I have, for my own part, seen no reason to dissent from these views, though in the sequel I shall endeavor to present some considerations which may tend to reconcile with them some of the hypotheses of a contrary nature now held. It must be admitted, however, that the majority of geologists and biologists have abandoned these views of Pictet and Bronn, and have gone over to the evolutionist philosophy, with how little reason I have endeavored to show elsewhere,[147] and shall farther illustrate in the Appendix. Let it be observed, however, that even evolution does not affect the grand idea of the unity of nature, or the fact that the plan of the Creator in the organic world was so vast that it required the whole duration of our planet, in all its stages of physical existence, to embrace the whole. There is but one system of organic nature; but, to exhibit the whole of it, not only all the climates and conditions now existing are required, but those also of all past geological periods. Further, the progress of nature being mainly in the direction of differentiation of functions once combined, it has a limit backward in the most general forms and conditions, and forward in the most specialized. This is the history of the individual and probably also of the type, of the world itself and of the universe; and for this reason material nature necessarily lacks the eternity of its author. It appears, from the above facts and reasonings, that geology informs us--1. That the materials of our existing continents are of secondary origin, as distinguished from primitive or coeval with the beginning. 2. That a chronological order of formation of these rocks can be made out. 3. That the fossil remains contained in the rocks constitute a chronology of animal and vegetable existence. 4. That the history of the earth may be divided in this way into distinct periods, all pre-Adamite. 5. That the pre-Adamite periods were of enormous duration. 6. That during these periods the existing general laws of nature were in force, though the dispositions of inorganic nature were different in different periods, and the animals and plants of successive periods were also different from each other. 7. The introduction of new species of animals and of plants, while indicating advance in the perfection of nature, does not prove spontaneous development, but rather a definite plan and law of creation. The parallelism of these conclusions of careful inductive inquiry into the structure of the earth's crust, with the results which we have already obtained from revelation, may be summed up under the following heads: