But the subterranean vegetation was not confined to these fungi. Farther on rose groups of tall trees of colourless foliage and easy to recognise. They were lowly shrubs of earth, here attaining gigantic size; lycopodiums, a hundred feet high; the huge sigillaria, found in our coal mines; tree ferns, as tall as our fir-trees in northern latitudes; lepidodendra, with cylindrical forked stems, terminated by long leaves, and bristling with rough hairs like those of the cactus. "Wonderful, magnificent, splendid!" cried my uncle. "Here is the entire flora of the second period of the world--the transition period. These, humble garden plants with us, were tall trees in the early ages. Look, Axel, and admire it all. Never had botanist such a feast as this!" "You are right, my uncle. Providence seems to have preserved in this immense conservatory the antediluvian plants which the wisdom of philosophers has so sagaciously put together again." "It is a conservatory, Axel; but is it not also a menagerie?" "Surely not a menagerie!" "Yes; no doubt of it. Look at that dust under your feet; see the bones scattered on the ground." "So there are!" I cried; "bones of extinct animals." I had rushed upon these remains, formed of indestructible phosphates of lime, and without hesitation I named these monstrous bones, which lay scattered about like decayed trunks of trees. "Here is the lower jaw of a mastodon," [1] 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." [1] These animals belonged to a late geological period, the Pliocene, just before the glacial epoch, and therefore could have no connection with the carboniferous vegetation. (Trans.) "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."