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.
Sixteenthly. There is evidence, in regard to some parts of the world, that the continents are now experiencing slow vertical movements--some places sinking, and others rising. And hence a presumption is derived that, in early times, such changes may have been often repeated, and on a great scale.
Seventeenthly. Every successive change of importance on the earth's surface appears to have been an improvement of its condition, adapting it to beings of a higher organization, and to man at last, the most perfect of all.
Finally. The present races of animals and plants on the globe are for the most part disposed in groups, occupying particular districts, beyond whose limits the species peculiar to those provinces usually droop and die. The same is true, to some extent, as to the animals and plants found in the rocks; though the much greater uniformity of climate, that prevailed in early times, permitted organized beings to take a much wider range than at present; so that the zoölogical and botanical districts were then probably much wider. But the general conclusion, in respect to living and extinct animals, is, that there must have been several centres of creation, from which they emigrated as far as their natures would allow them to range.
It would be easy to state more principles of geology of considerable importance; but I have now named the principal ones that bear upon the subject of religion. A brief statement of the leading truths of theology, whether natural or revealed, which these principles affect, and on which they cast light, will give an idea of the subjects which I propose to discuss in these lectures.
