In order to obtain a clear idea and a firm conviction of this cosmic evolution by natural law, the eternal birth and death of millions of suns and stars, one needs some mathematical training and a lively imagination, as well as a certain competence in astronomy and physics. The evolutionary process is much simpler, and more readily grasped in geology. Every shower of rain or wave of the sea, every volcanic eruption and every pebble, gives us a direct proof of the changes that are constantly taking place on the surface of our planet. However, the historical significance of these changes was not properly appreciated until 1822, by Karl von Hoff of Gotha, and modern geology was only founded in 1830 by Charles Lyell, who explained the whole origin and composition of the solid crust of the earth, the formation of the mountains, and the periods of the earth's development, in a connected system by natural laws. From the immense thickness of the stratified rocks, which contain the fossilised remains of extinct organisms, we discovered the enormous length--running into millions of years--of the periods during which these sedimentary rocks were deposited in water. Even the duration of the _organic_ history of the earth--that is to say, the period during which the plant and animal population of our planet was developing--must itself be put at more than a hundred million years. These results of geology and paleontology destroyed the current legend of the six days' work of a personal Creator. Many attempts were made, it is true, and are still being made, to reconcile the Mosaic supernatural story of creation with modern geology.[3] All these efforts of believers are in vain. We may say, in fact, that it is precisely the study of geology, the reflection it entails on the enormous periods of evolution, and the habit of seeking the simple mechanical causes of their constant changes, that contribute very considerably to the advance of enlightenment. Yet in spite of this (or, possibly, because of this), geological instruction is either greatly neglected or entirely suppressed in most schools. It is certainly eminently calculated (in connection with geography) to enlarge the mind, and acquaint the child with the idea of evolution. An educated person who knows the elements of geology will never experience _ennui_. He will find everywhere in surrounding nature, in the rocks and in the water, in the desert and on the mountains, the most instructive stimuli to reflection.