We do not know what brought about the change: though we do know that during it there was great volcanic activity over Europe and that the waning forests of vegetation and the steaming swamps gave place to desert plains. Vegetation sank lower and lower. The forests disappeared or dwelt only in clusters. The soft sappy trees gave place to hardy pines which clung to the plains and the mountains, and other sterner types began to appear, allied to the spruces, yews, and ginkgo. The ginkgo tree is one of the oldest of the tree type which now has a living representative. Any reader interested enough in the matter to walk along Royal Hospital Road, Chelsea, will find a ginkgo tree just outside the Old Physic Garden; and of course a good many other examples are preserved in botanic gardens. The cycads, offshoots of the ferns, through the strange group of trees known as the cycado-filices, spread through the woods.
The trilobites, to turn to animal life, all but disappeared, though one elegant example remained; the corals were changing; and the lamp-shells were dropping out. There were a few new species of fishes, but none of any great strength or capacity, and all preserving still the tail which is part of the backbone. There was an all-round impoverishment of life--so great, indeed, that the early geologists used to believe that a complete destruction of all life followed this, the closing stage of the Palæozoic era, and that a re-creation followed. They would have been confirmed in this belief had they but known that intense cold and glaciation were setting in where the tropics were situated and that the dryness of vast deserts was sweeping away life elsewhere. But we now know that life was not entirely lost; that many species survived, and that others, altering to suit altering conditions, became stronger in the process. Nevertheless, life was greatly impoverished. A census made a few years ago gave the known animal species of the Carboniferous period as 10,000, while those of the Permian period were only 300, or three per cent. Possibly the percentage was larger than that, but still it was small.
But if the Permian was poor in life it was very interesting. The amphibians had been growing in strength during the later stages of the Carboniferous age, and may possibly have been more numerous then than at any other time, for the vast swamps were very favourable for them. They diminished in the Permian, though the Permian amphibians showed some advances, and began to assume a likeness to reptiles. Perhaps the reptiles may have first appeared in the Carboniferous, but they declared themselves in the Permian age. Two great branches of reptiles seem already to have defined themselves; perhaps they had never formed a common group as reptiles, but had separated while still amphibians. The one bore resemblance to, and were perhaps the forerunners of, the great hosts of lizards, crocodiles, dinosaurs, ichthyosaurs, and flying saurians, which are the most pronounced of the reptiles, and of which we shall have a great deal to say presently. The other group were perhaps the ancestors of the turtles and plesiosaurs which appeared later, and possibly led the way to the mammals. This rapid and diverse spreading out of the reptiles in a period when life as a whole was at a low ebb is not a little remarkable. These creatures seem to show the arrival of a more pronounced form of _air-breathing_ animal; and that may have been the consequence of the presence of more oxygen in the earth's atmosphere. Of the Permian amphibians, one of the most interesting was like the Sphenodon, which still creeps about the northern islands of New Zealand. The most striking of the reptiles was the _Naosaurus_, a beast-like creature with a high back of spines webbed together like a solid porcupine. It was from three to ten feet in length.