By mid-day 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 silurian 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."
"Do you think so?"
"Look close, and examine."
I obliged the Professor to move his lamp over the walls of the gallery.
I expected some signs of astonishment; but he spoke not a word, and went on.
Had he understood me or not?
Did he refuse to admit, out of self-love as an uncle and a philosopher, that he had mistaken his way when he chose the eastern tunnel? or was he determined to examine this passage to its farthest extremity?
It was evident that we had left the lava path, and that this road could not possibly lead to the extinct furnace of Sn?fell.
Yet I asked myself if I was not depending too much on this change in the rock.
Might I not myself be mistaken?
Were we really crossing the layers of rock which overlie the granite foundation?
If I am right, I thought, I must soon find some fossil remains of primitive life; and then we must yield to evidence.
I will look.
I had not gone a hundred paces before incontestable proofs presented themselves.
It could not be otherwise, for in the Silurian age the seas contained at least fifteen hundred vegetable and animal species.
My feet, which had become accustomed to the indurated lava floor, suddenly rested upon a dust composed of the debris of plants and shells.
In the walls were distinct impressions of fucoids and lycopodites.
Professor Liedenbrock could not be mistaken, I thought, and yet he pushed on, with, I suppose, his eyes resolutely shut.
This was only invincible obstinacy.
I could hold out no longer.
I picked up a perfectly formed shell, which had belonged to an animal not unlike the woodlouse: then, joining my uncle, I said:
"Look at this!"
"Very well," said he quietly, "it is the shell of a crustacean, of an extinct species called a trilobite.
Nothing more."
"But don't you conclude—?"
"Just what you conclude yourself.
Yes; I do, perfectly.
We have left the granite and the lava.
It is possible that I may be mistaken. But I cannot be sure of that until I have reached the very end of this gallery."
"You are right in doing this, my uncle, and I should quite approve of your determination, if there were not a danger threatening us nearer and nearer."
"What danger?"
"The want of water."
"Well, Axel, we will put ourselves upon rations."
CHAPTER XX. THE FIRST SIGNS OF DISTRESS
In fact, we had to ration ourselves.
Our provision of water could not last more than three days. I found that out for certain when supper-time came.
And, to our sorrow, we had little reason to expect to find a spring in these transition beds.
The whole of the next day the gallery opened before us its endless arcades.