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.”