The Progress of the Century

by Unknown

We have now a great blank of fifteen centuries—the dark ages of human progress—after which the era of observation and experiment began, and for the first time men really set themselves to study nature, thus laying the foundation for all the great theoretical advances of our time. As leading to the next great step in theories of evolution, we must note the life-long observations by Tycho Brahe of the apparent motions of the planets; the grand discovery of Kepler that all these apparently erratic motions were due to their revolution round the sun in elliptic orbits, with a fixed relation between their distance from the sun and their periods of revolution; and Newton’s epoch-making theory of universal gravitation by which all these facts and many others since discovered were harmonized and explained.

But all this implied no law of development, and it was long thought that the solar system was fixed and unchangeable—that some altogether unknown or miraculous agency must have set it going, and that it had in itself no principle of change or decay, but might continue as it now is to all eternity. It was at the very end of the eighteenth century that Laplace announced his “Nebular Hypothesis,” the first attempt ever made to explain the origin of the solar system under the influence of the known laws of motion, gravitation, and heat, acting upon an altogether different antecedent condition of things—a true process of evolution.

Laplace supposed that the whole matter of the solar system was once in a condition of vapor, and that it formed an enormous nebulous mass many times larger than the then known dimensions of the planetary sphere. He showed how, under the influence of gravitation, this nebula would condense, and that such irregularities of motion and density as would be sure to exist would lead to rotation of the mass. Under the law of gravitation this would lead to outer rings being left behind by the contraction of the central mass, which rings would at a later period become drawn together at some point of initial greater density and thus form planets. The whole process is admitted to be mathematically demonstrable, given the initial conditions; but recent extensions of our knowledge of the interplanetary and interstellar spaces have shown that the supposed void is really full of invisible solid matter, ranging from the bulk of the smaller planets down to the finest dust, and it is very difficult to imagine any possible causes which would keep all the solid matter of the system in a state of vapor, when subject, on the confines of the mass, to the cold of interstellar space. The antecedent condition of our system is now thought to have been either wholly or partially meteoritic, but in either case we have a genuine theory of its evolution which has now been so extended as to include the appearance of comets and meteors, of nebulæ, and star clusters, of temporary, periodic, and colored stars, and many other phenomena of the stellar universe. It is no objection to these grand theories to urge that they do not explain the origin of the matter of the universe, either what it is or how it came to be where we now find it. We can only take one step at a time, and even if in these greater problems any further advance should be as yet denied us, it is still a great thing to have been able to take even one secure step into the vast and mysterious depths of the interstellar spaces.

EVOLUTION OF THE EARTH’S CRUST

Although Pythagoras (500 B. C.) believed that sea and land must often have changed places, and a few other observers at different epochs came to the same conclusion, yet, till quite recent times, the earth was generally supposed to have been always very much as it is now; people spoke of “the eternal hills”; and the great mountain ranges, the mighty ravines and precipices, as well as the deep seas and oceans, were believed to be the direct work of the Creator.

It was only in the latter half of the eighteenth century that a few observers began to see the importance of studying the nature of the earth’s crust, so far as it could be reached in ravines, quarries, and mines; and one of the most earnest of these students, Dr. Hutton, of Edinburgh, after more than thirty years of travel and study, published his great work, The Theory of the Earth, which must be considered to be the starting-point of modern geology. He maintained that it was only by observing causes now in action that we can explain the phenomena presented by the stratified and igneous rocks; he showed that the former must have been laid down by water, and that the larger part of them, containing as they do marine shells and other fossils, must have been deposited on the sea-bottom. He showed how rain and rivers, frost and snow, wind and heat disintegrated the hardest rocks and would in time excavate the deepest valleys; while earthquakes, however small an elevation any one of them might produce, would in time raise the sea-bottom sufficiently high to form, when denuded, mountain ranges, plains, and valleys like those we now see everywhere upon the earth’s surface. He also showed that the most ancient stratified rocks, those that lie at the very base of the series, presented every indication of having been formed in exactly the same way as the most recent ones. Hence he stated a conclusion which excited a storm of opposition, in these words: “In the economy of the world I can find no traces of a beginning, no prospect of an end.” This was thought to imply a denial of creation, and was quite sufficient at that period to prevent the work of any man of science from being judged impartially.

But although Playfair and a few others upheld Hutton’s views, they were too novel to receive much support by his contemporaries, and this was especially the case as regards the slow and continuous action of existing causes being sufficient to account for all the known phenomena presented by the crust of the earth. Hence the belief in catastrophes and cataclysms—in great convulsions tearing mountains asunder, and vast floods sweeping over whole continents—continued to prevail, till finally banished by the genius and perseverance of one man, Sir Charles Lyell. His Principles of Geology was first published in 1830, and successive editions, revised and often greatly extended, continued to appear till the author’s death, forty-five years later. As this work affords a fine example of the application of the principles of evolution to the later phases of the earth’s history, and as it not only revolutionized scientific opinion in its own domain, but prepared the way for the acceptance of the still more novel and startling application of the same principles to the entire organic world, it will be necessary to show what opinions prevailed at the time it first appeared in order that we may understand how great was the change it effected.

In the earlier years of the nineteenth century the standard geological work, both in Great Britain and on the Continent, was Cuvier’s Essay on the Theory of the Earth. In 1827 a fifth edition of the English translation appeared, and there was a German translation so late as 1830—sufficient proofs of its wide popularity. Yet this work abounds in statements which are positively ludicrous to any one conversant with modern geology. It never appeals to known causes, but again and again assumes forces to be at work for which no evidence is adduced and which are totally at variance with what we see in the world to-day. A few examples justifying these statements must be here given. Cuvier shows that he was acquainted with the theory of modern causes, but he altogether rejects it, saying that “the march of nature is changed, and none of the agents she now employs would have been sufficient for the production of her ancient works.” He adduces “the primitive mountains” whose “sharp and bristling ridges and peaks are indications of the violent manner in which they have been elevated.” He allows that atmospheric agencies may form sea-cliffs, alluvial deposits, and taluses of loose matter at the foot of the precipices, but he adds: “These are but limited effects to which vegetation in general puts a stop, and which, besides, presuppose the existence of mountains, valleys, and plains—in short, all the inequalities of the globe—and which, therefore, cannot have given rise to those inequalities.” He contrasts the calm and peaceful aspect of the surface of the earth with the appearances discovered when we examine its interior. Here, in the raised beds of shells, the fractured rocks, the inclined or even vertical stratification, he finds abundant proofs “that the surface of the globe has been broken up by revolutions and catastrophes.”

He also refers to the numerous large blocks of the primitive rocks scattered over the surface of secondary formations, and separated by deep valleys or even by arms of the sea from the peaks or ridges from which they must have been derived, as further proofs of catastrophes; for, it is argued, they must have been either ejected by volcanic eruptions or carried by waters, which, in either case, “must have exceeded in violence anything we can imagine at the present day,” and he therefore concludes that “it is in vain we search among the powers which now act upon the surface of the earth for causes sufficient to produce the revolutions and catastrophes, the traces of which are exhibited in its crust.” He is quite confident that all these changes go on rapidly, periods of catastrophe alternating with periods of repose. The present surface of the earth he holds to be quite recent, and he maintains “that, if anything in geology be established, it is that the surface of our globe has undergone a great and sudden revolution, the date of which cannot be referred to a much earlier period than five or six thousand years ago; that this revolution overwhelmed and caused to disappear the countries which were previously inhabited by man, and the species of animals now best known; that, on the other hand, it laid dry the bottom of the last sea, and formed of it the countries which are at the present day inhabited.” And he further declares that “this event has been sudden, instantaneous, without any gradation; and what is so clearly demonstrated with respect to this last catastrophe is not less so with reference to those which preceded it.”

The method followed by Lyell was the very reverse of that of Cuvier. Instead of assuming hastily that modern causes were totally inadequate, and appealing constantly to purely imaginary and often inconceivable catastrophes, Lyell investigated these causes with painstaking accuracy, applying the tests of survey and time measurement, so as in many cases to prove that, given moderately long periods of time—not a few thousands only, but hundreds of thousands of years—they were fully adequate to explain the phenomena. He also showed that the imaginary causes of Cuvier would not explain the facts, for that everywhere in the crust of the earth we found conclusive proofs of very slow continuous changes exactly analogous to what now occur, never of great convulsions, except quite locally, as we have them now. He showed that modern volcanoes had poured out vast masses of melted rock during a single eruption, covering areas as extensive as those which any ancient volcano could be proved to have ejected in an equally short period; that strata were now in process of formation comparable in extent and thickness with any ancient strata; that organic remains are being preserved in them just as in the older rocks; that the land is almost everywhere rising or sinking as of old; that valleys are being excavated and plateaus or mountains upheaved; that earthquake shocks are producing faults beneath the surface; that vegetation is still preparing future coal beds; that limestones, clays, sandstones, metamorphic and igneous rocks are all still being formed; and that, given time, and the intermittent or continuous action of the causes we can now trace in operation, and all the varied features of the earth’s surface, as well as all the contortions and fractures which we discover in its crust, and every other phenomenon supposed to necessitate catastrophes and cataclysms will be again produced.