“Here is the lower jaw of a mastodon,” I said. “These are the molar teeth of the Deinotherium; this femur must have belonged to the greatest of those beasts, the Megatherium. It certainly is a menagerie, for these remains were not brought here by a deluge. The animals to which they belonged roamed on the shores of this subterranean sea, under the shade of those arborescent trees. Here are entire skeletons. And yet I cannot understand the appearance of these quadrupeds in a granite cavern.”
“Why?”
“Because animal life existed upon the earth only in the secondary period, when a sediment of soil had been deposited by the rivers, and taken the place of the incandescent rocks of the primitive period.”
“Well, Axel, there is a very simple answer to your objection that this soil is alluvial.”
“What! at such a depth below the surface of the earth?”
“No doubt; and there is a geological explanation of the fact. At a certain period the earth consisted only of an elastic crust or bark, alternately acted on by forces from above or below, according to the laws of attraction and gravitation. Probably there were subsidences of the outer crust, when a portion of the sedimentary deposits was carried down sudden openings.”
“That may be,” I replied; “but if there have been creatures now extinct in these underground regions, why may not some of those monsters be now roaming through these gloomy forests, or hidden behind the steep crags?”
And as this unpleasant notion got hold of me, I surveyed with anxious scrutiny the open spaces before me; but no living creature appeared upon the barren strand.