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.