The growth of plants was then most wonderful; but although coal is found in many different parts of the world, it was not all formed at one time, and though it is plentiful in England and Wales, Scotland, Ireland, France, Belgium, Russia, Hungary, Australia, New Zealand, China, and Borneo, it is older in some countries than in others. It is fortunate, however, that this useful material was made in Nature’s workshop in so many different countries, or it would have to be carried from one to another. The coal forests were not the same trees as we have now—oaks, elms, ashes, limes, and so on. Most of them had rather hollow trunks and splendid waving tops like ferns and reeds, though there were some like our fir-trees. If you lie down in the long grass before it is mown, and look through the stalks and fancy yourself an inch high only, you will have some idea how the coal forest would have looked if you had lived then. But there were no human beings on the Earth then, and I do not think there were any large animals, at least none have been found in the coal itself, except in Switzerland, where a few bones of the mammoth (an ancient elephant) and of the rhinoceros have been discovered in the much newer beds of coal, and also those of a large reptile like a crocodile in the coal beds of Ohio in America. [Illustration: II. _Fossil Tree Fern._ _Calamites._ _Lepidodendron._ _Different Kinds of Plants of the Coal Forests._] In such immense forests insects must certainly have been plentiful, and some of the fossil bodies of beetles, dragon-flies, and spiders, have been preserved, and a few tree lizards.[4] Of course the edges of the coal forests were washed here and there by the salt sea, and there must have been some fresh water rivers and ponds, for we find both fresh and salt water shells in these beds. It was almost dark in these forests, so thickly did the plants grow together. There were enormous club-mosses close together and as high as most houses, with their leaves interlaced making a complete network to shut out the sun. But the sun which shone on the forests was warm, and the air which went through them was soft, or they would not have grown so wonderfully. Indeed, there can be no doubt that the climate of northern regions was once much warmer than it is now. A thick bed of coal was discovered by the Arctic Expedition in 1875-6 actually within five hundred miles of the North Pole, where the ice on the sea is now thirty or forty feet thick![5] The forest which formed this coal could only have grown in a temperate climate, and there are no forests there now; it is so intensely cold they could not live. There must then have been a great change in the climate of the Arctic regions since that coal was living vegetation. The few plants and mosses which can live there now are of a very different and more hardy kind than those of the coal forests.