But both geology, and palæontology which depends on it, have the singular destiny of showing at one and the same time both great certainties and insoluble doubts. The stratification of rocks, for example, gives us very clearly the notion of the succession of these rocks with regard to one another. But it leaves us in absolute ignorance of all which has passed between the deposit of one stratum and the deposit of that which we meet with above it; in this unknown time all may take place, ten series of rocks may have been placed upon it, and then have been so well mingled together that we cannot discover their individual trace. Who will tell us about the continents engulphed by the sea; has it not already ground up under its waves those memorials of ancient days, which would be so useful to us as a means of reconstructing the history of man? Geology is a gigantic inscription lacerated for ever: each age will decipher some fragment, but we shall never be able to read it in its perfect state. Besides its great advantages, palæontological inquiry has its great inconveniences. Its advantages are the studying of animal forms which are fixed for ever, and not seeing the field of such studies continually increasing on our view. The limit of its inquiries is the origin of the alluvium; all the facts which we are thereby called upon to study are within this boundary. Palæontology alone, among the sciences of the present day, knows the extent of its domain. But palæontology, proceeding step by step, by blows of the pickaxe in an otherwise inaccessible mass, is composed of two orders of facts, which must be distinguished one from the other, resting either on affirmative evidence (the existence of organic remains in a rock) or on negative evidence (the absence of organic remains in a rock). Human palæontology itself has its own inconveniences. A bone or a skull of a man are things which are well known; they have not that strange appearance in the eyes of the crowd which makes them take ammonites for petrified serpents, hamites[324] for leeches, radiated animals for stars; when we dig up some singular bone, some carapace of a lizard, a fish, or of some unknown animal, we pick it up, and take great care of it. But if it is a man’s head, it is generally replaced religiously in the earth, and these remains are for ever lost to the scientific world.