt.

"Well," said the Professor quickly, "what is the matter?"

"The fact is, I am dreadfully tired," was my earnest reply.

"What," cried my uncle, "tired after a three hours' walk, and by so easy a road?"

"Easy enough, I dare say, but very fatiguing."

"But how can that be, when all we have to do is to go downwards."

"I beg your pardon, sir. For some time I have noticed that we are going upwards."

"Upwards," cried my uncle, shrugging his shoulders, "how can that be?"