“Hardly fifteen degrees (59° Fahr), nine degrees only since our departure.”
“Well, what is your conclusion?”
“This is my conclusion. According to exact observations, the increase of temperature in the interior of the globe advances at the rate of one degree (1 4/5° Fahr.) for every hundred feet. But certain local conditions may modify this rate. Thus at Yakoutsk in Siberia the increase of a degree is ascertained to be reached every 36 feet. This difference depends upon the heat-conducting power of the rocks. Moreover, in the neighbourhood of an extinct volcano, through gneiss, it has been observed that the increase of a degree is only attained at every 125 feet. Let us therefore assume this last hypothesis as the most suitable to our situation, and calculate.”
“Well, do calculate, my boy.”
“Nothing is easier,” said I, putting down figures in my note book. “Nine times a hundred and twenty-five feet gives a depth of eleven hundred and twenty-five feet.”
“Very accurate indeed.”
“Well?”
“By my observation we are at 10,000 feet below the level of the sea.”
“Is that possible?”
“Yes, or figures are of no use.”
The Professor’s calculations were quite correct. We had already attained a depth of six thousand feet beyond that hitherto reached by the foot of man, such as the mines of Kitz Bahl in Tyrol, and those of Wuttembourg in Bohemia.
The temperature, which ought to have been 81° (178° Fahr.) was scarcely 15° (59° Fahr.). Here was cause for reflection.
Chapter XIX.
Geological Studies In Situ
Next day, Tuesday, June 30, at 6 a.m., the descent began again.
We were still following the gallery of lava, a real natural staircase, and as gently sloping as those inclined planes which in some old houses are still found instead of flights of steps. And so we went on until 12.17, the, precise moment when we overtook Hans, who had stopped.
“Ah! here we are,” exclaimed my uncle, “at the very end of the chimney.”
I looked around me. We were standing at the intersection of two roads, both dark and narrow. Which were we to take? This was a difficulty.
Still my uncle refused to admit an appearance of hesitation, either before me or the guide; he pointed out the Eastern tunnel, and we were soon all three in it.
Besides there would have been interminable hesitation before this choice of roads; for since there was no indication whatever to guide our choice, we were obliged to trust to chance.
The slope of this gallery was scarcely perceptible, and its sections very unequal. Sometimes we passed a series of arches succeeding each other like the majestic arcades of a gothic cathedral. Here the architects of the middle ages might have found studies for every form of the sacred art which sprang from the development of the pointed arch. A mile farther we had to bow or heads under corniced elliptic arches in the romanesque style; and massive pillars standing out from the wall bent under the spring of the vault that rested heavily upon them. In other places this magnificence gave way to narrow channels between low structures which looked like beaver’s huts, and we had to creep along through extremely narrow passages.
The heat was perfectly bearable. Involuntarily I began to think of its heat when the lava thrown out by Snæfell was boiling and working through this now silent road. I imagined the torrents of fire hurled back at every angle in the gallery, and the accumulation of intensely heated vapours in the midst of this confined channel.
I only hope, thought I, that this so-called extinct volcano won’t take a fancy in his old age to begin his sports again!
I abstained from communicating these fears to Professor Liedenbrock. He would never have understood them at all. He had but one idea - forward! He walked, he slid, he scrambled, he tumbled, with a persistency which one could not but admire.
By six in the evening, after a not very fatiguing walk, we had gone two leagues south, but scarcely a quarter of a mile down.
My uncle said it was time to go to sleep. We ate without talking, and went to sleep without reflection.
Our arrangements for the night were very simple; a railway rug each, into which we rolled ourselves, was our sole covering. We had neither cold nor intrusive visits to fear. Travellers who penetrate into the wilds of central Africa, and into the pathless forests of the New World, are obliged to watch over each other by night. But we enjoyed absolute safety and utter seclusion; no savages or wild beasts infested these silent depths.
Next morning, we awoke fresh and in good spirits. The road was resumed. As the day before, we followed the path of the lava. It was impossible to tell what rocks we were passing: the tunnel, instead of tending lower, approached more and more nearly to a horizontal direction, I even fancied a slight rise. But about ten this upward tendency became so evident, and therefore so fatiguing, that I was obliged to slacken my pace.
“Well, Axel?” demanded the Professor impatiently.
“Well, I cannot stand it any longer,” I replied.
“What! after three hours’ walk over such easy ground.”
“It may be easy, but it is tiring all the same.”
“What, when we have nothing to do but keep going down!”
“Going up, if you please.”
“Going up!” said my uncle, with a shrug.
“No doubt, for the last half-hour the inclines have gone the other way, and at this rate we shall soon arrive upon the level soil of Iceland.”
The Professor nodded slowly and uneasily like a man that declines to be convinced. I tried to resume the conversation. He answered not a word, and gave the signal for a start. I saw that his silence was nothing but ill-humour.
Still I had courageously shouldered my burden again, and was rapidly following Hans, whom my uncle preceded. I was anxious not to be left behind. My greatest care was not to lose sight of my companions. I shuddered at the thought of being lost in the mazes of this vast subterranean labyrinth.
Besides, if the ascending road did become steeper, I was comforted with the thought that it was bringing us nearer to the surface. There was hope in this. Every step confirmed me in it, and I was rejoicing at the thought of meeting my little Gräuben again.
By midday there was a change in the appearance of this wall of the gallery. I noticed it by a diminution of the amount of light reflected from the sides; solid rock was appearing in the place of the lava coating. The mass was composed of inclined and sometimes vertical strata. We were passing through rocks of the transition or silurian9 system.
“It is evident,” I cried, “the marine deposits formed in the second period, these shales, limestones, and sandstones. We are turning away from the primary granite. We are just as if we were people of Hamburg going to Lubeck by way of Hanover!”
I had better have kept my observations to myself. But my geological instinct was stronger than my prudence, and uncle Liedenbrock heard my exclamation.
“What’s that you are saying?” he asked.
“See,” I said, pointing to the varied series of sandstones and limestones, and the first indication of slate.
“Well?”
“We are at the period when the first plants and animals appeared.”