I dare say you have remarked while reading that all the plants and animals of the early ages of the world seem to be made on a simple plan, and as the Earth grows older they become more perfect, and this is just what I want you to take notice of all through. The plants of the coal period, you have seen, were nothing like so perfect in construction, beautiful as they were, as the forest trees of the present time, neither were the animals so perfect as those living now. There has been _progress_, step by step, throughout the vegetable and animal creation; and, though many of the lower forms of the early ages exist now, there are others far superior to them which did not exist then: but all this will come in “The Animal Part.” About the middle of the Earth’s age came the wonderful period of vegetation which gave us our coal, and after that there was a great and busy time, when huge reptiles and reptile-like birds, and then true birds, made their appearance. But that belongs to the next part of the “puzzle of life.” If we look with astonishment at the coal forests, we may also well think of them with thankfulness. Here is the sunshine of past ages stored up for our use, and we bring it out again to warm ourselves, cook our food, make all our iron things, and drive our steam-engines! Can any romance be finer than this, that we are carried across to America and India and Australia in steam-boats driven by the “fossil sunlight” of ages and ages past, and whirled along at sixty miles an hour over iron rails by the same stored-up strength? If you doubt this, think of living trees. Do they not live by the air and sunlight? Will they grow without these? They spread their branches and leaves to gather the warmth and light from the air, and when they are cut down and dried, and you put a match to the wood, all the old warmth and light come out again; and we know that the coal is only fossil wood. Our Creator wastes nothing. Even when there were no people living to rejoice in the sun, He thought of those people who _should_ come in time, and not one of the fiery rays of the fierce sun was lost. These mighty forests were sent to gather it, and when they had died down they sank below the surface and were covered from the air, that none of their light or heat should escape. In such forests it is strange that there were no birds, especially as there were swarms of insects, and no doubt abundance of worms. But no bone of bird or any trace of feathered songster of these lovely groves has yet been found. Little lizards chased flies and beetles up and down the stems of the club-mosses and ferns, and larger reptiles lurked in the long damp grass under the shade. The pools and ponds were filled with curious fishes, and reefs of beautiful white coral fringed all the shores of the seas.