Geology, then, teaches us that the physical features which now distinguish the earth's surface have been produced as the ultimate result of an almost endless succession of precedent changes. Palæontology teaches us, though not yet in such assured accents, the same lesson. Our present animals and plants have not been produced, in their innumerable forms, each as we now know it, as the sudden, collective, and simultaneous birth of a renovated world. On the contrary, we have the clearest evidence that some of our existing animals and plants made their appearance upon the earth at a much earlier period than others. In the confederation of animated nature some races can boast of an immemorial antiquity, whilst others are comparative _parvenus_. We have also the clearest evidence that the animals and plants which now inhabit the globe have been preceded, over and over again, by other different assemblages of animals and plants, which have flourished in successive periods of the earth's history, have reached their culmination, and then have given way to a fresh series of living beings. We have, finally, the clearest evidence that these successive groups of animals and plants (faunæ and floræ) are to a greater or less extent directly connected with one another. Each group is, to a greater or less extent, the lineal descendant of the group which immediately preceded it in point of time, and is more or less fully concerned with giving origin to the group which immediately follows it. That this law of "evolution" has prevailed to a great extent is quite certain; but it does not meet all the exigencies of the case, and it is probable that its action has been supplemented by some still unknown law of a different character. We shall have to consider the question of geological "continuity" again. In the meanwhile, it is sufficient to state that this doctrine is now almost universally accepted as the basis of all inquiries, both in the domain of geology and that of palæontology. The advocates of continuity possess one immense advantage over those who believe in violent and revolutionary convulsions, that they call into play only agencies of which we have actual knowledge. We _know_ that certain forces are now at work, producing certain modifications in the present condition of the globe; and we _know_ that these forces are capable of producing the vastest of the changes which geology brings under our consideration, provided we assign a time proportionately vast for their operation. On the other hand, the advocates of catastrophism, to make good their views, are compelled to invoke forces and actions, both destructive and restorative, of which we have, and can have, no direct knowledge. They endow the whirlwind and the earthquake, the central fire and the rain from heaven, with powers as mighty as ever imagined in fable, and they build up the fragments of a repeatedly shattered world by the intervention of an intermittently active creative power.