1. The Earth carries within it the evident traces of its formation. One can follow the phases of it with a mathematical precision in the different rocks which compose its framework. The whole of these studies constitute the science of geology, a science born of this century, and which has thrown light upon the much controversial question of its origin, and of that of the living beings which inhabit it. Here there is no point upon which one can hang a hypothesis. It is the rigorous result of the observation of facts, and into the presence of facts doubt is forbidden to enter. A history of the formation of the globe is written in the geological beds of the Earth in a clearer manner than in books hitherto written, because it is Nature itself who speaks and not the imagination of men that created systems. Where one sees the traces of fire, one can say with certitude that fire has existed; where those of water are seen, one says with no less certainty that water has been there; where one sees those of animals, one infers that animals have lived there.
Geology is therefore a science of observation: it draws conclusions only from that which it sees. Upon doubtful points it affirms nothing. It utters only debatable opinions concerning phenomena, of which the definite solution awaits more complete observations. Without the discoveries of geology, as well as those of astronomy, the genesis of the world would still lie in legendary shadows. Thanks to it, today man knows the history of his habitation; and the trelliswork fables which surrounded his cradle is crushed, never to rise again.