I shall not contend, with some geologists, that even the primary crystalline rocks may once have been filled with organic remains, which have been obliterated by heat; and that, in this way, there may have been a number of creations of organized beings on the globe, of which no trace now remains. I take as the basis of my argument only the relics of animals and plants actually found in the rocks. And when one sees mountain masses, often of small shells, and spread over wide areas, he is amazed to learn how prolific nature has been. What a countless number of vegetables, too, must have been required to produce beds of coal from one to fifty feet thick, and extending over thousands of square miles, and alternating several times with sandstone in the same basin! There is reason to believe, too, that the number of animals preserved in the strata bears only a small proportion to those which have been utterly destroyed and decomposed into their original elements. For example, in the sandstone along Connecticut River, the tracks of more than forty species of bipeds and quadrupeds have been found most distinctly marked. Some of these bipeds must have been of colossal size—as much as twelve or fifteen feet in height. And yet scarcely any other vestige of their existence has been discovered. They were the giant rulers of that valley for centuries; but they have all vanished. How numerous, then, may have been the softer animals of the ancient world, which have not left even a footmark to certify their existence to coming generations!
But the facts recently brought to light respecting infusoria and polythalamia fill us with the greatest admiration of the extent of organic life upon the globe. We have already seen that some of these animals are so minute that eight millions of them are found in a space not larger than a mustard-seed; and yet they had skeletons of silex, lime, and iron; and, of course, these skeletons have been preserved; and, though of the smallest size, it requires not less than forty-one billions to make a single cubic inch; yet deposits of them, or of species not much larger, occur, several feet in thickness, and extending over several square miles. Nay, the chalk of Northern Europe, and also of Western Asia, where it constitutes most of Mount Lebanon, and extends southerly through Palestine into Arabia and Egypt, and also deposits in North and South America, thousands of miles in extent,—this rock, I say, is nearly half composed of microscopic shells. The oölite, also, contains them; and, indeed, infusorial remains occur in flint and opal; and, as instruments and observations are perfected, more and more of the solid rocks are found to have once constituted the framework of animals. It is hardly to be doubted that such was the fact with nearly all the limestone on the globe, occupying at least a seventh part of its surface. In fact, we seem fast coming to regard as sober truth the ancient adage, apparently so extravagant—Omnis calx e vermibus; omne ferrum e vermibus; omnis silex e vermibus. Indeed, it is the opinion of so competent a geologist as Dr. Mantell that “probably there is not an atom of the solid materials of the globe which has not passed through the complex and wonderful laboratory of life.”—Wond. of Geology, vol. ii. p. 670.—What a vast field here opens before us to contemplate the far-reaching plans, the benevolence, and the wisdom of the Deity!
In the third place, geology shows us that the present system of organic life on the globe is but one link of a series, extending very far backward and infinitely forward.
Revelation describes only the existing species, leaving to science the task and the privilege to lift up the veil that hangs over the past, and to disclose other economies that have passed away. How many of them have existed we do not certainly know. If, with Agassiz, we characterize them by their predominant tribes, we might say that all the period previous to the new red sandstone constituted the reign of fishes; from thence to the chalk, the reign of reptiles; from thence to the drift, the reign of mammifera. But this is a less philosophical view than that of Deshayes, who finds five great groups of animals, specifically independent of one another. But who will attempt to fix the chronological limits of these systems? We can only say that they must have been exceedingly long, if we can place any dependence upon existing analogies; and we know that each one of them is made up of numerous subdivisions, or minor groups, widely, though not entirely, different in composition and organic contents. We know that the more we examine the whole series, the deeper does our conviction become that its commencement runs back far, very far, into the depths of past eternity. We know, also, from the joint testimony of Scripture and geology, that another change is to pass over the world, to prepare it for inhabitants far more elevated than those now living upon it, and in possession of perfect holiness and perfect happiness. And it may be it will experience far greater changes, adapting it for higher and higher grades of being, through periods of duration to which we can assign no limits. O, what a vast chain of being is here spread out before the imagination, reaching immeasurably far into the depths of the eternity which is past, and into the eternity which is to come! What a field for the display of God’s infinite perfections! What a vista does it open to us into the vast plans and purposes of Jehovah!
In the fourth place, geology reveals to us a curious series of improvements in the condition of worlds, as they pass through successive changes.
If the earth began its existence in the state of vapor, we can hardly imagine it in that state capable of sustaining any organic natures, formed upon the general type of those now existing. Nor, when the vapor was condensed into a molten globe, could such natures inhabit it, till a crust had formed over its surface, and the heat had been so reduced as not to decompose animals and plants. Even then, the natures placed upon it must have been of a peculiar and low type of organization, capable of enduring the high temperature and catastrophes which would destroy those of more delicate and complicated organization. But gradually did the temperature diminish, while aqueous and atmospheric agencies were accumulating a deeper and a richer soil, so that the next change of inhabitants would allow natures of a higher organization and a denser population to occupy the surface. Their remains, buried in the earth, would increase the quantity of carbonate of lime in a form available for the use of animals and plants; that is, lime would gradually be eliminated, by plants and animals, from its more concealed combinations in the crystalline rocks, and be converted into carbonates, sulphates, and humates. A larger amount of organic matter would also be converted into humus. Now, limestone soils are of all others most favorable to vegetation, when there is a sufficient supply of organic matter. Hence every successive change becomes more and more adapted for animals and plants, because the lime and the organic matter in a state favorable for their support have been increasing; and the present state of the surface is more favorable than any conditions which have preceded it, and accordingly it is peopled with more perfect and more numerous organic natures. Can we doubt but that, if another change passes over the earth, this same great principle of progressive improvement will be manifested in the renovated world? I am not prepared to maintain, however, that this future change will be, like the past ones, an improvement as to soil and climate; for the change, as Scripture teaches, will be accomplished by fire; and so different will be the state of existence in the new earth, wherein dwelleth righteousness, that we cannot say how far the present system of nature will be introduced. But that it will be an improved condition, we can hardly doubt, if we infer any thing from the splendid figures by which it is described in the Bible, and from the character of those who are to be its denizens.
Some of the facts of modern astronomy impress us with the idea that this principle of progress may extend to other worlds. Some of these are in a gaseous state, some condensed into fiery liquid globes, some covered with a crust of solidified volcanic matter, and some surrounded by a liquid, like water. Do not these facts justify the supposition, that the changes which our earth has undergone are merely a single example of a great principle in God’s government of the natural world? If so, it presents the divine wisdom in an interesting aspect. We see the Deity employing the same matter for different purposes. Instead of creating it for one single economy of organic beings, he seems to have made it the theatre for the display of his benevolence through successive periods; but at the same time not losing sight of the highest use he intended to make of it, by the introduction of rational and immortal natures upon it. Human wisdom would have pronounced this impossible; but divine wisdom, prompted by divine benevolence, could accomplish it.
Finally, geology discloses to us chemical change as a great animating, controlling, and conservative principle of the material universe.
When Newton brought to light the principle of gravitation, and showed how it controls and keeps in harmonious movement the heavenly bodies, he developed the great mechanical power by which the universe is governed. And this power was supposed for a long time to be superior to all others. But geology has brought out a second great controlling and conservative agency,—the chemical power,—“the second right hand of the Creator,” as Dr. McCulloch expressively calls it. Suppose matter under the control of gravity, and let it be balanced by a centrifugal force. You have, indeed, harmonious motions among the celestial bodies, and, if no disturbing cause come in, you have endless motion. But until you introduce chemical agencies, every thing in the individual worlds would be compacted by gravity into one dead mass of matter, destined to no resurrection. But let chemical agencies leaven that mass, let affinity and cohesion commence their segregating processes, and constant motion and change would follow, with a thousand new and splendid forms. Especially when the Deity had infused the living principle into portions of that matter, and put chemistry, and her handmaid electricity, under the control of the vital power, would these worlds teem with animation, and countless exhibitions of beauty.
And in all known worlds, these chemical changes are at work unceasingly. We know not whether those worlds are all inhabited, but we have evidence that all are undergoing the transmutations of chemistry; not on their surface merely, but in their deep interior. The consequence is, universal change; change often upon a vast scale; change extending through thousands and millions of years, and through the entire mass of immense worlds. We have glanced, in these lectures, at the most important of those changes which this world has undergone, and we have seen it to be almost universal. We have found that the entire crust of the globe, many miles in thickness, and probably to its centre, has been dissolved by heat, and much of it also by water; that a large part of it, at least, has, by the same chemistry, been made to constitute portions of the animal frame; that, even now, much of its interior is held in igneous solution, and that probably the time was when its entire mass was a molten, self-luminous world. Indeed, the conjecture is not without some foundation, which carries back this chemical action one step farther, and makes the world originally a diffused mass of nebula.