"What is the matter now?" he said, in a tone of great gravity. "Well," cried I, "do you not see these different layers of calcareous rocks and the first indication of slate strata?" "Well; what then?" "We have arrived at that period of the world's existence when the first plants and the first animals made their appearance." "You think so?" "Yes, look; examine and judge for yourself." I induced the Professor with some difficulty to cast the light of his lamp on the sides of the long winding gallery. I expected some exclamation to burst from his lips. I was very much mistaken. The worthy Professor never spoke a word. It was impossible to say whether he understood me or not. Perhaps it was possible that in his pride--my uncle and a learned professor--he did not like to own that he was wrong in having chosen the eastern tunnel, or was he determined at any price to go to the end of it? It was quite evident we had left the region of lava, and that the road by which we were going could not take us back to the great crater of Mount Sneffels. As we went along I could not help ruminating on the whole question, and asked myself if I did not lay too great a stress on these sudden and peculiar modifications of the earth's crust. After all, I was very likely to be mistaken--and it was within the range of probability and possibility that we were not making our way through the strata of rocks which I believed I recognized piled on the lower layer of granitic formation. "At all events, if I am right," I thought to myself, "I must certainly find some remains of primitive plants, and it will be absolutely necessary to give way to such indubitable evidence. Let us have a good search." I accordingly lost no opportunity of searching, and had not gone more than about a hundred yards, when the evidence I sought for cropped up in the most incontestable manner before my eyes. It was quite natural that I should expect to find these signs, for during the Silurian period the seas contained no fewer than fifteen hundred different animal and vegetable species. My feet, so long accustomed to the hard and arid lava soil, suddenly found themselves treading on a kind of soft dust, the remains of plants and shells. Upon the walls themselves I could clearly make out the outline, as plain as a sun picture, of the fucus and the lycopods. The worthy and excellent Professor Hardwigg could not of course make any mistake about the matter; but I believe he deliberately closed his eyes, and continued on his way with a firm and unalterable step. I began to think that he was carrying his obstinacy a great deal too far. I could no longer act with prudence or composure. I stooped on a sudden and picked up an almost perfect shell, which had undoubtedly belonged to some animal very much resembling some of the present day. Having secured the prize, I followed in the wake of my uncle. "Do you see this?" I said.