Ninthly. In the earliest times in which animals and plants lived, the climate over the whole globe appears to have been as warm as, or even warmer than, it is now between the tropics. And the slow change from warmer to colder appears to have been the chief cause of the successive destruction of the different races; and new ones were created, better adapted to the altered condition of the globe; and yet each group seems to have occupied the globe through a period of great length, so that we have here another evidence of the vast cycles of duration that must have rolled away even since the earth became a habitable globe. Tenthly. There is no small reason to suppose that the globe underwent numerous changes previous to the time when animals were placed upon it; that, in fact, the time was when the whole matter of the earth was in a melted state, and not improbably also even in a gaseous state. These points, indeed, are not as well established as the others that have been mentioned; but, if admitted, they give to the globe an incalculable antiquity. Eleventhly. It appears that the present condition of the earth's crust and surface was of comparatively recent commencement; otherwise the steep flanks of mountains would have ceased to crumble down, and wide oceans would have been filled with alluvial deposits. Twelfthly. Among the thirty thousand species of animals and plants found in the rocks,[5] very few living species have been detected; and even these few occur in the most recent rocks, while in the secondary group, not less than six miles thick, not a single species now on the globe has been discovered. Hence the present races did not exist till after those in the secondary rocks had died. No human remains have been found below those alluvial deposits which are now forming by rivers, lakes, and the ocean. Hence geology infers that man was one of the latest animals that was placed on the globe. Thirteenthly. The surface of the earth has undergone an enormous amount of erosion by the action of the ocean, the rivers, and the atmosphere. The ocean has worn away the solid rock, in some parts of the world, not less than ten thousand feet in depth, and rivers have cut channels through the hardest strata, hundreds of feet deep and several miles long; both of which effects demand periods inconceivably long. Fourteenthly. At a comparatively recent date, northern and southern regions have been swept over and worn down by the joint action of ice and water, the force in general having been directed towards the equator. This is called the _drift_ period. Fifteenthly. Since the drift period, the ocean has stood some thousands of feet above its present level in many countries.