The very slight changes in climate, situation, and food, that will destroy most species of animals and plants, is hard to be realized by man, whose nature will sustain very great changes of this kind. So will most of the animals and plants that have been domesticated by man, and which accompany him into every soil and climate. But the great mass of animals and plants would perish by such a transplantation. They are adapted to a particular region, often of narrow limits; and to remove them from thence, even to one slightly diverse, is to cause their deterioration and final destruction. In other words, their natures are exactly adapted to the place of habitation assigned them. And it must have required infinite wisdom thus to fit the delicate machinery of animal and vegetable organization to the great variety of circumstances on the globe in which it is placed. But we find that same wisdom to have been manifested in all the vast periods of organic life. We have the most unequivocal evidence that the condition of the earth has undergone important changes. We cannot examine the remarkable flora and fauna of the older rocks, the gigantic sauroid fishes, the huge orthoceratites and ammonites, the heteroclitic trilobites, and the strange sigillaria and lepidodendra, calamites and asterophyllites, the lofty coniferae, and the anomalous cycadeae,--we cannot examine these without realizing that a state of the globe very different from the present must have existed when they had possession of it. And when we contemplate also the enormous saurians and batrachians of the middle secondary rocks, and the colossal quadrupeds of the tertiary strata, we cannot doubt that a tropical or an ultra-tropical climate must have prevailed in high northern latitudes during their existence. We perceive that there has been a gradual decrease of temperature on the surface from the earliest times. In each successive race of organized beings which have been placed on the globe, there must have been, therefore, some change of constitution to adapt them to the altered state of the climate and productions of the earth. And we find this alteration to have been always made with consummate skill, so as to secure the most complete development of organic beings, and the greatest enjoyment to sensitive natures. Malevolence would not have done this; for it might with infinite knowledge at command, have filled each successive period of the world with natures unadapted to the mutable condition of things, capable, indeed, of a prolonged existence, not to enjoy, but only to suffer. But infinite benevolence was fitting up this world by slow secondary agencies for the elevated races which now occupy it, especially for one species, rational and immortal; and it lavished its kindness and wisdom by filling the world, during those preparatory ages, with multitudes of happy beings, fitted exactly to each altered condition of the air, the water, and the soil.